Costello syndrome (CS) is a rare multisystemic disorder characterized by failure to thrive, short stature, developmental delay or intellectual disability, joint laxity, soft skin, and distinctive facial features. Cardiac and neurological involvement is common and there is an increased lifetime risk of certain tumors. The disease is Costello syndrome (Monarch Disease Ontology entry MONDO_0009026). Also known as: FCS syndrome, congenital myopathy with excess of muscle spindles, faciocutaneoskeletal syndrome.