Pediatric Phelan-McDermid Syndrome

Phelan-McDermid syndrome causes neurodevelopmental delays that affect how a child talks and moves. Some children with Phelan-McDermid syndrome also have autism.

There are fewer than 50 neurodevelopmental disability specialists in the country, and Children’s Health℠ has some of the best. At the Center for Autism and Developmental Disabilities, we help families manage this lifelong condition.

What is Pediatric Phelan-McDermid Syndrome?

Phelan-McDermid syndrome is a rare genetic condition. Children with this syndrome have a genetic change or mutation that causes developmental delays. Most children with Phelan-McDermid syndrome are nonverbal, which means they don’t talk.

The condition also causes poor muscle tone (hypotonia), which is why a child may have trouble rolling over, sitting up and walking. Some children never walk and need wheelchairs.

What are the signs and symptoms of Pediatric Phelan-McDermid Syndrome?

Symptoms of Phelan-McDermid syndrome often appear within a child’s first 6 months of life. A child with poor muscle tone may not be able to hold up their head and may seem floppy. They may roll over, sit up or walk later than usual or not at all.

Some symptoms, like speech delays, are noticeable as a child grows up. It’s estimated that 75% of children with Phelan-McDermid syndrome have an autism spectrum disorder.

Other signs of Phelan-McDermid syndrome include:

A child with Phelan-McDermid syndrome may also have unique facial features, such as:

  • Bulbous nose
  • Deep-set eyes
  • Flat midface
  • Full, puffy cheeks
  • Large, prominent ears
  • Long head
  • Wide brow and nasal bridge

How is Pediatric Phelan-McDermid Syndrome diagnosed?

Phelan-McDermid syndrome is so uncommon that some doctors haven’t heard of it. Others don’t have experience diagnosing a child with this condition. Our neurodevelopmental neurologists are among fewer than 50 specialists in the U.S. with expertise in this disease. We have helped many kids with the condition live their best lives.

This condition shares many similarities with Pitt-Hopkins syndrome. We’re experts at assessing a child’s symptoms and providing families with an accurate diagnosis.

We offer:

Genetic testing

Genetic testing to check for differences in chromosomes that may explain a child’s condition. When possible, we use cheek swabs to make the process easier for your child. Sometimes, blood samples are needed.

Diagnostic evaluations for autism

Diagnostic evaluations for autism that include observing your child perform tasks.

Electroencephalogram (EEG)

Electroencephalogram (EEG) to diagnose seizures and measure electrical activity in the brain.

Magnetic resonance imaging (MRI)

Magnetic resonance imaging (MRI) to assess how the brain is formed structurally.

Neurological tests

Neurological tests to evaluate muscle and nerve function.

What causes Pediatric Phelan-McDermid Syndrome?

A mutation (change) in a gene called SHANK3 causes Phelan-McDermid syndrome. This gene produces an important protein the body needs to function properly. The SHANK3 gene is found in the 22q13 segment of chromosome 22 (chromosomes are tiny structures in your body that carry DNA). Some children are missing this segment altogether. Phelan-McDermid syndrome is sometimes called 22q13 deletion syndrome.

Experts don’t know why this gene change occurs or why certain children get Phelan-McDermid Syndrome. In many cases, the mutation is a brand new change in the patient. This means it was not inherited (passed down) from their parents and could not have been prevented or predicted.

Many parents feel responsible that their child has this syndrome. But it isn’t parents’ fault and there is nothing they could have done to prevent it. Parents should never, ever feel guilty when their child has a genetic disease.

How is Pediatric Phelan-McDermid Syndrome treated?

Phelan-McDermid syndrome is a lifelong condition that requires care from many different specialists. At Children’s Health, your family sees all these specialists in one convenient location. Our experts work as a team to customize treatments specific to your child’s unique needs.

Treatments vary depending on symptoms and may include:

Behavioral therapy

Helps children function better in the classroom and at home, and to manage aggressive behaviors


Medications for seizures, sleep issues, behavioral problems, stomach problems or other medical problems

Nutrition counseling

Helps to manage feeding problems that may impact how they grow and develop, and to help stomach issues like constipation

Occupational therapy (OT)

This is for fine-motor skills and to foster self-care skills like feeding and dressing oneself

Physical therapy (PT)

Helps to improve core strength, muscle function and mobility

Speech therapy

This is for feeding issues and to improve communication through sign language, picture boards or language apps on a tablet or handheld device

Pediatric Phelan-McDermid Syndrome Doctors and Providers

The Center for Autism and Developmental Disabilities brings together specialists from a variety of fields to help families manage Phelan-McDermid syndrome.

Frequently Asked Questions

  • How common is Phelan-McDermid syndrome?

    Phelan-McDermid syndrome was only identified in 1985. It’s very rare, affecting as few as 2 to 10 babies out of 1 million. It’s estimated that 1% of people with autism also have Phelan-McDermid syndrome.

  • Is Phelan-McDermid syndrome inherited?

    Phelan-McDermid syndrome occurs from an unexplained change in a gene. The condition isn’t inherited (passed down from parent to child). Having one child with the syndrome doesn’t increase the risk of siblings having it.

  • Does Phelan-McDermid syndrome affect more boys than girls?

    The syndrome affects boys and girls equally.