nutritional disorders
Carnitine Deficiency
Introduction
Carnitine deficiency results from inadequate intake of or inability to metabolize the amino acid carnitine. It can cause a heterogeneous group of disorders. Muscle metabolism is impaired, causing myopathy, hypoglycemia, or cardiomyopathy. Infants typically present with hypoglycemic, hypoketotic encephalopathy. Most often, treatment consists of dietary L-carnitine. (See also Overview of Undernutrition .) The amino acid carnitine is required for the transport of long-chain fatty acyl coenzyme A (CoA) esters into myocyte mitochondria, where they are oxidized for energy. Carnitine is obtained from foods, particularly animal-based foods, and via endogenous synthesis. Causes of carnitine deficiency include the following: Inadequate intake (eg, due to fad diets, lack of access, or long-term Total Parenteral Nutrition (TPN) ) 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 ofzidovudine) Use of valproate The deficiency may be generalized (systemic) or may affect mainly muscle (myopathic). 