Background The RASopathies are a class of human genetic syndromes caused by germline mutations in genes that encode protein components of the Ras/mitogen-activated protein kinase (MAPK) pathway. Costello syndrome (CS) is a RASopathy caused by mutations in the HRAS gene, a key regulator of signal transduction. Objective To quantify the specific cutaneous phenotype observed in 46 individuals with Costello syndrome with confirmed HRAS mutations. Methods This was a cross-sectional study. Dermatological surveys were designed by the authors and were completed by parents of mutation-positive individuals with CS at the Costello Syndrome Family Network (CSFN) conferences in 2007 and 2009. Dermatological examinations were performed by the authors at the CSFN conferences. Results Cutaneous papillomas were reported in 33 of the 46 (72%) participants, with age of onset ranging from infancy to 22 years. Individuals with CS are more likely than patients with cardiofaciocutaneous syndrome (CFC) to present with cutaneous papillomas (72% vs. 5%, P < 0·001) and palmoplantar keratoderma (76% vs. 36%, P < 0·001). Individuals with CS are less likely than individuals with CFC to present with sparse or absent eyebrows (9% vs. 90%, P < 0·001) or keratosis pilaris (33% vs. 80%, P = 0·001). This study also identified that loose, redundant skin on the hands and feet, 'stippled' dermatoglyphs (pachydermatoglyphia) on the fingertips (eight of 26, 31%) and acanthosis nigricans (17 of 46, 37%) are frequent features of CS. Conclusions While there is significant phenotypic overlap among syndromes of the Ras/MAPK pathway, individuals with CS are more likely than individuals with CFC syndrome to present with cutaneous papillomas, palmoplantar keratoderma and full eyebrows, and are less likely to present with ulerythema ophryogenes, keratosis pilaris or multiple naevi. The dermatological features of CS, a Ras dysregulation syndrome, share many features with cutaneous paraneoplastic syndromes. This may provide further insight into the role of Ras signalling in cutaneous paraneoplastic syndromes.
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