Nutrition in children affected by inherited metabolic diseases

Diet-therapy represents an elective approach to the treatment of several inborn errors of metabolism. According to the type of disease, dietary intervention can be addressed to three different goals: a) dietary restriction (global or partial) of one or more nutritional components become "toxic" because of the occurring enzymatic defect; b) supplementation with a given defective nutritional component; c) elimination through the use of diet and drugs of the accumulated "toxic" compounds. These interventions are aimed at overtaking the metabolic block and to avoid the accumulation of intermediate "toxic" substrates. The efficacy of the therapy should then be evaluated by means of a thorough biochemical and clinical follow-up (including anthropometric and psychomotor development parameters). In particular, nutritional indexes should be constantly monitored in order to support the dietary therapy, discover and correct any possible nutritional deficiency secondary to the "by exclusion dietary regimen". To elucidate these general principles, we discuss in detail some hereditary diseases of amino acid (phenylketonuria) and carbohydrate (glycogen storage disease and galactosemia) metabolism that, being responsive to the nutritional intervention, can be considered reliable examples of all the problems linked to diagnosis, acute and long-term therapy and follow-up of these diseases.