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.     

Detection of a common mutation in the RSH or Smith‐Lemli‐Opitz syndrome by a PCR‐RFLP assay: IVS8‐1G → C is found in over sixty percent of US propositi

The RSH or Smith‐Lemli‐Opitz syndrome (SLOS) is a relatively common autosomal recessive disorder of cholesterol biosynthesis resulting from a deficiency of the enzyme 7‐dehydrocholesterol Δ7‐reductase (7‐DHCR). Mutations in 7‐DHCR gene cause SLOS. Among these, a G → C transversion in the splice acceptor site of exon 9 (IVS8‐1G → C) was suspected to be a frequent mutation, having been detected in about 18% of SLOS patients so far. This mutation results in the elimination of a AIwN1 restriction endonuclease site. We report a simple PCR‐RFLP assay to detect the IVS8‐1 G → C mutation. Using this method, we identified the IVS8‐1G → C mutation in 21 of 33 SLOS propositi. This mutation was detected in one of 90 normal adult Caucasian Americans; but not among 121 Africans from Sierra Leone, 120 Caucasians from Finland, 95 Chinese or 103 Japanese adults. The results of this study provide further evidence that IVS8‐1G → C transversion is a very common mutation in SLOS patients from the US and that the carrier rate in US caucasians may be high. The simple PCR‐RFLP assay developed makes identification of this mutation convenient for diagnosis and for carrier detection. Am. J. Med. Genet. 90:347–350, 2000 © 2000 Wiley‐Liss, Inc.     

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.     

Smith‐Lemli‐Opitz (RHS) syndrome: holoprosencephaly and homozygous IVS8‐1G→C genotype

Smith‐Lemli‐Opitz syndrome (RHS) (SLOS, OMIM 270400) is an autosomal recessive disorder of cholesterol biosynthesis caused by mutations of the 3β‐hydroxysterol Δ⁷‐Δ⁸‐reductase gene, DHCR7. We report a fetus with holoprosencephaly and multiple congenital anomalies who was homozygous for the IVS8‐1G→C mutation. Following termination of pregnancy, both the elevated amniotic fluid 7‐dehydrocholesterol level and the DHCR7 mutations were demonstrated. Two other newborn infants with IVS8‐1G→C/IVS8‐1G→C genotype are described. This report illustrates a severe phenotypic extreme of SLOS associated with a null genotype, underscores the complex relationship between SLOS and holoprosencephaly, and discusses the possible pathogenetic mechanisms of the development of holoprosencephaly in SLOS. © 2001 Wiley‐Liss, Inc.     

Detection of a common mutation in the RSH or Smith-Lemli-Opitz syndrome by a PCR-RFLP assay: IVS8-G-->C is found in over sixty percent of US propositi

The RSH or Smith-Lemli-Opitz syndrome (SLOS) is a relatively common autosomal recessive disorder of cholesterol biosynthesis resulting from a deficiency of the enzyme 7-dehydrocholesterol delta7-reductase (7-DHCR). Mutations in 7-DHCR gene cause SLOS. Among these, a G-->C transversion in the splice acceptor site of exon 9 (IVS8-1G-->C) was suspected to be a frequent mutation, having been detected in about 18% of SLOS patients so far. This mutation results in the elimination of a AlwN1 restriction endonuclease site. We report a simple PCR-RFLP assay to detect the IVS8-1G-->C mutation. Using this method, we identified the IVS8-1G-->C mutation in 21 of 33 SLOS propositi. This mutation was detected in one of 90 normal adult Caucasian Americans; but not among 121 Africans from Sierra Leone, 120 Caucasians from Finland, 95 Chinese or 103 Japanese adults. The results of this study provide further evidence that IVS8-1G-->C transversion is a very common mutation in SLOS patients from the US and that the carrier rate in US caucasians may be high. The simple PCR-RFLP assay developed makes identification of this mutation convenient for diagnosis and for carrier detection.     

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.     

