Midgestational maternal urine steroid markers of fetal Smith–Lemli–Opitz (SLO) syndrome (7-dehydrocholesterol 7-reductase deficiency)

Abstract

Smith–Lemli–Opitz syndrome (SLOS) is a malformation syndrome associated with 7-dehydrocholesterol (7DHC) 7-reductase deficiency. Although SLOS can be detected in an affected fetus before midpregnancy by measurement of 7DHC levels in amniotic fluid or chorionic villus cells, a noninvasive, more routine method is needed. Accordingly, this study was instigated to search for specific steroids in maternal urine in an affected pregnancy that reflect the 7-reductase deficiency of the fetus, ie, steroids retaining 7,8-unsaturation. Steroids were characterized by gas chromatography/mass spectrometry after urinary extraction, conjugate separation, and derivatization. Most steroids in maternal urine from a patient carrying a SLOS fetus were identified as progesterone metabolites, and these were entirely conventional, showing no evidence of additional unsaturation. Unsaturated homologues of the cortisol metabolites were also not detected. However, unsaturated homologues of pregnane-3,16,20-triols and pregnane-3,17,20-triol were found. Most likely, these are 7,8-unsaturated homologues, but 8,9-unsaturation is also possible because of the known activity of Δ 7-Δ 8-isomerase on 7DHC, which results in 8DHC being a prominent sterol in SLOS. Among these novel human steroids, the following were provisionally characterized: 5β-pregn-7(or 8)-ene-3α,17α,20α-triol, 5β-pregn-7(or 8)-ene-3α,16α,20α-triol, and 5α-pregn-7(or 8)-ene-3,16α,20α-triol. Confirmation of the position of unsaturation will require steroid synthesis. These novel steroids are not present in normal pregnancy urine and, therefore, are valuable for prenatal diagnosis of SLOS. In addition, separate studies have shown that 5β-pregn-7(or 8)-ene-3α,17α,20α-triol is present in urine of children and adults with SLOS, and so is a useful analyte for confirmation of the disorder throughout life.