Maternal apo E genotype is a modifier of the Smith-Lemli-Opitz syndrome

Isolated autism is not an indication for Smith-Lemli-Opitz syndrome biochemical testing

Several studies have demonstrated a high incidence of autistic spectrum features in individuals with Smith-Lemli-Opitz syndrome (SLOS). However, do these findings imply a converse relationship that has diagnostic utility? Is SLOS testing implicated when autism spectrum disorder (ASD) is the only clinical indication?

AIM

To determine if there is any correlation with a clinical indication of ASD and a biochemical diagnosis of SLOS, based on historical test request and assay data.

METHODS

Six years (2008-2013) of clinical test requests for 7-dehydrocholesterol (7-DHC) level were classified and summarised according to indication and final test result.

RESULTS

From the audit period, 988 valid test results from post-natal samples were identified. In plasma/serum, mean 7-DHC level was 264.7 μmol/L (normal range < 2.0) for confirmed SLOS cases. No tests performed due to an isolated clinical indication of ASD or where no clinical information was supplied were associated with 7-DHC levels diagnostic for SLOS.

CONCLUSIONS

Historical test data analysis supports the recommendation that autism/ASD as a single clinical feature is not an appropriate indication for SLOS (7-DHC) biochemical testing.

Analysis of Gene-Environment Interactions Related to Developmental Disorders

Various genetic and environmental factors are associated with developmental disorders (DDs). It has been suggested that interaction between genetic and environmental factors (G × E) is involved in the etiology of DDs. There are two major approaches to analyze the interaction: genome-wide and candidate gene-based approaches. In this mini-review, we demonstrate how these approaches can be applied to reveal the G × E related to DDs focusing on zebrafish and mouse models. We also discuss novel approaches to analyze the G × E associated with DDs.

Anthropometric characteristics of 65 Polish Smith-Lemli-Opitz patients

Smith-Lemli-Opitz syndrome (SLOS) belongs to a group of multiple congenital anomaly/developmental delay disorders. Its primary cause lies in the defect in cholesterol biosynthesis-7-dehydrocholesterol reductase (DHCR7)-caused by pathogenic variants in the homonymous gene. Anthropometric anomalies, especially growth restriction and microcephaly, are among the most common physical manifestations of SLOS. There have been no studies analyzing the correlation between genotype, biochemical marker (7-dehydrocholesterol), and the birth and growth parameters for individuals with SLOS. This paper presents anthropometric data from the group of 65 Polish patients (aged 0.1 to 18 years) with Smith-Lemli-Opitz syndrome, with genotype and biochemical correlations for birth parameters, as well as growth in relation to molecular DHCR7 variants.

Familial DHCR7 genotype presenting as a very mild form of Smith-Lemli-Opitz syndrome and lethal holoprosencephaly

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive metabolic disorder caused by variants in the DHCR7 gene. In cholesterol biosynthesis, 7-dehydrocholesterol (7-DHC) is converted to cholesterol by the enzyme 7-DHC reductase, which is encoded by the gene DHCR7. Thus, an elevated 7-DHC is indicative of SLOS. Characteristically SLOS is usually associated with congenital anomalies, dysmorphisms, and moderate to severe neurodevelopmental delay. However, there are rare descriptions of individuals with milder phenotypes. We report a mild case of SLOS presenting with short stature, cleft palate, imperforate anus, and mild language delay with subtle dysmorphic features. 7-DHC was not elevated at 1 year of age and SLOS considered excluded at this time. The parents had two pregnancies with holoprosencephaly. Whole exome sequencing of one of the fetuses identified compound heterozygous pathogenic variants in the DHCR7 gene (c.964-1G>C (p.?) and c.1039G>A (p.Gly347Ser) causative of SLOS. The proband with a mild form of SLOS was also found to have the same DHCR7 variants as the fetus and repeat testing of 7-DHC at 4 years of age was elevated, in keeping with SLOS. This case is the first to describe a wide intrafamilial phenotypic spectrum of SLOS as a result of the same DHCR7 genotype. This case also supports the findings of others that a normal or near normal development should not exclude SLOS. As demonstrated in this case exclusion of a metabolic diagnosis because of a negative biochemical marker such as 7-DHC is not absolute and if clinical suspicion remains genomic sequencing is warranted.

Trace elements and APOE polymorphisms in pregnant women and their new-borns

We investigated the relationship between lipid binding glycoprotein apolipoprotein E (apoE; gene APOE) polymorphisms (ε4 allele carriers versus no carriers = ε4+/ε4-) and trace elements (TEs) (e.g., (methyl)mercury, arsenic, lead, cadmium, selenium, manganese, copper, and zinc) in mothers (N = 223) and their new-borns (N = 213) exposed to potentially toxic metal(loid)s from seafood consumption. The apoE isoform encoded by the ε4 allele is believed to have beneficial effects in early life but represents a risk factor for age-associated diseases. Under certain conditions ε4 carriers are more susceptible to oxidative stress and metal(loid) toxicity. DNA from Croatian pregnant women (N = 223, third trimester) and their new-borns (N = 176), was genotyped for APOE by TaqMan® SNP assay - rs429358 and rs7412. Seafood intake data and TE levels in maternal urine, milk, hair, peripheral venous blood, mixed cord blood, and new-borns' urine were available from previous studies. We compared TEs between ε4+ and ε4- carriers using Mann-Whitney U tests and applied multiple linear regression models to analyse the TE's dependence on the presence of allele ε4 (genotypes ε3/ε4, ε4/ε4) in combination with other explanatory variables. We identified 17% (n = 37) and 20% (n = 35) ε4 allele carriers in mothers and new-borns, respectively. The Mann-Whitney U test showed that mothers with the ε4 allele had significantly higher mean levels of (methyl)mercury in peripheral venous blood, cord blood, and hair; arsenic in urine and cord blood; and selenium in peripheral venous blood and plasma. However, taking confounders into account, only the maternal plasma selenium remained statistically significant in the linear regression models (ε4 carriers vs non-carriers: 62.6 vs 54.9 ng/mL, p < 0.001). Literature suggestions of possible ε4 allele impact on Hg levels were not observed, while superior selenium status observed in healthy pregnant women carrying allele ε4 could be linked to the proposed APOE ε4 beneficial effects early in life.

