Rapid identification of smith-lemlip-opitz syndrome homozygotes and heterozygotes (carriers) by measurement of deficient 7-dehydrocholesterol-Δ7-reductase activity in fibroblasts

Tint

et al. 2000

J of Inher Metab Disea

The Smith-Lemli-Opitz syndrome (SLOS) is a recessively inherited birth disorder caused by a defect in 7-dehydrocholesterol (3beta-hydroxysteroid) delta7-reductase, the final enzyme in cholesterol biosynthesis. To investigate in vivo regulation of the cholesterol biosynthetic pathway in SLOS, we measured hepatic microsomal sterol concentrations and activities of several key enzymes in the pathway, including HMG-CoA synthase, HMG-CoA reductase, squalene synthase and 7-dehydrocholesterol delta7-reductase in liver specimens from a patient with SLOS and 11 controls. Hepatic microsomal 7-dehydrocholesterol delta7-reductase activity in the patient was less than 1% of the control mean, and decreased cholesterol concentration and markedly increased 7- and 8-dehydrocholesterol concentrations were observed in the patient's microsomes. HMG-CoA synthase and squalene synthase activities in the patient were upregulated to 149% and 532%, respectively, while the activity of HMG-CoA reductase, the rate-limiting enzyme in the pathway, was reduced to 39% of the control mean. Downregulation of HMG-CoA reductase activity in SLOS was supported by measuring plasma levels of mevalonic acid, the immediate product of HMG-CoA reductase. The levels in SLOS patients (n = 9) were significantly low compared with age-matched controls (n = 8) (12+/-2 vs 28 + 6nmol/L, p < 0.05). These results suggest that in most SLOS patients in vivo HMG-CoA reductase is not stimulated in spite of blocked cholesterol biosynthetic pathway and reduced plasma and hepatic cholesterol concentrations.

Section: Discussionsupporting

confidence: 40%

Section: Discussionmentioning

confidence: 95%

Regulation of cholesterol biosynthetic pathway in patients with the Smith–Lemli–Opitz syndrome

Tint

et al. 2000

J of Inher Metab Disea

“…Although the erythrocyte plasmalogen levels were normal, there were markedly increased plasma levels of 8DHC and 8(9)-cholestenol, an abnormal sterol profile not previously reported in any known genetic disorder or toxic condition. When cultured in cholesterol-depleted medium, lymphoblasts from the same patient developed a markedly increased level of 8(9)-cholestenol and an abnormally increased but, compared to the level in plasma, smaller amount of 8DHC, a sterol that is abundant in SLOS plasma but accumulates very slowly in cultured SLOS fibroblasts and lymphoblasts [Shefer et al, 1997;R. Kelley, unpublished observations].…”

Section: Resultsmentioning

confidence: 95%

Abnormal sterol metabolism in patients with Conradi-H�nermann-Happle syndrome and sporadic lethal chondrodysplasia punctata

et al. 1999

The term, "chondrodysplasia punctata" (CDP) denotes a pattern of abnormal punctate calcification of dystrophic epiphyseal cartilage and certain other cartilaginous structures, such as the larynx. CDP occurs in a variety of genetic disorders associated with skeletal dwarfism and can also be caused by prenatal exposure to warfarin. Although the most studied clinical syndrome with CDP, rhizomelic chondrodysplasia punctata (RCDP), is known to be caused by several different abnormalities of plasmalogen biosynthesis, there are many other genetic disorders with CDP for which the biochemical cause is unknown. Because patients with Smith-Lemli-Opitz syndrome, a primary disorder of sterol biosynthesis, often have rhizomesomelic limb shortness and, less commonly, CDP, we assessed sterol levels and metabolism in patients with different clinical forms of CDP. By quantitative sterol analysis of a variety of tissues, we identified 5 patients with similar radiological findings and abnormally increased levels of 8-dehydrocholesterol and cholest-8(9)-en-3beta-ol, suggesting a deficiency of 3beta-hydroxysteroid-delta8,delta7-isomerase, a principal enzyme of cholesterol biosynthesis. Cultured cells available from one patient showed increased levels of the same two sterols, decreased synthesis of cholesterol, and a pattern of inhibition by triparanol and AY-9944 consistent with a deficiency of 3beta-hydroxysteroid-delta8,delta7-isomerase. Clinical diagnoses among the 5 patients included X-linked dominant Conradi-Hünermann-Happle syndrome and nonspecific lethal CDP. We conclude that abnormal cholesterol biosynthesis is a characteristic of some clinical syndromes with rhizomesomelic dwarfing and CDP.

