New Genetic Test for Autism Could Help Improve Diagnosis and Treatments
Genetic cause is thought to be a factor in about 15% of autism spectrum disorder (ASD) patients. A genetic test for autism currently used as a secondary approach may be better able to pick out the underlying causes for the condition more than that of a first-tier screening test.
The chromosomal microarray analysis (CMA) test was developed in 2006 at the Children’s Hospital in Boston. The most recent study, co-authored by Bai-Lin Wu of Harvard Medical School said that CMA would allow doctors to find the underlying genetic cause of 7% of autism cases. "From the number itself, 7 percent does not look like a large percentage," Wu said. "However, there are a lot of kids being diagnosed with autism, so it is 7 percent of a very large number."
Wu said the tests currently used as a first-tier test for autism may only detect 2 percent of the genetic abnormalities that could be behind the development of autism. Linking an additional 5 percent of these cases to a genetic cause would mean an explanation for 2,000 more cases of autism each year.
The other two genetic tests for autism include G-banded karyotype testing and Fragile X testing. Karyotype tests, available since the 1960s, identify chromosomal abnormalities associated with autism in about 2.2% of patients. The Fragile X genetic mutation is found in 0.46% of cases.
CMA tests two known chromosome locations - chromosome 16 (16p11.2) and chromosome 15 (15q13.2q13.3) – which accounted for 17 percent of abnormal findings. Both chromosome abnormalities were initially linked with ASDs by Children's Hospital Boston and collaborators in The New England Journal of Medicine and the Journal of Medical Genetics in 2008. Children's Hospital is one of the few centers around the country that now offers specific tests targeting both of these locations.
The test is not intended to replace current screening tests, but complement them in an overall comprehensive care plan. The detection of more genes associated with autism could bring a better understanding of the cause of autism spectrum disorders and could lead to better treatments tailored to each patient.
Dr. Nancy Minshew, professor of psychiatry and neurology and director of the University of Pittsburgh's Autism Center of Excellence and not involved in the study, said the test could also help parents of an autistic child determine the risk of having another child with autism in the future. If tests point to a chromosomal abnormality, parents are usually offered testing to determine if the deletion or duplication occurred by chance or if the parents have a higher chance of giving birth to another child with autism.
Unfortunately, because the current guidelines do not list CMA as a first-tier treatment, many insurance companies will not reimburse for the additional screening, which can cost a couple thousand dollars.
The study will be published in the April issue of Pediatrics, but is available online March 15.