Brain teaser: Although commonly used, functional magnetic resonance imaging offers only an indirect measure of neuronal activity. 

Combining functional magnetic resonance imaging (fMRI) of rat brains with a technique that uses light to detect neuronal activity can help researchers hone in on the source of the activity, according to a study published 6 May in Nature Methods¹. 

To identify the brain regions involved in a particular task, researchers often rely on fMRI, a non-invasive imaging method that detects changes in blood flow and oxygen levels in the brain. But this is an indirect measure of neuronal activity, and cannot determine whether neurons in the region are sending or receiving a signal. It also cannot discriminate between the activity of neurons and other brain cells, such as glia, which are support cells in the brain.

Researchers have used animal studies to address some of these issues. In one study, they scanned monkey brains while using an electrical probe to record neuronal activity. However, the metal probe can interfere with the magnetic signals detected during fMRI, making it difficult to interpret the results².

In the new study, the researchers combined fMRI with a technique that records the activity of neurons using light rather than electrical activity. This allowed them to use a small optical probe inserted into a rat’s skull, which they found does not interfere with fMRI signals.

The researchers gave rats sitting in an fMRI scanner a slight shock in their front paws, and then recorded the response in the somatosensory cortex, a brain region that responds to touch. They also detected neuronal activity by injecting rat brains with an indicator dye that fluoresces in response to calcium, which is released when neurons fire.

Neuronal activity is so closely tied to the fMRI signal that in some cases one can predict the other, the study found. However, by using a dye that discriminates between neurons and glia, the researchers found that in some cases glial activity, rather than neuronal activity, contributes to the fMRI response.

The results suggest that interpreting these fMRI signals is not as simple as previously thought, the researchers say.

The researchers also plan to use techniques such as optogenetics to detect signaling from certain subpopulations of neurons. For example, researchers could express a different indicator in neurons that inhibit signals compared with those that activate signals and parse out the relative contribution of each to an fMRI response.

References:

1: Schulz K. et al. Nat. Methods Epub ahead of print (2012) PubMed

2: Oeltermann A. et al. Magn. Reson. Imaging 25, 760-774 (2007) PubMed

Rowdy rodents: Mice lacking SHANK2, an autism-linked protein that functions at neuronal junctions, are hyperactive.

Mice lacking the autism-associated gene SHANK2 show autism-like behaviors similar to those seen in mice lacking SHANK3, another member of the same gene family. But SHANK2 and SHANK3 mice have distinct alterations at neuronal junctions. The results, which were presented at the 2011 Society for Neuroscience annual meeting, were published 29 April in Nature.

SHANK2 and SHANK3 proteins sit at the signal-receiving ends of neurons and help to organize other proteins at synapses, the junctions between neurons. A number of mutations in each SHANK protein have been found in individuals with autism.

Researchers have also engineered several mouse models lacking different regions of the SHANK3 gene. All of these mice exhibit varying degrees of social deficits, repetitive behaviors, such as obsessive self-grooming, and anxiety.

In the new study, researchers created mice lacking either one or both copies of the SHANK2 gene. As with SHANK3 mutant mice, the SHANK2 mice show less interest than controls in other mice and engage in long bouts of repetitive self-grooming. They also have significantly heightened anxiety and hyperactivity, fearing brightly lit corridors and covering twice as much ground as controls do when exploring an open space.

The synapses of neurons from the SHANK2-deficient mice have more NMDA and AMPA receptors, which transmit activating signals to neurons, and more SHANK3 protein compared with controls. By contrast, the synapses from SHANK3 mutant mice have fewer copies than controls do of most versions of these receptors.

Neurons from SHANK2-deficient mice also have fewer dendritic spines, the branches of neurons that receive activating signals, and have weaker excitatory signaling compared with controls.

The results suggest that mutations in different SHANK proteins lead to distinct synaptic alterations that would respond differently to therapies, even though they have a similar effect on behavior, the researchers say.

Alysson Muotri, assistant professor of pediatrics at the University of California, San Diego, has given a whole new meaning to the tradition of the tooth fairy.

A couple of years ago, Muotri and his collaborators developed a way to use stem cells from dental pulp, collected from the innards of lost teeth, to create induced pluripotent stem (iPS) cells — adult cells that have been reprogrammed to a more flexible state.

Muotri is planning to build a bank of such cells from children with autism. By differentiating the stem cells into neurons, he says he hopes to understand the molecular and cellular changes that underlie the disorder, particularly for so-called idiopathic autism — with no known cause — which makes up the bulk of cases.

The tooth fairy approach avoids a trip to the doctor and a skin biopsy, both of which can be especially distressing for children with autism. (iPS cells are typically derived from skin samples.) And teeth can be sent from anywhere in the world.

Ultimately, neurons derived from an individual with autism could be used to select the best therapy for that person. Muotri is already trying a simplified version of this approach, which he presented last month at the Translational Neuroscience Symposium in Switzerland.

Starting with samples from a child in Brazil, researchers discovered the child has a translocation, or DNA swap, affecting two genes: VPRVP, which is involved in the cell cycle but not expressed in the nervous system, and TRPC6, a calcium channel expressed in parts of synapses, the connections between neurons, throughout development.

Gene expression studies revealed that iPS cells derived from the child produce only half the normal amount of TRPC6 protein. After differentiating iPS cells in a dish into cortical neurons, researchers found his cells have fewer dendritic spines — small bumps on neurons that receive inputs from other cells — than those derived from controls. 

Analyzing a second child who has similar outward symptoms to the child with the translocation, researchers found some molecular similarities. Although this child does not have a deletion or translocation of TRPC6, he also has fewer spines on iPS cell-derived neurons. 

What’s more, both have fewer glutamate synapses, neuronal connections that mediate excitatory signals. Muotri says that is similar to neurons from people with Rett syndrome, a rare inherited disorder that shares some symptoms of autism.

He speculates that MeCP2, the gene that is disrupted in Rett syndrome, regulates TRPC6. When they examined iPS cell-derived neurons from someone with Rett, they found low expression of the TRPC6 gene, he says. These results have not yet been published.

How significant these differences are is a matter of some debate. Some scientists argue that the variability inherent in making iPS cells makes it difficult to determine whether the disparities can be attributed to the disorder itself or merely to small differences in the cells’ origins.

Muotri says he hopes that the National Institutes of Health or other organizations will spearhead an iPS cell consortium to try to answer some of these questions. Academic labs such as his own don’t have the resources to create and bank large numbers of cell lines, he says. In fact, the tooth fairy project is on hold, because the lab doesn’t have enough people to process the cells.

