DHCR7 genotypes of cousins with Smith‐Lemli‐Opitz syndrome

Smith‐Lemli‐Opitz syndrome (SLOS) is an autosomal recessive disorder of cholesterol biosynthesis caused by mutations of the 7‐dehydrocholesterol reductase gene (DHCR7). We report on three cousins with SLOS, all of whom were found to be compound heterozygotes for the common splice site mutation IVS8‐1G→C and the missense mutation T289I. DNA analysis of one set of parents demonstrated that the father carried the missense mutation and the mother carried the IVS8–1G→C mutation. By extension, the two unrelated mothers were both heterozygous for IVS8‐1G→C. This finding supports the notion of a high carrier frequency of the IVS8‐1G→C null mutation in Northern European Caucasians. © 2001 Wiley‐Liss, Inc.     

DHCR7 mutations and genotype-phenotype correlation in 37 Polish patients with Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder of cholesterol biosynthesis caused by mutations in the DHCR7 gene. Thirty-seven ethnic Polish patients with SLOS underwent mutation analysis. The mutation frequencies in Polish patients were significantly different from those observed in Western European populations. Two mutations, W151X (22/68 alleles, 32%) and V326L (19/68 alleles, 28%), accounted for 60% of all observed in our cohort. Two missense mutations L68P and L360P have not been reported previously. In total, we report 15 DHCR7 mutations identified in Polish patients. By comparing clinical severity scores and the biochemical and molecular data, a genotype-phenotype correlation was attempted. In compound heterozygotes with one null mutation, the phenotype severity depends on the localization and type of the second mutation: mild phenotypes are correlated with mutations affecting the putative transmembrane domains TM1-TM6 or CT regions and severe phenotypes with mutations localized in TM7 and 4L region. The phenotypic differences of patients with the same genotype suggest that severity of the disease may be affected by other factors.     

Smith-Lemli-Opitz Syndrome and the DHCR7 Gene

Smith‐Lemli‐Opitz syndrome, a severe developmental disorder associated with multiple congenital anomalies, is caused by a defect of cholesterol biosynthesis. Low cholesterol and high concentrations of its direct precursor, 7‐dehydrocholesterol, in plasma and tissues are the diagnostic biochemical hallmarks of the syndrome. The plasma sterol concentrations correlate with severity and disease outcome. Mutations in the DHCR7 gene lead to deficient activity of 7‐dehydrocholesterol reductase (DHCR7), the final enzyme of the cholesterol biosynthetic pathway. The human DHCR7 gene is localised on chromosome 11q13 and its structure has been characterized. Ninety‐one different mutations in the DHCR7 gene have been published to date. This paper is a review of the clinical, biochemical and molecular genetic aspects.     

Frequency and ethnic distribution of the common DHCR7 mutation in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an inherited multiple malformation syndrome caused by enzymatic deficiency of 3beta-hydroxysterol-Delta(7)-reductase (DHCR7). SLOS is thought to be most common among European Caucasians, with an incidence of 1 in 20,000 to 1 in 30,000 births. To define the carrier rate and ethnic distribution of SLOS, we screened DNA samples from 2,978 unrelated individuals for the most common SLOS mutation (IVS8-1G-->C). Twenty-four heterozygotes of the IVS8-1G-->C mutation were detected in 2,978 individuals of European Caucasian and Black backgrounds. For European Caucasians, the carrier rate for SLOS may be as high as 1 in 30, suggesting an incidence of 1 in 1,700 to 1 in 13,400. This high number is supported by the recent observation of newborn and prenatal incidence of 1 in 22,000 in the Caucasian population. Ours is the first report of the IVS8-1G-->C mutation in persons of African ancestry. Published 2001 Wiley-Liss, Inc.     

