Familial Dysautonomia (FD), also known as Riley-Day Syndrome, is a disease that causes the autonomic and sensory nervous systems to malfunction. The autonomic nervous system controls bodily functions such as swallowing and digestion, regulation of blood pressure and body temperature and the body's response to stress. The sensory nervous system helps the body to taste, recognize hot and cold and identify painful sensations. The disease is also known as HSAN III (hereditary sensory and autonomic neuropathy, type III).
The hallmark of FD is the lack of overflow tears with emotional crying. Children with FD may have difficulty feeding. They also may be unable to feel pain, and can break bones or burn themselves without realizing they've been injured.

The disease is caused by mutations in the IKBKAP gene, on chromosome #9. An estimated one in 30 Ashkenazi Jews carries the FD gene change.

Currently, there is no cure for FD. Treatments aim at controlling symptoms and avoiding complications. Treatment strategies can include using special feeding techniques and special therapies, medications, artificial tears, respiratory care and orthopaedic management.