U.S. researchers looking for genetic changes linked to autism reported on Monday an advanced gene test that searches for deleted or extra DNA in chromosomes worked three times better than standard tests.

They said the test, known as a chromosomal microarray analysis or CMA, should be used in the first round of testing done to look for a genetic cause for a child's autism.

Autism is a mysterious condition that affects as many as one in 110 U.S. children. The so-called spectrum ranges from mild Asperger's syndrome to severe mental retardation and social disability, and there is no cure or widely accepted 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 percent of autism cases.

The newer chromosomal microarray analysis 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," Dr. David Miller of Children's Hospital Boston, who worked on the study published in the journal Pediatrics, said in a telephone interview.

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 percent of patients. Fragile X tests were abnormal in 0.46 percent of patients, while results of the CMA test turned up abnormalities in 7.3 percent of patients.

"What we showed here 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 5 percent of cases.

Miller said genetic testing helps families that already have one child diagnosed with autism assess their risk of having another child with autism. And it can help parents get early intervention for a younger sibling that might be too young for an autism diagnosis.