Clinical approach to inherited metabolic disorders in neonates

Most inborn errors of intermediary metabolism presenting in the neonatal period fall schematically into three clinical categories: (1) those which lead to a neurological distress 'intoxication type' with a symptom-free interval, vomiting, comas, hypertonia, abnormal movements and frequent humoral disturbances (organic acidaemias, congenital urea cycle defects); (2) those which lead to a neurological distress 'energy deficiency' type. Frequent symptoms in this group include hyperlactacidaemia, severe hypotonia, cardiomyopathy, failure to thrive and malformations (congenital lactic acidaemias, fatty acid oxidation defects, peroxysomal disorders); (3) those which present evidence of liver dysfunction and hepatomegaly (glycogenesis, neoglucogenesis defects, galactosaemia, fructosaemia, tyrosinaemia type I). According to these three major clinical presentations and according to the proper use of few screening tests (blood gases, glucose, ammonia, lactic acid, electrolytes, acetest), we propose a method of diagnosis which groups these children into five schematical syndromes: type I MSUD; type II organic acidaemias; type III; congenital lactic acidosis; type IVa, urea cycle defects; type IVb, non-ketotic hyperglycinaemia, sulfite oxidase deficiency, peroxisomal disorders; type V liver dysfunctions. Once the above classification has been made, sophisticated and specific investigations can be planned (amino acid chromatography, organic acid chromatography, enzymatic studies, etc).