In addition, by pinpointing bits of chromosomes that are deleted or duplicated, CMA can help researchers zero in on specific causative genes within that stretch of DNA. They can also begin to classify patients according to the type of deletion or duplication they have, and try to find specific treatment approaches for each sub-type of autism.

"Just in the last two years, a number of studies have revealed the clinical importance of ever smaller chromosome deletions and duplications found with advanced microarray technology," says Wu. "These new, highly-efficient tests can help in the evaluation or confirmation of autism spectrum disorders and other developmental disorders, leading to early diagnosis and intervention and a significantly improved developmental outcome."

Two known chromosome locations - on chromosome 16 (16p11.2) and chromosome 15 (15q13.2q13.3) accounted for 17 percent of abnormal CMA 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, respectively, in 2008. Children's now offers specific tests targeting both of these "hot spots."

However, the researchers note that most copy-number changes were unique or identified in only a small number of patients, so their implications need further study. Many of them are presumed to be related to ASDs because they involve important genes, cover a large region of the chromosome, or because the child is the first person in that family to have the change.

"Some deletions and duplications are rare and specific to one individual or one family," says Miller. "Learning about them is going to be an evolving process. There won't be one single test that finds all genetic changes related to autism, until we completely understand the entire genome."

Source: Children's Hospital Boston