Mutation analysis and description of sixteen RSH/Smith‐Lemli‐Opitz syndrome patients: Polymerase chain reaction–based assays to simplify genotyping

We report the clinical and molecular data of 16 patients with RSH/Smith‐Lemli‐Opitz syndrome (RSH/SLOS) with varying phenotypic severity, for which we have identified mutations in both alleles. RSH/SLOS is an autosomal recessive malformation syndrome caused by mutations in the gene encoding the sterol Δ⁷‐reductase. This protein catalyzes the reduction of 7‐dehydrocholesterol to cholesterol in the last step of cholesterol biosynthesis via the Kandutsch‐Russell pathway. In addition to previously reported mutations (T93M, L109P, G147D, W151X, T154M, R242C, A247V, T289I, IVS8‐1G→C, Y408H, and E448K), we have identified six previously undescribed mutations (321G→C, W177R, R242H, Y318N, L341P, and C444Y). We also report rapid polymerase chain reaction (PCR)–based assays developed to detect four of the recurring mutations (T93M, W151X, V326L, and R404C) and six other RSH/SLOS mutations (321G→C, L109P, T154M, T289I, Y318N, and L341P). The purpose of this article is to correlate detailed clinical information with molecular data in order to improve our understanding of the genotype–phenotype correlation of RSH/SLOS and to report the development of PCR‐based assays that will allow more rapid mutation analysis. Am. J. Med. Genet. 94:214–227, 2000. Published 2000 Wiley‐Liss, Inc.     

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.     

DHCR7 mutation carrier rates and prevalence of the RSH/Smith-Lemli-Opitz syndrome: where are the patients?

RSH/Smith-Lemli-Opitz (SLOS) is an inborn error of metabolism with protean manifestations. Its exact incidence and prevalence are not known; however, the carrier rate for the most frequently occurring mutation, the null mutation IVS8-1G > C, is approximately 1 in 100 for the Caucasian population in North America (1%) and possibly as high as 1 in 50 to 1 in 30 in Central European populations (2-3.3%). Based on the allele frequencies and the proportion of this mutation observed in various patient populations, the expected incidence of RSH/SLOS in those populations was calculated and reported to be between 1 in 1,590 and 1 in 17,000. However, around the world the observed prevalence and incidence are much lower than those calculated from the individual mutation carrier rates observed in any given population. The discrepancy between the expected incidence and prevalence can be explained only in part by the neonatal and infancy deaths of the most severely affected children with RSH/SLOS and the under ascertainment of mild and atypical cases at the mild end of the spectrum. RSH/SLOS may be responsible for a high number of miscarriages. Recent observations estimate the prevalence of SLOS at 16 weeks of gestation as similar to that observed at birth (approximately 1 in 60,000) suggesting that either reduced fertility of carrier couples or losses of affected embryos or fetuses in the first trimester play a significant role in reducing the second trimester prevalence of RSH/SLOS. It is possible that the estimates of carrier rates based on population screening for the most commonly occurring mutations may not reflect the true carrier rates in the population. In order to reconcile the above-mentioned paradoxes, we propose a model based on a higher than observed carrier frequency of the most common mutation and on very high fetal loss of homozygotes for that mutation.     

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 Δ7 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. Am. J. Med. Genet. 91:138–140, 2000. © 2000 Wiley‐Liss, Inc.     

Incidence of Smith‐Lemli‐Opitz syndrome in Ontario,Canada

Smith‐Lemli‐Opitz syndrome (OMIM 270400) (SLOS) is caused by inherited enzymatic deficiency of 3β‐hydroxysterol‐Δ⁷‐reductase (7‐dehydrocholesterol‐Δ⁷‐reductase, DHCR7). SLOS is diagnosed clinically by the demonstration of elevated levels of 7‐dehydrocholesterol (7DHC) in body fluids or tissues. SLOS is associated with mental retardation of variable degree and severe behavior abnormalities. The physical abnormalities range from minor facial anomalies to lethal malformations of the central nervous system, heart, kidneys, and other organs. The exact incidence of SLOS is not known. Although there exist estimates of the incidence of SLOS ranging from 1 in 20,000 to 1 in 60,000, no prospective studies of the incidence of SLOS, based on the clinical data and biochemical diagnosis of SLOS, have been performed. Five unrelated cases of SLOS were diagnosed in Ontario during a 12‐month period. The diagnoses were made based on the demonstration of elevated 7DHC in plasma or amniotic fluid. The birth rate for Ontario for that period was 132,000 births. The incidence of SLOS in Ontario was at least 1 in 26,500 pregnancies in 1999–2000. Given that 86% of the population of Ontario is of European origin, the incidence of SLOS in the Ontario population of European origin was at least 1 in 22,700. As infants with mild forms of SLOS born during this period may remain undiagnosed, these numbers likely are underestimates. This observation has implications for prenatal and newborn screening for this potentially treatable inherited disorder. © 2001 Wiley‐Liss, Inc.     

