Doctors have known for many years that patients with fragile X syndrome, the most common form of inherited intellectual disability, are often also diagnosed with autism. But little has been known about how the two diagnoses are related. Now a collaborative research effort at Duke University Medical Center and Rockefeller University has pinpointed the precise genetic footprint that links the two. The findings, published online in the journal Nature on Dec. 12, 2012, point the way toward new genetic testing that could more precisely diagnose and categorize the spectrum of autism-related disorders.