Chicago ? Scientists have found a new genetic link to autism that appears to affect about 1 percent of people with the disorder and could help resolve some of the mystery surrounding what causes it.

A study published online Wednesday in the New England Journal of Medicine identified a stretch of 25 genes that were either missing or duplicated in 10 children who were diagnosed with autism or a similar developmental disorder.

Experts now must figure out which of the deleted genes contribute most to autism. Understanding that could help researchers develop new therapies for the condition, which affects more than a million Americans.

At the least, identifying the genetic flaw makes it possible to give children a relatively inexpensive diagnostic test for this rare form of autism.

The new report, by researchers with the Autism Consortium, follows a similar finding published last month by a team at the University of Chicago Medical Center. Both groups have zeroed in on the same stretch of genes that appear linked to autism.

“This allows us to really start chasing down the biology of the disorder,” said Dr. Bill Dobyns, a leader of the University of Chicago team that published its results last month in the journal Human Molecular Genetics.

Scientists have long known that autism has strong genetic roots, but previous studies found specific genetic causes for only about 10 percent of cases. In many such cases, autism is just one feature within a developmental defect that can also include mental disability or other cognitive problems.

To find the genetic flaw, the Chicago and Boston researchers ran tests on DNA from more than a thousand patients with autism, scanning their genomes for distinctive variations. They found some people with a patch of genes missing from chromosome 16. In a few cases the defect appeared to be inherited, but in most patients it likely was the result of a spontaneous error in DNA replication.

The Boston team found that some patients had an extra copy of the affected genes, though the Chicago researchers could identify a link to autism only in people who were missing the genes.

No one understands the precise function of the genes, but scientists are intrigued that some appear to regulate the development of synapses – connections between brain cells.