Toward a more effective genetic test for autism

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Expecting parents who have one child or other family members with an autism spectrum disorder often request genetic testing to determine their unborn child’s risk for autism. Currently, however, the most frequently used genetic tests—karyotyping, which examines a sample of cells for abnormalities and testing for Fragile X syndrome, a condition that can cause developmental problems and is known as a leading genetic cause of autism spectrum disorders—most often come up negative. Yet another technique, known as chromosomal microarray analysis (CMA), which examines the entire genome, homing in on tiny variations in DNA sequences, may offer better, more accurate results, according to a large-scale study published in the April issue of the journal Pediatrics.

Researchers from Children’s Hospital Boston and Autism Consortium analyzed the results of the three types of genetic testing on a group of 933 children between the ages of 13 months and 22 years, who had all been diagnosed with an autism spectrum disorder. (Roughly half of the patients had been diagnosed with autism, and half with a condition known as pervasive developmental disorder not otherwise specified (PDD-NOS), and a small group, about 3% of patients, had been diagnosed with Asperger’s syndrome.)

Though all of the children included in the study had been diagnosed with an autism spectrum disorder, the karyotyping test showed abnormal results for just 2.23% of study participants, and tests for Fragile X syndrome yielded abnormal results in just .46% of cases. In contrast, the CMA test showed abnormal results for 7.3% of patients.

The findings suggest that CMA testing is substantially more effective than the two currently used genetic tests. What’s more, because of its detailed assessment of the entire genome, CMA testing may help autism researchers and specialists home in on very specific genetic DNA variations causing autism and tailor treatments accordingly, the researchers say. That’s a promising development considering that some 15% of autism cases have a genetic cause.

Yet, even though CMA testing may produce more accurate results—yielding genetic diagnoses in 5% more cases than the other two tests combined, according to researchers’ estimates—it still won’t provide any answers for the vast majority of people given the test. Still, in the ongoing battle toward better understanding and diagnosis of autism, it’s a step forward.

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