Within this region, there are over 90 genes, but the critical region identified for the manifestation of the syndrome is an area of approximately 100 kb that primarily contains three genes: ACR, SHANK3 and RABL2B, of which SHANK3 is considered the hallmark gene for the development of Phelan-McDermid Syndrome (4, 5). Here, SHANK3 is linked to Phelan-McDermid syndrome.