A genetic disorder tied to autism turns out to affect 1 in 7,300 people

Phelan-McDermid syndrome, a rare genetic disorder in which many patients also have autism, may affect about 1 in 7,300 people, according to researchers at Mount Sinai in New York. That works out to 13.7 cases per 100,000 and, by the team’s reckoning, more than 45,000 people in the United States, far above the number who carry a diagnosis today.

An estimate built from autism testing records

The figure is a modelled estimate rather than a head count of the general public, and the distinction governs how every number in the study should be read. The study’s authors at Mount Sinai’s Seaver Autism Center for Research and Treatment pooled genetic testing results from nearly 180,000 people with autism, drawn from ten independent sources, then adjusted for several gaps in the record to reach a rate for the population as a whole.

The ten sources, as Mount Sinai’s release lists them, include the commercial testing laboratories GeneDx, Labcorp and Ambry Genetics, the SPARK research study, the Autism Sequencing Consortium and several large children’s hospitals. The adjustments covered undiagnosed cases, the limits of the tests themselves, and people with the syndrome who do not meet criteria for autism, all of whom a database built from autism testing would otherwise miss or undercount.

Tess Levy, a genetic counselor at the center and first author of the paper, said the gap between known and estimated cases is probably due in large part to the fact that many people with developmental disabilities and autism are never offered genetic testing. Joseph Buxbaum is the senior author. The paper appeared in the journal Autism Research in 2026, and the release gives June 28, 2026 as its publication date, so the finding is several months old rather than fresh. The work was supported by CureSHANK, the patient-advocacy group, and by Neuren Pharmaceuticals, according to News-Medical’s account.

The SHANK3 gene and the autism link

Phelan-McDermid syndrome is usually traced to a deletion near the end of chromosome 22, or to a change in the SHANK3 gene that sits there. MedlinePlus Genetics, from the National Library of Medicine, describes developmental delay, intellectual disability and impaired speech as characteristic signs, and notes that some people with the condition have autism or autistic-like traits. The link to autism is therefore real but partial: the syndrome is not a form of autism, and not everyone who has it meets the criteria.

That partial overlap is why the new estimate had to correct for people outside autism clinics. A rate calculated only from autism testing would lean toward patients who were tested because of an autism diagnosis, and the team’s adjustments were meant to account for that. How much the final figure depends on those adjustments is the main thing a reader cannot judge from the press materials, since the release reports a single point estimate and does not walk through the correction steps.

Clinical trials and the diagnosis gap

CureSHANK said the estimate more than doubles the earlier working figure of roughly 1 in 15,000, a number the group cites as the prior understanding in its account of the study. The same page quotes its board chair, Geraldine Bliss, saying there are likely tens of thousands of people with the syndrome who have never received a genetic diagnosis, and it flags that some current tests may not adequately evaluate SHANK3.

The timing matters to families because treatments are being tested, and a diagnosis is the gateway to enrolling in a trial or receiving specialist care. Mount Sinai’s release ties the revised prevalence to clinical trials of targeted therapies now underway, on the logic that patients cannot benefit from precision medicine if they are never diagnosed. Bliss made essentially that argument in the CureSHANK statement, and the same sentence appears in the Mount Sinai release.

The Mount Sinai team’s own wording is “may.” A short HealthDay item for clinicians reports the same result as approximately 1 in 7,300, or 13.7 per 100,000, in the general population. None of the accounts read presents it as a count of confirmed patients; all of them describe a calculated prevalence.

How many of the 45,000 or so estimated Americans can actually be found is unsettled. MedlinePlus counts more than 2,200 people diagnosed with the 22q13.3 deletion form worldwide, a figure that sits far below what the Mount Sinai model implies for the American population alone, though the two numbers count different things, one being diagnoses recorded worldwide for the deletion form and the other a modelled total of people living with the syndrome. The study itself attributes much of the distance between diagnosed and estimated cases to testing that was never ordered.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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