A strain of mice lacking the TRPC6 gene is available but has been little studied. Neurons from adult mice, however, have fewer glutamate synapses, similar to those seen in human TRPC6-deficient cells made from the boys with autism, says Muotri.

Muotri and his collaborators are trying to figure out whether these findings can be used for personalized therapy. Hyperforin, a component of the herbal remedy St. John’s wort, has been shown to activate TRPC6 channels. In neurons, hyperforin increases activation of TRPC6, says Muotri.

The outcome of the story is somewhat muddy, as expected in a trial of one. One of the children was given St. John’s wort, which is available over the counter, by his parents. After several months of treatment, the father and therapists reported a behavioral change, and the school reported improved attention, but the mother says she did not see any changes.

If there is behavioral change, “We don’t know if it’s due to the drug or not,” says Muotri. “But it’s very exciting that we found a kid with a similar phenotype to the child with the translocation and saw similar molecular defects in iPS cell-derived neurons.”

Rising rates: Eric Fombonne says the new CDC report does not necessarily mean that autism prevalence is increasing.

In March, the Centers for Disease Control and Prevention (CDC) released what on the surface seemed to be an alarming report. It found that the rate of autism has increased 23 percent — from 1 in 110 children to 1 in 88 — in the past two years, and a whopping 78 percent between 2002 and 2008¹.

The findings immediately raised questions about how much of the rise is because of heightened awareness of autism or changes in the way it is diagnosed, and how much can be attributed to a true increase in its incidence.

The CDC data were collected in 2008 at 14 sites across the U.S. that are part of the Autism and Developmental Disabilities Monitoring Network. Researchers looked at medical and education records for 337,093 8-year-olds and determined whether they met diagnostic criteria for autism spectrum disorders.

Eric Fombonne, Canada Research Chair in child psychiatry at McGill University in Montreal, has spent the past 20 years analyzing the prevalence of autism. He digs into the CDC data with SFARI.org, explaining that big differences among different states and among children of different ethnicities, driven by the challenge of identifying all children with autism, are likely to be major contributors to the apparent increase. 

SFARI.org: Do the numbers in the CDC report represent a real increase in the prevalence of autism?

Eric Fombonne: This interpretation is only one of many. My approach has been to look at these data and systematically examine how alternative explanations could explain these trends. The idea that the incidence is increasing should only be accepted if alternative explanations can confidently be ruled out.

SFARI.org: What are some of these other factors?

EF: Differences in ascertainment [the ability to identify cases in surveys] and in diagnostic concepts and criteria are still significant issues.

Variability in prevalence among different sites provides evidence of ascertainment difficulties. First, it is important to realize that the current CDC rate of 1.1 percent is only an average that is obtained by pooling together different figures and is not more ‘true’ than each estimate that contributes to it.

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CDC

Vast variability: There is a more than four-fold difference between the prevalence of autism in Alabama, which has the lowest rate, and Utah, which has the highest. The U.S. average rate is highlighted in red. States that used only health records (green) tend to have lower rates than those that used both health and educational records (blue).

The variability in ingredients of this average is also important to consider. In the CDC study, there is a roughly four-fold difference in the estimates between Alabama, the state with the lowest prevalence (4.8 per 1,000 children), and Utah, the state with the highest prevalence (21.2 per 1,000). (See graph, right.) Nobody interprets these site differences as differences in incidence. It’s a difference in ascertainment.

This variability within the same study can be compared to that between surveys conducted six years apart: 6.6 per 1,000 children according to a 2002 survey and 11.3 per 1,000 children according to the most recent survey, from 2008.

If the four-fold difference in the new survey does not raise concerns about different incidence rates across states, why should a less than two-fold rate difference in surveys conducted six years apart raise concerns about an ‘epidemic’?  

SFARI.org: Were you surprised by the numbers in the new report?

EF: No. I predicted three years ago that we would see such an increase². Some states are improving their identification of children with autism due to better services, heightened public awareness and the development of local expertise. This will continue in the future, especially in states or population subgroups where identification of children with autism is currently lagging behind. I therefore predict that we will see additional increases in national U.S. estimates.

SFARI.org: Why is there so much variability?

EF: [Researchers] try their best to apply uniform methods to identify children with autism in all areas, but they cannot do it as efficiently across states. The prevalence is probably severely underestimated in certain areas. Alabama, Florida and Wisconsin, for example, have rates that are much too low compared with the averages in the U.S. or other parts of the world, which are more or less at one percent. 

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CDC

Margin of error: The states with the highest prevalence, Utah and New Jersey, also have the widest error bars because of their small sample sizes. States that used only medical records to assess prevalence (open circles) tend to have lower rates than those that used both medical and education records (filled circles).

Some states use only medical records, others use both medical and educational records. If next time all states include educational sources, the rates will go up, not because of an increased incidence but because the method will be more efficient at identifying cases. (See figure, left.)

SFARI.org: The changes in prevalence seem to vary among different ethnic backgrounds. From 2006 to 2008, rates among non-Hispanic whites have increased 16 percent, compared with 42 percent among blacks and 29 percent among Hispanics. Is that significant?

EF: Yes. Traditionally, there has been systematic under-ascertainment of these groups, especially Hispanics, in the U.S.

If you look backward to 2006, rates were much lower in children from these ethnic backgrounds, and they were therefore expected to rise relatively more than in more mainstream groups. Indeed, the rates have now disproportionately increased in these ethnic minorities. That is good; it means more children from ethnic minorities are being identified, and hopefully accessing support services. Note, however, that the overall prevalence among Hispanic and black children is still much lower than that among white children by factors ranging from 17 to 33 percent. As a consequence, in future CDC surveys, the rates will ‘catch up’ in these groups, leading to further increases in mean rates in the U.S.

SFARI.org: Do the states with the highest rates reflect the true prevalence of autism?

EF: That is more difficult to evaluate. However, I noted some methodological  peculiarities in the survey methods employed in the two states with the highest rates.

If you look at the figure (above, left), Utah has the highest rate but also the biggest error bar. That is because it had an extremely low sample size, a surveyed population of about 2,100 children, compared with more than 36,000 in Alabama and even over 50,000 in Georgia. Also, New Jersey surveyed a population of 7,000, under the 10,000 initial CDC requirement to be included in the study. Utah and New Jersey were added to the study at a later stage and relied on different sampling strategies (using school districts as compared to entire counties). The consequence is that the denominators used to calculate prevalence in these states had to be estimated with different methods, leaving open the question of their validity.

