The human gene SLC22A5 encodes the organic cation/carnitine transporter 2 (OCTN2). OCTN2 is strongly expressed in the kidney, skeletal muscle, heart and placenta (Tamai et al. 1998). Defects in SLC22A5 are the cause of systemic primary carnitine deficiency (CDSP) (Tang et al. 1999) and susceptibility to Crohn disease (CD) (Peltekova et al. 2004). The human gene SLC22A15 encodes the fly-like putative transporter1 (FLIPT1). FLIPT1 is a novel transporter highly expressed in kidney and brain is shown to be homologous to other carnitine transporters (Eraly & Nigan 2002). The human gene SLC22A16 encodes the organic cation/carnitine transporter 6 (also called the fly-like putative transporter 2, FLIPT2) (Enomoto et al. 2002). FLIPT2 is strongly expressed in the testis and epididymas as well as generally in other tissues and in leukaemia cells ( Enomoto et al. 2002, Gong et al. 2002). All of these transporters are sodium-dependent, high affinity carnitine cotransporters.