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 mutations in the 7-dehydrocholesterol reductase gene of 13 patients with Smith–Lemli–Opitz syndrome

Smith–Lemli–Opitz syndrome (SLOS) is caused by mutations in the DHCR7 gene leading to deficient activity of 7-dehydrocholesterol reductase (DHCR7; EC 1.3.1.21), the final enzyme of the cholesterol biosynthetic pathway, resulting in low cholesterol and high concentrations of its direct precursor 7-dehydrocholesterol in plasma and tissues. We here report mutations identified in the DHCR7 gene of 13 children diagnosed with SLOS by clinical and biochemical criteria. We found a high frequency of the previously described IVS8–1 G > C splice acceptor site mutation (two homozygotes, eight compound heterozygotes). In addition, 13 missense mutations and one splice acceptor mutation were detected in eleven patients with a mild to moderate SLOS-phenotype. The mutations include three novel missense mutations (W182L, C183Y, F255L) and one novel splice acceptor site mutation (IVS8–1 G > T).
Two patients, homozygous for the IVS8–1 G > C mutation, presented with a severe clinical phenotype and died shortly after birth. Seven patients with a mild to moderate SLOS-phenotype disclosed compound heterozygosity of the IVS8–1 G > C mutation in combination with different novel and known missense mutations.     

Prepregnancy body mass index and risk of multiple congenital anomalies

Familial dysautonomia (FD) is an autosomal recessive congenital neuropathy that occurs almost exclusively in the Ashkenazi Jewish (AJ) population. Mutations in the IκB kinase complex‐associated protein (IKBKAP) gene cause FD. Two IKBKAP mutations, IVS20^{+6T → C} and R696P, have been identified in FD patients of AJ descent. The splice site mutation IVS20^{+6T → C} is responsible for > 99.5% of known AJ patients with FD, and haplotype analyses were consistent with a common founder. In contrast, the R696P mutation has been identified in only a few AJ patients. To facilitate carrier detection, a single PCR and allele‐specific oligonucleotide (ASO) hybridization assay was developed to facilitate the detection of both the IVS20^{+6T → C} and R696P mutations. Screening of 2,518 anonymous AJ individuals from the New York metropolitan area revealed a carrier frequency for IVS20^{+6T → C} of 1 in 32 (3.2%; 95% CI, 2.5–3.9%), similar to the previously estimated carrier frequency (3.3%) based on disease incidence. No carrier was identified for the R696P lesion, indicating that the mutation was rare in this population (< 1 in 2,500). This sensitive and specific assay should facilitate carrier screening for FD mutations in the AJ community, as well as postnatal diagnostic testing. © 2002 Wiley‐Liss, Inc.     

Smith-Lemli-Opitz (RHS) syndrome: holoprosencephaly and homozygous IVS8-1G-->C genotype

Smith-Lemli-Opitz syndrome (RHS) (SLOS, OMIM 270400) is an autosomal recessive disorder of cholesterol biosynthesis caused by mutations of the 3beta-hydroxysterol Delta(7)-Delta(8)-reductase gene, DHCR7. We report a fetus with holoprosencephaly and multiple congenital anomalies who was homozygous for the IVS8-1G-->C mutation. Following termination of pregnancy, both the elevated amniotic fluid 7-dehydrocholesterol level and the DHCR7 mutations were demonstrated. Two other newborn infants with IVS8-1G-->C/IVS8-1G-->C genotype are described. This report illustrates a severe phenotypic extreme of SLOS associated with a null genotype, underscores the complex relationship between SLOS and holoprosencephaly, and discusses the possible pathogenetic mechanisms of the development of holoprosencephaly in SLOS.     