It is also possible that, because New Jersey historically has been good about financing special education and other services, it attracted more families that have children with autism. Or those families are more likely to stay there.

When I reviewed the data, I also found that children with autism from the Utah sample are unusual in several ways. They have the lowest rate of mental retardation, 13 percent compared with the U.S. average of 38 percent. They also have the lowest male-to-female ratio, 2.7 to 1, compared with the typical average of 4.6 to 1. Taken together, these characteristics are really puzzling, because typically you expect a greater sex ratio at the higher-functioning end of the spectrum. The opposite pattern reported in Utah points to a very atypical sample.

SFARI.org: Do all these factors explain the increase?

EF: We do not know. We cannot demonstrate that all this adds up to the entire increase. Equally, we also cannot infer that the incidence is increasing, which the CDC researchers rightly point out in their abstract.

Irrespective of whether the incidence is increasing, the rate is important to know because it has implications for services.

SFARI.org: How can we better determine whether there is a true increase?

EF: Given its means and funding power, the CDC is the best machine to do this presently in the U.S. Their methods are quite consistent across surveys and over time. It is worth noting, however, that the CDC surveys do not typically screen for autism in children in mainstream schools or home-schooled children. Children are also not directly evaluated for diagnostic confirmation. The CDC has provided convincing data on small subsamples that its indirect approach to diagnosis is valid, but we do not know if this holds true across sites or over time.

One option is to follow large birth cohorts prospectively, as is being done in Norway. If you follow them over time, you can capture most kids with autism at a later age. But the costs would be prohibitive.

I have other ideas, but I’m not sure I would put my money or energy into it. The whole point of demonstrating changes in incidence is to identify causes of autism, such as environmental events, that could potentially be controlled to prevent disease occurrence. But so far, the exposures we know of, such as prenatal exposure to various medications and possibly some neurotoxins or infectious agents, have only weak associations (if any) with autism and can at most explain only a tiny fraction of the increase. We need more persuasive evidence. 

References:

1: Autism and Developmental Disabilities Monitoring Network Surveillance Year 2008 Principal Investigators MMWR Surveill. Summ. 61, 1-19 (2012) PubMed

2: Fombonne E. Pediatr. Res. 65, 591-598 (2009) PubMed

Neural links: Diffusion tensor imaging, which detects the flow of water in the brain, maps connections between brain regions.

The bundles of nerve fibers that connect two regions important for language are abnormal in the brains of children with autism, according to a study published 5 April in the American Journal of Neuroradiology¹.

This difference is more significant in individuals who have both autism and language impairment than in those who have autism alone. It is also more pronounced in the left hemisphere than in the right, the study found.

Scientists have found abnormalities in the structure of white matter, which contains the connecting processes of neurons, and in the connections between brain regions in individuals with autism. In the new study, researchers looked specifically at the superior longitudinal fasciculus, or SLF, a bundle of nerve fibers that connects two language regions called Broca’s area and Wernicke’s area.  

They used a method called diffusion tensor imaging, or DTI, which measures the rate of diffusion of water molecules along long swaths of white matter. Overall, the 35 children with autism in the study have greater diffusion of water in the SLF compared with 25 controls, the researchers found.

This may be because the neurons in these fibers bundle together less tightly, allowing the water to diffuse more freely and lessening the connectivity between brain regions, the researchers say.

These alterations are more pronounced in the 17 participants who have both autism and language impairment than in the 18 children who have autism alone. Overall, all children, including controls, who have lower scores on the Clinical Evaluation for Language Fundamentals test show more diffusion than those with higher scores. This is particularly true in the left hemisphere of the brain, according to the study.

These findings suggest that white-matter abnormalities in the SLF may underlie the language deficits seen in autism, the researchers say.

References:

1: Nagae L.M. et al. Am. J. Neuroradiol. Epub ahead of print (2012) PubMed

Muted markers: Clinical trials for autism rely on behavioral assessments of children, like those used for diagnosing the disorder, rather than on quantitative biomarkers.

The past few years have seen an unprecedented number of clinical trials for experimental drugs to treat autism-related disorders, most notably fragile X syndrome. But as the trials progress, scientists are calling for better methods to measure the drugs’ effectiveness.

“There’s been a big focus on basic science research, but not on quality clinical research,” says Randall Carpenter, president of Seaside Therapeutics, a company in Cambridge, Massachusetts, that is running several clinical trials. “That’s an impediment now because we have all these targets but don’t have the tools to properly do clinical testing.”

The ideal solution, of course, would be a biomarker such as a pattern of brain activity that can be used to quantitate response to treatment. Although the hunt is on for such a biomarker, it’s unlikely to be available in the near future. 

“In the short term, will have to work with tools that are already in use,” says Carpenter. Given that the autism field has seen few placebo-controlled, blinded and randomized drug trials, “there is not much known about how to measure efficacy in clinical trials of people with autism,” he says.

The best-studied tools for assessing autism were developed primarily for diagnosing the disorder, not measuring response to treatment.

“Existing tools were perfected to capture “trait variables” — relatively constant features of an individual over time — but they are not well-designed to capture shifts with respect to autism symptoms,” says John Constantino, professor of psychiatry and pediatrics at Washington University in St. Louis. They are also often cumbersome and time-consuming, he says, not ideal qualities for use in large-scale clinical trials.

The ABCs:

Most ongoing clinical trials for fragile X use parts of the Aberrant Behavior Checklist (ABC), a 58-item questionnaire with five different subscales — irritability, hyperactivity, lethargy/withdrawal, stereotypy and inappropriate speech — that was originally developed for use in people with intellectual disability. These trials rely on the ABC largely because it was used in clinical trials of risperidone and aripiprazole, antipsychotics that are approved to treat irritability in autistic spectrum disorders. Those trials used the irritability subscale of the ABC.

“For anything else — the core symptoms — we have nothing that has been tested before,” says Luca Santarelli, head of neuroscience at the pharmaceutical company Roche, headquartered in Basel, Switzerland.

Companies running clinical trials must define an endpoint before the start of a trial. But most researchers collect additional data along the way, in case the designated endpoint fails but other indicators show an effect. (The new endpoint would then need to be tested in a subsequent trial.)

Roche, which is running clinical trials of an mGluR5 antagonist for fragile X, includes a hypothesis-generating arm in its clinical program to test endpoints that might be sensitive to a given therapeutic approach, says Santarelli. ‘There is no certainty in terms of which will turn out to be successful.”

Based on the emerging data, Roche is building a new instrument tailor-made for use in people with fragile X.

The process for getting new tools approved for clinical trials by the U.S. Food and Drug Administration (FDA), however, can be both time-consuming and expensive. 

