Characteristic Metabolites for Inborn Errors of Amino Acid Metabolism

Inborn errors of metabolism are caused by changes in specific enzymatic reactions and hundreds of different such alterations, which affect about 1 of every 5000 newborns, have been characterized. The first inborn errors of metabolism, which have been described in the beginning of the 20th century by Sir Archibald Garrod, dealt with alkaptonuria, pentosuria, cystinuria and albinism. Infants and children with treatable errors of metabolism can be identified by screening newborns for meaningful metabolite biomarkers. Several classic inborn errors of metabolism can be detected by the accumulation of certain amino acids as metabolites in body fluids like serum and urine. Phenylketonuria (PKU) is an inherited metabolic disorder. Individuals having phenylketonuria do not have the ability to further metabolize phenylalanine. Fortunately this metabolic disorder can be analyzed by the urinary excretion of phenylalanine and individuals with this metabolic disorder can be successfully treated by dietary restriction.

Urinary excretion of the branched chain amino acids leucine, valine and isoleucine is an indicator for maple syrup urine disease, N-acetylaspartic acid for Canavan disease and tyrosine and N-acetyltyrosine for tyrosinemia type I. The identification of new amino acid biomarkers for metabolic disorders is of major importance to biomedical research, and a generic approach for the large-scale prediction of specific biomarkers has been described.

Newborns are not typically screened for other metabolic disorders and as a result, these disorders are often only detected in infants and children after damage has occurred and effects such as developmental delay and mental retardation become apparent. Early detection involving a blood sample analysis for a metabolic marker can reduce such consequences by nutritional adaptations and dietary restriction. Simultaneous enzyme and metabolite tests from a single patient sample are needed for the efficient diagnosis of inborn errors of metabolism in an individual.