Duchenne Muscular Dystrophy / Becker Muscular Dystrophy (DMD)
Both Duchenne and Becker muscular dystrophies are X-linked, pan-ethnic disorders caused by pathogenic variants in the gene DMD. Duchenne muscular dystrophy is characterized by progressive muscle weakness beginning in early childhood, with confinement to a wheelchair by age 13. Progressive cardiomyopathy and respiratory difficulties usually lead to death by age 30. Becker muscular dystrophy has a delayed progression relative to Duchenne muscular dystrophy; confinement to a wheelchair occurs after the age of 16, and on average, death occurs by age 45 due to heart failure. A genotype-phenotype correlation occurs in more than 90% of patients. Null variants, including out-of-frame deletions or duplications, are likely to result in Duchenne muscular dystrophy, whereas pathogenic variants that result in the retention of some protein are more likely to result in Becker muscular dystrophy.
For information about carrier frequency and residual risk, please see the residual risk table.