March 15, 2010 -- A new genetic test for autism, known as chromosomal microarray analysis (CMA), finds more genetic abnormalities than two older tests, a study shows.
''CMA is much better than karyotyping or fragile X testing at detection -- it's at least three times better," Bai-Lin Wu, PhD, medical director of the genetics diagnostic laboratory at Children's Hospital, Boston, and a study co-researcher, tells WebMD.
While the other two tests are now standard practice, Wu and his colleagues say the new test should also be part of the initial diagnostic evaluation of patients when a clinical diagnosis of autism or autism spectrum disorder has been made or is suspected.
The study results are published online in Pediatrics.
Autism, a complex disorder, involves impairments in social interaction as well as deficits in language and communication along with rigid and repetitive behaviors. It affects about one person per 1,000, the researchers write; autism spectrum disorder (ASD) affects six per 1,000.
Comparing CMA With Other Tests
The researchers compared the results of the three tests in more than 800 patients. Among the findings:
- The standard genetic test known as G-banded karyotype testing found abnormal results in 19 of 852 patients, or about 2%.
- The fragile X testing found abnormalities in four of 861patients, or about 0.5%. (Fragile X syndrome is a condition associated with autism.)
- The CMA test found abnormalities in 154 of 848 patients, or about 18%; 59 of these, or about 7%, were associated with possible or known genetic disorders.
''Karyotype testing is looking for changes visible by the microscope," Wu, a clinical molecular geneticist, tells WebMD. "CMA is looking at the molecular level."
Wu and co-researcher Yiping Shen, PhD, assistant director of the genetics diagnostic laboratory, compare karyotype testing to a map that can detect a highway that's missing in a state, and CMA testing to a map that can detect individual highway exits that are missing.
In the study, Shen and his colleagues say that CMA ''should be considered as part of the initial diagnostic evaluation of patients with ASD."
CMA an 'Excellent' Test
The new study confirms smaller studies finding that CMA is an excellent test, says Randi Hagerman, MD, medical director of the MIND Institute at University of California, Davis, and an autism expert.
''This [new study] demonstrated that the CMA picked up abnormalities at a much higher rate [than other tests]," says Hagerman, who reviewed the findings for WebMD.
The patients studied, she says, were a relatively high functioning group of people with ASD. That population, she says, ''reflects more closely what clinicians are seeing now in their office." She says the rate of intellectual disabilities of those with autism and ASD has gone down in recent years.
The bottom line of the study? "You should do genetic testing on everyone with autism or ASD," Hagerman says. "That's been the recommendation for years." With the new study findings, she says, the message is clear that "you should include CMA."
Doing all three tests would be ideal, she says. But if you can only do two, she would pick fragile X and CMA. If someone has autism or ASD, she says, the CMA test "is the No. 1 test to yield an abnormal result."
Limits of Autism Testing
Genetic testing can help parents get early intervention, Wu says. And it can help them in family planning, predicting the risk of having another affected child.
But genetics still only explains a minority of autism and ASD cases, Wu says, perhaps up to 15%. CMA can help detect about half of that 15%.
One other obstacle, Hagerman and others say, is that insurance does not always cover the costs. Fees vary, but the CMA alone can cost about $1,200 in California, Hagerman says.
Andy Shih, PhD, a spokesman for Autism Speaks, cautioned in an email to WebMD that "this CMA methodology is not yet ready for commercial application and does not specifically test for autism and therefore is a tool of limited value for concerned parents and families."
He calls for more research on the new test, "especially on how to interpret the findings from CMA relative to autism risk, before it can help families make more informed health care decisions."