Becker's Muscular Dystrophy - Genetics

Genetics

The disorder is inherited with an X-linked recessive inheritance pattern. The gene is located on the X chromosome. Since women have two X chromosomes, if one X chromosome has the non-working gene, the second X chromosome will have a working copy of the gene to compensate. Because of this ability to compensate, women rarely develop symptoms. However, they may do so due to mosaicism. For example, carrier females of mutations are at increased risk for dilated cardiomyopathy. Since men have an X and a Y chromosome and because they don't have another X to compensate for the defective gene, they will develop symptoms if they inherit the non-working gene.

All dystrophinopathies are inherited in an X-linked recessive manner. The risk to the siblings of an affected individual depends upon the carrier status of the mother. Carrier females have a 50% chance of passing the DMD mutation in each pregnancy. Sons who inherit the mutation will be affected; daughters who inherit the mutation will be carriers. Men who have Becker muscular dystrophy can have children, and all their daughters are carriers, but none of the sons will inherit their father's mutation. Prenatal testing through amniocentesis or chorionic villus sampling (CVS) for pregnancies at risk is possible if the DMD mutation is found in a family member or if informative linked markers have been identified. A significant number of Becker muscular dystrophy mutations are spontaneous and are not inherited from a parent.

Becker muscular dystrophy occurs in approximately 3 to 6 in 100,000 male births, making it much less common than Duchenne muscular dystrophy. Symptoms usually appear in men at about ages 8–25, but may sometimes begin later. Patients can lose the ability to walk as early as age 15 in the very rare severe form.

Genetic counseling may be advisable when potential carriers or patients want to have children. Sons of a man with Becker muscular dystrophy do not develop the disorder, but daughters will be carriers (and some carriers can experience some symptoms of muscular dystrophy). The daughters' sons may develop the disorder.