SMITH-LEMLI-OPITZ SYNDROME DIAGNOSED BY USING TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRY

We describe a rapid and sensitive method involving time-of-flight seco ndary-ion mass spectrometry (TOF-SIMS) for specific laboratory diagnos is of the Smith-Lemli-Opitz syndrome, which is characterized by massiv e (similar to 1000-fold) accumulation of the biosynthetic cholesterol precursor 7-dehydrocholesterol. Minute amounts of blood (1-50 mu L) we re extracted with n-hexane, and aliquots were analyzed by TOF-SIMS. 7- Dehydrocholesterol and its isomers were detected at 491.3 mass units ( [M + Ag-107](+)) and cholesterol at 495.3 mass units ([M + Ag-109](+)) . Quantitation of 7-dehydrocholesterol and cholesterol was achieved af ter saponification and addition of stigmasterol as internal standard. Whereas 7-dehydrocholesterol and isomeric dehydrocholesterol were not detectable in controls, the patients revealed concentrations ranging b etween 0.84 and 1.25 mmol/L. Comparison with results obtained by gas c hromatography indicated that quantitation by TOF-SIMS yielded the sum of 7-dehydrocholesterol, isomeric dehydrocholesterol II, and sterol II I, the latter two also being increased in the patients. Consistent wit h quantitation by gas chromatography, the cholesterol concentrations i n the patients ranged between 1.54 and 2.12 mmol/L (controls: 6.10 +/- 1.37 mmol/L).