“The level of data you have to have to validate these tools for acceptance by the FDA is much higher than [what] you need to publish in an academic journal,” says Carpenter.

Carpenter and his collaborators have instead opted to modify an existing tool, which he discussed at the Translational Neuroscience Symposium in Switzerland in April. They developed a new algorithm, specialized for people with fragile X, for analyzing the results of the ABC.

For example, the lethargy/withdrawal subscale of the ABC includes a number of questions that focus on lethargic behavior. Children with fragile X, however, tend to be hyperactive, so the new algorithm focuses on questions relating to social withdrawal. “We are now validating it in clinical trials to see if it’s sensitive to change,” Carpenter says.

Natural history:

Autism Speaks, a research and advocacy organization, aims to provide some guidance for those embarking on clinical trials. It has convened two working groups to analyze tests that assess social communication deficits, anxiety, and restrictive and repetitive behavior. The results of those efforts have not yet been made public, but are expected to be published soon.

Joseph Horrigan, Autism Speaks’ assistant vice president, says the organization is willing to discuss different clinical outcome measures with researchers.

One of the aspects the organization is evaluating is how well tests developed for other disorders can be used to assess changes in autism symptoms. The Yale-Brown Obsessive Compulsive Scale, for example, is a checklist developed to assess people with obsessive-compulsive disorders. It is sometimes used to measure repetitive behaviors in autism.

“While there are some similarities between the behaviors in those two disorders, there are some significant differences as well,” says Srinivas Rao, chief executive officer of California-based Kyalin Biosciences, a biotech company that is developing an oxytocin-based drug for autism.

Building better tests will, in part, require a better understanding of the natural history of autism.

“Few measures that quantify autism states have been measured in the normal population, so we don’t know how much of a difference is really significant,” says Constantino.

His team is planning to follow both typically developing toddlers and those with autism, using a number of tools to identify changes over time, as well as the most realistic indices to measure those changes.

He and his collaborators are also looking for more efficient and practical ways of evaluating children with autism. They have a paper in press that evaluates a new version of the Childhood Autism Rating Scale, showing that even clinicians with minimal training can reliably score symptom severity based on a 15-minute video of a child¹. 

The potential benefits aren’t limited to drug testing. “For young children, a massive amount of resources are invested in early intervention,” says Constantino, “and there are almost no standardized tools used systematically to track changes over time.”

For more reports from the 2012 Roche Translational Neuroscience Symposium, please click here.

References:

1. Constantino J.N. et al. Neuropsychiatry 2, 1-11 (2012)

Gus Alusi, a British surgeon and cancer researcher, has spent the past couple of years trying out different treatments for his son Kenz, who has fragile X syndrome, one of the most common forms of inherited intellectual disability.

Alusi, his wife Reem, and a team of therapists have tried a number of different drug treatments, such as antidepressants and antipsychotics, hoping to dampen some of the anxiety that goes along with the disorder. 

Alusi videotaped his son’s progress along the way. In early shots, Kenz (pictured at left with his parents) is clearly agitated, whimpering and whining in distress as his mother or therapists try to help him put on clothes and shoes. But in videos taken a year later, he is much calmer. He still has occasional outbursts, but seems better able to pacify himself.

Alusi, who along with his wife has launched a nonprofit advocacy group, Cure4x.org, ascribes the change to the drugs, but also to an intensive regimen of behavioral therapy. The experience has convinced him that medication and behavioral therapy must go hand in hand.

“Behavioral therapy alone is like reading a book in the dark, and medications are like the light,” Alusi said. “You need both to get the full benefit.” (Alusi declined to give the name of the drug that he thinks has most helped his son, saying only that it is approved for pediatric use.)

This approach is not new to psychiatry. Large-scale studies have shown that combining antidepressants with cognitive behavioral therapy is more effective than either treatment alone. People with moderate to severe forms of depression are typically given both.

But this is a tall order for a field that is struggling to develop its first successful drug. No medicines are available to treat the core symptoms of fragile X, though children with the disorder are often treated with drugs approved to alleviate secondary symptoms, such as anxiety, attention deficits and aggression.

Parents, physicians and scientists are anxiously awaiting the results of ongoing clinical trials for a class of drugs, known as mGluR5 antagonists, that have been highly successful in treating animal models of the disorder.

Speaking in April at the Translational Neuroscience Symposium sponsored by pharmaceutical company Roche, Alusi criticized the short length of early-stage clinical trials.

“It’s a waste of time to put my son through clinical trials that last two weeks, which isn’t long enough to see a change in cognition,” he said. “As a parent, I can see you need months of treatment, along with some form of education and stimulation, to produce a tangible benefit beyond simple calming down.”

Randall Carpenter, president of Seaside Therapeutics, which is testing two drugs for fragile X and autism, agrees that this combination is critically important, and something they aim to implement at Seaside. “Even if you normalize brain plasticity and the ability to learn,” he says, “children need training, especially if they are trying make up for lost time.”

For more reports from the 2012 Roche Translational Neuroscience Symposium, please click here.

Click here to enlarge

Joint inheritance: An individual with autism who has a SHANK1 mutation (arrow) shares the mutation with both affected (black and hashed) and unaffected family members.

Researchers have identified deletions in SHANK1 — the third member of a gene family that is closely linked to autism — in five men with the disorder, they reported 4 May in the American Journal of Human Genetics. This is the first study linking SHANK1 mutations to people with autism¹.

Several studies have found mutations in individuals with autism in SHANK3 and SHANK2, which code for proteins that organize the connections between neurons. Mice with mutations in SHANK3 show behaviors reminiscent of autism, such as low social interest and repetitive self-grooming. SHANK2 mutant mice also show social impairments and hyperactivity.

Mice with mutations in SHANK1 have motor deficits and are more anxious than controls, but do not appear to have social deficits. However, they are less likely to communicate with other mice using ultrasonic vocalizations, sounds that are inaudible to the human ear. 

In the new study, researchers looked for copy number variations — duplications or deletions of regions of DNA — in 1,614 individuals with autism and 15,127 controls. They found deletions in SHANK1 in two men with autism, but none of the controls.

One of these men inherited the deletion: Three of his male relatives also have the deletion, and have a diagnosis of high-functioning autism or autism-like symptoms, dubbed the broad autism phenotype. By contrast, two female relatives who have the deletion do not have symptoms of the disorder. The results support the theory that protective factors raise the threshold for autism risk in women compared with men, the researchers say.