Founder effect for the T93M DHCR7 mutation in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive MCA-MR disorder caused by mutations within the 7-dehydrocholesterol reductase gene, DHCR7. The diagnosis is based on the biochemical findings of elevated plasma 7-dehydrocholesterol (7DHC) levels. It is a panethnic condition with variable mutation frequencies in different populations. Ten Cuban patients and four Canadian patients of Mediterranean ancestry with SLOS are reported herein. All these patients are at the mild end of the clinical spectrum (the highest Kelley-Hennekam severity score was 28 in one patient). All patients had genotypes which were compound heterozygous or homozygous for T93M; in all the Mediterranean patients the T93M mutation appeared to be associated with the J haplotype. Another compound heterozygote for T93M was of Ukrainian/Irish ancestry; in this patient the T93M was associated with a new haplotype designated K. The T93M mutation was initially reported as the most common in a series of patients from Italy. Our identification of a single haplotype associated with the T93M mutation in patients whose ancestors originate in the region of the Mediterranean Sea basin suggests a founder effect.     

Identification of nine novel DHCR7 missense mutations in patients with Smith-Lemli-Opitz syndrome (SLOS)

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple congenital anomaly syndrome caused by deficiency of 7-dehydrocholesterol reductase (DHCR7), which catalyzes the last step of endogenous cholesterol synthesis. Surveys of SLOS patients have identified more than one hundred point mutations of the DHCR7 gene, most of which are missense mutations. Here, we report the identification of nine novel missense mutations of the DHCR7 gene.     

Molecular studies in Portuguese patients with Smith-Lemli-Opitz syndrome and report of three new mutations in DHCR7

Smith-Lemli-Opitz syndrome (SLO) is an autosomal recessive disorder characterised by craniofacial dysmorphism, mental retardation, multiple congenital anomalies, and increased levels of 7-dehydrocholesterol (7-DHC) in body tissues and fluids. SLO is caused by mutations in the DHCR7 gene which encodes 7-dehydrocholesterol reductase, the last enzyme of cholesterol biosynthesis pathway. In our investigation, we screened 682 dysmorphic/mentally retarded Portuguese patients for abnormal levels of 7-DHC in blood by UV spectrometry. We identified six unrelated patients with SLO (0.87% of total). Mutational analysis of the DHCR7 gene led to the identification of seven distinct mutations, three of which are new (F174S, H301R, and Q98X). The common IVS8-1G > C and T93M variants together with the H301R accounted for 70% of the all SLO alleles in our population. Our findings contribute to the variegate array of pathological changes in the DHCR7 gene among different European populations.     

Identification of 14 novel mutations in DHCR7 causing the Smith-Lemli-Opitz syndrome and delineation of the DHCR7 mutational spectra in Spain and Italy

The Smith-Lemli-Opitz syndrome (SLOS) is a phenotypically variable metabolic malformation and mental retardation syndrome for which more than 80 mutations in the DHCR7 disease-causing gene have been described. The DHCR7 mutational spectra differ significantly in different areas of Europe, and several common putative founder mutations account for a substantial fraction of all mutations in some ethnic groups. Here we have analysed 47 SLOS patients and describe 14 newly identified mutations in 18 SLOS patients of Ashkenazi Jewish, Austrian, British, German, Italian, Irish, Polish, Portuguese, and Spanish origins. Half of the new mutations are in the transmembrane domains of the protein. In addition, there were two null mutations, one mutation in the 4th cytoplasmic loop, two mutations in the first and last codons, and three mutations in other regions such as the second cytoplasmic loop and the first endoplasmic loop. The analysis included 20 Spanish and 12 Italian SLOS patients and revealed very different mutation spectra in these patients compared to previously described patients from Czechoslovakia, Germany, Poland, and the UK and implicated p.Thr93Met on the J haplotype as the most frequent Mediterranean founder mutation.     

