The M and H subunits are encoded by two different genes:
* The M subunit is encoded by LDHA, located on chromosome 11p15.4 ().
* The H subunit is encoded by LDHB, located on chromosome 12p12.2-p12.1 ().
* A third isoform, LDHC or LDHX, is expressed only in the testis (); its gene is likely a duplicate of LDHA and is also located on the eleventh chromosome (11p15.5-p15.3).
* The fourth isoform is localized in the peroxisome. It is tetramer containing one LDHBx subunit, which is also encoded by the LDHB gene. The LDHBx protein is seven amino acids longer than the LDHB (LDH-H) protein. This amino acid extension is generated by functional translational readthrough.
Mutations of the M subunit have been linked to the rare disease exertional myoglobinuria (see OMIM article), and mutations of the H subunit have been described but do not appear to lead to disease.