Noonan syndrome and related disorders

Noonan syndrome is a common multiple malformation syndrome seen in children with congenital heart disease. Recently, a mutation in the PTPN11 gene was found to be present in about 50% of individuals with Noonan syndrome. Over 80% of these patients have some form of congenital heart disease with pulmonary stenosis often associated with a dysplastic valve being, by far, the most common lesion. Hypertrophic cardiomyopathy occurs in 20-30%. Characteristic facies, chest deformity, short stature, undescended testes in the male and learning disabilities comprise the Noonan phenotype but there is wide phenotypic variation and a changing phenotype with age. This phenotype is noted in several other syndromes which share similar cardiac defects. These include LEOPARD, neurofibromatosis, Noonan syndrome, cardio-facio-cutaneous syndrome and Costello syndrome. A definitive diagnosis is particularly difficult in infancy.