SLC22A5 and systemic primary carnitine deficiency disease: Primary carnitine deficiency (PCD) (OMIM #212140) is an autosomal-recessive disorder caused by variants in the SLC22A5 gene, which encodes the Organic Cation Transporter Novel 2 (OCTN2) protein.6 OCTN2 maintains the intracellular carnitine concentrations through transport of carnitine into cells, including reabsorption of carnitine in the renal tubuli.7 8 Impaired function of OCTN2 leads to decreased intracellular free carnitine concentrations.