Balearic archipelago: three islands,three beta‐thalassemia population patterns

López‐Escribano H, Parera MM, Guix P, Serra JM, Gutierrez A, Balsells D, Oliva‐Berini E, Castro JA, Ramon MM, Picornell A. Balearic archipelago: three islands, three beta‐thalassemia population patterns. The mutation spectrum of 175 β‐thalassemia (β‐thal) carriers, identified in pilot carrier screening on 22,713 individuals from Balearic Islands (Spain), is reported. The β⁰ CD39 (C>T) mutation is the most frequent (61.1%), followed by β⁺ IVS‐I‐110 (G>A) (12.0%), β⁺ IVS‐I‐6 (T>C) and β⁰ IVS‐1‐1 (G>A) (3.4% both) and eight other rare mutations (2.9–0.6%); with a distinct prevalence and distribution between islands. Minorca shows the highest prevalence in Iberian populations, with a single mutation, CD39 (C>T), present in most β‐thal carriers. Ibiza is the only Western Mediterranean population where the most frequent β‐thal mutation is IVS‐I‐110 (G>A). These results can be explained by a combination of historical–demographic characteristics together with evolutionary forces such as founder effect, genetic drift and probably selection by malaria. Knowledge of the mutational spectrum in the Balearic Islands will enable to optimize mutation detection strategy for genetic diagnosis of β‐thal in these islands.     

SLOS carrier frequency in Poland as determined by screening for Trp151X and Val326Leu DHCR7 mutations

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder of cholesterol biosynthesis caused by mutations in the DHCR7 gene. Previous studies estimated the prevalence of SLOS between 1 in 10,000 to 1 in 70,358 based on case frequency surveys. Although panethnic, SLOS appears to be most frequent in Central European populations (Czech Republic 1 in 10,000, Slovakia 1 in 15,000 – 1 in 20,000). In Polish individuals with SLOS two DHCR7 mutations, c.452G > A (p.Trp151X) and c.976G > T (p.Val326Leu), account for 65.2% of all observed DHCR7 mutations. We analyzed 2169 samples for the p.Trp151X mutation and 2087 for the p.Val326Leu mutation. The combined carrier frequency of these two mutations of was 2.40 ± 0.32%, yielding a calculated incidence of SLOS in Poland of 2.5 4 × 10⁻⁴–4.3 5 × 10⁻⁴ (1 in 2,300 to 1 in 3,937) placing SLOS among the most common recessive genetic disorders in Poland.     

Identification of three patients with a very mild form of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive malformation syndrome characterized by mental retardation, congenital anomalies, and growth deficiency. The syndrome is caused by a block in cholesterol biosynthesis at the level of 7-dehydrocholesterol reductase (7-DHCR), which results in elevated levels of the cholesterol precursor 7-dehydrocholesterol (7-DHC) and its isomer 8-dehydrocholesterol (8-DHC). We report on three patients from two families with a very mild clinical presentation of SLOS. Their plasma cholesterol values were normal and their plasma levels of 7- and 8- DHC were only slightly elevated. In cultured skin fibroblasts, a significant residual 7-DHCR activity was found. All three patients were compound heterozygotes for a novel mutation affecting translation initiation (M1L). Two of them had the common IVS8-1G>C null mutation and the third patient an E448K mutation in the 7-DHCR gene. Our findings emphasize the importance of using a sensitive method for measuring precursors of cholesterol in combination with mutation analysis to analyze patients with only minimal clinical SLOS-like signs.     

Smith-Lemli-Opitz syndrome: new mutation with a mild phenotype

Smith-Lemli-Opitz syndrome (SLOS) (Online Mendelian Inheritance in Man, OMIM, 2001, http://www.ncbi.nlm.nih.gov/omim/ for SLOS, MIM 270400) is an autosomal recessive disorder of cholesterol biosynthesis caused by mutations of the 3beta-hydroxysterol Delta(7)-reductase gene, DHCR7. We report on a female infant with an exceptionally mild phenotype of SLOS, in whom molecular studies identified a new mutation in DHCR7. The proposita initially presented with feeding difficulties, failure to thrive, hypotonia, mild developmental delay, and oral tactile aversion. She had minor facial anomalies and 2-3 syndactyly of her toes in both feet. The plasma cholesterol was borderline low at 2.88 mmol/L (normal 2.97-4.40 mmol/L). Elevated plasma 7-dehydrocholesterol level of 200.0 micromol/L confirmed the clinical diagnosis of SLOS. Molecular analysis demonstrated compound heterozygosity for IVS8-1G -->C and Y280C, a new missense mutation in DHCR7. Since the other mutation in this patient is a known null mutation, this newly discovered mutation is presumably associated with significant residual enzyme activity and milder expression of clinical phenotype.