Phelan-McDermid syndrome, also known as 22q13.3 deletion syndrome, is a very rare genetic condition that affects brain development. It can lead to developmental delays, intellectual disability and other health problems.
Children with Phelan-McDermid syndrome often have speech delays, muscle weakness (called hypotonia) and symptoms of autism. Symptoms of autism can include poor eye contact, sensitivity to touch, difficulty with social interaction, repeating actions like rocking, aggression and eating non-food items (pica). The condition can also affect many other parts of the body, including the kidneys, endocrine system and digestive system.
Phelan-McDermid syndrome happens when a child has diseases causing changes in a gene called SHANK3. This gene plays a big role in how brain cells connect and communicate.
The gene can be changed to not work correctly by a small deletion on chromosome 22 or a change (variant) in the spelling of the SHANK3 gene itself. These changes usually happen randomly and are not inherited.
Symptoms of Phelan-McDermid syndrome can vary widely. It can affect how a child looks and behaves. Most symptoms are related to intellectual and developmental delays. You may notice that your baby or young child is missing milestones or losing skills they previously had. Most children with PMS need care from a team of specialists. Common symptoms include:
Common appearance-related signs include:
In addition, brain imaging may show differences, such as delayed brain growth or unusual brain structures.
Doctors may suspect Phelan-McDermid syndrome based on a child’s symptoms and development and refer you to a geneticist. The geneticist orders genetic tests to confirm the diagnosis. These tests look for missing pieces of chromosome 22 or changes in the SHANK3 gene. The doctor may also recommend brain imaging with an MRI if your child has certain signs including an unusually small head, weakness on one side of the body, unusual eye movements, seizures, muscle stiffness or loss of previously acquired skills such as speech.
There is no cure for Phelan-McDermid Syndrome, though experimental therapies are currently in clinical trial. But many treatments can help manage a child’s symptoms and improve their quality of life. Treatment plans are tailored to each child.
Common treatments include:
Some children may need a feeding tube or help with hormone issues. Doctors may also suggest genetic counseling for the family.
Researchers are studying new treatments that target the SHANK3 gene. These treatments are still being tested but may offer hope in the future.
Each child with Phelan-McDermid syndrome is unique. Some children will learn to walk and talk with support. Others may need more help throughout their lives.
Most children benefit from early therapy and coordinated care. Ongoing support from a medical team, educators and family can help each child reach their full potential.
Our specialized clinic helps families navigate Phelan-McDermid syndrome with coordinated care, personalized treatment plans and guidance from diagnosis through every stage of development.
Last Updated 01/2026
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