Noonan syndrome is a genetic defect that causes a number of physical abnormalities, including short stature, heart defects, and an abnormal appearance.
A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or more types of cells in the body (see Genes and Chromosomes for a discussion about genetics). Genes contain instructions that determine how the body is supposed to function.
Noonan syndrome can be inherited from a parent who has an affected gene or can result from a spontaneous gene mutation in a child whose parents have unaffected genes. One of several different genes may be involved. Noonan syndrome is relatively common, occurring in about 1 in 1,000 to 2,500 people. Both boys and girls can be affected.
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. Puberty may be delayed for both boys and girls, and young men with Noonan syndrome may have low levels of testosterone and be infertile. Girls usually begin menstruating somewhat later than unaffected girls, but fertility is typically normal.
To confirm the diagnosis of Noonan syndrome, genetic tests are done to check for mutations.
There is no cure for Noonan syndrome. However, some specific symptoms and problems caused by the syndrome can be treated. Doctors monitor and repair heart defects as needed.
Growth may be stimulated 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. Estrogen therapy may be necessary for young women to develop typical adult characteristics.
Children suspected of having Noonan syndrome should be screened for heart, vision, and hearing problems.