Voltammetry of 7-dehydrocholesterol as a new and useful tool for Smith-Lemli-Opitz syndrome diagnosis

7-Dehydrocholesterol is an essential biomarker of Smith-Lemli-Opitz syndrome, a congenital autosomal recessive disorder. This study shows for the first time that electrochemical oxidation of 7-dehydrocholesterol can be used for its voltammetric determination. Two classes of supporting electrolytes in acetonitrile and a mixture of acetonitrile-water were used: inorganic acids known to promote structural changes of steroids and indifferent electrolytes. Oxidation of 7-dehydrocholesterol at ca +0.8 V (vs. Ag/AgNO₃ in acetonitrile) in 0.1 mol L^-1 NaClO₄ in acetonitrile is useful for its voltammetric detection using common bare electrode materials. Detection limits for 7-dehydrocholesterol lie in the low micromolar range for all the working electrodes, including boron-doped diamond (0.4 μmol L^-1) and disposable thin-film platinum electrodes (0.5 μmol L^-1), which are advantageous because of the low volumes of studied solutions. After Bligh-Dyer extraction, quantification of 7-dehydrocholesterol concentration (boron-doped diamond) or concentration range (thin-film platinum) is easily attainable in artificial serum. The mere knowledge of the concentration range provides clinically valuable information, as 7-dehydrocholesterol levels are employed for SLOS diagnosis as a binary criterion (elevated, tens to hundreds μmol L^-1 in symptomatic/non-elevated, typically bellow 1 μmol L^-1 in healthy individuals in plasma). Moreover, it is shown that 7-dehydrocholesterol (provitamin D₃) and cholecalciferol (vitamin D₃) can be oxidized in 0.1 mol L^-1 HClO₄ in acetonitrile. Under these conditions, their voltammetric response changes dramatically, and their oxidation potential difference transiently increases from 0.08 V to 0.25 V, which should facilitate their simultaneous voltammetric determination. This work constitutes a foundation for a reliable and straightforward method for Smith-Lemli-Opitz syndrome diagnosis and monitoring 7-dehydrocholesterol's biotransformation to cholecalciferol.