Duchenne muscular dystrophy (DMD) is an inheritable condition that is one of nine types of muscular dystrophy. It is characterized by progressive muscle wasting (atrophy) and weakness in the skeletal and heart muscles, leading to a decline in muscle function and heart problems.
The disease is caused by a mutation in the DMD gene, which encodes for a protein called dystrophin. Dystrophin acts to protect the muscles at each contraction, and a lack of dystrophin results in an accumulation of damage and eventual death of the muscle cells.
Inheritance of DMD
Genes are organized in chromosomes, long pieces of tightly packaged DNA. We all have 23 pairs of chromosomes. Pairs 1 to 22 have the same genes on them. However, the final pair, called the “sex chromosomes” and designated X and Y, carry different genes. Females inherit two copies of the X chromosome (one from their mother and one from their father), while males inherit one X chromosome from their mother and one Y chromosome from their father.
The DMD gene is located on the X chromosome, so Duchenne muscular dystrophy is an X-linked disease and mostly affects males because they have only one copy of the X-chromosome. Because females have two X chromosomes, the second one can compensate for the mutated DMD gene by producing enough functional dystrophin protein to either prevent the symptoms of DMD or cause only mild symptoms. However, these individuals are so-called “carriers” of DMD who can pass the disease to their children without having it themselves. A DMD carrier woman has a 50 percent chance of having a son affected by DMD and a 50 percent chance of having a daughter who also is a carrier.
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