HRAS and Costello syndrome: Mutations in HRAS mutating codon G12 of the HRAS protein have been identified in Costello syndrome when present in the germline [172], but postzygotic and embryonic occurrences of mutations in this residue have been observed in Schimmelpenning syndrome [164], sebaceous nevus [164], keratinocytic epidermal nevi [173], and early-onset bladder cancer [157, 174].