DMD gene

The DMD gene is the largest known human gene and provides instructions for making dystrophin, a protein critical for maintaining the structural integrity of muscle fibers.

Normal Function

DMD, the largest known human gene, provides instructions for making a protein called dystrophin. This protein is located primarily in muscles used for movement (skeletal muscles) and in heart (cardiac) muscle. Small amounts of dystrophin are also present in nerve cells in the brain.

In skeletal and cardiac muscles, dystrophin is part of a protein complex that strengthens muscle fibers and protects them from injury during contraction and relaxation. The dystrophin complex acts as an anchor, connecting each muscle cell's structural framework (cytoskeleton) with the lattice of proteins and other molecules outside the cell (extracellular matrix). The complex may also play a role in cell signaling. In nerve cells, research suggests dystrophin is important for the normal structure and function of synapses.

Health Conditions Related to Genetic Changes

Duchenne and Becker muscular dystrophy

More than 2,000 mutations in the DMD gene have been identified in people with the Duchenne and Becker forms of muscular dystrophy. These conditions occur almost exclusively in males and are characterized by progressive muscle weakness, wasting (atrophy), and a heart condition called dilated cardiomyopathy.

• Becker muscular dystrophy: Mutations typically lead to an abnormal version of dystrophin that retains some function, resulting in milder features that appear at a later age.
• Duchenne muscular dystrophy: Mutations typically prevent any functional dystrophin from being produced, leading to more severe symptoms.

Skeletal and cardiac muscle cells without enough functional dystrophin become damaged as muscles contract and relax. Over time, these cells weaken and die, causing the characteristic muscle weakness and heart problems.

X-linked dilated cardiomyopathy

More than 30 mutations in the DMD gene can cause an X-linked form of familial dilated cardiomyopathy. This condition enlarges and weakens the cardiac muscle, preventing the heart from pumping blood efficiently. Unlike Duchenne and Becker muscular dystrophy, this condition is typically not associated with the weakness and wasting of skeletal muscles.

These mutations preferentially affect the activity of dystrophin in cardiac muscle cells. Affected individuals typically have little or no functional dystrophin in the heart, leading to damaged cardiac muscle cells that weaken and die over time.

Other Names for This Gene

• BMD
• DMD_HUMAN
• dystrophin (muscular dystrophy, Duchenne and Becker types)

Genomic Location

The DMD gene is found on the X chromosome.