A team of scientists at the Hopkins Institute for Genetic Medicine has identified a potential genetic risk factor for autism, a devastating childhood brain disorder. The finding might help scientists to better understand the biological underpinnings of this condition.
A common variant in the gene, called CNTNAP2, increases the likelihood of developing autism. Around one-third of all individuals have this particular variant, a change of just one letter in the genetic code.
In most people the change does not affect health at all, but in a small number of people with autism, the same change can play a part in a complicated web of genetic and environmental causes that lead to autism.
It has long been known that autism runs in families, but specific genetic causes have been hard to pin down. As many as 80 to 90 percent of all autism cases may be genetic, so the search for genes related to the illness has long been a pressing concern.
The Hopkins researchers, led by Aravinda Chakravarti at the School of Medicine, analyzed the DNA of members of 78 families in which at least one child had autism.
Genetic samples were analyzed on microchips for over half a million small genetic markers that together comprise a snapshot of an individual's genetic makeup. By comparing the genotype at each of these markers, called SNPs, scientists can identify regions of DNA that are more commonly found in people with an illness than in the general population.
The gene the Hopkins group found, CNTNAP2, is part of a large family of proteins called neurexins which are responsible for connecting brain cells. Since autism arises in the developing brain, this genetic discovery could help scientists who are investigating the biology of the illness.
Interestingly, the variant was much more likely to be found in autistic boys than girls, and it was also much more likely to come from the mother than the father. This is consistent with the known inheritance patterns of autism, which affects boys over four times as often as girls.
The CNTNAP2 variant increases the risk of developing autism but does not cause the disease on its own. Because this genetic variant is found in a large number of neurologically normal individuals as well, it is unlikely to be useful in predictive tests for autism.
