Noonan syndrome.
Incidence
1 in 1000-2500 affecting both males and females. Autosomal dominant inheritance in some families, conferring an overall 15% recurrence risk for affected individuals to have a fully affected child.
Clinical Characteristics
Pattern of manifestations including short stature, ptosis, anteverted ear lobes, connective tissue changes (pectus, hernias, joint laxity), cardiac anomalies (pulmonic stenosis, septal defects), hypogonadism, learning differences. Some similarity to Turner syndrome. Noonan syndrome is quite common, having an incidence of 1 in 1000-2500 live births. The cause is unknown, although the embryologic abnormalities derive from abnormal lymphatic circulation with a cystic hygroma (swollen neck) that also occurs in fetuses with Turner syndrome. The fetal hygroma may cause the webbed neck, forwardly placed ear lobes, and chest deformities that are observed after birth. Direct transmission from parent to child has been observed in 30% of cases and is consistent with autosomal dominant inheritance. Since there is no laboratory test for Noonan syndrome, the diagnosis is made by recognizing the typical pattern of clinical features. Females with Noonan syndrome may be misdiagnosed as having Turner syndrome until the different heart lesion (coarctation of the aorta rather than pulmonic stenosis) and the abnormal karyotype are documented. The major complications of Noonan syndrome involve the heart, eyes, ears, teeth, trunk, coagulation system, and musculoskeletal system. Although some patients experience motor and speech delays, the outlook for overall intelligence and learning is excellent, with 80-90% having normal intelligence and only 11% requiring special education. Ocular problems such as ptosis, strabismus, and amblyopia together with chronic otitis media or anomalies of the ear ossicles may produce vision and hearing impairment. Dental malocclusion is common and cherubism (cystic enlargement of the jaws) is occasionally seen in Noonan syndrome. The cardiac anomalies in Noonan syndrome often involve the pulmonary valve as opposed to aortic defects in the Turner or Williams syndromes. A bleeding diathesis is present in as many as 56% of patients, and this has been attributed to a clotting factor deficiency. Autoimmune inflammation of the thryoid gland is common, and there is early enlargement of the liver and spleen without known cause.
Precipitants
none
Provocation Tests
none
Diagnostic Procedures
Since there is no laboratory test for Noonan syndrome, the diagnosis is made by recognizing the typical pattern of clinical features. Both sexes are affected in Noonan syndrome and the karyotype is normal.