“…A deficiency of this enzyme activity due to genetic mutation in humans has been found to cause Smith-Lemli-Opitz syndrome (SLOS) (4, 28). SLOS is an autosomal-recessive multiple congenital anomaly and/or mental retardation disorder caused by inborn error of postsqualene cholesterol biosynthesis that leads to the elevation of 7-dehydrocholesterol in serum body fluids and tissues (19,21,27).…”

mentioning

confidence: 99%

Identification of a Sterol Δ7 Reductase Gene Involved in Desmosterol Biosynthesis in Mortierella alpina 1S-4

Zhang

Sakuradani

Shimizu

2007

Appl Environ Microbiol

Molecular cloning of the gene encoding sterol ⌬7 reductase from the filamentous fungus Mortierella alpina 1S-4, which accumulates cholesta-5,24-dienol (desmosterol) as the main sterol, revealed that the open reading frame of this gene, designated Mo⌬7SR, consists of 1,404 bp and codes for 468 amino acids with a molecular weight of 53,965. The predicted amino acid sequence of Mo⌬7SR showed highest homology of 51% with that of sterol ⌬7 reductase (EC 1.3.1.21) from Xenopus laevis (African clawed frog). Heterologous expression of the Mo⌬7SR gene in yeast Saccharomyces cerevisiae revealed that Mo⌬7SR converts ergosta-5,7-dienol to ergosta-5-enol (campesterol) by the activity of ⌬7 reductase. In addition, with gene silencing of Mo⌬7SR gene by RNA interference, the transformant accumulated cholesta-5,7,24-trienol up to 10% of the total sterols with a decrease in desmosterol. Cholesta-5,7,24-trienol is not detected in the control strain. This indicates that Mo⌬7SR is involved in desmosterol biosynthesis in M. alpina 1S-4. This study is the first report on characterization of sterol ⌬7 reductase from a microorganism.Sterols are major components of eukaryotic cell membranes. The end products and the sterol biosynthetic pathway differ among species. Cholesterol (cholesta-5-enol) is typical in animals, ergosterol (ergosta-5,7,22-trienol) is common in fungi, and sitosterol (24-ethyl cholesta-5-enol), campesterol (ergosta-5-enol), and stigmasterol (24-ethyl cholesta-5,22-dienol) are the main end sterols in plants (7). These end sterols are composed of a similar four-ringed structures, including an unsaturation at the ⌬5 position on ring B and a specific branched side chain. Ergosterol, unlike other end sterols, contains an additional unsaturation at the ⌬7 position on ring B. On the other hand, desmosterol (cholesta-5,24-dienol) was found to be an end sterol in the zygomycetes fungus Mortierella alpina (20). Recently, the sterol biosynthetic pathway in M. alpina was demonstrated to produce 13 sterols but no ergosterol (12).The biosynthetic reactions that allow conversion of lanosterol (4,4-dimethyl cholesta-8,24-dienol) resulting from the oxidative cyclization of squalene to cholesterol have been well studied (14,15,18). As a representative of microorganisms, yeast, the biosynthetic steps of ergosterol and the related enzymes were characterized in Saccharomyces cerevisiae (5, 13). From zymosterol (cholesta-8,24-dienol) to cholesterol in mammals, ergosterol in fungi, and phytosterols in plants, there are multiple alternative pathways leading to terminal sterols. In the sequential steps of cholesterol biosynthesis in mammals, sterol ⌬7 reductase (⌬7SR; EC 1.3.1.21) is a terminal enzyme, which is absent in yeast, catalyzes the reduction of the ⌬7 double bond in sterol intermediates with presence of NADPH under anaerobic conditions (6, 10). A deficiency of this enzyme activity due to genetic mutation in humans has been found to cause Smith-Lemli-Opitz syndrome (SLOS) (4, 28). SLOS is an autosomal-recessive multiple congenital an...