Noonan syndrome

Noonan syndrome is a genetic defect that causes a number of physical abnormalities, usually including short stature, heart defects, and an abnormal appearance.
Noonan syndrome can be inherited or can develop unpredictably in children whose parents have normal genes. Although children with the syndrome have normal chromosomal structure, they have many characteristics typical of Turner syndrome. In the past, Noonan syndrome was called "male Turner syndrome." Boys or girls can be affected. The gene responsible for Noonan syndrome has been localized to chromosome 12.

Symptoms may include webbing of the neck, low-set ears, droopy eyelids, short stature, shortened fourth (ring) fingers, a high-arched palate, and heart and blood vessel abnormalities. 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 infertility may develop.

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.