A simple detection of sialic acid storage disorders by urinary ‘free’ and ‘total’ sialic acid determinations

Abstract

The tbiobarbituric acid (TBA) method [l] is the most widely used for the estimation of sialic acid in biological samples. Nevertheless, a number of substances which yield malonaldehyde after the periodate oxidation (e.g. 2-deoxyribose) interfere with this assay, giving a red condensation product with TBA. Therefore, the method does not give reliable results with crude samples and some procedures are needed either to eliminate the interference before the calorimetric reaction (e.g. the ion exchange step suggested by Svennerholm [2]) or to correct the measures by a mathematical approach [l]. A further method was recently proposed based on the pH-dependent solubility of the chromophore of 2-deoxyribose and sialic acid in cyclohexanone [3]. The elimination of interference in urine is important since the ratio between total carbohydrates to sialic acid is high, and accurate evaluation of both ‘free’ and ‘total’ sialic acid may be useful to discriminate among genetic metabolic diseases. In this paper we report an application to urine of the ‘pH-dependent extraction’ method of Roboz et al [3] and present evidence that in urine of normal children sialic acid levels are related to age. Therefore metabolic disorders with abnormal sialic acid excretion may be detected using this age-dependent figure.