Duchenne Muscular Dystrophy - Pathogenesis

Pathogenesis

Duchenne muscular dystrophy (DMD) is caused by a mutation of the dystrophin gene at locus Xp21. Dystrophin is responsible for connecting the cytoskeleton of each muscle fiber to the underlying basal lamina (extracellular matrix) through a protein complex containing many subunits. The absence of dystrophin permits excess calcium to penetrate the sarcolemma (cell membrane). Alterations in these signalling pathways cause water to enter into the mitochondria which then burst. In skeletal muscle dystrophy, mitochondrial dysfunction gives rise to an amplification of stress-induced cytosolic calcium signals and an amplification of stress-induced reactive-oxygen species (ROS) production. In a complex cascading process that involves several pathways and is not clearly understood, increased oxidative stress within the cell damages the sarcolemma and eventually results in the death of the cell. Muscle fibers undergo necrosis and are ultimately replaced with adipose and connective tissue.

DMD is inherited in an X-linked recessive pattern. Females will typically be carriers for the disease while males will be affected. Typically, a female carrier will be unaware they carry a mutation until they have an affected son. The son of a carrier mother has a 50% chance of inheriting the defective gene from his mother. The daughter of a carrier mother has a 50% chance of being a carrier or having two normal copies of the gene. In all cases, the father will either pass a normal Y to his son or a normal X to his daughter. Female carriers of an X-linked recessive condition, such as DMD, can show symptoms depending on their pattern of X-inactivation.