A Sterol Panel for Multiple Rare Lipid Disorders: Validation and Application for Sitosterolemia, Cerebrotendinous Xanthomatosis and Smith-Lemli-Opitz Syndome

BACKGROUND. Disease-specific sterols accumulate in the blood of patients with several rare lipid disorders. Biochemical measurement of these sterols is important for correct diagnosis and sometimes monitoration of treatment. Existing methods to measure sterols in blood, particularly plant sterols, are often laborious and time consuming. Partly as a result, clinical access to sterol measurements are limited in many parts of the world. METHODS. A simple and rapid method to extract free sterols from human serum and quantitate their concentration using isotope-dilution liquid chromatography tandem mass spectrometry (LC-MS/MS) without derivatization was developed. The method was designed to be “compatible” with routine workflows (eg. 96-well format) in a clinical lab and was extensively validated. Serum from 73 controls were analyzed and used to estimate the upper reference limits for sitosterol, campesterol, stigmasterol, desmosterol, 7-dehydrocholesterol (7DHC), lathosterol and cholestanol. Serum from patients with the rare lipid disorders sitosterolemia (n=7), Smith-Lemli-Optiz syndrome (SLOS; n=1) and cerebrotendinous xanthomatosis (CTX; n=1) were analyzed. RESULTS. All seven sitosterolemia patients were measured to have greatly elevated levels of free plant sterols (sitosterol, campesterol and stigmasterol) compared to the controls. The SLOS serum contained massively increased concentrations of 7DHC and an unidentified compound (likely 8-dehydrocholesterol). CTX serum contained greatly increased concentrations of cholestanol, as well as 7DHC and lathosterol. Spiking experiments indicated that the method is likely also useful in the diagnosis of desmosterolosis and lathosterolosis. CONCLUSION. The reported method is a relatively simple and fast method capable of quantitating diagnostically important sterols and differentiating patients with several rare lipid disorders from controls.