Four members of the SLC16A gene family encode classical monocarboxylate transporters MCT1-4. Widely expressed, they all function as proton-dependent transporters of monocarboxylic acids such as lactate and pyruvate and ketone bodies such as acetacetate and beta-hydroxybutyrate. These processes are crucial in the regulation of energy metabolism and acid-base homeostasis.

SLC16A1 encodes MCT1, a ubiquitiously expressed protein. Defects in SLC16A1 are the cause of symptomatic deficiency in lactate transport (SDLT aka erythrocyte lactate transporter defect; MIM:245340), resulting in an acidic intracellular environment and muscle degeneration with the release of myoglobin and creatine kinase. This defect could compromise extreme performance in otherwise healthy individuals. Mutations that can cause SDLT are K204E and G472R (Merezhinskaya et al. 2000). All patients had erythrocyte lactate clearance rates that were 40-50% of normal control values. Partial loss of function cannot be readily displayed in terms of product levels in Reactome so assume a reduced product level in this case causes SDLT.