Phelan-McDermid syndrome (PMS), a genetic disorder strongly linked to autism, may be dramatically more common than previously believed, according to a new study led by the Seaver Autism Center at Mount Sinai. Published in Autism Research, the analysis estimates that the condition affects roughly 1 in 7,300 people — a major jump from earlier figures — and that more than 45,000 people in the United States could be living with it.
The researchers combined data from nearly 180,000 people with autism who had undergone genetic testing, drawing on ten sources including GeneDx, Labcorp, Ambry Genetics, the SPARK study, and several children's hospitals. After accounting for undiagnosed cases and testing limitations, they arrived at a prevalence of 13.7 per 100,000. The large gap between known and estimated cases likely stems from many individuals with developmental disabilities never being offered genetic testing, as well as insurance barriers or tests that inadequately evaluate the SHANK3 gene, said first author Tess Levy.
The findings arrive as several clinical trials for PMS-targeted therapies are underway. Senior author Joseph Buxbaum recommended that every child with autism receive genetic testing, noting that identifying the genetic cause enables more targeted trials and potential treatments. CureSHANK and Neuren Pharmaceuticals, which supported the study, emphasized that patients cannot benefit from advancing therapies without a diagnosis. The results reinforce the global "Start Genetic" campaign and broader efforts to expand access to genetic testing for autism-related conditions.