Sterol balance in the Smith-Lemli-Opitz syndrome: reduction in whole body cholesterol synthesis and normal bile acid production

Abstract

The Smith-Lemli-Opitz syndrome (SLOS) is a multiple malformation/mental retardation syndrome caused by a deficiency of the enzyme 7-dehydrocholesterol ⌬ 7 -reductase. This enzyme converts 7-dehydrocholesterol (7-DHC) to cholesterol in the last step in cholesterol biosynthesis. The pathology of this condition may result from two different factors: the deficiency of cholesterol itself and/or the accumulation of precursor sterols such as 7-DHC. Although cholesterol synthesis is defective in cultured SLOS cells, to date there has been no evidence of decreased whole body cholesterol synthesis in SLOS and only incomplete information on the synthesis of 7-DHC and bile acids. In this first report of the sterol balance in SLOS, we measured the synthesis of cholesterol, other sterols, and bile acids in eight SLOS subjects and six normal children. The diets were very low in cholesterol content and precisely controlled. Cholesterol synthesis in SLOS subjects was significantly reduced when compared with control subjects (8.6 vs. 19.6 mg/kg per day, respectively, P Ͻ 0.002). Cholesterol precursors 7-DHC, 8-DHC, and 19-nor-cholestatrienol were synthesized in SLOS subjects (7-DHC synthesis was 1.66 ؎ 1.15 mg/kg per day), but not in control subjects. Total sterol synthesis was also reduced in SLOS subjects (12 vs. 20 mg/kg per day, P Ͻ 0.022). Bile acid synthesis in SLOS subjects (3.5 mg/kg per day) did not differ significantly from control subjects (4.6 mg/kg per day) and was within the range reported previously in normals. Normal primary and secondary bile acids were identified. This study provides direct evidence that whole body cholesterol synthesis is reduced in patients with SLOS and that the synthesis of 7-DHC and other cholesterol precursors is profoundly increased. It is also the first reported measure of daily bile acid synthesis in SLOS and provides evidence that bile acid supplementation is not likely to be necessary for treatment. These sterol balance studies provide basic information about the biochemical defect in SLOS and strengthen the rationale for the use of dietary cholesterol in its treatment.

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

“…Mildly elevated levels of the ⌬ 7 sterol have been noted previously in SLOS plasma (14,16) and amniotic fluid (14,17). This elevation is not attributable to the known (48 -53) correlation of ⌬ 7 levels with the rate of sterol synthesis, which is depressed in SLOS subjects (20,45). Because of interrelationships among ⌬ 7 levels, sterol synthesis, and rate of growth, ⌬ 7 levels in SLOS children are quite variable and will likely defy simple explanations.…”

“…When the rate of sterol synthesis diminishes, the ⌬ 5,8 sterol can be slowly metabolized via the ⌬ 5,7 sterol to cholesterol. The proportions of ⌬ 5,7 and ⌬ 5,8 sterols may also depend on their relative rates of esterification, rates of incorporation into lipoproteins and membranes, the clearance rate of sterols from plasma (20), and the microarchitecture of the endoplasmic reticulum (e.g., proximity of the ⌬ 8 -⌬ 7 isomerase, ⌬ 5 desaturase, and DHCR7). Notably, the ⌬ 5 , ⌬ 5,7 , and ⌬ 5,8 sterols were esterified to different extents in both our results and findings of another study (10).…”

“…Zone II (t R 40 -42 min), a 57:26:6:6:3:2 mixture of ⌬ 5,8 , ⌬ 5 , ⌬ 5,8 (14) , ⌬ 8 (14) , ⌬ 5,24 , and ⌬ 8 sterols by NMR, was subfractionated on Ag ϩ -HPLC (SS-1, CL-5) as follows: zone II-1 (t R 7 -8 min), 3:1 mixture of ⌬ 8 (14) and ⌬ 8 sterols by GC-MS, NMR, and Ag ϩ -HPLC; zone II-2 (t R 10 -TABLE 1. Concentration ranges and structural evidence for the ⌬ 5,7,9 (11) (20), 253 (17), 213 (26); ⌬ 5,7,9 (11) TMS ether, m/z 454 (16), 439 (10), 364 (100), 349 (25), 251 (26); ⌬ 5,7,9 (11) acetate, m/z 424 (4), 364 (100), 349 (62), 251 (46), 235 (29), 209 (65).…”

“…As shown in Fig. 1 , many additional sterols have been reported to be present in SLOS (8)(9)(10)(11)(13)(14)(15)(16)(17)(18)(19)(20)(21) or animal models (25,26): 19norcholesta-5,7,9-trien-3 ␤ -ol (9, 18-21, 25, 26), 24,25dihydrolanosterol (15), and ⌬ 5,7,9 (11) (19), ⌬ 7 (8,(15)(16)(17)26), ⌬ 8 (26), ⌬ 5,24 (8), ⌬ 6,8 (1,16,17), ⌬ 6,8 (14) (11), ⌬ 8 (14) (16), and ⌬ 5,7,24 (11,16) sterols. Most of these substances were characterized as minor components of complex sterol mixtures by gas chromatography-mass spectrometry (GC-MS) or GC, although some analyses were done by high performance liquid chromatography (HPLC) (21), HPLC-MS (19), or thin-layer chromatography (TLC) followed by GC-MS (8,13) and other characterization (13).…”

“…The major noncholesterol sterols in SLOS are the ⌬ 5,7 and ⌬ 5,8 dienes, 3 which have been found in blood, other fluids, tissues, and feces (1)(2)(3)(4)(5)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21). As shown in Fig.…”