SNP Shot: Genomic Insights

Glycogen storage disease type V (GSDV), also known as McArdle disease, is a genetic condition where muscles cannot properly break down glycogen, a complex sugar. This impaired glycogen breakdown disrupts normal muscle cell function.

Individuals with GSDV commonly experience fatigue, muscle pain, and cramps early in exercise (exercise intolerance). Activities like weight lifting or jogging often trigger these symptoms. Rest typically relieves the discomfort. A characteristic "second wind" phenomenon allows individuals to resume exercise with reduced or no discomfort after resting and allowing the pain to subside.

Extended or strenuous exercise in people with GSDV can lead to muscle damage. Roughly half of individuals with GSDV experience rhabdomyolysis, a breakdown of muscle tissue. Severe episodes release myoglobin, a protein, into the bloodstream. The kidneys filter this protein, which is then excreted in the urine (myoglobinuria), causing it to appear red or brown. Myoglobin can harm the kidneys, with approximately half of GSDV patients experiencing myoglobinuria developing potentially fatal kidney failure.

The symptoms of GSDV vary greatly among individuals. Onset typically occurs during the teens or twenties, but can range from infancy to adulthood. Muscle weakness usually worsens over time, although it remains stable in about one-third of affected individuals. Some experience mild symptoms like reduced stamina, while others are asymptomatic.

Inheritance:

GSDV follows an autosomal recessive inheritance pattern. This means that both copies of the responsible gene in each cell must have mutations for the condition to manifest. Parents of an individual with GSDV each carry one copy of the mutated gene but usually do not exhibit any signs or symptoms of the disease.