Embryonic lethality in mice due to carnitine transporter OCTN2 defect and placental carnitine deficiency

l-Carnitine plays a crucial role in uptake and subsequent β-oxidation of long-chain fatty acids in the mitochondria. Placental trophoblast cells oxidize long-chain fatty acids for energy production. Here we present data showing that l-carnitine deficiency due to a defect in the carnitine transporter OCTN2 (SLC22A5) in a mouse model leads to embryonic lethality. Placental levels of l-carnitine are reduced to <10% of normal and deficiency of l-carnitine is associated with markedly reduced expression of several growth factors and transforming growth factor β (TGF-β) genes. This report links for the first time reduced l-carnitine levels in the placenta to embryonic lethality.