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1 in 7,300: the genetic condition most families never get a name for

Qurexa Editorial Team26 September 20265 min read 0 0
1 in 7,300: the genetic condition most families never get a name for

What happened

Researchers have published an estimate suggesting a genetic condition thought to be rare is a good deal more common than anyone believed. The condition is Phelan-McDermid syndrome, usually shortened to PMS. It is caused by changes affecting a gene called SHANK3, and it is closely linked with autism and developmental disability. The work came from the Seaver Autism Center for Research and Treatment at Mount Sinai in New York, and was published in the journal Autism Research on 25 September 2026. The team pulled together data on nearly 180,000 people with autism from ten different sources. Those included the genetic testing companies GeneDx, Labcorp and Ambry Genetics, and the large SPARK research study. From that, they estimated a prevalence of 13.7 cases per 100,000 people. That works out at roughly 1 in 7,300. Applied to the United States population, that would mean more than 45,000 people have the condition. Very few of them are currently diagnosed. The researchers point to a straightforward reason for that gap. Many people with developmental disabilities and autism are simply never offered genetic testing at all.

Why this matters

For a lot of families, a diagnosis is not a label. It is a key. It tells you which specialists to see. It tells you what to watch for, because many genetic conditions come with known medical issues, such as seizures, kidney problems or particular feeding difficulties. It connects you to other families who have already worked out the practical things. It also changes how people treat a child. "We don't know why" and "this is a known genetic condition" get very different responses from schools, services and relatives. Lead author Tess Levy identified the core problem: "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." Joseph D. Buxbaum, the centre's director, argued for testing more widely: "We recommend that every child with autism undergo genetic testing, because knowledge is power." He added that he expects successful examples of new treatments within the next five years. That last part is a prediction, not a finding, and we would treat it as such. But the underlying logic holds. Treatments under development are usually aimed at a specific genetic cause, and they can only reach people who know they have it.

What the evidence actually says

This is a prevalence estimate, and estimates need reading carefully. The strength here is the size and the breadth. Nearly 180,000 people with autism, across ten separate data sources including several large commercial testing laboratories and a major research cohort. That is a lot of data. The weakness is the method. This is not a study where a whole population was tested. It works by looking at how often the condition turns up among people with autism who did get tested, then scaling up. Every step of that scaling carries assumptions. People who receive genetic testing are not a random sample. They are more likely to have more significant difficulties, or more engaged advocates, or better access to healthcare. That can push an estimate in either direction. The figures are also drawn from US data, and applied to the US population. The 45,000 figure is American. We do not have a verified UK equivalent, and we are not going to calculate one and present it as fact. What the study supports is a clear, useful claim: Phelan-McDermid syndrome is substantially under-diagnosed, and the main reason is that testing is not routinely offered.

Practical advice

If this is relevant to your family, here is what is worth doing in the UK. Ask your paediatrician or GP whether genetic testing has been considered. In England, genomic testing is available through the NHS Genomic Medicine Service, and eligibility is set out in the National Genomic Test Directory. Your clinician can check whether your child meets the criteria. If testing has already been done, ask what kind. Genetic testing has changed a lot, and an older test may not have looked for what a newer one would. Write down your child's history before the appointment. Milestones, seizures, speech, feeding, sleep, any hospital admissions. Clinicians make decisions on detail. If you get a diagnosis, look for a condition-specific charity. Groups such as Unique, the rare chromosome and gene disorder support group, exist precisely to help families through this stage, and their information is free. Be careful with direct-to-consumer genetic tests. They are not the same as clinical genomic testing and can produce results that are hard to interpret, or falsely reassuring. And take your time. A diagnosis does not change who your child is. It changes what support you can ask for.

What to know

Researchers at Mount Sinai estimate that Phelan-McDermid syndrome, caused by changes affecting the SHANK3 gene, affects about 13.7 people per 100,000, or roughly 1 in 7,300. That would mean more than 45,000 people in the United States have it, most of them undiagnosed. The estimate was built from data on nearly 180,000 people with autism across ten sources, published in Autism Research on 25 September 2026. The researchers say the main reason for under-diagnosis is that many people with autism and developmental disabilities are never offered genetic testing. This is a modelled estimate from US data, not a direct count, and there is no verified UK figure. Sources: Seaver Autism Center, Mount Sinai, via ScienceDaily, "This 'rare' autism-linked genetic disorder may be far more common than scientists thought", 25 September 2026, https://www.sciencedaily.com/releases/2026/09/260924020405.htm; Autism Research, 25 September 2026, https://onlinelibrary.wiley.com/journal/19393806; NHS England, "NHS Genomic Medicine Service", accessed 26 September 2026, https://www.england.nhs.uk/genomics/nhs-genomic-med-service/. This article is for general information and does not replace advice from a doctor, paediatrician, genetic counsellor, pharmacist or other qualified healthcare professional. If you have concerns about your child's development, speak to your GP or health visitor.

#genetics#autism#rare conditions#diagnosis#families#research

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