The contribution of genetics to autism is well established. Studies in twins provide early evidence that the risk of having siblings with autism in the same family is higher than would be expected by chance. Since then, more and more studies have shown that autism is transmitted in families. Heritability studies estimate that genetic variation is responsible for as much as 90 percent of the variability seen in autism. New research suggests that the recurrence risk may be even higher given that “affected” siblings of autistic children often suffer from milder, under-diagnosed, pervasive learning disabilities.
Because scientific evidence points to genetics as the primary contributor to autism, medical societies, such as the American College of Medical Genetics, recommend genetic testing for all children with autism and developmental disorders. A powerful new technology known as chromosomal microarray (CMA) is recommended as the first-line test because it has the ability to detect even the smallest genetic variations that can disrupt a genome and cause a spectrum of neurodevelopmental disorders. Older genetic tests such as standard karyotyping do not offer the same resolution as CMA, and so searching for important genetic mutations using conventional tests is no longer considered as accurate as it once was. DNA samples that are analyzed by CMA can now be obtained from a simple cheek swab.
In many cases, CMA genetic results provide physicians with quick, objective answers to a child’s disorder and clues about the underlying biology. A genetic assessment also allows clinicians to provide personalized clinical management based on the child’s result. In some cases, CMA discovers well-known genetic findings associated with a disorder that resembles autism for which there are established medical treatment guidelines. An example here would be Angelman syndrome. Such CMA findings underscore the critical importance of genetic results and the impact it has on clinical decision-making and positive changes to a child’s clinical management.
In addition to Angelman syndrome, there are an estimated 700 disorders of childhood development with overlapping symptoms that resemble autism. This fact explains why an accurate diagnosis using clinical symptoms alone is difficult and why genetic testing has such a powerful impact on the diagnostic evaluations of children. Another genetic disorder whose clinical presentation resembles autism is fragile X syndrome, for which there are also medical treatment guidelines and promising new therapies. Doctors recommend that children with autism undergo testing for fragile X syndrome.
Combined CMA and fragile X testing currently provides a genetic answer in approximately 20-30 percent of children with autism and related neurodevelopmental disorders. Because CMA technology keeps improving with higher resolution platforms and the identification of more target genes for autism, the number of affected children with clinically meaningful genetic variants continues to climb. Although CMA provides definitive answers for many of these children, in some cases, findings are identified that are suggestive of causing autism or that have only recently been associated with autism and related disorders. Because the clinical meaning of such results are less clear, genetic testing in autism is not medically recommended as a predictive test for autism. This means that genetic testing is currently not recommended in very young children (i.e. newborns) who do not have worrisome symptoms.
As the future of genetic testing for autism unfolds, it is highly likely— perhaps almost certain— that genetic tests will be developed to detect autism in infancy. These future developments mean a great deal for children with autism because early intervention is crucial. Research has shown that the earlier a child with autism receives intervention, the more positive his or her outcomes are likely to be. Children who receive top-quality, intensive behavioral intervention from a young age can make tremendous gains, with a minority achieving functioning levels that are equal to same-age, typically developing peers. Genetic testing is the best hope for identifying the need for intervention at the earliest possible age because behavioral symptoms will never be detectable as early as genetic testing can be done.