The researchers also sequenced SHANK1 in 509 people with autism and 340 people with intellectual disability to look for single-letter DNA changes. They found 26 missense mutations, which alter the protein code, in 23 people with autism and 7 people with intellectual disability, but none in 285 controls. However, only two of these mutations are likely to affect the overall structure of the protein.

Mutations in SHANK1 may increase autism risk, but less so than SHANK2 and SHANK3, which are strongly linked to the disorder, the researchers say. This is consistent with SHANK1’s role at neuronal junctions, which is to support connections formed by the other SHANK proteins. 

References:

1: Sato D. et al. Am. J. Hum. Genet. 90, 879-887 (2012) PubMed

Meat eater: Genetic defects in the body's ability to make the molecule carnitine, which is found in high levels in red meat, may be linked to autism.

A genetic defect in the synthesis of carnitine, a molecule that plays a central role in the body’s ability to make energy, might slightly increase risk for autism in some children, according to research published 8 May in the Proceedings of the National Academy of Sciences¹.

The study found that in families that have two boys with autism, those boys are 2.82 times more likely than controls to have a deletion in the gene trimethyllysine hydroxylase epsilon (TMLHE). This gene codes for the first enzyme in a biochemical reaction that synthesizes carnitine in the body. The project was funded in part by the Simons Foundation, SFARI.org’s parent organization.

The finding is interesting because it suggests both “a potential mechanism and also a potential treatment,” says Joseph Gleeson, professor of neurosciences at the University of California, San Diego, who was not involved in the study. Carnitine supplements are available over the counter, and the molecule is abundant in red meat.

He and others caution, however, that the findings are preliminary and need to be replicated in a larger population, particularly in more multiplex families, which have two or more children with autism, says Gleeson.

Even if TMLHE defects have a small effect compared with other genetic risk factors, the fact that it is a risk factor that can potentially be treated with a simple supplement makes it important to study further, says Arthur Beaudet, professor of molecular and human genetics at Baylor College of Medicine in Houston, Texas, and senior scientist on the research.

Two observations from the study argue against TMLHE playing a major role in autism. The researchers did not find a link between the mutation and autism in simplex families, which have only one affected child and unaffected parents and siblings. (That may change once larger groups are studied.)

Moreover, they found that mutations in TMLHE are fairly common in typical males, found at a rate of 1 in 366. Only about three percent of males with the deletion have autism.

Body builder:

Carnitine, which helps transport fatty acids into the mitochondria, can either be made by the body or derived from the diet. Meat eaters get roughly 75 percent of their carnitine from food. Vegetarians and especially vegans, on the other hand, must synthesize the majority of the molecule.

The TMLHE deletion is the first example of an inherited disorder of carnitine synthesis within the body. Scientists have known about more severe genetic defects that prevent the molecule from getting into cells, disabling the body’s ability to process fats for energy. This disorder can be detected in routine newborn screening. Symptoms typically occur in infancy or early childhood and include severe brain dysfunction, but these disorders are not generally linked to autism.

Beaudet’s team first linked TMLHE to autism when they were scanning for small deletions in the exome — the protein-coding portion of the genome — in families that have a child with autism. They discovered one child with a deletion of the second exon in the gene².

All together, researchers have identified the same deletion in 22 people with autism, but also in 24 healthy males. The team focused on males because the gene is located on the X chromosome. Males have only one copy of the gene and are more likely to show symptoms.

After failing to find a significant link between autism and the mutation in simplex families, Beaudet and his colleagues decided to focus on families that have two boys with the disorder. They hypothesized that the mutation might be enriched in this group because a mother with one bad copy of the gene has a 50 percent chance of passing the mutation to each son.

Sequencing 900 males from sibling pairs in which both boys have the disorder, the researchers found the mutation at a rate of 7.7 percent compared with 2.7 percent of controls. (These were mainly unaffected fathers from several different autism projects.) In six out of seven of the cases, the second brother has the mutation as well.

The researchers also analyzed data from 43 boys with autism who have a sister with autism, but found no cases of the deletion.

Biochemical studies showed that those with the deletion have very low or undetectable levels of the enzyme produced by TMLHE. But the effect on carnitine levels, and the link to autism, is still unclear. Two of the boys with the mutation, age 15 and 17, have normal blood levels of carnitine.

“This is a brand-new metabolic error, and a lot more needs to be learned to know what’s going on,” says Ellen Elias, a member of the autism subcommittee at the American Academy of Pediatrics, who was not involved in the study. “Time will tell how significant this really is for the autism community.”

Aside from the potential link to autism, the frequency of this disorder in the general population is a surprise, researchers say.

“It’s rather startling because it’s 20 times more common than PKU in males,” says Beaudet, referring to phenylketonuria, a metabolic condition in which people can’t break down a specific amino acid. Inherited metabolic disorders typically occur in only about 1 in 10,000 children, he says.

Bigger numbers:

Beaudet says his priority now is to replicate the finding in a larger sample. His team aims to recruit 1,000 male sibling pairs, and he says he hopes the new publication will encourage families and physicians to participate.

Because dietary carnitine is supplied mainly through meat, Beaudet says he suspects that risk associated with this gene might be higher among vegetarian families. He aims to study such families, either in the U.S. or in countries such as India where vegetarianism is more common.

Beaudet also speculates that carnitine metabolism could play a broader role in autism than is suggested by this particular gene. “We are interested in other aspects, such as the amount of carnitine in diet, and genetic variation in the ability to transport carnitine across the blood-brain barrier,” he says.

Beaudet’s laboratory plans to offer free genetic testing to boys with autism who are younger than 5 and are non-dysmorphic, meaning they don’t have unusual facial features or birth defects. Dysmorphology would typically signal that a more severe genetic mutation is at play.

Some tenuous links between carnitine and autism already exist. Defects in the mitochondria, which have previously been linked to autism, can sometimes lead to carnitine deficiency. And treating children with autism with valproic acid, an anti-seizure medicine that can lower carnitine levels, can have serious side effects.

Douglas Wallace, director of the Center for Mitochondrial and Epigenomic Medicine at The Children’s Hospital of Philadelphia, says Beaudet’s findings are in line with his own theory that a number of the genetic defects underlying autism affect mitochondrial function.

“We think this kind of partial energy defect may be an important factor in autism,” says Wallace. He published a paper on 17 April identifying a number of copy number variants — deletions or duplications in stretches of DNA — in people with autism encompassing genes involved in cellular energy production, the structure of neuronal connections, and ion transport³.

Elias says it’s too soon to know whether giving carnitine to children with autism would help. The supplement, which is currently used to treat severe inherited or drug-induced carnitine deficiency, can cause side effects in children, such as intestinal troubles.

