PHOX2B and congenital heart disease: FMTC/MEN2A, Waardenburg syndrome, and intellectual disability are all linked to RET mutations; EDNRB mutations are linked to Waardenburg syndrome, special physical characteristics, and multiple sclerosis; and PHOX2B mutations can cause respiratory symptoms, anisocoria, congenital central hypoventilation syndrome, and congenital heart disease.