Occurrence of c.976 G>T (p.Val326Leu) and c.452 G>A (p.Trp151Ter) variants in DHCR7 gene in population of polish women with recurrent miscarriage

INTRODUCTION

Recurrent miscarriage is a serious clinical problem that affects 1-5 % of all couples trying to conceive. Although the incidence of Smith-Lemli-Opitz Syndrome (SLOS, OMIM #270400), an autosomal recessive condition caused by variants in the DHCR7 gene, is very low, (1:83 000), the observed carrier frequency of DHCR7 gene variants in the Polish population is high, ranging from 1:24 to 1:31. It is possible that this carriage may be responsible for early pregnancy loss.

OBJECTIVES

The aim of the study is to determine the carrier frequency of the p c.976 G>T (p.Val326Leu) and c.452 G>A (p.Trp151Ter) variants in the DHCR7 gene in patients experiencing recurrent miscarriage.

METHODS

The study group included 480 patients: a study group of 380 with at least 2 miscarriages before the 20th week of pregnancy, and a control group of 100 who had not experienced miscarriage. The variants were identified by genotyping: c.976 G>T (p.Val326Leu) by the TaqMan® SNP Genotyping Assay system, and c.452 G>A (p.Trp151Ter) using the BfaI restriction enzyme. Statistical analysis was performed using R software.

RESULTS

No examples of c.976 G>T (p.Val326Leu) were found in either group. c.452 G>A (p.Trp151Ter) was found in 22 participants from the study group and 4 from the control group; however, this difference was not significant (Chi2 test p = 0.61).

CONCLUSIONS

Being a carrier of the c.976 G>T (p.Val326Leu) and c.452 G>A (p.Trp151Ter) variants in theDHCR7 gene is not a risk factor for recurrent miscarriage in the Polish population.

Genetic innovations and our understanding of stillbirth

Stillbirth after 20 weeks gestation happens in 1 in 200 pregnancies and occurs more commonly than neonatal loss and sudden infant death syndrome (SIDs) combined. The stillbirth rate is several times greater in low as opposed to high-resource countries. However, among high-resource countries, although a lower overall stillbirth rate exists, there has been little change for several decades. Molecular genetic technologies are emerging as important contributors to our understanding of stillbirth. Initially, genetic etiologies included alterations in chromosome number or structure such as aneuploidy and microduplications and deletions. More recently, next-generation sequencing analysis in two genetic conditions, Smith Lemli Optiz Syndrome (SLOs) and the channelopathy disorders (such as long QT syndrome (LQTS)) provide examples into the association of pathogenic gene variants with stillbirth. Although these specific conditions individually account for only a small number of stillbirths, investigating these disorders provides a new and innovative approach for further understanding genetic contributors to adverse pregnancy outcomes. Our knowledge of the role of genetic disease as an etiology for stillbirth is elementary. Genomic interrogation of maternal-fetal genotypes, gene-gene, and genotype-environment interaction is lacking in stillbirth research. At the DNA sequence level, further investigation of variants of unknown significance is an opportunity for exploration of biologic pathways of importance to pregnancy loss. This review concentrates on SLO as an example of a single gene disorder with a high carrier but low affected liveborn proband rate. The channelopathy disorders are included as initial examples of genetic conditions with variable presentation including an association with sudden infant death syndrome. Highlighted are the challenges when numerous genes and variants are involved, and the task of assigning pathogenicity. The advantages and limitations of genetic evaluations are presented and avenues for further research considered.

Phenotypic severity in a family with MEND syndrome is directly associated with the accumulation of potentially functional variants of cholesterol homeostasis genes

Background

Male EBP disorder with neurologic defects (MEND) syndrome is an X‐linked disease caused by hypomorphic mutations in the EBP (emopamil‐binding protein) gene. Modifier genes may explain the clinical variability among individuals who share a primary mutation.

Methods

We studied four males (Patient 1 to Patient 4) exhibiting a descending degree of phenotypic severity from a family with MEND syndrome. To identify candidate modifier genes that explain the phenotypic variability, variants of homeostasis cholesterol genes identified by whole‐exome sequencing (WES) were ranked according to the predicted magnitude of their effect through an in‐house scoring system.

Results

Twenty‐seven from 105 missense variants found in 45 genes of the four exomes were considered significant (−5 to −9 scores). We found a direct genotype–phenotype association based on the differential accumulation of potentially functional gene variants among males. Patient 1 exhibited 17 variants, both Patients 2 and 3 exhibited nine variants, and Patient 4 exhibited only five variants.

Conclusion

We conclude that APOA5 (rs3135506), ABCA1 (rs9282541), and APOB (rs679899 and rs12714225) are the most relevant candidate modifier genes in this family. Relative accumulation of the deficiencies associated with variants of these genes along with other lesser deficiencies in other genes appears to explain the variable expressivity in MEND syndrome.

Normal IQ is possible in Smith-Lemli-Opitz syndrome

Children with Smith-Lemli-Opitz syndrome (SLOS) are typically reported to have moderate to severe intellectual disability. This study aims to determine whether normal cognitive function is possible in this population and to describe clinical, biochemical and molecular characteristics of children with SLOS and normal intelligent quotient (IQ). The study included children with SLOS who underwent cognitive testing in four centers. All children with at least one IQ composite score above 80 were included in the study. Six girls, three boys with SLOS were found to have normal or low-normal IQ in a cohort of 145 children with SLOS. Major/multiple organ anomalies and low serum cholesterol levels were uncommon. No correlation with IQ and genotype was evident and no specific developmental profile were observed. Thus, normal or low-normal cognitive function is possible in SLOS. Further studies are needed to elucidate factors contributing to normal or low-normal cognitive function in children with SLOS.

