Common cause of familial mental retardation
Second most common genetic cause of mental retardation (after down syndrome)
broad forehead, elongated face, large prominent ears, strabismus, highly arches palate, hyperextensible joints, hand calluses, pectus excavatum, mitral valve prolapse, ENLARGED TESTICLES, hypotonia, soft, fleshy skin, flat feet, seizures
Macro-orchidism is the only notable physical abnormality in 90% of postpubertal males
Approximately 30% of females carrying the premutation have premature ovarian failure (before the age of 40 years), and about one third of premutation-carrying males exhibit a progressive neurodegenerative syndrome starting in their sixth decade.
Behavior characteristics: ADHD, short attention span, impulsivity, hand flapping, poor eye contact, poor adaptation to changes in routine, anxiety, resistance to veing touched or held, pervasive developmental disorder (like autism)