Although the causes of autism remain unclear, research has demonstrated that many factors likely play a role in autism spectrum disorders (ASD). The elements that contribute to an ASD could be complex and interrelated, and the reasons underlying one individual case may differ from those present in another case. Researchers continue to search for genes that may be connected to ASDs, and in a study published yesterday in the Journal of Medical Genetics, researchers from the Stony Brook University Medical Center in New York report a new genetic link. The gene, contactin 4, aids in the formation of axons, the fibers that connect neurons to each other. Alterations in this gene can disrupt the brain's ability to form neural connections, greatly affecting a child's development.
The researchers analyzed the genetic makeups of 92 individuals with an ASD from 81 families. They then compared the results of these subjects with those of 560 individuals without an ASD. The analysis identified three individuals with ASDs who had variations in contactin 4 on chromosome 3. While all control subjects had two copies of the gene, the normal number, two autistic siblings had only one copy, and another unrelated subject had three copies. Subsequent analysis of the parents’ DNA revealed that in all three cases the variation had been inherited from the father. These variations disrupt the ability of contactin 4 to create neural connections and can result in significant developmental delays, social impairment, and mental retardation. The researchers estimate that disruptions to this gene may be responsible for as many as 2.5% of ASD cases. In the grand scheme of the disorder, this percentage is small, but considering the CDC's estimate that 1 in 150 American children is now diagnosed with an ASD, this small percentage will translate into a large number of cases.
While analyzing the subjects' DNA, the researchers also took their family histories into account. The three subjects highlighted in this study all inherited the variation from their fathers, but the fathers, though they also possessed the variation, were not autistic. It's possible that the fathers in these cases have Asperger's syndrome, a mild form of autism, and were never officially diagnosed. However, the researchers also suggest that disruptions in the contactin 4 gene result in an ASD only in combination with some other environmental or genetic factor. They plan to continue their study of contactin 4 using a larger group of subjects and controls.
Other recent studies have pointed toward a related gene, contactin associated protein-like 2, as another potential genetic factor behind some ASD cases, and researchers should continue investigating the role played by variations in genes that facilitate neural connections. By studying potential contributing factors, we may develop a clearer understanding of the origins of ASDs. Treatment is crucial to the lives of children with autism, and as we understand more of how ASDs develop and what factors are involved, we may be able to diagnose children more quickly and provide them with appropriate treatments as early as possible.
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