If the link between carnitine deficits and autism is repeated in a larger study, clinical trials would then be needed to determine whether carnitine supplements can help prevent or treat the disorder.

References:

1: Celestino-Soper P.B. et al. Proc. Natl. Acad. Sci. USA Epub ahead of print (2012) Abstract

2: Celestino-Soper P.B. et al. Hum. Mol. Genet. 20, 4360-4370 (2011) Pubmed

3: Smith M. et al. Biochim. Biophys. Acta Epub ahead of print (2012) PubMed

Self assembly: Sponge-like structures of inhibitory RNA start as long strands, then fold into flat streets and finally ball up into individual complexes.

Researchers have created sponge-like assemblies of hundreds of thousands of short fragments of RNA, which can be used to dampen the expression of certain genes, according to a study published 26 February in Nature Materials¹.

These complexes, dubbed ‘microsponges,’ merge the delivery system and its contents, potentially allowing the RNAs to better access target tissue and to do so at higher local concentrations.

Short interfering RNAs, or siRNAs, can silence RNA messages that code for protein, and be used to dampen gene expression in cell culture and in living animals. The molecules are also the basis for gene therapy, which might one day be a viable treatment for human disease. 

In the new study, researchers created long strands of RNA designed to self-assemble into complex structures. These strands are composed of repeating stretches of RNA that are complementary to the target sequence. They form long thick sheets and then ball up into particles that are two micrometers in size and contain about half a million copies of the RNA sequence. When these particles enter a cell, the cell’s own RNA machinery cleaves them, releasing individual siRNAs, which can then bind to their targets and suppress gene expression.

To test the function of microsponges in live animals, the researchers injected a cancer-causing virus into the haunches of mice. The cancer cells also express a blue protein that helps researchers gauge levels of gene expression. Injecting siRNAs against this blue protein into the tumors lessens the amount of color after four days, the study found.

Similar constructs could be used to dampen the expression of autism-associated genes in mice, or in other models, such as zebrafish.

References:

1: Lee J.B. et al. Nat. Mater. 11, 316-322 (2012) PubMed

Memory booster: Individuals with autism have more trouble holding on to information required to complete a cognitive task than do controls, which could be alleviated by an anxiety drug.

Propranolol, a drug used to treat heart disease and anxiety, might improve memory and attention deficits in autism, according to a study published in the May issue of the Journal of the International Neuropsychological Society¹.

Individuals with autism often have attention deficits and problems with working memory — the ability to temporarily store and manage information to complete cognitive tasks — although these are not core features of the disorder. Researchers consider these skills to be part of a cognitive process called ‘executive function,’ which is regulated by the prefrontal cortex.

Propranolol, sometimes marketed as Mylan 6180, inhibits the chemical messenger norepinephrine, which is known to play a role in the prefrontal cortex.

In the new study, researchers gave 13 individuals with autism and 13 controls a test to assay three types of executive function: working memory, the ability to inhibit actions and the ability to pay attention to a specific task. The researchers showed the participants a series of letters and asked them to press one button when they saw an ‘X’ after an ‘A,’ but another button when they saw a different letter after the ‘A.’

The majority, 70 percent, of the letter combinations they presented to participants were ‘AX.’ The researchers also presented three other combinations, each ten percent of the time: ‘AY’ to assay inhibition, ‘BX’ to test working memory (in particular whether participants remembered the relevance of ‘A’ to the task) and ‘BY’ to measure whether participants remembered the task at all.

Individuals with autism show deficits in working memory compared with controls; they erroneously pressed the button 19 percent of the time compared with 3 percent of the time in response to a ‘BX’ combination, the study found. They also show some problems with attention, making an error 4.1 percent of the time for a ‘BY’ combination compared with 0.5 percent for controls. They did not show a significant difference in error rate for the ‘AY’ combination, a test of their ability to inhibit a response, however.

The participants each visited the facility and were tested twice. In one case they took propranolol and in the other a placebo. Neither the participants nor the researchers knew which compound had been administered. Treating individuals with propranolol improves working memory and attention in individuals with autism, but has little to no effect on controls, the study found.

Individuals with autism made an error on the working memory task 7 percent of the time on propranolol and 19 percent of the time on placebo, and their error rate on the attention task improved by a little more than one percent with propranolol.

The results are preliminary, but suggest that compounds that target the norepinephrine pathway show potential for treating executive function deficits in autism, the researchers say. 

References:

1: Bodner K.E. et al. J. Int. Neuropsychol. Soc. 114, 1-9 (2012) PubMed

PNAS

One of the most striking findings in recent years regarding the genetics of neurodevelopment is the variety of problems that can result in different people from spontaneous deletion of the exact same stretch of DNA.

Deletion or duplication of a chromosomal region known as 16p11.2, for example, present in about one percent of people with autism, is also linked to schizophrenia, speech delay and other cognitive impairments. And sometimes people with this genetic event have no observable symptoms.

What leads some people to develop more severe disorders and others to have much milder problems, or none at all? One possibility, of course, is that those who are more severely affected have secondary mutations that influence the outcome, or were exposed to environmental risk factors. But some scientists are flipping that logic on its head, looking for protective factors that might prevent people with high-risk mutations from developing a disorder.

“We are all looking for susceptibility genes, but we should also look for protective genes,” because insights from how those mutations exert their beneficial effects could provide important leads to developing treatments, says Thomas Bourgeron, professor of genetics at the Institut Pasteur in Paris, said at the Translational Neuroscience Symposium in Switzerland in April.

When searching for the effects of mutations in SHANK2, a gene that has been linked to autism and other disorders, Bourgeron has found rare instances of people with a deletion of this gene who have no discernable features of autism. “We want to study more people like that, whom I call ‘survivors,’” he says.

Bourgeron and others are searching the genomes of families that have both children with autism and unaffected siblings, with the idea that mutations more common in unaffected siblings could be protective.

Rather than searching the genome, Kevin Pelphrey is looking for protective factors in the brain itself. His team has done brain imaging studies of children with autism, their unaffected siblings and typically developing children. The researchers presumed that although unaffected siblings show no outward signs of autism, because of the hereditary nature of the disorder, they might have some genetic risk factors.

In research published in 2010, Pelphrey’s team found significant differences in brain activity between controls and unaffected siblings, even though their outward behavior was the same. Those differences, seen in the right posterior superior temporal sulcus and ventromedial prefrontal cortex (and highlighted in green in the image above), could reflect the brain’s successful attempt to compensate for changes driven by genetic risk factors. The two brain areas have previously been implicated in aspects of social perception and social cognition.

