PGAM deficiency is due to deficiency of the muscle form of the enzyme PGAM. The symptoms are limited to muscle and include exercise intolerance, cramps, and recurrent myoglobinuria.

PGAM deficiency, like muscle LDH deficiency, retains some (usually about 5%) residual activity attributable to the presence in muscle of a small amount of another enzyme isoform. Thus the block in glycolysis is incomplete, and lactate levels may increase 2-3 fold with ischemic exercise in contrast to the flat lactate responses typical of complete glycolytic blocks. Also such partial glycolytic defects, by preserving the capacity to generate pyruvate for oxidative metabolism, are generally not associated with the sever limitations of oxidative metabolism and major fluctuations in exercise capacity related to changes in extramuscular fuel availability that are typical of muscle phosphorylase and muscle PFK deficiencies.