From OMIMNoonan syndrome (NS) is an autosomal dominant disorder characterized by short stature, facial dysmorphism, and a wide spectrum of congenital heart defects. The distinctive facial features consist of a broad forehead, hypertelorism, downslanting palpebral fissures, a high-arched palate, and low-set, posteriorly rotated ears. Cardiac involvement is present in up to 90% of patients. Pulmonic stenosis and hypertrophic cardiomyopathy are the most common forms of cardiac disease, but a variety of other lesions are also observed. Additional relatively frequent features include multiple skeletal defects (chest and spine deformities), webbed neck, mental retardation, cryptorchidism, and bleeding diathesis (summary by Tartaglia et al., 2002).
Genetic Heterogeneity of Noonan Syndrome
See also NS3 (609942), caused by mutation in the KRAS gene (190070); NS4 (610733), caused by mutation in the SOS1 gene (182530); NS5 (611553), caused by mutation in the RAF1 gene (164760); NS6 (613224), caused by mutation in the NRAS gene (164790); NS7 (613706), caused by mutation in the BRAF gene (164757); NS8 (615355), caused by mutation in the RIT1 gene (609591); NS9 (616559), caused by mutation in the SOS2 gene (601247); NS10 (616564), caused by mutation in the LZTR1 gene (600574); NS11 (618499), caused by mutation in the MRAS gene (608435); NS12 (618624), caused by mutation in the RRAS2 gene (600098); and NS13 (619087), caused by mutation in the MAPK1 gene (176948).
Autosomal recessive forms of Noonan syndrome include NS2 (605275), caused by mutation in the LZTR1 gene (600574), and NS14 (619745), caused by mutation in the SPRED2 gene (609292).
See also Noonan syndrome-like disorder with loose anagen hair-1 (NSLH1; 607721), caused by mutation in the SHOC2 gene (602775); Noonan syndrome-like disorder with loose anagen hair-2 (NSLH2; 617506), caused by mutation in the PPP1CB gene (600590); and Noonan syndrome-like disorder with or without juvenile myelomonocytic leukemia (NSLL; 613563), caused by mutation in the CBL gene (165360).
Mutations in the neurofibromin gene (NF1; 613113), which is the site of mutations causing classic neurofibromatosis type I (NF1; 162200), have been found in neurofibromatosis-Noonan syndrome (NFNS; 601321).
http://www.omim.org/entry/163950 From MedlinePlus GeneticsNoonan syndrome is a condition that affects many areas of the body. It is characterized by mildly unusual facial features, short stature, heart defects, bleeding problems, skeletal malformations, and many other signs and symptoms.
People with Noonan syndrome have distinctive facial features such as a deep groove in the area between the nose and mouth (philtrum), widely spaced eyes that are usually pale blue or blue-green in color, and low-set ears that are rotated backward. Affected individuals may have a high arch in the roof of the mouth (high-arched palate), poor teeth alignment, and a small lower jaw (micrognathia). Many children with Noonan syndrome have a short neck, and both children and adults may have excess neck skin (also called webbing) and a low hairline at the back of the neck.
Between 50 and 70 percent of individuals with Noonan syndrome have short stature. At birth, they are usually a normal length and weight, but growth slows over time. Abnormal levels of growth hormone, a protein that is necessary for the normal growth of the body's bones and tissues, may contribute to the slow growth.
Individuals with Noonan syndrome often have either a sunken chest (pectus excavatum) or a protruding chest (pectus carinatum). Some affected people may also have an abnormal side-to-side curvature of the spine (scoliosis).
Some people with Noonan syndrome develop cancer, particularly those involving the blood-forming cells (leukemia). It has been estimated that children with Noonan syndrome have an eightfold increased risk of developing leukemia or other cancers over age-matched peers.
Noonan syndrome is one of a group of related conditions, collectively known as RASopathies. These conditions all have similar signs and symptoms and are caused by changes in the same cell signaling pathway. In addition to Noonan syndrome, the RASopathies include cardiofaciocutaneous syndrome, Costello syndrome, neurofibromatosis type 1, Legius syndrome, and Noonan syndrome with multiple lentigines.
Most people with Noonan syndrome have some form of critical congenital heart disease. The most common heart defect in these individuals is a narrowing of the valve that controls blood flow from the heart to the lungs (pulmonary valve stenosis). Some have hypertrophic cardiomyopathy, which enlarges and weakens the heart muscle.
A variety of bleeding disorders have been associated with Noonan syndrome. Some affected individuals have excessive bruising, nosebleeds, or prolonged bleeding following injury or surgery. Rarely, women with Noonan syndrome who have a bleeding disorder have excessive bleeding during menstruation (menorrhagia) or childbirth.
Adolescent males with Noonan syndrome typically experience delayed puberty. They go through puberty starting at age 13 or 14 and have a reduced pubertal growth spurt that results in shortened stature. Most males with Noonan syndrome have undescended testes (cryptorchidism), which may contribute to infertility (inability to father a child) later in life. Females with Noonan syndrome can experience delayed puberty but most have normal puberty and fertility.
Noonan syndrome can cause a variety of other signs and symptoms. Most children diagnosed with Noonan syndrome have normal intelligence, but a few have special educational needs, and some have intellectual disability. Some affected individuals have vision or hearing problems. Affected infants may have feeding problems, which typically get better by age 1 or 2 years. Infants with Noonan syndrome may be born with puffy hands and feet caused by a buildup of fluid (lymphedema), which can go away on its own. Older individuals can also develop lymphedema, usually in the ankles and lower legs.
https://medlineplus.gov/genetics/condition/noonan-syndrome