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Harvard Medical School

Familial Dysautonomia

What Is It?

Familial dysautonomia (FD), also called Riley-Day syndrome, is an inherited form that affects the nervous system. People born with FD have fewer nerve fibers for to carry sensations around the body. For this reason, they have trouble feeling pain, temperature, skin pressure and the position of their arms and legs. They can't fully experience taste. They also have abnormally low levels of a natural chemical called norepinephrine, which helps to relay messages between nerve cells.

In addition, people born with FD have a hard time regulating bodily functions, a condition called dysautonomia. These functions are managed by the autonomic nervous system — the network of nerves that controls such "automatic" functions as breathing and sweating.

In people with FD, dysautonomia can affect many vital functions. It can cause difficulties in swallowing, digestion and passing urine. It also can interfere with the control of blood pressure, body temperature and the production of tears to keep the eyes moist.

FD primarily affects Jews of Eastern European (Ashkenazi) background. It is a genetic problem that is caused by an inherited mutation, or change, in a gene called IKBKAP. Scientists believe that a mutation in this gene interferes with the body's ability to produce a key protein necessary for nerves to develop and function normally.

FD only occurs when someone inherits two copies of the mutated or changed gene, one from each parent. If a child inherits only one copy of the mutated IKBKAP gene from one parent, and one normal gene from the other parent, he or she will be a "carrier" of FD. Although he will not show symptoms of the illness, a carrier can pass the gene to his or her children without ever even knowing that they have it.

Doctors estimate that about one out of every 30 Ashkenazi Jews is a carrier of FD. This means that roughly one in every 3,600 children of Ashkenazi families is born with the disorder. In most cases, an FD carrier is unaware of the genetic problem until a close family member — child, sibling, niece or nephew — shows symptoms of the disorder.