FAST-TYPE ELECTROPHORETIC VARIANT OF LACTATE-DEHYDROGENASE M(A) AND COMPARISON WITH OTHER MISSENSE MUTATIONS IN LACTATE-DEHYDROGENASE M(A) AND H(B) GENES

An electrophoretic variant of lactate dehydrogenase (LD) M(A) subunit was discovered in a female patient with chest pain. Her LD activity in serum was within the normal reference interval, and analysis of her L D isoenzyme pattern showed an abnormal migration indicating a fast-typ e LD-M(A) subunit variant. DNA analysis of the mutant LD-M gene detect ed a single base substitution, an A to G transition at codon 220 (AAA- ->GAA). This mutation resulted in the replacement of a lysine by a glu tamic acid (mutation K220E) and produced a subunit variant (electropho retic fast type). This missense mutation was also observed in the pati ent's son, and genotypes of mother and son were consistent with their biochemical phenotypes, as evaluated by LD isoenzyme analysis.