Familial dysautonomia (FD), also known as Riley-Day syndrome, is a rare, progressive, recessive genetic disorder of the autonomic nervous system that affects the development and survival of sensory, sympathetic, and some parasympathetic neurons in the autonomic and sensory nervous system.
FD results in variable symptoms, including insensitivity to pain, inability to produce tears, poor growth, and labile blood pressure (episodic hypertension and postural hypotension). People with FD have frequent vomiting crises, pneumonia, problems with speech and movement, difficulty swallowing, and inappropriate perception of heat, pain and taste, as well as unstable blood pressure and gastrointestinal dysmotility.
Originally reported by Drs. Conrad Milton Riley and Richard Lawrence Day in 1949, FD is one example of a group of disorders known as hereditary sensory and autonomic neuropathies (HSANs). All HSANs are characterized by widespread sensory dysfunction and variable autonomic dysfunction caused by incomplete development of sensory and autonomic neurons. The disorders are believed to be genetically distinct from each other.