DNA-Based Techniques for Detection of Carriers of Duchenne and Becker Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is the most frequent muscle disease in children. The incidence of DMD is 1/4000 live-born males; one-third of the patients are the result of new mutation. DMD, a progressive, lethal, X-linked neuromuscular disorder, and its milder, less-frequently occurring allelic variant, Becker muscular dystrophy (BMD), are caused by defects in the dystrophin gene, located on the X chromosome (Xp21), which is, with 2.4 Mb of the genomic sequence, the largest human gene known to date. It harbors 79 exons, which together produce a 14-kb transcript (mRNA) and code for a 427-kDa protein called dystrophin, a muscle-specific protein, which is located underneath the sarcolemma membrane. In DMD, patients’ dystrophin is absent, except for an occasional revertant, dystrophin-positive fiber (< 3%). In BMD patients′ muscle cells, the dystrophin protein is reduced and less functional than in normal muscle cells (see also Chapter 3 ).