A new genetic test for autism is a big improvement but still has a long way to go

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For a reality check on how much scientists know about the genetics of autism, consider a study being published in Monday’s edition of the journal Pediatrics.

The study reports that a kind of genetic testing method known as a chromosomal microarray analysis – CMA for short – is about three times better at finding genetic variants related to autism-spectrum disorders than the two kinds of tests currently used.

Researchers from Children’s Hospital Boston and their colleagues ran the tests on DNA samples from 933 patients age 13 months to 22 years. All were diagnosed with autism-spectrum disorders. Here’s how the tests stacked up:

• A karyotyping test, which analyzes the size, shape and number of chromosomes, found “abnormal results” in 2.23% of patients.
• A test for Fragile X syndrome, a genetic condition known to cause autistic behavior, found abnormal results in 0.46% of patients.
• The CMA test, which looked for telltale duplications and deletions of DNA, found abnormal results in 7.3% of patients.

Clearly, the CMA test was most effective, and the study’s authors say the test should be offered to patients as a first-line test.

“CMA clearly detects more abnormalities than other genetic tests that have been the standard of care for many years,” said study coauthor Dr. David Miller, of the hospital’s Division of Genetics and its Department of Laboratory Medicine, in a statement. “We’re hoping this evidence will convince insurance companies to cover this testing universally.”

However, for the overwhelming majority of patients who take it, the test won’t turn up anything suspicious. That’s not necessarily surprising, considering that only about 15% of autism cases have a known genetic cause. But it certainly underscores the limitation of all of these types of tests, said Andy Shih, vice president for scientific affairs for Autism Speaks, which funds research on the disease.

“The utility of this test in actual clinical settings is not clear,” Shih said. “Until we know more about the association between some of these variants and actual autism risk, it’s difficult to see how this could benefit the family now.”

-- Karen Kaplan