Noonan syndrome: introduction and basic clinical features.

Noonan syndrome (NS) is a fairly common (1 per 1,000-2,500 live births) autosomal dominantly inherited disorder and the most common syndromal cause of congenital heart disease after Down's syndrome. The clinical features vary with age, but typical signs of NS include characteristic facial features with hypertelorism, down-slanting palpebral fissures, low-set posteriorly rotated ears, chest and spinal deformities, short stature, specific heart defects, learning disabilities and mild mental retardation. This article gives a brief introduction to NS and its basic clinical features using the established and generally accepted NS scoring system based on family history and facial, cardiac, growth, chest wall and other criteria. Aspects discussed include the definition, epidemiology, etiology, diagnosis and genetics of NS, as well as growth, skeletal and gonadal anomalies, pubertal development, ophthalmic and cutaneous abnormalities and the incidence of cancer in patients with NS.