Familial dysautonomia: A genetic disorder of the autonomic nervous system, affecting especially Ashkenazi Jewish children. Familial dysautonomia is inherited in an autosomal recessive manner and is due to mutation in the IKBKAP gene on chromosome 9q31. Dysautonomia refers to the dysfunction of the autonomic nervous system. Familial dysautonomia is symbolized DYS.

The features of familial dysautonomia include lack of tears, emotional lability, relative indifference to pain, increased sweating, cold hands and feet, red blotching of the skin, corneal anesthesia and corneal ulcers, paroxysmal hypertension, taste deficiency and lack of the fungiform papillae. Scoliosis may be severe. The disease may be manifest in first days of life. Two-thirds of patients die before age 20.

The syndrome was first described by Riley, Day, Greeley, and Langford in 1949. It is also called the Riley-Day syndrome after the American pediatricians Conrad Riley (1913-) and Richard L. Day (1905-1989). For some odd reason, Greeley and Langford were omitted from the eponym. An alternative name for the syndrome is hereditary sensory & autonomic neuropathy III (HSAN III).