Facts About Myopathies
Muscular Dystrophy Association

Introduction Questions and Answers Part I Part II 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?

On being told they have a genetic disorder such as an inheritable myopathy, patients often ask, "But it doesn't run in the family, so how could it be genetic?" Inheritable myopathies can run in a family, even if only one person in the biological family has it.

This is because genetic diseases can be inherited in three different ways: X-linked, autosomal dominant and autosomal recessive. Inheritable myopathies are inherited in all three ways.

X-linked means that the genetic mutation (or defect) is located on the X chromosome. For many X-linked diseases, a normal copy of the gene can compensate for the defective copy. Because males have only one X chromosome while females have two, X-linked diseases almost always affect males.

Autosomal means the mutationoccurs on a chromosome other than the X or Y. Therefore, autosomal diseases affect males and females equally.

Autosomal recessive means that two copies of a defective gene are required for the full-blown disease. One copy is inherited from each parent, neither of whom would normally have the disease. Autosomal dominant means that one copy of a defective gene is enough to cause disease. So, a person who inherits the defective gene from a parent will have the disease, as will the parent.

Inheritable myopathies passed on in an autosomal dominant pattern can be easy to trace through the family tree. In contrast, X-linked or autosomal recessive disorders might seem to occur "out of the blue." But in reality, one or both parents might be carriers who silently harbor a genetic mutation. Many parents have no idea they're carriers of a disease until they have a child with the disease.

Inheritable myopathies actually can occur "out of the blue," when a new mutation occurs during the child's conception. These are called spontaneous mutations, and after they occur, they can be passed on to the next generation.

A good way to find out more about your risk of inheriting or passing on an inheritable myopathy is to talk to your MDA clinic physician or a genetic counselor. Also, see MDA's pamphlet "Genetics and Neuromuscular Diseases."