Duchenne muscular dystrophy (DMD; OMIM 310200) and Becker muscular dystrophy (BMD; OMIM 300376) are both X-linked recessive conditions that result from different mutations of the same gene, known as dystrophin, on the long arm of the chromosome. BMD and DMD are quite different clinically. DMD is a very severe disorder that first appears at a young age, progresses rapidly, and is often fatal in the late teens to 20s. BMD, on the other hand, is much milder. Often symptoms don't first appear until the 40s or 50s, the progression of the disease is slow, and fatalities due to BMD are infrequent. Go to https://www.ncbi.nlm.nih/omim and survey the information describing the gene mutations causing these two conditions. Discuss the information you find with a few others in a small group, and write a single summary explaining your findings.

Key Concepts

X-linked Recessive Inheritance

X-linked recessive inheritance refers to a pattern of genetic transmission where a gene located on the X chromosome is expressed in males (who have one X and one Y chromosome) and can be carried by females (who have two X chromosomes). Males are more likely to express X-linked recessive disorders because they have only one copy of the X chromosome. In females, a second, normal copy of the gene can mask the effects of a mutated gene, making them carriers without showing symptoms.

Dystrophin Gene and Its Role

The dystrophin gene encodes the dystrophin protein, which is crucial for maintaining the structural integrity of muscle cells. Mutations in this gene can lead to the absence or dysfunction of dystrophin, resulting in muscle degeneration and conditions like Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD). The severity of the condition often correlates with the type of mutation; DMD typically results from complete loss of dystrophin, while BMD is associated with partially functional dystrophin.

Clinical Differences Between DMD and BMD

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) exhibit distinct clinical features despite being caused by mutations in the same gene. DMD is characterized by early onset, rapid progression, and severe muscle weakness, often leading to early mortality. In contrast, BMD has a later onset, milder symptoms, and a slower progression, allowing individuals to live into middle age or beyond. Understanding these differences is crucial for diagnosis, management, and genetic counseling.