RNA-seq reveals conservation of function among the yolk sacs of human, mouse, and chicken

The yolk sac is phylogenetically the oldest of the extraembryonic membranes. The human embryo retains a yolk sac, which goes through primary and secondary phases of development, but its importance is controversial. Although it is known to synthesize proteins, its transport functions are widely considered vestigial. Here, we report RNA-sequencing (RNA-seq) data for the human and murine yolk sacs and compare those data with data for the chicken. We also relate the human RNA-seq data to proteomic data for the coelomic fluid bathing the yolk sac. Conservation of transcriptomes across the species indicates that the human secondary yolk sac likely performs key functions early in development, particularly uptake and processing of macro- and micronutrients, many of which are found in coelomic fluid. More generally, our findings shed light on evolutionary mechanisms that give rise to complex structures such as the placenta. We identify genetic modules that are conserved across mammals and birds, suggesting these modules are part of the core amniote genetic repertoire and are the building blocks for both oviparous and viviparous reproductive modes. We propose that although a choriovitelline placenta is never established physically in the human, the placental villi, the exocoelomic cavity, and the secondary yolk sac function together as a physiological equivalent.

Metabolic Adaptations in Pregnancy: A Review

BACKGROUND

Pregnancy is a dynamic state involving multiple adaptations that are necessary in order to ensure a continuous supply of essential metabolites to support the growth and the development of the fetus.

OBJECTIVES

This review article is aimed to discuss important adaptations in metabolism that take place during non-complicated pregnancy.

MATERIALS AND METHODS

We searched the electronic database PubMed for pre-clinical as well as clinical controlled trials reporting the importance of metabolic adaptations during a non-complicated pregnancy. The preferred language was English and the most recent reports were selected to get an updated review.

RESULTS

It was observed clearly in the searched literature that metabolic adaptations are a crucial part of pregnancy, as they provide the mother with sufficient energy stores to meet the demands of pregnancy. These adaptions also help in preparing the mother for lactation and also help in providing proper environment for the proper growth of fetus in the womb. Moreover, multiple biomolecules including glucose, fatty acids, ketone bodies, hormones collectively contribute toward these metabolic adaptations.

CONCLUSIONS

This review article concludes that metabolic adaptations are crucial for proper fetus development.

DHCR7: A vital enzyme switch between cholesterol and vitamin D production

The conversion of 7-dehydrocholesterol to cholesterol, the final step of cholesterol synthesis in the Kandutsch-Russell pathway, is catalyzed by the enzyme 7-dehydrocholesterol reductase (DHCR7). Homozygous or compound heterozygous mutations in DHCR7 lead to the developmental disease Smith-Lemli-Opitz syndrome, which can also result in fetal mortality, highlighting the importance of this enzyme in human development and survival. Besides serving as a substrate for DHCR7, 7-dehydrocholesterol is also a precursor of vitamin D via the action of ultraviolet light on the skin. Thus, DHCR7 exerts complex biological effects, involved in both cholesterol and vitamin D production. Indeed, we argue that DHCR7 can act as a switch between cholesterol and vitamin D synthesis. This review summarizes current knowledge about the critical enzyme DHCR7, highlighting recent findings regarding its structure, transcriptional and post-transcriptional regulation, and its links to vitamin D synthesis. Greater understanding about DHCR7 function, regulation and its place within cellular metabolism will provide important insights into its biological roles.

Reduced cholesterol levels impair Smoothened activation in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a common autosomal-recessive disorder that results from mutations in the gene encoding the cholesterol biosynthetic enzyme 7-dehydrocholesterol reductase (DHCR7). Impaired DHCR7 function is associated with a spectrum of congenital malformations, intellectual impairment, epileptiform activity and autism spectrum disorder. Biochemically, there is a deficit in cholesterol and an accumulation of its metabolic precursor 7-dehydrocholesterol (7DHC) in developing tissues. Morphological abnormalities in SLOS resemble those seen in congenital Sonic Hedgehog (SHH)-deficient conditions, leading to the proposal that the pathogenesis of SLOS is mediated by aberrant SHH signalling. SHH signalling is transduced through the transmembrane protein Smoothened (SMO), which localizes to the primary cilium of a cell on activation and is both positively and negatively regulated by sterol molecules derived from cholesterol biosynthesis. One proposed mechanism of SLOS involves SMO dysregulation by altered sterol levels, but the salient sterol species has not been identified. Here, we clarify the relationship between disrupted cholesterol metabolism and reduced SHH signalling in SLOS by modelling the disorder in vitro. Our results indicate that a deficit in cholesterol, as opposed to an accumulation of 7DHC, impairs SMO activation and its localization to the primary cilium.

Pathogenesis, Epidemiology, Diagnosis and Clinical Aspects of Smith-Lemli-Opitz Syndrome

INTRODUCTION

Smith-Lemli-Opitz Syndrome (SLOS) is a malformation syndrome inherited in an autosomal recessive fashion. It is due to a metabolic defect in the conversion of 7-dehydrocholesterol to cholesterol, which leads to an accumulation of 7-dehydrocholesterol and frequently a deficiency of cholesterol. The syndrome is characterized by typical dysmorphic facial features, multiple malformations, and intellectual disability.

AREAS COVERED

In this paper we provide an overview of the clinical phenotype and discuss how the manifestations of the syndrome vary depending on the age of the patients. We then explore the underlying biochemical defect and pathophysiological alterations that may contribute to the many disease manifestations. Subsequently we explore the epidemiology and succinctly discuss population genetics as they relate to SLOS. The next section presents the diagnostic possibilities. Thereafter, the treatment and management as is standard of care are presented.

EXPERT OPINION

Even though the knowledge of the underlying molecular mutations and the biochemical alterations is being rapidly accumulated, there is currently no efficacious therapy addressing neurological dysfunction. We discuss the difficulty of treating this disorder, which manifests as a combination of a malformation syndrome and an inborn error of metabolism. A very important factor in developing new therapies is the need to rigorously establish efficacy in controlled trials.

