Smith-Lemli-Opitz syndrome

Fig. 5.1.2 Cholesterol biosynthesis branch of the isoprenoid biosynthetic pathway. Enzymes are numbered as follows 1 squalene synthase 2 squalene epoxidase 3 2,3-oxidosqua-lene sterol cyclase 4 sterol A24-reductase (desmosterolosis) 5 sterol C-14 demethylase 6 sterol A14-reductase (hydrops-ectopic calcification-moth-eaten, HEM, dysplasia) 7 sterol C-4 demethylase complex (including a 3/ -hydroxysteroid dehydrogenase defective in congenital hemidyspla-sia with ichthyosiform nevus and limb defects, CHILD, syndrome) 8 sterol A8-A7 isomerase (Conradi-Hunermann syndrome CDPX2) 9 sterol A5-desaturase (lathosterolosis) 10 sterol A7-reductase (Smith-Lemli-Opitz syndrome). Enzyme deficiencies are indicated by solid bars across the arrows...

Syndrome Mevalonate kinase deficiency (MA/HIDS) CHILD syndrome CDPX2 HEM skeletal dysplasia Lathosterolosis Desmosterolosis Smith-Lemli-Opitz syndrome... 

Fig. 5.1.3 Sterol analysis in patients with defective cholesterol biosynthesis. Gas chromatography-mass spectrometry analysis of trimethylsilyl derivatives of sterols extracted from primary skin fibroblasts of a control subject, a Smith-Lemli-Opitz syndrome (SLOS) patient, and a Con-radi-Hunermann syndrome (CDPX2) patient, and lymphoblasts of a desmosterolosis patient cultured in lipoprotein-deficient medium reveals the accumulation of sterol intermediates indicative of a defect in cholesterol biosynthesis. Similar spectra can be obtained by sterol analysis of the plasma of such patients...

As an alternative, primary skin fibroblasts or lymphoblasts of patients suspected to be affected with a cholesterol biosynthesis defect can be cultured for 3-7 days in medium supplemented with fetal calf serum depleted of lipoproteins to induce cholesterol biosynthesis, whereupon the specific defect can be determined by sterol analysis using GC-MS as described above. This procedure will readily identify patients affected with Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, hydrops-ectopic calcification-motheaten (HEM) skeletal dysplasia and most patients with Conradi-Hunermann syndrome (CDPX2). Patients with congenital hemidys-plasia with ichthyosiform nevus and limb defects (CHILD) syndrome may not be identified with this assay, but they can be readily diagnosed on the basis of their typical clinical presentation. 

Honda M, Tint GS, et al (1996) Measurement of 3/ -hydroxysteroid A7-reductase activity in cultured skin fibroblasts utilizing ergosterol as a substrate a new method for the diagnosis of the Smith-Lemli-Opitz syndrome. J. Lipid Res 37 2433-2438... 

Kelley RI, Hennekam RCM (2000) The Smith-Lemli-Opitz syndrome. J Med Genet 37 321-335... 

As an example of specificity improvement, Fig. 5.3.3 shows the full scan and product-ion MS/MS spectrum for 8-dehydroestriol, a prenatal hallmark of a fetus affected by Smith-Lemli-Opitz syndrome (SLOS), usually found in low concentrations. When using full scan mode, the detection of the most abundant ions (m/z 412, 397, 322, and visual appearance of the full spectrum) was compromised by the high background (Fig. 5.3.3, left). In contrast, acquisition in MS/MS mode (precursor ion m/z 412) provides a cleaner mass spectrum and a superior signal to noise ratio, especially for the transition product ion m/z 322 (Fig. 5.3.3, right). 

Smith-Lemli-Opitz syndrome (SLOS) DHCR7 Ilql2-ql3 602858(270400)... 

Craig WY, Haddow JE, Palomaki GE, Kelley RI, Kratz LE, Shackleton CH, Marcos J, Steven Tint G, MacRae AR, Nowaczyk MJ, Kloza EM, Irons MB, Roberson M, (2006) Identifying Smith-Lemli-Opitz syndrome in conjunction with prenatal screening for Down syndrome. Prenat Diagn 26 842-849... 

