#WEBBED NECK SKIN#
Affected infants also often have excessive skin in the neck area (nuchal skin) and a low hairline at the back of the neck (low posterior hairline). Affected infants may also have a small jaw (micrognathia) crowding of the lower teeth, low-set, posteriorly rotated external ears (pinnae) and/or distinctive abnormalities of the nose including a depressed nasal root, a wide base, and a rounded (bulbous) tip. These may include an unusually deep vertical groove in the middle of the upper lip (philtrum) and/or a small chin. Many infants with Noonan syndrome also have additional craniofacial features.
Affected infants may have several findings affecting the eyes including widely set eyes (ocular hypertelorism) that are unusually prominent drooping of the upper eyelids (ptosis) and/or unusually thick, “hooded” eyelids an eye that turns in or turns out (strabismus) downwardly slanting eyelids (palpebral fissures) skin folds (epicanthal folds) that may cover the eyes’ inner corners and/or strikingly blue or bluish green colored portions of the eyes (irides). In many cases, the head appears relatively large. Most infants with Noonan syndrome have characteristic craniofacial features. Some affected individuals have only minor facial abnormalities others may have the majority of symptoms and findings associated with the disorder, such as distinctive features of the head and facial (craniofacial) area, a broad or webbed neck, short stature, skeletal malformations, congenital heart defects, malformations of certain blood and lymph vessels, blood clotting and platelet deficiencies, attention issues, mild intellectual disability, and/or other abnormalities.
Individuals with Noonan syndrome have associated symptoms and physical findings that vary greatly in range and severity from person to person. Noonan syndrome caused by pathogenic variants in LZTR1 can be inherited in either an autosomal dominant or an autosomal recessive manner. Noonan-like disorders are found in association with mutations in SHOC2 and CBL. Fewer individuals have a mutation in NRAS, BRAF, MEK2, RRAS, RASA2, A2ML1, and SOS2. The five most commonly involved genes are: PTPN11 (50%), SOS1 (10-13%), RAF1 (5%), RIT1 (5%), and KRAS (less than 5%). In the majority of cases Noonan syndrome is an autosomal dominant genetic disorder caused by abnormalities (mutations) in more than eight genes. Additional abnormalities may include malformations of certain blood and lymph vessels, blood clotting and platelet deficiencies, learning difficulties or mild intellectual disability, failure of the testes to descend into the scrotum (cryptorchidism) by the first year of life in affected males, and/or other symptoms and findings. Many infants with Noonan syndrome also have heart (cardiac) defects, such as obstruction of proper blood flow from the lower right chamber of the heart to the lungs (pulmonary valvular stenosis) and thickening of the ventricular heart muscle (hypertrophic cardiomyopathy). 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 (cubitus valgus). Characteristic features of the head and facial (craniofacial) area may include widely set eyes (ocular hypertelorism) skin folds that may cover the eyes’ inner corners (epicanthal folds) drooping of the upper eyelids (ptosis) a small jaw (micrognathia) a depressed nasal root a short nose with broad base and low-set, posteriorly rotated ears (pinnae). In many affected individuals, associated abnormalities include a distinctive facial appearance a broad or webbed neck a low posterior hairline a typical chest deformity and short stature. The disorder is characterized by a wide spectrum of symptoms and physical features that vary greatly in range and severity. Noonan syndrome is a genetic disorder that is typically evident at birth (congenital).
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