Cholesterol in myelin biogenesis and hypomyelinating disorders

The largest pool of free cholesterol in mammals resides in myelin membranes. Myelin facilitates rapid saltatory impulse propagation by electrical insulation of axons. This function is achieved by ensheathing axons with a tightly compacted stack of membranes. Cholesterol influences myelination at many steps, from the differentiation of myelinating glial cells, over the process of myelin membrane biogenesis, to the functionality of mature myelin. Cholesterol emerged as the only integral myelin component that is essential and rate-limiting for the development of myelin in the central and peripheral nervous system. Moreover, disorders that interfere with sterol synthesis or intracellular trafficking of cholesterol and other lipids cause hypomyelination and neurodegeneration. This review summarizes recent results on the roles of cholesterol in CNS myelin biogenesis in normal development and under different pathological conditions. This article is part of a Special Issue entitled Brain Lipids.

Involvement and alteration of the Sonic Hedgehog pathway is associated with decreased cholesterol level in trisomy 18 and SLO amniocytes

BACKGROUND

Trisomy 18 and Smith-Lemli-Opitz syndrome are two polymalformative conditions in which a cholesterol defect has been noted. When they occur prenatally, they are associated with a decreased maternal unconjugated estriol (uE(3)) level. Cholesterol plays an essential role in the Sonic Hedgehog pathway, allowing Shh protein maturation leading to its maximal activity. Many malformations in these two syndromes occur in Shh dependent tissues. We thus sought to assess whether a cholesterol defect could affect the Shh pathway and explain some of the observed malformations.

MATERIALS AND METHODS

We selected 14 cases of trisomy 18 and 3 cases of SLO in which the maternal uE(3) level was decreased and reported malformations were observed after fetopathological examination. We correlated the number of malformations with maternal uE(3) level. We then carried out cholesterol concentrations in separate culture media consisting of trisomy 18, SLO and control amniocytes. Finally, we analyzed the Shh pathway by testing the gene expression of several Shh components: GLI transcription factors, BMP2, BMP4, TGFβ1, COL1A1 and COL1A2.

RESULTS AND DISCUSSION

There was an inverse correlation between phenotypic severity and maternal uE(3) levels in SLO and trisomy 18. The cholesterol levels in the amniocyte culture media were correlated with maternal uE3 levels and were significantly lower in T18 and SLO amniocytes, reflecting cholesterol defects. There was an alteration in the Shh pathway since expression of several genes was decreased in T18 and SLO amniocytes. However, these cholesterol defects were not solely responsible for the altered Shh pathway and the malformations observed.

Sterol metabolism disorders and neurodevelopment-an update

Cholesterol has numerous quintessential functions in normal cell physiology, as well as in embryonic and postnatal development. It is a major component of cell membranes and myelin, and is a precursor of steroid hormones and bile acids. The development of the blood brain barrier likely around 12-18 weeks of human gestation makes the developing embryonic/fetal brain dependent on endogenous cholesterol synthesis. Known enzyme defects along the cholesterol biosynthetic pathway result in a host of neurodevelopmental and behavioral findings along with CNS structural anomalies. In this article, we review sterol synthesis disorders in the pre- and post-squalene pathway highlighting neurodevelopmental aspects that underlie the clinical presentations and course of Smith-Lemli-Opitz Syndrome (SLOS), mevalonic aciduria (MVA) or the milder version hyper-immunoglobulinemia D and periodic fever syndrome (HIDS), Antley-Bixler syndrome with genital anomalies and disordered steroidogenesis (ABS1), congenital hemidysplasia with icthyosiform nevus and limb defects (CHILD) syndrome, CK syndrome, sterol C4 methyl oxidase (SC4MOL) deficiency, X-linked dominant chondrodysplasia punctata 2(CDPX2)/ Conradi Hunermann syndrome, lathosterolosis and desmosterolosis, We also discuss current controversies and share thoughts on future directions in the field.

Mutational spectrum of smith-lemli-opitz syndrome patients in hungary

Smith-Lemli-Opitz (SLO) syndrome is an autosomal recessive disorder characterized by multiple congenital abnormalities and mental retardation. The condition is caused by the deficiency of 7-dehydrocholesterol reductase (DHCR7) which catalyzes the final step in cholesterol biosynthesis. Biochemical diagnosis is based on increased concentration of 7-dehydrocholesterol (7-DHC) in the patient serum. Both life expectancy and quality of life are severely affected by the disease. The estimated prevalence of SLO syndrome ranges between 1:20,000 and 1:40,000 among Caucasians. Although the mutational spectrum of the disease is wide, approximately 10 mutations are responsible for more than 80% of the cases. These mutations show a large interethnic variability. There are no mutation distribution data from Hungary to date. Thirteen patients were diagnosed with SLO syndrome in our laboratory. As first-line tests, serum 7-DHC and total cholesterol were measured and, in positive cases, molecular genetic analysis of the DHCR7 gene was performed. Complete genetic background of the disease could be identified in 12 cases. In 1 case only 1 mutation was detected in a heterozygote form. One patient was homozygous for the common splice site mutation c.964-1G>C, while all other patients were compound heterozygotes. One novel missense mutation, c.374A>G (p.Tyr125Cys) was identified.

