What is The Phelan-McDermid Syndrome?

What is Phelan-McDermid Syndrome?

Phelan-McDermid Syndrome (PMS) is a rare genetic condition caused by a deletion or other structural change of the terminal end of chromosome 22 in the 22q13 region or a syndrome-causing mutation of the SHANK3 gene. PMS is sometimes called 22q13 Deletion Syndrome. The deletion or mutation causes many different yet related symptoms that vary from person to person. It can occur randomly (de novo) or be inherited from a parent who carries a related genetic change.

What are some of its characteristics?

Because the genetic changes vary, the symptoms of PMS vary too and can cause a wide range of medical, intellectual, and behavioral challenges. The most common characteristics found in those with PMS are an intellectual disability of varying degrees, delayed or absent speech, low muscle tone, motor delays, and epilepsy.

People diagnosed with PMS also have moderate to severe developmental and intellectual impairment, most do not develop functional language, and about 75 percent have been diagnosed with an Autism Spectrum Disorder. Sleep disorders are commonly reported, as are difficulties with toilet training, and problems with eating. About 40% of people develop seizures.

Common facial characteristics include dolichocephaly (a head shape that is longer than usual, from front to back), flat midface, wide brow, wide nasal bridge, deep-set eyes, full cheeks, puffy eyelids, long eyelashes, and bulbous nose. Large fleshy hands, dysplastic toenails, sacral dimple, and large, differently formed ears are frequently observed.

Is there a cure or treatment?

There is no cure or treatment specifically for PMS, but there are ways to manage many of the symptoms. Researchers are working to improve our knowledge of PMS and to find drugs and therapies that can help people affected by PMS.

The gene SHANK3 is located within the affected 22q13 segment of the chromosome and is thought to be the most important gene in causing PMS. Some people with PMS don’t have a deletion, but instead have a misspelling in the SHANK3 gene, called a mutation. Mutations are also typically new events and not inherited from a parent.

Families may come across several different descriptions of this syndrome based on varying genetic descriptions and varying symptoms. Therefore, those who receive a genetic report showing a pathogenic mutation of SHANK3 or deletion on the 22q13 region of chromosome 22 are encouraged to join the Phelan-McDermid Syndrome Foundation.

How common is PMS?

It’s unclear how many cases of PMS there are in the world, and the Phelan-McDermid Syndrome Foundation does not have a reliable estimate. It is estimated that 1percent of people with autism have Phelan-McDermid Syndrome. That means that between 1/8,000-15,000 (including 22q13.3 deletions and SHANK3 gene variants) have PMS. However, this may be an underestimate since not all patients with PMS will present with autism.

As of February 2018, PMSF’s membership and International Patient Registry include more than 1,800 individuals who have been diagnosed with PMS.  However, the syndrome is under-diagnosed, and this number does not reflect all of the diagnosed cases, but PMSF does have the largest PMS membership in the world.

How to Learn more

For more information about PMS, go to www.pmsf.org.

Contact the Phelan-McDermid Syndrome Foundation at info@pmsf.org.

This article was submitted by Nick Assendelft

Vice-president, Phelan-McDermid Syndrome Foundation

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