Irons M, Elias ER, Salen G, Tint GS, Batta AK (1993) Defective cholesterol biosynthesis in Smith-Lemli-Opitz syndrome. Lancet 341 1414... 

Kelley RI (1995) Diagnosis of Smith-Lemli-Opitz syndrome by gas chromatography/mass spectrometry of 7-dehydrocholesterol in plasma, amniotic fluid and cultured skin fibroblasts. Clin Chim Acta 236 45-58... 

Palomaki GE, Bradley LA, KnightGJ, Craig WY, HaddowJE (2002) Assigning riskfor Smith-Lemli-Opitz syndrome as part of 2nd trimester screening for Down s syndrome J Med Screen... 

Pitt JJ (2007) High-throughput urine screening for Smith-Lemli-Opitz syndrome and ce-rebrotendinous xanthomatosis using negative electrospray tandem mass spectrometry. Clin Chim Acta 380 81-88... 

Shackleton CH, Roitman E, Kelley R (1999) Neonatal urinary steroids in Smith-Lemli-Opitz syndrome associated with 7-dehydrocholesterol reductase deficiency. Steroids 64 481-490... 

Shackleton CH, Roitman E, Kratz L, Kelley R (2001) Dehydro-oestriol anddehydropregnane-triol are candidate analytes for prenatal diagnosis of Smith-Lemli-Opitz syndrome. Prenat Diagn 21 207-212... 

Shackleton C, Roitman E, Guo LW, Wilson WK, Porter FD (2002) Identification of 7(8) and 8(9) unsaturated adrenal steroid metabolites produced by patients with 7-dehydrosterol-A7-reductase deficiency (Smith-Lemli-Opitz syndrome). J Steroid Biochem Mol Biol 82 225-232... 

Shackleton CHL, Marcos J, Palomaki GE, Craig WY, Kelley RE, Kratz LE, Haddow JE (2007) Dehydrosteroid measurements in maternal urine or serum for the prenatal diagnosis of Smith-Lemli-Opitz syndrome (SLOS). Am J Med Genet A 143 2129-2136... 

Sterol-A -isomerase deficiency, known as Conradi-HUnermann syndrome (CDPX2), is an X-linked dominant disorder. Clinical manifestations of this disorder include skeletal abnormalities, chondrodysplasia punctata, craniofacial anomalies, cataracts, and skin abnormalities. The 7-dehydrocholesterol reductase deficiency, known as Smith-Lemli-Opitz syndrome (SLO) is an autosomal recessive disorder occurring in about 1 in 20,000 births. Clinical manifestations of affected individuals include craniofacial abnormalities, microcephaly, congenital heart disease, malformation of the limbs, psychomotor retardation, cerebral maldevelopment, and urogenital anomalies. Measurement of 7-dehydrocholesterol in amniotic fluid during second trimester or in neonatal blood specimen has been useful in the identification of the disorder. The sterol-A " -reductase deficiency causes a developmental phenotype similar to SLO syndrome and is associated with accumulation of desmosterol. The inability of de novo fetal synthesis of cholesterol combined with its inadequate transport from the mother to the fetus appears... 

C. Cunniff, L. E. Kratz, A. Mosher, et al. Clinical and biochemical spectrum of patients with RSH/Smith-Lemli-Opitz syndrome and abnormal cholesterol metabolism. American Journal of Medical Genetics 68,263 (1997). 

R. 1. Kelley RSH/Smith-Lemli-Opitz syndrome Mutations and metabolic morphogenesis. American Journal of Human Genetics 63, 322 (1998). 

A second metabolic defect in cholesterol synthesis leads to Smith-Lemli-Opitz syndrome (SLOS) (B.U. Fitzkey, 1999) [11]. SLOS is one of the most common autosomal D cessive disorders, with estimates of incidence ranging from 1 in 10,000 to 1 in 60,000 of live births [12]. Individuals with SLOS have markedly elevated levels of plasma 7-DHC and low plasma cholesterol levels. 7-DHC A7-reductase activity is deficient in SLOS patients samples, and cloning of the 7-DHC A7-reductase gene led to identification of over 100 missense and many null mutations in SLOS patients (RE. lira, 2003). 

