Determination of cholesteryl sulphate by isotope dilution-mass spectrometry for diagnosis of steroid sulphatase deficiency.

A specific and accurate method for determination of cholesteryl sulphate in serum based on isotope dilution-mass spectrometry has been developed. 2H-labelled cholesteryl sulphate was synthesized and used as internal standard. After addition of the internal standard to serum, the cholesteryl sulphate is extracted with butanol and purified by thin-layer chromatography. The material is then solvolysed, converted into trimethylsilyl ether, and analysed by combined gas chromatography-mass spectrometry. The ratio between unlabelled and labelled cholesterol is determined by selected ion monitoring of the ions at m/e 458 (corresponding to the molecular ion of derivative of unlabelled cholesterol) and m/e 465 (corresponding to the molecular ion of derivative of 2H7-labelled cholesterol). The concentration of cholesteryl sulphate is calculated with use of a standard curve. The coefficient of variation of the method was found to vary between 4% and 9% in different concentration ranges. Nine healthy male infants (age range, 1-3 yr) had concentrations of cholesteryl sulphate varying between 0.2 and 11 mumol/l (mean, 3.8 mumol/l). A boy with suspected steroid sulphatase deficiency had a concentration of cholesteryl sulphate of 69 and 64 mumol/l at the age of 12 and 18 months, respectively.