United States researchers looking for genetic changes linked to autism have reported an advanced gene test that searches for deleted or extra DNA in chromosomes and worked three times better than standard tests.
They said the test, known as a chromosomal microarray analysis (CMA), should be used in the first round of testing to look for a genetic cause for a child's autism.
Autism is a mysterious condition that affects as many as one in 110 US children, but there is no cure or good treatment. Standard genetic tests to look for chromosomal abnormalities and testing for Fragile X, the single largest known genetic cause of autism, often fail to detect anything, even though genes are responsible for up to 15 per cent of autism cases. The newer CMA test is far more sensitive. It searches the whole genome for places where chromosomes have been added, are missing or are in the wrong place. But because it is not recommended for the first round of testing, some insurance companies do not cover it.
"What we're hoping is to provide evidence to make it harder for insurance companies to say we don't want to pay for this," said Dr David Miller of Boston Children's Hospital, who worked on the study published yesterday in the journal Pediatrics.
Miller, a geneticist, said the hospital has been offering all three tests as part of a standard genetic work-up for autism since 2006.
For the study, they compared the performance of the tests done on more than 900 patients with a clinical diagnosis of autism spectrum disorder who got clinical genetic testing in 2006, 2007 and 2008. They found that the standard test spotted genetic abnormalities in 2.23 per cent of patients. Fragile X tests were abnormal in 0.46 per cent of patients, while results of the CMA test turned up abnormalities in 7.3 per cent of patients.
"What we showed is what happens when you order all three of these tests up front. You end up getting more information from ordering the microarray test than from both of the two other tests combined," Miller said.
Based on the findings, the CMA test should be considered a part of the routine diagnostic evaluation for people with autism spectrum disorders, said Bai-Lin Wu, Director of Children's DNA Diagnostic Lab, who led the team. They estimated that without the CMA test, they would have missed a genetic diagnosis of autism in at least five per cent of cases.
Miller said genetic testing helps families who already have one child diagnosed with autism assess their risk of having another child with autism. It can help parents get early intervention for a sibling who might be too young for a diagnosis.