Two major genetic evidences underpin the pivotal role of OCTN2 in carnitine homeostasis in eukaryotes: (i) children diagnosed with systemic carnitine deficiency (OMIM212149) carry loss-of-function mutations in the SLC22A5 gene (Nezu et al., 1999), (ii) the juvenile visceral steatosis (jvs) mouse, characterized by impaired intestinal absorption, tissue distribution and reabsorption of carnitine, lack the octn2 transporter (Koizumi et al., 1988; Horiuchi et al., 1993; Hashimoto et al., 1998; Yokogawa et al., 1999; Tamai et al., 2001; Kato et al., 2006). This evidence concerns the gene SLC22A5 and systemic primary carnitine deficiency disease.