On the cover: Barbara Williams of Clackamas, Ore., first had FSHD symptoms in childhood. Recent surgery has given her less pain and better use of her right arm. Introduction Questions and Answers Does it Run in the Family? MDA's Search for Treatments and Cures MDA is Here to Help You

Does it Run in the Family?

FSHD certainly can “run in families.” In this condition, a small section of the DNA on chromosome 4 that’s shorter than usual is inherited in an autosomal dominant pattern, meaning it only takes one such mutation (from one parent) to cause the disorder. This altered piece of DNA also can occur spontaneously in a child as he or she develops in the womb.

FSHD can affect either males or females. In a small number of people with FSHD, the usual chromosome 4 mutation can’t be identified. In most affected people, it can be, with genetic testing.

FSHD is one of many genetic disorders in which germ line mosaicism is believed to occur. Germ line refers to egg or sperm cells. In this phenomenon some, but not all, sperm or egg cells in a parent carry a particular mutation.

In families with more than one child with FSHD but no previous family history, it’s likely that one parent has germ line mosaicism and that affected children were conceived with egg or sperm cells carrying the FSHD mutation. In these situations, the parents have no symptoms, and, if their blood cells are tested, they don’t show the mutation.

More information can be found on MDA’s Web site.

For help in understanding your family’s specific situation and planning for future children, it’s best to meet with a genetic counselor. You can obtain a referral to a counselor through your MDA clinic.