What Are the Symptoms of Phelan-McDermid Syndrome?

Medically Reviewed on 1/11/2023
Symptoms of Phelan-McDermid Syndrome
People who have Phelan-McDermid syndrome are treated after symptoms appear.

Most infants with Phelan-McDermid syndrome experience normal intrauterine and postnatal growth (postnatally). The earliest physical sign of Phelan-McDermid syndrome is neonatal hypotonia (low muscle tone), which is frequently associated with feeding difficulties, faint cries, and shaky head control.

Because of weak muscles, children are significantly slow at achieving early developmental milestones, including:

  • Rolling over
  • Sitting
  • Crawling
  • Walking

These typical noticeable symptoms prompt families to visit a doctor.

Symptoms of Phelan-McDermid syndrome

All children with Phelan-McDermid syndrome will not experience every symptom of the condition.

Typical symptoms could include:

What is Phelan-McDermid syndrome?

Phelan-McDermid syndrome is a rare genetic disorder brought on by a mutation in the SHANK3 gene or a deletion of the terminal end of chromosome 22 in the 22q13 region. 22q13.3 deletion syndrome is another name for Phelan-McDermid syndrome.

Although the symptoms due to deletion or mutations are numerous and interconnected, they vary among people. Phelan-McDermid can develop by chance (de novo) or be passed down from a parent with a related genetic mutation.

The Phelan-McDermid Syndrome Foundation does not have a reliable estimate of the number of Phelan-McDermid syndrome cases worldwide. Phelan-McDermid Syndrome is thought to affect one percent of individuals with autism. Between 8,000 and 15,000 people (including those with SHANK3 gene variations and 22q13.3 deletions) have Phelan-McDermid syndrome. However, this could be underestimated because not everyone with Phelan-McDermid syndrome will have autism.

What causes Phelan-McDermid syndrome?

Chromosomes are components found inside cells. They contain DNA, and genes are in DNA. Genes contain the operation manual for the body and describe your character traits (such as height, eye color, and risks for medical conditions).

A human usually has 23 pairs of chromosomes (a total of 46) in each cell. If a child has Phelan-McDermid syndrome, a piece of chromosome 22 is missing since birth.

  • Usually, the illness is not passed down via generations. Chromosomal deletion normally happens randomly (spontaneously) during the development of an egg, sperm, or fetus.
  • The 22q13.3 deletion syndrome can be inherited. There is a 50 percent chance that each child will inherit the condition from a parent. It can be inherited from one parent even if the other is healthy.

How is Phelan-McDermid syndrome diagnosed?

Phelan-McDermid syndrome can be identified by a genetic alteration in the 22q13.3 region of the chromosome.

The following tests can detect Phelan-McDermid syndrome or reveal additional risks:

  • Chromosomal microarray analysis (CMA): Locates genetic duplicated or absent material. CMA is usually used in the initial testing stage for those with intellectual difficulties.
  • Cytogenetic testing: Chromosomes are visible during cytogenetic examinations. They look for changes in chromosome shape, number, and some copies. It is necessary for people with 22q13.3 deletions for the following reasons:
    • Cytogenetic testing can identify the possibility of Phelan-McDermid syndrome inheritance.
    • Two types of cytogenetic tests are frequently employed:
      1. Conventional karyotyping
      2. Fluorescence in situ hybridization
    • Karyotyping: Can be used to find Ring 22. Ring 22 is the result of deletions on both ends of chromosome 22. Chromosome ends that have been broken up may come together to form a circle or ring. Ring 22 may result in nervous system tumors. It is necessary to have medical supervision.
    • Whole exome sequencing or whole genome sequencing.

How to treat Phelan-McDermid syndrome

People who have Phelan-McDermid syndrome are treated after symptoms appear. There are no unique therapies, medications, or prescriptions for Phelan-McDermid syndrome. A management team composed of multiple medical and developmental or educational specialists may address problems.

A few conditions that can exist are lymphedema, hypotonia, poor nutritional practices, chronic constipation, gastric reflux, renal problems, decreased sweating, heat sensitivity, and seizures.

Medically Reviewed on 1/11/2023
Image Source: iStock image

Phelan-McDermid Syndrome. https://www.childneurologyfoundation.org/disorder/phelan-mcdermid-syndrome

Phelan-McDermid Syndrome: Causes and Symptoms. https://www.massgeneral.org/children/phelan-mcdermid-syndrome

Phelan-McDermid Syndrome. https://my.clevelandclinic.org/health/diseases/23087-phelan-mcdermid-syndrome

Phelan-McDermid Syndrome. https://www.childrenshospital.org/conditions/phelan-mcdermid-syndrome