What causes muscular dystrophy?

All of the muscular dystrophies (MDs) are inherited and involve a mutation in one of the thousands of genes that program proteins critical to muscle integrity. The body's cells donVt work properly when a protein is altered or produced in insufficient quantity. Many cases of MD occur from spontaneous mutations that are not found in the genes of either parent, and this defect can be passed to the next generation.

Muscular dystrophies can be inherited in three ways:

Autosomal dominant inheritance occurs when a child receives a normal gene from one parent and a defective gene from the other parent. Autosomal means the genetic mutation can occur on any of the 22 nonsex chromosomes in each of the body's cells. Dominant means only one parent needs to pass along the abnormal gene in order to produce the disorder. In families where one parent carries a defective gene, each child has a 50 percent chance of inheriting the gene. Males and females are equally at risk. Autosomal recessive inheritance means that both parents carry and pass on the faulty gene. The parents each have one defective gene but are not affected by the disorder. Children in these families have a 25 percent chance of inheriting both copies of the defective gene and a 50 percent chance of inheriting one gene and therefore becoming a carrier-able to pass along the defect to their children. Children of either sex can be affected by this pattern of inheritance. X-linked (or sex-linked) recessive inheritance occurs when a mother carries the affected gene on one of her two X chromosomes and passes it to her son (males always inherit an X chromosome from their mother and a Y chromosome from their father). Sons of carrier mothers have a 50 percent chance of inheriting the disorder. Daughters also have a 50 percent chance of inheriting the defective gene but usually are not affected, since the healthy X chromosome they receive from their father can offset the faulty one received from their mother. Affected fathers cannot pass an X-linked disorder to their sons, but their daughters will be carriers of that disorder. Carrier females occasionally can exhibit milder symptoms of MD.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.