Phelan-McDermid Syndrome (PMS) is a genetic syndrome caused by disruption of the SHANK3/ProSAP2 gene on the terminal end of chromosome 22. The most common form of PMS is caused by a de novo chromosomal deletion. For this reason the original name for PMS was 22q13 deletion syndrome.
There is a wide range of severity of symptoms observed in people with the Phelan McDermid Syndrome, but most exhibit moderate to severe developmental delays, physically and intellectually, but especially in speaking and communicating. Very low muscle tone is a common trait of the syndrome, and many kids with PMS have problems with eating, sleeping and emotional stability.