Creatine kinase is markedly elevated in which neuromuscular disorder due to X-linked mutations affecting dystrophin?

Creatine kinase is markedly elevated in which neuromuscular disorder due to X-linked mutations affecting dystrophin?

• A. Becker muscular dystrophy
• B. Limb-girdle muscular dystrophy type 1
• C. Amyotrophic lateral sclerosis
• D. Duchenne muscular dystrophy

Answer: (D)

Creatine kinase rises when muscle fibers are damaged and leak their contents into the bloodstream. In dystrophinopathies, the membrane around muscle fibers is unstable because dystrophin is missing or defective, so contraction causes more fiber injury and CK escapes into the blood. In Duchenne muscular dystrophy, X-linked mutations abolish dystrophin entirely, leading to severe membrane fragility and rapid muscle breakdown from early childhood. This produces very high CK levels, often much higher than normal. Becker muscular dystrophy also involves dystrophin defects but with some functional dystrophin remaining, so CK elevations tend to be present but not as dramatic as in Duchenne. The other disorders listed—ALS, or different autosomal-dominant limb-girdle dystrophies—do not produce the same pattern of massively elevated CK from a primary dystrophinopathy.

Creatine kinase rises when muscle fibers are damaged and leak their contents into the bloodstream. In dystrophinopathies, the membrane around muscle fibers is unstable because dystrophin is missing or defective, so contraction causes more fiber injury and CK escapes into the blood.

In Duchenne muscular dystrophy, X-linked mutations abolish dystrophin entirely, leading to severe membrane fragility and rapid muscle breakdown from early childhood. This produces very high CK levels, often much higher than normal. Becker muscular dystrophy also involves dystrophin defects but with some functional dystrophin remaining, so CK elevations tend to be present but not as dramatic as in Duchenne. The other disorders listed—ALS, or different autosomal-dominant limb-girdle dystrophies—do not produce the same pattern of massively elevated CK from a primary dystrophinopathy.