Causes of carnitine deficiency include the following: Inadequate intake (eg, due to fad diets, lack of access, or long-term total parenteral nutrition) Inability to metabolize carnitine due to enzyme deficiencies (eg, carnitine palmitoyltransferase deficiency, methylmalonicaciduria, propionicacidemia, isovalericacidemia) Decreased endogenous synthesis of carnitine due to a severe liver disorder Excess loss of carnitine due to diarrhea, diuresis, or hemodialysis A hereditary disorder in which carnitine leaks from renal tubules Increased requirements for carnitine when ketosis is present or demand for fat oxidation is high (eg, during a critical illness such as sepsis or major burns; after major surgery of the gastrointestinal tract) Decreased muscle carnitine levels due to mitochondrial impairment (eg, due to use of zidovudine) Use of valproate The deficiency may be generalized (systemic) or may affect mainly muscle (myopathic).