OCTN1, or SLC22A4, is a gene that encodes a protein involved in the transport of organic cations, which are positively charged molecules. This protein is primarily found in the kidneys and intestines, where it helps in the absorption and excretion of various substances, including drugs and metabolites. Mutations in the OCTN1 gene can lead to a condition known as primary carnitine deficiency, which affects the body's ability to transport carnitine. Carnitine is essential for the metabolism of fatty acids, and its deficiency can result in muscle weakness and other health issues.