Final answer:
Duchenne's and Becker's muscular dystrophies are linked to a deficiency of A. dystrophin, a critical muscle membrane protein required for the structural integrity of muscle cells.
Step-by-step explanation:
Duchenne's and Becker's muscular dystrophies are both disorders linked to an absence or deficiency of the muscle membrane protein dystrophin. This protein is essential for the structural stability of muscle cells. In the absence of sufficient dystrophin, muscle contractions can damage the sarcolemma, leading to an influx of calcium ions and resulting in cellular damage and muscle fiber degradation. Over time, this leads to progressive skeletal muscle weakness and muscle tissue death, which are characteristic signs of muscular dystrophy. Although treatments have attempted to introduce healthy myoblasts or boost the production of utrophin—a protein similar to dystrophin—these efforts have seen limited success. Duchenne muscular dystrophy (DMD) is particularly notable as an X-linked recessive disorder, predominantly affecting males.