pediatrics
Duchenne Muscular Dystrophy and Becker Muscular Dystrophy
Diagnosis
DNA mutation analysis Sometimes muscle biopsy with immunostaining analysis of dystrophin Diagnosis is suspected by characteristic clinical findings, age at onset, and family history suggestive of X-Linked Recessive . Myopathic changes are noted on electromyography (rapidly recruited, short duration, low-amplitude motor unit potentials) and, when done, muscle biopsy shows necrosis and marked variation in muscle fiber size not segregated by motor unit. Creatinine kinase levels are elevated up to 100 times normal. Mutation analysis of DNA from peripheral blood leukocytes using multiplex ligation-dependent probe amplification (MLPA) is the primary confirmatory test; it can identify abnormalities in thedystrophingene. If an abnormality is not detected by MLPA but Duchenne or Becker dystrophy is still suspected, full sequencing of thedystrophingene can be done to detect small genetic changes, such as point mutations. If genetic testing does not confirm the diagnosis, then analysis of dystrophin with immunostaining of muscle biopsy samples should be done. Dystrophin is undetectable in patients with Duchenne dystrophy. In patients with Becker dystrophy, dystrophin is typically abnormal (lower molecular weight) or present in low concentration. Patients with Duchenne dystrophy should have a baseline assessment of cardiac function with ECG and echocardiography at the time of diagnosis or by age 6 years. Carrier detection and prenatal diagnosis are possible by using conventional studies (eg, pedigree analysis, creatinine kinase determinations, fetal sex determination) combined with recombinant DNA analysis and dystrophin immunostaining of muscle tissue. 