Noonan syndrome

Noonan syndrome A congenital malformation syndrome that is characterized by mildly short stature, a congenital heart defect, a broad or webbed neck, an unusual chest shape (prominent above and caved in below), low-set nipples, a characteristic facial appearance, and, in boys, testes that do not descend normally into the scrotum (cryptorchidism). Abbreviated NS. Although NS was once called Turner-like syndrome, it is a distinctive entity that affects both males and females and carries an elevated risk of developmental and language delay, learning disabilities, hearing loss, and mild mental retardation. NS is inherited in an autosomal dominant manner. It is relatively common, with an estimated incidence of 1 in 1,000–2,500 live births. Mutations in multiple genes, including the KRAS and PTPN11 genes, can cause Noonan syndrome.