Phelan-Mcdermid syndrome (PHMDS)

What is Phelan-Mcdermid syndrome (PHMDS)?

Phelan-Mcdermid syndrome or 22q13 deletion syndrome as it is also known may trigger varying levels of symptoms. 75% of individuals diagnosed with the syndrome are also on the Autism spectrum.

This rare disease also presents with global developmental delay, intellectual disability, low muscle tone, and distinct facial features.

What gene changes cause Phelan-Mcdermid syndrome (PHMDS)?

The syndrome is caused by a continuous gene deletion in the distal long arm of chromosome 21. This usually affects the SHANK 3 gene.

In the case of autosomal dominant inheritance just one parent is the carrier of the gene mutation, and they have a 50% chance of passing it onto each of their children. Syndromes inherited in an autosomal dominant inheritance are caused by just one copy of the gene mutation.

What are the main symptoms of Phelan-Mcdermid syndrome (PHMDS)?

Individuals with the syndrome experience varying symptoms and varying severity of symptoms. Individuals may have mild to severe intellectual disability, and most have delayed or absent speech. Motor delay is also common and issues with toilet training are also common. Individuals may also experience sleep disorders and feeding problems related to the syndrome.

Facial and physical characteristics include low muscle tone, large hands, misformed ears, dysplastic toenails, long eyelashes, a large head, flat midface, wide brow, wide nasal bridge, deep-set eyes, full cheeks and puffy eyelids.

Other health conditions include heart and kidney defects and epilepsy. Many individuals appear to experience a high pain tolerance and may sweat less leading to an increased risk of overheating.

How does someone get tested for Phelan-Mcdermid syndrome (PHMDS)?

The initial testing for Phelan-Mcdermid syndrome can begin with facial analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the need for further testing. A consultation with a genetic counselor and then a geneticist will follow. 

Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.   

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With a hospital technology recommended by leading geneticists, our unique platform connects patients with genetic experts to answer their most pressing questions and clarify any concerns they may have about their symptoms.

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