Duchenne muscular dystrophy can arise from any one of several mutations in the DMD gene—the largest human gene known—which encodes a protein called dystrophin. This protein helps muscle cells contract, and the lack of a functional dystrophin protein is the underlying problem for DMD patients. Males are disproportionately affected; since the DMD gene is found on the X chromosome and males possess only one X chromosome (paired with a paternally inherited Y chromosome), a single mutated copy of DMD leaves them wholly devoid of healthy dystrophin. Females, however, have two X chromosomes and thus
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