AMPD (AMP deaminase), an enzyme catalyzing AMP to IMP, plays an important role in purine/urate metabolism. AMPD is encoded in 3 genes for 3 isozymes M, L and E (H), respectively. In humans, 2 AMPD deficiencies have been reported in skeletal muscles (AMPD1 deficiency) and red blood cells (AMPD3 deficiency). AMPD1 deficiency has been found in patients with metabolic myopathy. AMPD regulates important purine nucleotides including ATP, ADP, AMP, IMP et al. Also, AMPD deficiency may change the level of adenosine, an important bioactive molecule. In addition, AMP activated protein kinase (AMPK) activity, controlled by intracellular AMP, has an important role as an energy sensor. Therefore, AMPD may control the systemic metabolic status by changing AMPK activity through the AMP level.