Noonan's syndrome is a genetic defect that causes a number of physical abnormalities, including short stature, heart defects, and an abnormal appearance.
Noonan's syndrome can be inherited or can develop unpredictably from a spontaneous gene mutation in children whose parents have normal genes. It is relatively common, occurring in about 1 in 1,000 to 2,500 people. In the past, Noonan's syndrome was called male Turner's syndrome because of similarities in the two syndromes. However, the genetic defects causing the disorders are different. Boys or girls can be affected. The gene responsible for Noonan's syndrome has been localized to chromosome 12.
Children may have webbing of the neck, low-set ears, droopy eyelids, widely spaced eyes, shortened fourth (ring) fingers, a high-arched palate, and heart and blood vessel abnormalities. Hearing problems can occur, and intelligence may be impaired. Most affected people are short. Boys may have underdeveloped or undescended testes. In girls, the ovaries may be underactive or stop working. Puberty may be delayed, and young men with Noonan's syndrome may be infertile.
Growth may be improved by treatment with growth hormone. After satisfactory growth, testosterone treatment may help boys whose testes are underdeveloped. Testosterone stimulates the development of a more masculine appearance. As in Turner's syndrome, estrogen therapy may be necessary for young women to develop typical adult characteristics. Children suspected of having Noonan's syndrome should be screened for heart problems and hearing problems.
Resource: Merck Manual Home Edition