Waterham, H.R., Wanders, R.J. 2000. Biochemical and genetic aspects of 7-dehydrocholesterol reductase and Smith-Lemli-Opitz syndrome. Biochim. Biophys. Acta 1529 340-356. 

Kelley, R.I., Hennekam, R.C.M. 2001. Smith-Lemli-Opitz syndrome. In The Metabolic and Molecular Bases of Inherited Disease. C.R. Scriver, A.L. Beaudet, W.S. Sly, D. Valle, editors. New York McGraw-Hill, pp. 6183-6201. 

Yu, H., Patel, S.B. 2005. Recent insights into the Smith-Lemli-Opitz syndrome. Clin. Genet. 68 383-391. 

I in Smith-Lemli-Opitz syndrome, 3-methylglutatonic adduria, methylmdonic aciduria Absent together with hypoglycemia in fatty add oxidation disorders Present with metabolic acidosis (ketoacidosis) in organic addurias... 

De Fabiani, E., Caruso, D., Cavaleri, M. et al. (1996) Cholesta-5,7,9(ll)-trien-3p-ol found in plasma of patients with Smith-Lemli-Opitz syndrome indicates formation of sterol hydroperoxide. J. Lipid Res. 31 y 2280-7. 

P450 7A1 has also been demonstrated to convert lathosterol to 7-ketolathosterol (the immediate precursor of cholesterol in the normal pathway) to 7-ketoeholesterol and a trace of the 7,8-epoxide [1777]. The reaction with A -dehydrocholesterol is proposed to be responsible for the high level of the oxysterol 7-ketocho-lesterol in individuals with Smith-Lemli-Opitz syndrome [1777], and the ketone is formed in a direct reaction (carbocationic intermediate, with hydride transfer) rather than via rearrangement of the epoxide [1777], The relevance of this reaction has been demonstrated in Smith-Lemli-Optiz syndrome and cerebrotendinous xanthomatosis patients [1778],... 

Bjorkhem I, Diczfalusy U, Lovgren-Sandblom A, Starck L, Jonsson M, Tallman K, Schirmer H, Ousager LB, Crick PJ, Wang Y, GrilEths WJ, Guengerich FP (2014) On the formation of 7-keto-cholesterol from 7-dehydrocholesterol in patients with cerebrotendinous xanthomatosis and Smith-Lemli-Opitz syndrome. J Lipid Res 35 1165-1172... 

Mast N, Norcross R, Andersson U, Shou M, Na-kayama K, Bjorkhem I, Pikuleva lA (2003) Broad substrate specificity of human cytochrome P450 46A1 which initiates cholesterol degradation in the brain. Biochemistry 42 14284-14292 Bjorkhem I, Starck L, Andersson U, Lutjohann D, von Bahr S, Pikuleva I, Babiker A, Diczfalusy U (2001) Oxysterols in the circulation of patients with the Smith-Lemli-Opitz syndrome abnormal levels of 24S- and 27-hydroxycholesterol. J Lipid Res 42 366-371... 

Wassif CA, Zhu P, Kratz L, Krakowiak PA, Bat-taile KP, Weight FF, Grinberg A, Steiner RD, Nwo-koro NA, Kelley RI, Stewart RR, Porter FD (2001) Biochemical, phenotypic and neurophysiological characterization of a genetic mouse model of RSH/ Smith-Lemli-Opitz syndrome. Hum Mol Genet 10 555-564... 

Defects of the biosynthesis of cholesterol were not included in the previous edition of this book, because they were practically non-existing . Since the mid-nineties it has been recognized that patients with the Smith-Lemli-Opitz syndrome lack the final enzyme of cholesterol biosynthesis, i.e. 7-de-hydrocholesterol reductase. Consequently the patients have hypocholestero-lemia and accumulate 7-dehydrocholesterol and 8-dehydrocholesterol in their plasma [12]. 

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