Smith-Lemli-Opitz syndrome: phenotype, natural history, and epidemiology

Smith-Lemli-Opitz syndrome (SLOS) is a congenital multiple anomaly/intellectual disability syndrome caused by a deficiency of cholesterol synthesis resulting from a deficiency of 7-dehydrocholesterol (7DHC) reductase encoded by DHCR7. SLOS is inherited in an autosomal recessive pattern. It is characterized by prenatal and postnatal growth retardation, microcephaly, a variable degree of intellectual disability that encompasses normal intelligence to severe intellectual deficiency, and multiple major and minor malformations. External malformations include distinctive facial features, cleft palate, postaxial polydactyly, 2-3 syndactyly of the toes, and underdeveloped external genitalia in males, while internal anomalies may affect every organ system. The clinical spectrum is wide, and rare individuals have been described with normal development and only minor malformations. The clinical diagnosis of SLOS is confirmed by demonstrating an abnormally elevated concentration of the cholesterol precursor, 7DHC, in serum or other tissues, or by the presence of two DHCR7 mutations. The enzymatic deficiency results in decreased cholesterol and increased 7DHC levels, both during embryonic development and after birth. The malformations found in SLOS may result from decreased cholesterol, increased 7DHC or a combination of these two factors. This review discusses the physical and behavioral phenotype of SLOS, the diagnostic approaches, the natural history from the prenatal period to adulthood, and current understanding of the pathophysiology of SLOS.

Mutational spectrum of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS; OMIM #270400) is an autosomal recessive malformation syndrome characterized by a large spectrum of morphogenic and congenital anomalies. SLOS is caused by mutations in the DHCR7 gene, which encodes 7-dehydrocholesterol reductase, the enzyme that catalyzes the final step in cholesterol biosynthesis. We report on 154 currently known mutations in DHCR7 identified in patients affected with SLOS and discuss their coding consequences. These 154 mutations include 130 missense, 8 nonsense, 8 deletions, 2 insertions, 1 indel, and 5 splice site mutations. Using information available from published case reports and from patients identified in our clinical diagnostic laboratory, we analyzed correlations between genotype, clinical presentation and 7-dehydrocholesterol level.

The origin of fetal sterols in second-trimester amniotic fluid: endogenous synthesis or maternal-fetal transport?

OBJECTIVE

Cholesterol is crucial for fetal development. To gain more insight into the origin of the fetal cholesterol pool in early human pregnancy, we determined cholesterol and its precursors in the amniotic fluid of uncomplicated, singleton human pregnancies.

STUDY DESIGN

Total sterols were characterized by gas chromatography-mass spectrometry in the second-trimester amniotic fluid of 126 healthy fetuses from week 15 until week 22.

RESULTS

The markers of cholesterol biosynthesis, lanosterol, dihydrolanosterol, and lathosterol, were present in low levels until the 19th week of gestation, after which their levels increased strongly. β-sitosterol, a marker for maternal-fetal cholesterol transport, was detectable in the amniotic fluid. The total cholesterol levels increased slightly between weeks 15 and 22.

CONCLUSION

Our results support the hypothesis that during early life the fetus depends on maternal cholesterol supply because endogenous synthesis is relatively low. Therefore, maternal cholesterol can play a crucial role in fetal development.

Maternal ABCA1 genotype is associated with severity of Smith-Lemli-Opitz syndrome and with viability of patients homozygous for null mutations

The Smith-Lemli-Opitz syndrome (SLOS [MIM 270400]) is an autosomal recessive malformation syndrome that shows a great variability with regard to severity. SLOS is caused by mutations in the Δ7sterol-reductase gene (DHCR7), which disrupt cholesterol biosynthesis. Phenotypic variability of the disease is already known to be associated with maternal apolipoprotein E (ApoE) genotype. The aim of this study was to detect additional modifiers of the SLOS phenotype. We examined the association of SLOS severity with variants in the genes for ApoC-III, lecithin-cholesterol acyltransferase, cholesteryl-ester transfer protein, ATP-binding cassette transporter A1 (ABCA1), and methylene tetrahydrofolate reductase. Our study group included 59 SLOS patients, their mothers, and 49 of their fathers. In addition, we investigated whether ApoE and ABCA1 genotypes are associated with the viability of severe SLOS cases (n=21) caused by two null mutations in the DHCR7 gene. Maternal ABCA1 genotypes show a highly significant correlation with clinical severity in SLOS patients (P=0.007). The rare maternal p.1587Lys allele in the ABCA1 gene was associated with milder phenotypes. ANOVA analysis demonstrated an association of maternal ABCA1 genotypes with severity scores (logarithmised) of SLOS patients of P=0.004. Maternal ABCA1 explains 15.4% (R²) of severity of SLOS patients. There was no association between maternal ApoE genotype and survival of the SLOS fetus carrying two null mutations. Regarding ABCA1 p.Arg1587Lys in mothers of latter SLOS cases, a significant deviation from Hardy-Weinberg equilibrium (HWE) was observed (P=0.005). ABCA1 is an additional genetic modifier in SLOS. Modifying placental cholesterol transfer pathways may be an approach for prenatal therapy of SLOS.

Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple congenital malformation and intellectual disability syndrome, with clinical characteristics that encompass a wide spectrum and great variability. Elucidation of the biochemical and genetic basis for SLOS, specifically understanding SLOS as a cholesterol deficiency syndrome caused by mutation in DHCR7, opened up enormous possibilities for therapeutic intervention. When cholesterol was discovered to be the activator of sonic hedgehog, cholesterol deficiency with inactivation of this developmental patterning gene was thought to be the cause of SLOS malformations, yet this explanation is overly simplistic. Despite these important research breakthroughs, there is no proven treatment for SLOS. Better animal models are needed to allow potential treatment testing and the study of disease pathophysiology, which is incompletely understood. Creation of human cellular models, especially models of brain cells, would be useful, and in vivo human studies are also essential. Biomarker development will be crucial in facilitating clinical trials in this rare condition, because the clinical phenotype can change over many years. Additional research in these and other areas is critical if we are to make headway towards ameliorating the effects of this devastating condition.

Review: Transport of maternal cholesterol to the fetal circulation

Data obtained from recent studies in humans, rodents, and cell culture demonstrate that circulating maternal cholesterol can be transported to the fetus. The two major cell types responsible for the transport are trophoblasts and endothelial cells of the fetoplacental vasculature. Maternal lipoprotein-cholesterol is initially taken up by trophoblasts via receptor-mediated and receptor-independent processes, is transported by any number of the sterol transport proteins expressed by cells, and is effluxed or secreted out of the basal side via protein-mediated processes or by aqueous diffusion. This cholesterol is then taken up by the endothelium and effluxed to acceptors within the fetal circulation. The ability to manipulate the mass of maternal cholesterol that is taken up by the placenta and crosses to the fetus could positively impact development of fetuses affected with the Smith-Lemli-Opitz Syndrome (SLOS) that have reduced ability to synthesize cholesterol and possibly impact growth of fetuses unaffected by SLOS but with low birthweights.

