In primary carnitine deficiency (PCD), a recessive gene mutation in Solute Carrier Family 22 Member 5 (SLC22A5) causes a defect in the function of organic cation/carnitine transporter 2 (OCTN2), leading to a decrease in renal reabsorption of carnitine [69]. This evidence concerns the gene SLC22A5 and systemic primary carnitine deficiency disease.