AMP deaminase (AMPD) is an allosteric enzyme that plays a critical role in energy metabolism. There are three functional isoforms of AMPD. AMPD1 is the skeletal muscle-specific isoform M located in type II muscle fibers, neuromuscular junctions and in capillaries. Defects in AMPD1 are the cause of adenosine monophosphate deaminase deficiency muscle type (AMPDDM). AMPDDM is a metabolic disorder resulting in exercise-related myopathy. It is characterized by exercise-induced muscle aches, cramps, and early fatigue.