[Diagnostic approach and treatment of inherited mitochondrial fatty acid oxidation disorders]

Inherited mitochondrial fatty acid oxidation disorders are a complex set of genetically-based diseases in which up to 22 different entities are currently recognized. Their incidence is probably underestimated because a high level of diagnostic suspicion is required for their detection. Their clinical spectrum and prognosis are variable. In recent years knowledge of these diseases and improved treatment have reduced associated mortality. A common characteristic of all these diseases is hypoketotic hypoglycemia, although this is not constant and does not appear in the short-chain disorders and, sometimes, does not even appear in the medium-chain disorders. Cardiac or skeletal myopathy combined and/or hepatic involvement at periods of metabolic decompensation are typical, since these tissues depend on fatty acid oxidation. Diagnosis has been simplified by the study of acylcarnitines in blood, even in periods of metabolic stability. Determination of acylglycines, organic acids, carnitines, free fatty acids and 3-hydroxy-fatty acids, together with enzymic and genetic studies, complete the diagnosis. In certain circumstances, a provocation test should be carried out. Treatment basically consists of avoiding fasting, restricting fatty acid uptake and increasing carbohydrate uptake, depending on the type of metabolic disorder. Pharmacological treatment may also be added (carnitine, riboflavine or carbamylglutamate).