Hedgehog signaling update

In vertebrate hedgehog signaling, hedgehog ligands are processed to become bilipidated and then multimerize, which allows them to leave the signaling cell via Dispatched 1 and become transported via glypicans and megalin to the responding cells. Hedgehog then interacts with a complex of Patched 1 and Cdo/Boc, which activates endocytic Smoothened to the cilium. Patched 1 regulates the activity of Smoothened (1) via Vitamin D3, which inhibits Smoothened in the absence of hedgehog ligand or (2) via oxysterols, which activate Smoothened in the presence of hedgehog ligand. Hedgehog ligands also interact with Hip1, Patched 2, and Gas1, which regulate the range as well as the level of hedgehog signaling. In vertebrates, Smoothened is shortened at its C-terminal end and lacks most of the phosphorylation sites of importance in Drosophila. Cos2, also of importance in Drosophila, plays no role in mammalian transduction, nor do its homologs Kif7 and Kif27. The cilium may provide a function analogous to that of Cos2 by linking Smoothened to the modulation of Gli transcription factors. Disorders associated with the hedgehog signaling network follow, including nevoid basal cell carcinoma syndrome, holoprosencephaly, Smith-Lemli-Opitz syndrome, Greig cephalopolysyndactyly syndrome, Pallister-Hall syndrome, Carpenter syndrome, and Rubinstein-Taybi syndrome.

Genomic and transcriptomic analyses distinguish classic Rett and Rett-like syndrome and reveals shared altered pathways

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder characterized by derangements in nervous system especially in cognition and behavior. The present study aims to understand the molecular underpinnings of two subtypes of RTT, classic RTT and Rett-like, and to elucidate common pathways giving rise to common RTT phenotype using genomic and transcriptomic approaches. Mutation screening on selected nuclear genes revealed only MECP2 mutations in a subset of classic RTT patients. MLPA assays and mtDNA screenings were all negative. Genome-wide copy number analysis indicated a novel duplication on X chromosome. Transcriptional profiling revealed blood gene signatures that clearly distinguish classic RTT and RTT-like patients, as well as shared altered pathways in interleukin-4 and NF-κB signaling pathways in both subtypes of the syndrome. To our knowledge, this is the first report on investigating common regulatory mechanisms/signaling pathways that may be relevant to the pathobiology of the "common RTT" phenotype.

Malformation syndromes caused by disorders of cholesterol synthesis

Cholesterol homeostasis is critical for normal growth and development. In addition to being a major membrane lipid, cholesterol has multiple biological functions. These roles include being a precursor molecule for the synthesis of steroid hormones, neuroactive steroids, oxysterols, and bile acids. Cholesterol is also essential for the proper maturation and signaling of hedgehog proteins, and thus cholesterol is critical for embryonic development. After birth, most tissues can obtain cholesterol from either endogenous synthesis or exogenous dietary sources, but prior to birth, the human fetal tissues are dependent on endogenous synthesis. Due to the blood-brain barrier, brain tissue cannot utilize dietary or peripherally produced cholesterol. Generally, inborn errors of cholesterol synthesis lead to both a deficiency of cholesterol and increased levels of potentially bioactive or toxic precursor sterols. Over the past couple of decades, a number of human malformation syndromes have been shown to be due to inborn errors of cholesterol synthesis. Herein, we will review clinical and basic science aspects of Smith-Lemli-Opitz syndrome, desmosterolosis, lathosterolosis, HEM dysplasia, X-linked dominant chondrodysplasia punctata, Congenital Hemidysplasia with Ichthyosiform erythroderma and Limb Defects Syndrome, sterol-C-4 methyloxidase-like deficiency, and Antley-Bixler syndrome.

Abnormal sterol metabolism in holoprosencephaly

Holoprosencephaly (HPE) is the most common structural malformation of the developing forebrain in humans. The HPE phenotype is extremely variable and the etiology is heterogeneous. Among a variety of embryological toxins that can induce HPE, inhibitors, and other pertubations of cholesterol biosynthesis have been shown to be important factors, most likely because cholesterol is required in the Sonic hedgehog signaling cascade. Decreased levels of maternal cholesterol during pregnancy increase the risk for preterm delivery, but they are not associated with congenital malformations. However, if the fetus is affected by an inborn error of endogenous cholesterol synthesis, a reduction of maternal cholesterol concentration and cholesterol transport over the placenta aggravates the phenotypic expression. Exposure to lipophilic statins in early pregnancy may be associated with a substantial risk for structural CNS defects.

Cyclopia (synophthalmia) in Smith-Lemli-Opitz syndrome: First reported case and consideration of mechanism

Here we present a 24-week fetus with Smith-Lemli-Opitz syndrome (SLOS), alobar holoprosencephaly (HPE) and cyclopia (synophthalmia). Following birth, we suspected SLOS in this fetus due to the additional findings of ambiguous genitalia and bilateral 2-3 toe syndactyly. The diagnosis of SLOS was confirmed by finding an elevated amniotic fluid 7-dehydrocholesterol level (9,890 ng/ml; normal range = 3-9 ng/ml), and molecularly by detecting two different mutations in the DHCR7 gene, the gene causing SLOS. The first mutation was an IVS8-1G>T change and the second was a deletion of exons 3 and 4; this latter mutation has not been reported previously. The mother carries the deletion, while the father carries the splice-site mutation. Also of note, the father has an abnormally low total plasma cholesterol level (104-109 mg/dl). This is the most severe case of HPE described in any patient with SLOS. We postulate that the HPE in this case resulted from severe impairment of Sonic Hedgehog signaling secondary to abnormal cholesterol metabolism; however, the unique combination of mutations in the fetus functionally appears to be no different from other homozygous null mutations reported in DHCR7. Therefore, there must be other yet to be identified factors that contributed to the severity of HPE in SLOS.

