Genetics: Large chromosomal duplications can be harmless
The researchers identified four individuals who have large expansions within chromosome 16 that look similar under the microscope. Two of them have a duplication of the 16p11.2-12.2 region and severe developmental delay, whereas the other two have multiple repeats of a smaller region and no signs of developmental delay.
The similarity between these chromosomal abnormalities during prenatal testing can have grave consequences. For example, a 2006 study describes a woman who aborted a fetus with similar repeats, believing it to be a harmful 16p duplication2.
The new study identified two individuals with a duplication of 16p11.2-12.2. Both have intellectual disability, obsessive behaviors and dysmorphology, and one is diagnosed with autism.
The other two have chromosomes that also look abnormal under the microscope, but no symptoms. More detailed analysis found that both individuals have several extra copies of a relatively small region in the middle of 16p11.2 that does not overlap with the autism-linked region. One individual has six extra copies of a 692-kilobase section, and the other has at least eight extra repeats of a 945-kilobase section.
1: Barber J.C. et al. Eur. J. Hum. Genet. Epub ahead of print (2012) PubMed
2: Lopez Pajares I. et al. Prenatal Diagnosis 26, 535-538 (2006) PubMed