Noonan syndrome and related disorders: a review of clinical features and mutations in genes of the RAS/MAPK pathway.

Noonan syndrome (NS) is one of the most common syndromes transmitted by a mendelian mode. In recent years, germline mutations that affect components of the RAS-MAPK (mitogen-activated protein kinase) pathway were shown to be involved in the pathogenesis of NS and four rare syndromes with clinical features overlapping with NS: Leopard syndrome, cardio-facio-cutaneous syndrome, Costello syndrome and neurofibromatosis type 1. Several hormones act through receptors that stimulate the RAS-MAPK pathway, and therefore, NS and related disorders represent a remarkable opportunity to study the implication of the RAS-MAPK pathway in different endocrine systems. Additionally, children with NS frequently are referred to the endocrinologist because of short stature, delayed puberty and/or undescended testes in males. In this paper, we review the diagnostic, clinical and molecular aspects of NS and NS-related disorders.