To better understand these putative compensatory regions, Pelphrey and his collaborators are using transcranial magnetic stimulation — a non-invasive tool that can influence brain activity — guided by functional magnetic resonance imaging to inhibit activity in those areas. They then look at a variety of measures, including eye tracking and response to biological motion, both of which are impaired in people with autism, to see if they observe temporary autism-like behavior in these unaffected siblings.

As Bourgeron notes, searching for protective factors has its challenges. “It’s hard to get funding to look at healthy controls,” he says. And because protective factors may be rare, “you need to look at a lot of them.”

For more reports from the 2012 Roche Translational Neuroscience Symposium, please click here.

Counter point: An unprocessed version of the growth factor BDNF is overrepresented in autism brains.

The brains of individuals with autism have higher-than-typical levels of the precursor to a neuronal growth factor called BDNF, according to a study published in the April issue of the Journal of Neuropathology and Experimental Neurology¹. The results suggest a mechanism for altered brain development in autism.

BDNF, or brain-derived neurotrophic factor, plays a role in the growth and migration of neurons in the brain. It also functions at synapses, the junctions between neurons, and regulates processes that underlie learning and memory. Mice that model Rett syndrome, an autism-related disorder, have lower-than-typical brain levels of BDNF. Studies have also found elevated antibodies against BDNF in the blood of individuals with autism².

In the new study, researchers looked at levels of BDNF in the fusiform gyrus — a brain region that plays a role in face processing — from the postmortem brains of 11 individuals with autism and 14 controls.

The brains from individuals with autism have the same amount of BDNF mRNA, the genetic message that codes for protein, compared with controls, the study found. However, they have more antibodies that react with BDNF protein than do the control brains.

A technique that detects the amount of actual protein in the tissue shows that there is more of an uncleaved precursor form of BDNF — at 32 instead of 14 kilodaltons — in the autism brains compared with controls. The effects of the precursor are the opposite of the mature protein: Instead of stimulating growth, it dampens formation of dendritic spines, the signal-receiving branches of neurons, and can induce neuronal cell death³.

It also promotes a process called long-term depression, which is a period after neurons fire and before they are ready to signal again. By contrast, mature BDNF promotes long-term potentiation, which strengthens neuronal connections in response to experience and plays a role in learning and memory.

Changes to the balance of the precursor and mature form of BDNF may underlie some of the biological changes in the brains of individuals with autism, the researchers say.

References:

1: Garcia K.L. et al. J. Neuropathol. Exp. Neurol. 71, 289-297 (2012) PubMed

2: Nelson K.B. et al. Ann. Neurol. 49, 597-606 (2001) PubMed

3: Koshimizu H. et al. Mol. Brain 2, 27 (2009) PubMed

Food for cells: A new medium for growing induced pluripotent stem cells generates neurospheres — clusters of neural stem cells — more consistently than before.

After listening to a recent talk on induced pluripotent stem (iPS) cells — adult cells that have been reprogrammed to a more flexible state — a researcher who studies autism joked that his department head told him he had better start collecting skin cells from study participants or risk not getting tenure.

His joke illustrates how widespread the use of these cells has become since they were developed less than a decade ago¹. Their allure, especially for neuroscientists, stems from the fact that the cells can theoretically be differentiated into any cell type in the human body. Researchers can generate neurons from healthy people and compare them to those derived from people with different disorders to search for molecular and cellular flaws.

But as more money is being poured into the field, some are worried that the technique is not yet robust enough to truly reveal the underpinnings of human disease.

The major issue concerns the variability among different lines of cells. iPS cells are created by taking skin cells or other mature cells from an individual and adding them to a specific cocktail of chemicals, which returns them to a stem cell, or immature, state. But individual iPS cells vary in their ability to differentiate into specific types of adult cells. Even under the same laboratory conditions, one cell line might give rise to a large percentage of neurons while another might be much less efficient.

That variability stems from both their genetic background and the way they are isolated, says Rudolf Jaenisch, professor of biology at the Massachusetts Institute of Technology. Then the problem becomes, “If you find differences between diseased and healthy cells, is it due to the disease or to system variation?”

Suppressing variability:

Over the last few years, researchers have developed iPS cells from people with autism-related disorders, including Timothy syndrome and Rett syndrome, and used them to pinpoint differences between those cells and others derived from typically developing individuals^2,3. Cells derived from individuals with Rett syndrome, for example, tend to have smaller cell bodies and develop fewer synapses, which researchers say mirrors findings in animal models of the disease.

But previous research has suggested that the reprogramming process does not completely erase all the markings of the adult cell from which it is derived, a likely source of variability. This could prove a particular problem for disorders linked to genetic defects on the X chromosome, including the autism-related disorders Rett syndrome and fragile X syndrome. Because women have two copies of the X, one is randomly inactivated in all adult cells. That process appears to be variably affected during the reprogramming and differentiation of iPS cells and could influence the subsequent expression of many genes in the cells.

Two new studies published 4 May in Cell Stem Cell aim to clarify this issue by systematically analyzing X chromosome inactivation in iPS cells. One study, which analyzed more than two hundred lines of human stem cells, found considerable variability in expression of genes on the X chromosome^4,5. Both found that iPS cells initially maintained the inactivation pattern of their parent cells but gradually lost it, eventually expressing both copies of genes on the X.

In the second study, researchers analyzed a stem cell model of Lesch-Nyhan syndrome, a severe neurological disorder caused by mutations in the X-linked HPRT gene. Neurons derived from newly created iPS cells initially showed clear signs of disease, including shorter neural projections, then lost these traits as they went through more rounds of cell division.

This could explain some inconsistencies in iPS cells derived from people with Rett syndrome. In some studies, iPS cells from individuals with Rett seem to maintain the inactivation of their parent cell, while others reactivate both copies of the gene⁶.

As concerns over variability grow, some of those who have been working with these cells since the get-go are now trying to find ways around the problem.

Controlling the pipeline:

One approach to distinguishing changes that truly result from the disease-linked mutations rather than from the reprogramming process is to examine many cell lines, both from the same and different individuals, searching for changes that occur in a number of patient-derived lines but not in controls. But researchers say that is an expensive and time-consuming approach that is not practical for most labs. It costs about $7,000 to $15,000 to generate a single iPS cell line, which doesn’t include the cost to differentiate the cells into neurons and the subsequent analysis. Researchers typically create about three lines per person.

Jaenisch plans to study iPS cells from people with Rett syndrome, which is caused by mutations in a known gene. Rather than comparing these Rett iPS cells to cells from typically developing people, his team will correct the genetic defect in the same line of Rett cells. That will create a more closely matched control.

