A 27-year-old man has an 11-year history of intermittent muscle pain, weakness, and stiffness following exercise. During exercise, serum lactate concentration does not increase. The most likely explanation for these findings is a deficiency of which of the following in muscle?

Question

Quizplus · Accepted Answer

The symptoms and lack of increase in serum lactate during exercise suggest McArdle's disease, which is due to a deficiency in muscle phosphorylase activity.  Deficiency in muscle phosphorylase activity is associated with the development of McArdle disease (glycogen storage disease type V [GSDV]). The clinical presentation of GSDV is usually seen in young adulthood and is characterized by exercise intolerance and muscle cramps following slight exercise. Attacks of myoglobinuria frequently accompany the muscle symptoms of GSDV. About half of GSDV patients will exhibit burgundy-colored urine after exercise.

A 27-Year-Old Man Has an 11-Year History of Intermittent Muscle