Lowered DHCR7 activity measured by ergosterol conversion in multiple cell types in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder of cholesterol metabolism characterized by multiple congenital anomalies and mental retardation. SLOS results from mutations in 7-dehydrocholesterol Delta7 reductase (DHCR7), the gene encoding the final enzyme involved in cholesterol biosynthesis. The resulting cholesterol deficiency and excessive 7- and 8-dehydrocholesterol (7-DHC, 8-DHC) in plasma and tissues are almost always diagnostic for SLOS. We measured DHCR7 activity in fibroblasts, amniocytes, and chorionic villi from controls, heterozygotes, and SLOS subjects. The enzyme activity (expressed as percent conversion of substrate) was significantly lower in untransformed fibroblasts from SLOS subjects (4.47%+/-0.72) compared to untransformed fibroblasts from heterozygotes (26.6%+/-4.6, p<0.01) or controls (50.6%+/-5.3, p<0.001). We also measured plasma cholesterol and 7-DHC, determined the severity score and identified DHCR7 mutations for most of the subjects. There was no significant correlation of enzyme activity with severity score, plasma cholesterol level, plasma 7-DHC level, or the 7-DHC:cholesterol ratio. We conclude that even though enzyme activity as measured by the ergosterol assay may not correlate with severity, this assay has the potential to distinguish SLOS cells from carrier or unaffected cells in a variety of cell types, and should prove useful in confirming a diagnosis in atypical cases where sterol levels are equivocal. Additionally, it may be important to measure residual enzyme activity in SLOS subjects being considered for a trial of statins, as this treatment could theoretically be detrimental in subjects with little or no DHCR7 activity. Finally, the data suggest a threshold enzyme activity of 8% conversion, below which disease occurs.     

A Novel DHCR7 Mutation in a Smith-Lemli-Opitz Syndrome Infant Presenting with Neonatal Cholestasis

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive malformation syndrome caused by a defect in cholesterol biosynthesis. The incidence is very low in Asians and only one case has been reported in Korea thus far. Recently, we found an infant with neonatal cholestasis. He had microcephaly, ambiguous genitalia, cleft palate, syndactyly of toes, patent ductus arteriosus and hypertrophic pyloric stenosis. The serum cholesterol was decreased and serum 7-dehydrocholesterol was markedly elevated. Genetic analysis of the DHCR7 gene identified a novel missense mutation (Pro227Ser) as well as a known mutation (Gly303Arg) previously identified in a Japanese patient with SLOS. Although rare in Korea, SLOS should be considered in the differential diagnosis of neonatal cholestasis, especially in patients with multiple congenital anomalies and low serum cholesterol levels.     

Frequency gradients of DHCR7 mutations in patients with Smith-Lemli-Opitz syndrome in Europe: evidence for different origins of common mutations

Smith-Lemli-Opitz syndrome/RSH (SLOS) is a multiple congenital anomaly syndrome caused by mutations in the gene for Delta7-sterol reductase (DHCR7) which catalyses the last step in the biosynthesis of cholesterol. SLOS is among the common recessive disorders in Europeans but almost absent in most other populations. More than 40 mutations in the DHCR7 gene some of which are frequent have been described in SLOS patients of various origins. Here we report mutation analysis of the DHCR7 gene in SLOS patients from Poland (n = 15), Germany/Austria (n = 22) and Great Britain (n = 22). Altogether 35 different mutations were identified and the two null mutations IVS8-1G > C and W151X were the most frequent in the total sample. In all three populations three mutations accounted for >0.5 of SLOS chromosomes. The mutational spectra were, however, significantly different across these populations with each of the common mutations showing an east-west gradient (W151X, V326L) or vice versa (IVS8-1G > C). W151X is the most frequent (0.33) mutation in Polish SLOS patients. It has an intermediate frequency in German/Austrian patients (0.18) and is rare among British patients (0.02). V326L shows the same distribution pattern (Poland 0.23, Germany/Austria 0.18, Britain 0.02). In contrast IVS8-1G > C is most frequent in Britain (0.34) intermediate in Germany/Austria (0.20) and rare in Poland (0.03). All analysed IVS8-1G > C and V326L alleles shared the same DHCR7 haplotype, whereas the W151X mutation occurred on different haplotypes. There is evidence for both recurrent mutations and founder effects. Together this suggests that the common SLOS mutations in Europe have different geographic and historic origins and spread across the continent in opposite directions.     