Significant contributions of the extraembryonic membranes and maternal genotype to the placental pathology in heterozygous Nsdhl deficient female embryos

Mutations in the gene encoding the cholesterol biosynthetic enzyme NSDHL are associated with the X-linked male-lethal bare patches (Bpa) mouse. Mutant male embryos for several Nsdhl alleles die in midgestation with placental insufficiency. We examined here a possible role of the maternal genotype in such placental pathology. Pre-pregnancy plasma cholesterol levels were similar between wild-type (WT) and Bpa(1H)/+ dams fed a standard, cholesterol-free diet. However, there was a marked decrease in cholesterol levels between embryonic day (E)8.5 and E10.5 for both genotypes. Further, there was a significant lag between E11.5 and E13.5 (P = 0.0011) in the recovery of levels in Bpa(1H)/+ dams to their pre-pregnancy values. To investigate possible effects of the maternal genotype on fetal placentation, we generated transgenic mice that expressed human NSDHL and rescued the male lethality of the Bpa(1H) null allele. We then compared placenta area at E10.5 in WT and Bpa(1H)/+ female embryos where the mutant X chromosome was transmitted from a heterozygous mother or a rescued mutant father. In mutant conceptuses, placental areas were approximately 50% less than WT. Surprisingly, expression of Nsdhl in trophoblast lineages of the placenta and yolk sac endoderm, which occurs only from the maternally inherited allele in a female embryo, had the largest effect on placental area (-0.681 mm(2); P < 0.0001). The maternal genotype had a smaller effect, independent of the fetal genotype (-0.283 mm(2); P = 0.024). These data demonstrate significant effects of the mother and fetal membranes on pregnancy outcome, with possible implications for cholesterol homeostasis during human pregnancy.

Transport of maternal cholesterol to the fetus is affected by maternal plasma cholesterol concentrations in the golden Syrian hamster

The fetus has a high requirement for cholesterol and synthesizes cholesterol at elevated rates. Recent studies suggest that fetal cholesterol also can be obtained from exogenous sources. The purpose of the current study was to examine the transport of maternal cholesterol to the fetus and determine the mechanism responsible for any cholesterol-driven changes in transport. Studies were completed in pregnant hamsters with normal and elevated plasma cholesterol concentrations. Cholesterol feeding resulted in a 3.1-fold increase in the amount of LDL-cholesterol taken up by the fetus and a 2.4-fold increase in the amount of HDL-cholesterol taken up. LDL-cholesterol was transported to the fetus primarily by the placenta, and HDL-cholesterol was transported by the yolk sac and placenta. Several proteins associated with sterol transport and efflux, including those induced by activated liver X receptor, were expressed in hamster and human placentas: NPC1, NPC1L1, ABCA2, SCP-x, and ABCG1, but not ABCG8. NPC1L1 was the only protein increased in hypercholesterolemic placentas. Thus, increasing maternal lipoprotein-cholesterol concentrations can enhance transport of maternal cholesterol to the fetus, leading to 1) increased movement of cholesterol down a concentration gradient in the placenta, 2) increased lipoprotein secretion from the yolk sac (shown previously), and possibly 3) increased placental NPC1L1 expression.

Where does fetal and embryonic cholesterol originate and what does it do?

The development of a single-celled fertilized egg, through the blastocyst stage of a ball of cells and the embryonic stage when almost all organ systems begin to develop, and finally to the fetal stage where growth and physiological maturation occurs, is a complex and multifaceted process. A change in metabolism during gestation, especially when organogenesis occurs, can lead to abnormal development and congenital defects. Although many studies have described the roles of specific proteins in development, the roles of specific lipids, such as sterols, have not been studied as intensely. Sterol's functions in development range from being a structural component of membranes to regulating the patterning of the forebrain through sonic hedgehog to regulating expression of key proteins involved in metabolic processes. This review focuses on the roles of sterols in embryonic and fetal development and metabolism. Potential sources of cholesterol for the fetus and embryo are also discussed.

Characterization of placental cholesterol transport: ABCA1 is a potential target for in utero therapy of Smith-Lemli-Opitz syndrome

Patients with Smith-Lemli-Opitz syndrome (SLOS) are born with multiple congenital abnormalities. Postnatal cholesterol supplementation is provided; however, it cannot correct developmental malformations due to in utero cholesterol deficit. Increased transport of cholesterol from maternal to fetal circulation might attenuate congenital malformations. The cholesterol transporters Abca1, Abcg1, and Sr-b1 are present in placenta; however, their potential role in placental transport remains undetermined. In mice, expression analyses showed that Abca1 and Abcg1 transcripts increased 2-3-fold between embryonic days 13.5 and 18.5 in placental tissue; whereas, Sr-b1 expression decreased. To examine the functional role of Abca1, Abcg1 and Sr-b1 we measured the maternal-fetal transfer of (14)C-cholesterol in corresponding mutant embryos. Disruption of either Abca1 or Sr-b1 decreased cholesterol transfer by approximately 30%. In contrast, disruption of the Abcg1 had no effect. Treatment of pregnant C57Bl/6 female mice with TO901317, an LXR-agonist, increased both Abca1 expression and maternal-fetal cholesterol transfer to the fetus. In an SLOS mouse model (Dhcr7(-/-)), which is incapable of de novo synthesis of cholesterol, in utero treatment with TO901317 resulted in increased cholesterol content in Dhcr7(-/-) embryos. Our data support the hypothesis that Abca1, and possibly Sr-b1, contributes to transport maternal cholesterol to the developing fetus. Furthermore, we show, as a proof of principle, that modulating maternal-fetal cholesterol transport has potential for in utero therapy of SLOS.

