Nutrition des maladies métaboliques rares en pédiatrie

Inborn errors of metabolism are due to the inherited defect of an enzyme or transporter involved in metabolism. First symptoms may appear at every age, from neonatal period to adulthood, and are frequently responsible for admission in intensive care unit. Most of these diseases are treatable with specific diets. Nutritional management is aimed at stopping the build-up of potential toxic metabolites upstream from the metabolic blockage, and to restore metabolite production downstream. Early treatment, based on initial suspected diagnoses, greatly enhances the chance of a better outcome. Indeed, neurological deterioration with intoxication symptoms may suggest a disorder of amino acid metabolism, such as aminoacidopathy, organic aciduria or urea cycle disorder. After stabilisation, a high-calorie protein-free nutrition should be started for a 24 to 48-h period, followed by a careful and progressive introduction of natural proteins. Hypoglycaemia is the major feature of liver glycogen storage diseases and congenital hyperinsulinism. Associated symptoms and rate of glucose administration required to maintain normal glycaemia are helpful to clarify diagnosis. Acute deterioration with cardiac, muscle, and liver failure, eventually associated with fasting nonketotic hypoglycaemia, is suggestive of fatty acid oxidation defect. In such situation, the goal of nutritional management is to exclude fatty acids and provide sufficient glucose to suppress fatty acid oxidation and block lipolysis, both aimed at preventing the accumulation of toxic derivatives, and stimulating energy production from carbohydrates. Finally, several vitamin therapies may increase residual enzyme activity, which may be sufficient to markedly improve the clinical situation. These nutritional guidelines, developed from the paediatric experience of inborn errors of metabolism management, can be easily adapted to adult care in similar situations.