Duchenne muscular dystrophy (DMD) affects the muscles, leading to muscle wasting that gets worse over time. DMD occurs primarily in males, though in rare cases may affect females. The symptoms of DMD include progressive weakness and loss (atrophy) of both skeletal and heart muscle. Early signs may include delayed ability to sit, stand, or walk and difficulties learning to speak. Muscle weakness is usually noticeable in early childhood. DMD is caused by genetic changes (DNA variants) in the DMD gene. DMD is inherited in an X-linked recessive pattern and may occur in people who do not have a family history of DMD. Diagnosis of DMD is based on the symptoms, clinical exam, and the result of a biopsy to remove a small piece of muscle for examination under a microscope. The result of genetic testing may also help confirm the diagnosis. Becker muscular dystrophy (BMD), a milder form of muscular dystrophy, is also caused by genetic changes in the DMD gene.