SHANK3 and Phelan-McDermid syndrome: Phelan McDermid syndrome (PMDS, also 22q13 deletion syndrome or 22q13.3 deletion syndrome) is classified as a syndromic form of autism due to a majority of patients falling on the autism spectrum, displaying autistic or autism-like behavioral traits, caused by a 22q13.3 deletion that includes the SHANK3 gene.