Noonan syndrome is a genetic condition that affects the heart, growth, blood clotting, and mental and physical development. The children affected may have no obvious signs to the onlooker, but the problems may be many and complex with no clinical test available. Affected individuals may have behavior problems, learning difficulties and many other anomalies, including a distinctive facial appearance; a broad or webbed neck; a low hairline in the back of the head; and short stature. Characteristic abnormalities of the head and facial area may include widely set eyes; vertical skin folds that may cover the eyes' inner corners; drooping of the upper eyelids; a small jaw; a low nasal bridge; and low-set, prominent, abnormally rotated ears.
Distinctive skeletal malformations are also typically present, such as abnormalities of the breastbone (sternum), curvature of the spine (kyphosis and/or scoliosis), and outward deviation of the elbows. Many infants with Noonan syndrome also have heart defects, such as obstruction of proper blood flow from the lower right chamber of the heart to the lungs (pulmonary valvular stenosis). Additional abnormalities may include malformations of certain blood and lymph vessels, blood clotting and platelet deficiencies, mild mental retardation, and/or other symptoms.
In some affected individuals, Noonan syndrome appears to result from spontaneous genetic mutations. In others, the disorder may be transmitted as an autosomal dominant trait. Genetic analysis suggests that the disorder may result from mutations of a gene located on the long arm (q) of chromosome 12 (12q24).
Distinctive skeletal malformations are also typically present, such as abnormalities of the breastbone (sternum), curvature of the spine (kyphosis and/or scoliosis), and outward deviation of the elbows. Many infants with Noonan syndrome also have heart defects, such as obstruction of proper blood flow from the lower right chamber of the heart to the lungs (pulmonary valvular stenosis). Additional abnormalities may include malformations of certain blood and lymph vessels, blood clotting and platelet deficiencies, mild mental retardation, and/or other symptoms.
In some affected individuals, Noonan syndrome appears to result from spontaneous genetic mutations. In others, the disorder may be transmitted as an autosomal dominant trait. Genetic analysis suggests that the disorder may result from mutations of a gene located on the long arm (q) of chromosome 12 (12q24).