Haploinsufficiency of SHANK3, arising from mutations or deletions [4, 11–14] that disrupt SHANK3 protein expression or function is identified in a notable proportion (0.5-2%) of individuals with ASD and is the cause of Phelan-McDermid syndrome (PMS, 22q13.3 deletion) [15–18]. The gene discussed is SHANK3; the disease is Phelan-McDermid syndrome.