Is the prevalence of Phelan-McDermid higher than thought?

The prevalence of Phelan-McDermid syndrome (PMS) may be much higher than previously estimated, according to researchers in the United States and Australia.

PMS, a genetic condition caused by a deletion or mutation of the SHANK3 gene, causes a wide range of medical, cognitive, and behavioral problems, and the majority of people with the condition have autism spectrum disorders (ASD). SHANK3 deletions or mutations are believed to cause up to 1% of cases of ASD.

To determine the prevalence of PMD in the United States, Tess Levy and colleagues analyzed data from nearly 180,000 individuals with ASD who underwent genetic testing. The researchers combined data from 10 sources, including clinical genetic testing laboratories, academic medical centers, and autism research programs.

The researchers found that the prevalence of PMD in the United States is 13.7 cases per 100,000 births, far higher than earlier estimates of 2.5 to 10 cases per million births. This suggests, they say, that “more than 45,000 individuals in the United States are currently living with PMS, assuming an average lifespan.”

Levy comments, “The large gap between known and estimated cases is likely due in large part to the fact that many individuals with developmental disabilities and autism are never offered genetic testing. Families may also face insurance barriers or may receive tests that do not adequately evaluate the SHANK3 gene.”

The low rates of genetic testing are especially concerning, the researchers say, because “genetic diagnoses are becoming increasingly actionable.” They note, “Beyond providing families with a better understanding of their child’s condition and future trajectory, a genetic diagnosis may qualify individuals for clinical trials or targeted therapies that could significantly alter outcomes.”

Citations

“Prevalence of Phelan-McDermid syndrome estimated to be ~1:7300 using a multisource model,” Tess Levy, David Lapidus, Kate Friedman, Paige Siper, Larry Glass, Liza Squires, Mary Hames, Joseph D. Buxbaum, Genetic Testing Consortium, and Alexander Kolevzon, Autism Research, July 2026 (free online). Address: Alexander Kolevzon, [email protected].

—and—

“Autism research finds Phelan-McDermid syndrome may affect 1 in 7,300 people: More common than previously thought,” news release, Mount Sinai Hospital, July 10, 2026.