Sterols in blood of normal and Smith-Lemli-Opitz subjects

Smith-Lemli-Opitz syndrome (SLOS) is a hereditary disorder in which a defective gene encoding 7-dehydrocholesterol reductase causes the accumulation of noncholesterol sterols, such as 7- and 8-dehydrocholesterol. Using rigorous analytical methods in conjunction with a large collection of authentic standards, we unequivocally identified numerous noncholesterol sterols in 6 normal and 17 SLOS blood samples. Plasma or erythrocytes were saponified under oxygen-free conditions, followed by multiple chromatographic separations. Individual sterols were identified and quantitated by high performance liquid chromatography (HPLC), Ag⁺-HPLC, gas chromatography (GC), GC-mass spectrometry, and nuclear magnetic resonance. As a percentage of total sterol content, the major C₂₇ sterols observed in the SLOS blood samples were cholesterol (12-98%), 7-dehydrocholesterol (0.4-44%), 8-dehydrocholesterol (0.5-22%), and cholesta-5,7,9(11)-trien-3β-ol (0.02-5%), whereas the normal blood samples contained <0.03% each of the three noncholesterol sterols. SLOS and normal blood contained similar amounts of lathosterol (0.05-0.6%) and cholestanol (0.1-0.4%) and ∼0.003-0.1% each of the Δ⁸, Δ⁸⁽¹⁴⁾, Δ^5,8(14), Δ^5,24, Δ^6,8, Δ^6,8(14), and Δ^7,24 sterols. The results are consistent with the hypothesis that the Δ⁸⁽¹⁴⁾ sterol is an intermediate of cholesterol synthesis and indicate the existence of undescribed aberrant pathways that may explain the formation of the Δ^5,7,9(11) sterol. 19-Norcholesta-5,7,9-trien-3β-ol was absent in both SLOS and normal blood, although it was routinely observed as a GC artifact in fractions containing 8-dehydrocholesterol. The overall findings advance the understanding of SLOS and provide a methodological model for studying other metabolic disorders of cholesterol synthesis.