Molecular analysis of genetic mutation in electrophoretic variant of human lactate dehydrogenase-A(M) subunit

An electrophoretic variant of lactate dehydrogenase-A (M) subunit was discovered in a patient with multiple myeloma. DNA analysis of the variant allele revealed a nucleotide substitution (transition) of C to T at codon 314 (CGT-TGT), and this mutation resulted in the replacement of an arginine by a cysteine (R314C). This amino acid replacement affects the net charge of the subunit and makes the LDH-A variant have a faster electrophoretic mobility. The responsible missense mutation created a new restriction site, AGGCCT, which can be simply detected by endonuclease AatI digestion. In addition, four synonymous substitutions with no amino-acid replacements were found at codons 51, 119, 163 and 175 in the LDH-A gene from the patient.