Pseudohypertrophic muscular dystrophies (PHMDs) are a group of genetic disorders characterized by progressive muscle weakness and wasting. These conditions are collectively called "pseudohypertrophic" because initially, affected muscles may appear larger and firmer due to fatty infiltration and connective tissue replacement. However, this hypertrophy is deceptive, as it does not reflect an increase in functional muscle tissue but rather the infiltration of abnormal substances within the muscle fibers.
PHMDs are primarily caused by mutations in genes involved in muscle structure, function, or metabolism. One of the most well-known forms of PHMD is Duchenne muscular dystrophy (DMD), which is caused by mutations in the dystrophin gene. Other forms include Becker muscular dystrophy (BMD), caused by partially functional dystrophin, and other rarer subtypes such as Emery-Dreifuss muscular dystrophy, limb-girdle muscular dystrophy, and facioscapulohumeral muscular dystrophy.
Symptoms typically appear in childhood and may include delayed motor milestones, difficulty in walking or running, progressive muscle weakness, and fatigue. As the disease progresses, the muscle weakness spreads and can affect the heart and respiratory muscles, leading to cardiac and respiratory complications.
There is currently no cure for PHMDs, and treatment mainly focuses on managing symptoms, preserving mobility, and preventing complications. This may include physical therapy, assistive devices, respiratory support, and medication to manage symptoms like contractures and pain. Research efforts are ongoing to develop new therapies, including gene therapy, exon skipping, and other approaches to address the underlying genetic defects and improve the quality of life for individuals with PHMDs.
