Last updated 2mo ago
Log in to add personal notes on this page.
A 12-year-old boy with mild proximal weakness and calf hypertrophy has an elevated CK. His maternal uncle is wheelchair-bound at age 40. Genetic testing shows an in-frame deletion in DMD.
XLR; DMD gene - in-frame variants (truncated but partially functional dystrophin)
- Later onset (usually >5 years), milder course
- Ambulatory into adulthood (often into 40s-50s)
- Cardiomyopathy can be prominent/disproportionate
- Elevated CK (but less than DMD)
- Markedly elevated serum CK prompts molecular testing of DMD
- DMD deletion/duplication analysis (MLPA) first; sequencing if no large rearrangement found
- In-frame variants distinguish Becker from the out-of-frame (frameshift) variants of Duchenne (the reading-frame rule)
- Carrier testing for at-risk female relatives (X-linked recessive); offer reproductive counseling and prenatal options
- Cardiac surveillance with echocardiogram or cardiac MRI; cardiomyopathy can be disproportionate to skeletal weakness
- ACE inhibitors and beta-blockers for cardiomyopathy; corticosteroids in selected patients
- PT, orthopedic and respiratory monitoring; avoid statins where possible given myopathy overlap
- Multidisciplinary neuromuscular care with periodic functional and pulmonary assessment
"BEcker's has a BEtter prognosis": Becker muscular dystrophy results from in-frame (non-frameshift) mutations in dystrophin, producing a truncated but partially functional protein. This leads to a milder course compared to Duchenne.