OCTN2, or SLC22A4, is a gene that encodes a protein responsible for the transport of certain organic cations, including carnitine, across cell membranes. This protein plays a crucial role in cellular energy metabolism by facilitating the uptake of carnitine, which is essential for the transport of fatty acids into mitochondria for energy production. Mutations in the OCTN2 gene can lead to primary carnitine deficiency, a condition that results in low levels of carnitine in the body. This deficiency can cause various health issues, including muscle weakness and heart problems, highlighting the importance of OCTN2 in maintaining proper metabolic function.