To investigate the underlying cause of carnitine deficiency in SDT-f-DKD rats, we analyzed the carnitine profile in plasma; the expression levels of FAO enzymes and trimethyl lysine hydroxylase, epsilon (Tmlhe), a key biosynthesis enzyme of carnitine; and mitochondrial morphology at different time points in SDT-f-DKD rats. The gene discussed is TMLHE; the disease is systemic primary carnitine deficiency disease.