Potential of sterol analysis by liquid chromatography-tandem mass spectrometry for the prenatal diagnosis of Smith-Lemli-Opitz syndrome.

BACKGROUND: Smith-Lemli-Opitz syndrome (SLOS), a severe disorder of cholesterol synthesis, is classically diagnosed prenatally by GC-MS analysis of sterols in amniotic fluid. Considering the current trend toward tandem mass spectrometry (MS/MS) methodologies, we developed prototype LC-MS/MS methods for accurate diagnosis of the disorder.
METHODS: 3beta-Hydroxysterols in amniotic fluid are oxidized with cholesterol oxidase to their corresponding 3-ketones, which are then derivatized with Girard P (GP) hydrazine in a "one-pot" reaction. The resulting GP-hydrazones give an improved response in electrospray (ES)-MS/MS owing to the presence of a charged quaternary nitrogen and are analyzed by reversed-phase LC-ES-MS/MS. Both capillary and conventional LC-MS/MS formats are suitable, and the method is also applicable to paper-absorbed blood spots.
RESULTS: In a double-blind analysis of 18 amniotic fluid samples comprising 6 SLOS and 12 controls, the ratio of 7 + 8-dehydrocholesterol (7 + 8-DHC) to cholesterol was <0.02 [range 0.00-0.02, mean (SD) 0.01 (0.007)] in all control samples (intraassay variation 5.91%) and >0.20 [0.20-1.13, 0.79 (0.35)] in SLOS (intraassay variation 4.56%), corresponding to a difference in ratios between the 2 groups of at least a factor of 10. The limit of quantification was equivalent to that of 2 nL amniotic fluid injected on-column.
CONCLUSIONS: We describe a proof-of-concept for the prenatal diagnosis of SLOS. Further developments will be necessary to automate sample handling and reduce chromatographic time for the methodology to be used in pre- and postnatal diagnosis.