- Williams syndrome (WS) : Williams syndrome (WS) refers to a neurodevelopmental disorder characterized by a recognizable pattern of dysmorphic facial features, cardiovascular and physical abnormalities, mental retardation, a specific cognitive profile, and a distinct personality. It is a disorder that produces severe mental retardation but leaves language functions relatively intact. Moreover, it is a type of mental retardation (low IQ) in which the person has relatively good language skills in spite of extremely limited abilities in other regards