Mammals have two pyruvate kinase genes, PK-LR (which encodes for pyruvate kinase isozymes L and R) and PK-M (which encodes for pyruvate kinase isozyme M1), but only PKLR encodes for the red blood isozyme which effects pyruvate kinase deficiency. Over 250 PK-LR gene mutations have been identified and associated with pyruvate kinase deficiency. DNA testing has guided the discovery of the location of PKLR on chromosome 1 and the development of direct gene sequencing tests to molecularly diagnose pyruvate kinase deficiency.[20]