Measurement of 3 beta-hydroxysteroid delta 7-reductase activity in cultured skin fibroblasts utilizing ergosterol as a substrate: a new method for the diagnosis of the Smith-Lemli-Opitz syndrome.

A new sensitive and specific method for the evalua- tion of Sphydroxysteroid A'-reductase activity, the defective enzyme in the Smith-Lemli-Opitz (SLO) syndrome, is de- scribed. The assay is based on the use of gas chromatography- mass spectrometry with selected-ion monitoring to measure the mass of brassicasterol (ergosta-5,22dien-3bl) produced by the incubation of ergosterol (ergosta-5,7,22-trien-3bl) with cultured human skin fibroblasts. Although the conver- sion of ergosterol to brassicasterol was slower than the trans- formation of ('HI 7dehydrocholesterol to (3H)cholesterol, cells from control subjects produced brassicasterol efficiently. In contrast, cells from SLO patients produced very little brassi- casterol (P < 0.0001, patients vs. parents or vs. controls). These results indicate that the reduction of ergosterol can be used as an assay for Jkhydroxysteroid A7-reductase in human skin fibroblasts, which avoids the many problems caused by the instability and lack of availability of radiolabeled 7dehy- drocholestero1.l The present method made it possible to di- agnose the SLO syndrome with high sensitivity and reliability using a commercially available compound.-Honda, M., G. S. Tint, A. Honda, A. K. Batta, T. S. Chen, S. Shefer,zmd G. Salen. Measurement of 3phydroxysteroid A7-reductase ac- tivity in cultured skin fibroblasts utilizing ergosterol as a sub- strate: a new method for the diagnosis of the Smith-Lemli- Opitz syndrome. J. Lipid Res. 1996. 37: 2433-2438.