Phelan-McDermid Syndrome More Prevalent Than Previously Estimated

WEDNESDAY, July 22, 2026 (HealthDay News) — Phelan-McDermid syndrome (PMS), a genetic neurodevelopmental disorder, has a prevalence of 13.7 per 100,000, according to genetic data from multiple sources in a study published online June 28 in Autism Research.

Noting that PMS has an unknown true prevalence, Tess Levy, from the Icahn School of Medicine at Mount Sinai in New York City, and colleagues tried to establish its true prevalence. The study team reached out to a multitude of sources; sites provided the number of PMS diagnoses out of the total number of participants with autism. To adjust for the proportion of individuals with PMS who do not have autism, autism diagnosis age limitations, and type of genetic variant, further extrapolations were made. A total of 10 sources participated; data were evaluated from 179,837 autism cases.

The researchers noted variation in the frequency of PMS diagnoses, from 1.0 to about 2.5 percent. Different levels of sensitivity were seen in the studies based on the assay used. The final weighted average was 13.7 per 100,000 after applying extrapolations, including adjustments for assay sensitivity and other factors, indicating that 1 in about 7,300 individuals in the general population has PMS.

“This study confirms what many families, clinicians, and advocates have suspected for years,” Geraldine Bliss, cofounder and president of CureSHANK, said in a statement. “There are likely tens of thousands of individuals with Phelan-McDermid syndrome who have never received a genetic diagnosis. At a time when multiple therapeutics are advancing into clinical trials, finding these individuals has never been more important.”

Several authors disclosed ties to biopharmaceutical companies, including Neuren Pharmaceuticals, which funded the study together with CureSHANK.

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