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Phelan-McDermid Syndrome

Phelan-McDermid Syndrome



Overview

Phelan-McDermid syndrome is a rare genetic disorder that may cause a range of medical, intellectual and behavioral concerns. These concerns may include:

Feeding difficulties.

Muscle weakness.

Speech and developmental delays.

Autism spectrum disorder.

Epilepsy.

The disorder is also called 22q13.3 deletion syndrome.

Symptoms

The signs and symptoms of Phelan-McDermid syndrome vary widely. They may be mild, moderate or severe. They may appear at birth, during infancy or in early childhood. And they may be physical, behavioral, intellectual or a combination.

Symptoms your child may have include:

Developmental delay (not hitting milestones at expected times, such as rolling over, sitting up or walking).

High pain tolerance.

Muscle weakness (hypotonia).

Speech problems (absent or delayed ability to talk).

Sleep disorders.

Tendency to sweat less than normal, which can lead to overheating and dehydration.

Trouble eating or swallowing.

Gastrointestinal issues like frequent nausea and vomiting or gastroesophageal reflux disease.

Many people with Phelan-McDermid syndrome have autism spectrum disorder, which may cause certain behaviors. Your child may:

Avoid eye contact.

Be anxious in social situations.

Obsessively chew things that aren’t food.

Be oversensitive to touch.

People with 22q13.3 deletion syndrome often have particular physical features. Your child may have:

Deep-set eyes.

Drooping eyelids (ptosis).

Ears that are large or stick out.

Fusion of their second and third toes (syndactyly).

Large, fleshy hands or feet.

A long, narrow head.

A pointed chin.

Small or abnormal toenails.

Sometimes the disorder may involve congenital heart conditions and kidney problems. Rarely, people with Phelan-McDermid syndrome have arachnoid cysts (fluid-filled sacs on their brain). They may cause pressure in your child's head, leading to irritability, crying, headaches and epilepsy (seizures).

Causes

Phelan-McDermid syndrome is a chromosomal deletion syndrome. Chromosomes are structures inside cells. They contain DNA, and DNA contains genes. Genes are the instructions that control how your body functions. They also determine your traits (like height, eye color and risks for medical conditions).

In a human being, each cell usually contains 23 pairs of chromosomes, for a total of 46. If your child has Phelan-McDermid syndrome, they were born with a piece of chromosome 22 missing or “deleted.”

Most cases of the disorder aren’t inherited. The chromosomal deletion usually happens randomly (spontaneously) when the egg or sperm are forming or during fetal development. But 22q13.3 deletion syndrome can be inherited. A parent who has the condition has a 50% chance of passing it down to each child. One parent can pass it down even if the other parent doesn’t have the condition.

Diagnosis

The signs and symptoms associated with Phelan-McDermid syndrome can be subtle and difficult to detect. Your child may have several tests before an accurate diagnosis can be made. To diagnose the condition, your child's healthcare provider may:

Perform a physical exam.

Ask about your child's medical history to discuss signs, symptoms and developmental delays.

Ask about your child's biological family history to determine whether any relatives have had the disorder.

Request genetic testing to look for the chromosomal deletion. This usually requires a small sample of blood.

In rare cases, Phelan-McDermid syndrome may not be caused by a chromosomal deletion. Instead, it may be caused by a DNA change in the SHANK3 gene. Your healthcare provider may recommend testing for this gene if a deletion isn't found.

If testing confirms 22q13.3 deletion syndrome, your child's healthcare provider may recommend further tests:

Genetic testing of both parents to see whether the deletion was inherited or spontaneous.

MRI or CT scan of your child's brain to look for an arachnoid cyst.

Renal ultrasound to look for kidney defects.

Echocardiogram to look for heart abnormalities.

Hearing evaluation.

Detailed eye exam.

Sleep study.

Treatment

There’s no cure for Phelan-McDermid syndrome. Treatment aims to address your child’s symptoms, maximize their ability to function well and prevent any complications.

Your child’s care team may involve several specialists:

Cardiologist (heart).

Gastroenterologist (digestive system).

Nephrologist (kidney).

Neurologist (brain).

Occupational therapist, who can help improve performance with daily activities like eating and writing.

Orthopaedist (bones and joints).

Physical therapist, who can help strengthen affected body parts.

Speech/language pathologist.

Endocrinologist (hormones).

Type of Doctor Department : Neurologists, Developmental Pediatricians, Speech-Language Pathologists, Occupational/Physical Therapists, Gastroenterologists, & Endocrinologists

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