Novel 7-DHCR mutation in a child with Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder characterized by minor facial anomalies, mental retardation, and multiple congenital abnormalities. Biochemically, the disorder is caused by deficient activity of 7-dehydrocholesterol reductase, which catalyzes the reduction of the Delta7 double bond of 7-dehydrocholesterol to produce cholesterol. Recently, mutations in the gene encoding 7-dehydrocholesterol reductase (7DHCR) were found to cause SLOS. We report the first molecular characterization of an Italian SLOS patient. Interestingly, his paternal 7DHCR allele, of Arab origin, harbored a novel P329L mutation which in combination with a maternal splice-site (IVS8-1 G>C) mutation resulted in a relatively milder phenotype.     

Carrier frequency of the common mutation IVS8-1G>C in DHCR7 and estimate of the expected incidence of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a multiple congenital anomaly/mental retardation syndrome of variable severity with an incidence previously estimated at 1 in 20,000-60,000 based on case frequency surveys. Identification of the gene defect in SLOS has made it possible to calculate the carrier frequency and estimate disease incidence using molecular methods to identify carriers. Using a previously described PCR-RFLP assay we screened 1503 anonymous blood samples from random newborn screening blood spot cards for the presence of the common SLOS mutation IVS8-1G>C in order to determine the carrier frequency. Sixteen carriers were identified in the 1503 samples. Since the frequency of the IVS8-1G>C mutation among all SLOS gene mutations is known, the overall carrier frequency for all mutations can be calculated. The calculated carrier frequency for all mutations based on this result is 1 in 30, predicting an SLOS incidence of 1 in 1590 to 1 in 13,500. The current incidence estimate may, therefore, significantly underestimate the true incidence of SLOS. This discrepancy between calculated and observed incidence could be due to undiagnosed mild cases, misdiagnosed severe cases, death prior to diagnosis, or fetal loss. More comprehensive incidence studies are needed to determine if SLOS is as common as predicted by the very high (1 in 30) carrier frequency determined in this study.     

Fatal adenovirus type 7b infection in a child with Smith-Lemli-Opitz syndrome

Adenovirus type 7 causes worldwide respiratory tract infections, mainly in children. Severe systemic infections can occur, especially in immunocompromised patients and in patients with underlying chronic diseases. This report describes the first case of a fatal disseminated adenovirus type 7 infection in a child with Smith-Lemli-Opitz syndrome, a rare autosomal recessive disorder due to a primary enzymatic defect in cholesterol metabolism. Nasopharyngeal secretions and autopsy specimens including liver, lung, pleural fluid, and rectum were collected for viral culture. Adenovirus serotype 7 strains were obtained from all anatomic sites, except the liver. All these clinical isolates were analyzed using restriction endonuclease digestion of the genome, identifying them as genome type 7b, a virulent type. In this case, the fatal evolution could have been accelerated by the presence of an immunodeficiency although immunodeficiency is not included in the definition of Smith-Lemli-Opitz syndrome. The frequent recurrent banal infections in Smith-Lemli-Opitz syndrome could be prevented by a cholesterol supplementation regimen. Finally, this report emphasizes the need for efficient therapy for disseminated adenovirus infections, especially for virulent genome types.     

Smith-Lemli-Opitz syndrome

SLO syndrome is an autosomal recessive condition with multiple malformations. This syndrome is ascribed to deficiency of 7 dehydrocholesterol reductase, an enzyme in the cholesterol biosynthetic pathway. The characteristics of this syndrome are facial anomalies, syndactyly of the second and third toe, postaxial polydactyly and genital anomalies with sexual ambiguity. We report a fetal case with intrauterine growth retardation, genital anomalies, multiple malformations with cardiac anomalies, renal aplasia and facial anomalies detected by prenatal ultrasound. Medical abortion was induced at 24 weeks gestation. The diagnosis was considered after complete pathologic examination and biochemical analysis.