The inborn errors of sialic acid metabolism and their laboratory investigation.

Sialic acid (SA), a terminal monosaccharide of glycoconjugates, has a central role in human biological function. Various point mutations result in the malmetabolism of SA and inherited disorders: Defective SA synthesis causes sialuria and defective SA catabolism causes sialidosis and sialic acid storage disease (SASD). These inborn errors of metabolism are characterised by increased urinary free SA. This article reviews biochemical and clinical features that are distinct to each disorder. In view of recent evidence indicating a wide underestimation in the prevalence of sialic acid disorders, laboratory methods for determining urinary free SA and its implications for screening and prenatal diagnosis are evaluated.