Landmark Study Finds Phelan-McDermid Syndrome May Affect 1 in 7,300 People
This project was funded by CureSHANK and Seaver Autism Center, with additional support from Neuren Pharmaceuticals.
A newly published study has fundamentally changed how we understand the prevalence of Phelan-McDermid syndrome (PMS) and what it means for families still searching for answers.
The study, led by researchers at the Seaver Autism Center for Research and Treatment at Mount Sinai, analyzed genetic data from 179,837 individuals with autism across ten independent sources — including GeneDx, Labcorp, SPARK, and several leading children's hospitals. After adjusting for undiagnosed cases and testing limitations, researchers estimated a prevalence of approximately 1 in 7,300 individuals. That translates to more than 45,000 Americans who may be living with PMS today.
This is a dramatic shift from the previous estimate of 1 in 15,000. And it’s an urgent call to action.
What This Means for Families
While Phelan-McDermid syndrome remains a rare disease, this landmark study suggests far more individuals may be living with PMS than previously recognized. Therefore, the most important takeaway is this: thousands of individuals with PMS are likely undiagnosed.
"This study confirms what many families, clinicians, and advocates have suspected for years," said Geraldine Bliss, Board Chair and Co-Founder of CureSHANK. "There are likely tens of thousands of individuals with PMS 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."
Why Genetic Testing Is the Missing Link
The study identifies underutilization of genetic testing as a major contributor to missed diagnoses. Many individuals with developmental disabilities and autism are never offered genetic testing. Others face insurance barriers, limited access to genetics services, or receive tests that may not adequately evaluate SHANK3, the gene responsible for PMS.
A genetic diagnosis is no longer simply an explanation. It is increasingly a gateway to specialized care, research opportunities, clinical trials, and potentially life-changing therapies.
These findings reinforce the urgency behind CureSHANK's efforts to expand access to genetic testing and the broader goals of Start Genetic, the global awareness campaign launched to encourage patients, families, healthcare providers, and advocacy organizations to think genetic first.
"Every undiagnosed individual represents more than a missing statistic," Bliss said. "It represents a family searching for answers, a person disconnected from support, and a patient who may miss opportunities to participate in research or access emerging therapies. As treatments move closer to reality, identifying these individuals becomes a moral imperative."
A Pivotal Moment for the Field
This publication arrives at a pivotal moment. Multiple PMS clinical trials are underway, including precision medicine approaches designed to address the underlying biology of the condition. The findings underscore a fundamental truth: patients cannot benefit from precision medicine if they are never diagnosed. Expanding access to genetic testing is not simply about finding answers, it’s about opening the door to better care, research opportunities, clinical trials, and emerging therapies.
As the true scale of PMS comes into focus, so does the urgency: investing in research, expanding access to genetic testing, and accelerating treatment development has never been more critical.
Key Findings By the Numbers
PMS prevalence is estimated at approximately 1 in 7,300 individuals.
Researchers analyzed data from 179,837 autism cases across ten independent sources.
The study estimates that more than 45,000 Americans may be living with PMS.
Thousands of individuals with PMS are likely undiagnosed or disconnected from the PMS community.
The study identifies underutilization of genetic testing as a major contributor to missed diagnoses.
The findings underscore the growing importance of genetic testing as precision therapies advance toward patients.
Explore the PMS Prevalence Tracker
View an interactive summary of the study's methodology, prevalence estimates, confidence intervals, and key findings.
View the PMS Prevalence Tracker →Read the Full Study: The findings are published in Autism Research: Levy SE, et al. "Prevalence of Phelan-McDermid Syndrome Estimated to Be ~1:7300 Using a Multisource Model." Read the full publication here: https://onlinelibrary.wiley.com/doi/10.1002/aur.70297
