Costello syndrome is a rare genetic disorder caused by mutations in the Harvey Rat Sarcoma Viral Oncogene Homolog (HRAS) gene, leading to abnormal activation of the rat sarcoma/mitogen-activated protein kinase (RAS/MAPK) signaling pathway, which is part of a pathway that helps control cell growth and division [1]. The gene discussed is HRAS; the disease is sarcoma.