“Now you have two pairs of cells that are genetically identical and identical in derivation, so you’re comparing apples and apples,” says Jaenisch. “If you then find a difference between these lines, you can be reasonably confident that it is disease-relevant and not caused by differentiation.”

However, this approach will only work for monogenic diseases in which the responsible gene is known. Given that polygenic disorders and those of unknown genetic cause, including most cases of autism, are much more common, researchers need to find other solutions.

Alysson Muotri, assistant professor of cellular and molecular medicine at the University of California, San Diego, and one of the scientists who first created iPS cells from people with Rett, aims to reduce variability by improving the method for making neurons from iPS cells. At a conference in Switzerland last month, he described a systematic approach for creating new media for growing neurons. 

“We tried every condition for every ingredient in the stem cell media,” he says, eventually creating a brew with fewer ingredients that can be created in large volumes. “The medium was able to reduce the variability in our neuronal differentiation protocol, and the number and quality of the neurons we get are more homogenous and consistent.”

Thomas Südhof, professor of molecular and cellular physiology at Stanford University in Palo Alto, California, says it’s elegant work. But he is concerned that it doesn’t address the core problems associated with generating different cell lines from the same parent cell. 

Solving these questions might require larger-scale efforts, such as a new project at the Allen Institute for Brain Science in Seattle, which will focus in part on developing standardized methods for creating iPS cells and specific neuronal cell types, which will then be distributed to the broader research community.

“It’s going to be expensive to do right, but it’s important because it will help us decide if this is something we can use,” says Huda Zoghbi, professor of molecular and human genetics at Baylor College of Medicine in Houston. “We need to answer questions like how many cell lines need to be generated per person” to get a reliable result. She also points to the importance of publishing negative results, since scientists outside the field might not have a good sense of the level of variability inherent in this technique.

Pharmaceutical push:

Academic researchers aren’t the only ones interested in iPS cells. Pharmaceutical companies are beginning to use these cells to try to identify molecular and cellular deficits associated with specific disorders.

Roche, for example, aims to employ these cells to better understand neurodevelopmental disorders and help focus its drug development efforts.

“We plan to use them not just for drug screening, but to gather more information on the convergence of molecular pathways,” says Luca Santarelli, head of neuroscience at Roche.

Researchers there will create cell lines from people that have genetically defined types of autism, such as fragile X syndrome. Once they create neurons from these cells, “we will start studying those signatures we can see in different genetic types of the disorder,” he says.

But before they start, researchers are assessing the technology and identifying whether the variability among cell lines is smaller than the variability caused by disease-linked mutations.

Here, pharmaceutical companies have an advantage over most academic labs, thanks to greater resources and experience with large-scale standardization. Roche scientists will create several cell lines from each individual, as well as from each skin cell, in order to measure the variability of the procedure.

“If [changes caused by the disease-linked mutation] are washed away by the amount of variability the technique produces, then we have a problem,” says Santarelli. “But I don’t think anyone knows yet the endgame on that.”

For more reports from the 2012 Roche Translational Neuroscience Symposium, please click here.

References:

1: Takahashi K. et al. Cell 131, 861-872 (2007) PubMed

2: Paşca S.P. et al. Nat. Med. 17,  1657-1662 (2011) PubMed

3: Marchetto M.C.N. et al. Cell 143, 527-539 (2010) Abstract

4: Nazor K.L. et al. Cell Stem Cell 10, 620–634 (2012) PubMed

5: Mekhoubad S et al. Cell Stem Cell 10, 595-609 (2012) PubMed

6: Farra N et al. Mol Psychiatry Epub ahead of print (2012) Pubmed

Last week, some of the best minds in autism research gathered at a symposium in Switzerland to debate how to use recent advances, most notably in the genetics of the disorder, to aid development of new treatments.

It became clear that one of the biggest stumbling blocks is autism’s complexity. The disorder’s diversity has been evident for years, manifesting in the myriad different behaviors shown by people who have it. But now genetic studies have revealed a far greater level of molecular complexity than scientists anticipated, implicating hundreds of genes in the disorder.

Having hundreds of possible treatment targets makes it challenging to choose where to focus drug development efforts. But researchers hope to cut through this complexity by focusing on the synapse, the junction between neurons. A number of genes linked to autism code for proteins that function at the synapse, and dysfunction at these vital communication points is thought to underlie at least some of the deficits associated with autism.

Even there, drug developers hope for further simplification. Perhaps the symptoms of autism could be ameliorated with just a handful of drugs, some designed to turn up the activity of the synapse and some to turn it down.

But some research presented at the conference highlights just how complex the synapse is. Tom Südhof, professor of molecular and cellular physiology at Stanford University in Palo Alto, California, presented work showing that a single mutation can influence the activity of synapses differently depending on the cell type and its location in the brain. A single mutation can even affect the function of two synapses on the same neuron in different ways.

Südhof’s team studies mice with a mutation in neuroligin-3, one of the first synaptic genes linked to autism. Knockout mice, which lack the gene, have few outward symptoms of the disorder and no changes in strength of synapses. So-called knock-in mice, which are engineered to carry a version of the gene that mimics one of the human mutations, show increased excitatory synaptic strength in the hippocampus. The effect in the somatosensory cortex — an area involved in processing touch — however, is completely different.

“The mutation acts in a context-specific manner,” Südhof says. 

In unpublished research presented at the conference, Südhof and his collaborators recorded electrical signals at two inhibitory synapses on the same postsynaptic neuron in knockout and knock-in mice, a technically demanding experiment. They found that the same mutation has opposite effects on the postsynaptic cell, depending on the type of presynaptic cell. In one case, the mutation increases the strength of the synapse, while in the other, it is weakened. To make things more complicated, that response depends on the frequency at which the presynaptic cell is stimulated.

“Something like this has never been done on other mutations,” Südhof says. “It’s a level of complexity that I think is important for understanding the brain, but is not necessarily welcomed.”

Luca Santarelli, head of neuroscience at Roche, the pharmaceutical company that sponsored the conference, is still optimistic. “Understanding everything from the bottom up is very challenging,” he says. “As we think about drug discovery, we probably have to examine the effects of a number of genes until we identify clear patterns.”

If new mutations follow certain patterns, researchers may then be able to identify clusters of biological changes, each of which could be targeted with different drugs. “Then we are starting to talk about something more tractable from a pharma perspective,” Santarelli says.

For more reports from the 2012 Roche Translational Neuroscience Symposium, please click here.