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Noonan Syndrome

(Noonan's Syndrome)

By

Nina N. Powell-Hamilton

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Last full review/revision Jul 2020| Content last modified Jul 2020
Click here for the Professional Version

Noonan syndrome can be inherited from a parent who has an affected gene or can result from a spontaneous gene mutation Gene abnormalities Chromosomes are structures within cells that contain a person's genes. A gene is a segment of deoxyribonucleic acid (DNA) and contains the code for a specific protein that functions in one or... read more 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 Undescended testes Undescended testes (cryptorchidism) are testes that remain in the abdomen or the groin instead of descending into the scrotum. Retractile testes (hypermobile testes) have descended into the... read more Undescended testes . Puberty may be delayed Delayed Puberty Delayed puberty is defined as absence of the start of sexual maturation at the expected time. Most often, children simply develop later than their peers but ultimately develop normally. Sometimes... read more 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.

Treatment of Noonan Syndrome

  • Surgical repair of heart defects

  • Growth hormone therapy

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.

Children suspected of having Noonan syndrome should be screened for heart, vision, and hearing problems.

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