Karen W Gripp, Lindsey A Morse , Marni Axelrad, Kathryn C Chatfield, Aaron Chidekel, William Dobyns, Daniel Doyle, Bronwyn Kerr, Angela E Lin, David D Schwartz, Barbara J Sibbles, Dawn Siegel, Suma P Shankar, David A Stevenson, Mihir M Thacker, K Nicole Weaver, Sue M White, Katherine A Rauen

Costello syndrome (CS) is a RASopathy caused by activating germline mutations in HRAS. Due to ubiquitous HRAS gene expression, CS affects multiple organ systems and individuals are predisposed to cancer. Individuals with CS may have distinctive craniofacial features, cardiac anomalies, growth and developmental delays, as well as dermatological, orthopedic, ocular, and neurological issues; however, considerable overlap with other RASopathies exists. Medical evaluation requires an understanding of the multifaceted phenotype. Subspecialists may have limited experience in caring for these individuals because of the rarity of CS. Furthermore, the phenotypic presentation may vary with the underlying genotype. These guidelines were developed by an interdisciplinary team of experts in order to encourage timely health care practices and provide medical management guidelines for the primary and specialty care provider, as well as for the families and affected individuals across their lifespan.