Enhanced placental cholesterol efflux by fetal HDL in Smith-Lemli-Opitz syndrome

Previous studies from this laboratory have shown that maternal-derived cholesterol can be effluxed from trophoblasts to fetal HDL and plasma. We had the opportunity to study for the first time the ability of HDL and plasma from a fetus with the Smith-Lemli-Opitz syndrome (SLOS) to efflux cholesterol from trophoblasts. It was unclear whether cholesterol could be effluxed to fetuses with SLOS since lipoprotein levels are often very low. To answer this question, cord blood was collected from the placentas of an SLOS fetus and unaffected fetuses just after delivery. Plasma cholesterol concentrations were very low in the affected fetus; cholesterol, 7-dehydrocholesterol, and 8-dehydocholesterol concentrations were 14.1, 4.5, and 5.2 mg/dl, respectively. The HDL from the fetal SLOS effluxed approximately 50% more cholesterol from a trophoblast cell line, were smaller in size, and had a lower cholesterol to phospholipid ratio as compared to HDL from unaffected fetuses or adults. Plasma from the SLOS fetus effluxed cholesterol to a similar percentage as unaffected fetal plasma or adult plasma, possibly due to fewer HDL particles as demonstrated in previous SLOS patients. These novel data demonstrate that the cholesterol-deficient SLOS fetus is able to obtain cholesterol from trophoblasts at a time when cholesterol is playing a critical role in development, and has implications for design of treatments for cholesterol deficiency syndromes as well as understanding of prenatal cholesterol transport in humans.

Smith-Lemli-Opitz syndrome: pathogenesis, diagnosis and management

Smith-Lemli-Opitz syndrome (SLOS) is a malformation syndrome due to a deficiency of 7-dehydrocholesterol reductase (DHCR7). DHCR7 primarily catalyzes the reduction of 7-dehydrocholesterol (7DHC) to cholesterol. In SLOS, this results in decreased cholesterol and increased 7DHC levels, both during embryonic development and after birth. The malformations found in SLOS may result from decreased cholesterol, increased 7DHC or a combination of these two factors. This review discusses the clinical aspects and diagnosis of SLOS, therapeutic interventions and the current understanding of pathophysiological processes involved in SLOS.

Adverse birth outcome among mothers with low serum cholesterol

OBJECTIVE

The objective of this study was to assess whether low maternal serum cholesterol during pregnancy is associated with preterm delivery, impaired fetal growth, or congenital anomalies in women without identified major risk factors for adverse pregnancy outcome.

METHODS

Mother-infant pairs were retrospectively ascertained from among a cohort of 9938 women who were referred to South Carolina prenatal clinics for routine second-trimester serum screening. Banked sera were assayed for total cholesterol; <10th percentile of assayed values (159 mg/dL at mean gestational age of 17.6 weeks) defined a "low total cholesterol" prenatal risk category. Eligible women were aged 21 to 34 years and nonsmoking and did not have diabetes; neonates were liveborn after singleton gestations. Total cholesterol values of eligible mothers were adjusted for gestational age at screening before risk group assignment. The study population included 118 women with low total cholesterol and 940 women with higher total cholesterol. Primary analyses used multivariate regression models to compare rates of preterm delivery, fetal growth parameters, and congenital anomalies between women with low total cholesterol and control subjects with mid-total cholesterol values >10th percentile but <90th percentile.

RESULTS

Prevalence of preterm delivery among mothers with low total cholesterol was 12.7%, compared with 5.0% among control subjects with mid-total cholesterol. The association of low maternal serum cholesterol with preterm birth was observed only among white mothers. Term infants of mothers with low total cholesterol weighed on average 150 g less than those who were born to control mothers. A trend of increased microcephaly risk among neonates of mothers with low total cholesterol was found. Low maternal serum cholesterol was unassociated with risk for congenital anomalies.

CONCLUSIONS

Total serum cholesterol <10th population percentile was strongly associated with preterm delivery among otherwise low-risk white mothers in this pilot study population. Term infants of mothers with low total cholesterol weighed less than control infants among both racial groups.

Cholesterol Transport by the Placenta: Placental Liver X Receptor Activity as a Modulator of Fetal Cholesterol Metabolism?

Cholesterol is an important sterol in mammals. Defects in cholesterol synthesis or intracellular routing have devastating consequences already in utero: the Smith-Lemli-Opitz syndrome, desmosterolosis and Niemann-Pick C1 disease provide examples of severe human inherited diseases caused by mutations in cholesterol metabolism genes. On the other hand, elevated plasma cholesterol concentrations are associated with the development of atherosclerosis which represents a major health risk in Western societies. Moreover, several studies indicate that development of atherosclerosis may already start during fetal life. Hence, a carefully balanced regulation of cholesterol metabolism appears of critical importance for both the development of the fetus and health of the adult. In the adult, the liver X receptor is a key regulator of cholesterol metabolism. Its target genes regulate cellular cholesterol efflux and thereby modulate whole-body cholesterol fluxes. LXR and several of its target genes have recently been demonstrated to be expressed in the placenta, which would provide a means to control delivery of maternal cholesterol to the fetus. Here we discuss the potential role of the placenta in the regulation of fetal cholesterol homeostasis and strategies to influence maternal-fetal cholesterol transfer.

Loss of apolipoprotein E exacerbates the neonatal lethality of the Smith-Lemli-Opitz syndrome mouse

The Smith-Lemli-Opitz syndrome (SLOS) is caused by a genetic defect in cholesterol biosynthesis; mutations in the enzyme 3ss-hydroxysterol Delta7 reductase (Dhcr7) lead to a failure of cholesterol (and desmosterol) synthesis, with an accumulation of precursor sterols, such as 7-dehydrocholesterol. Extensive genotype-phenotype analyses have indicated that there is considerable variation in the severity of the disease, much of which is not explained by defects in the Dhcr7 gene alone. Factors ranging from variations in maternal-fetal cholesterol transfer during pregnancy, to other genetic factors have been proposed to account for this variability. Variations at the APOE locus affect plasma cholesterol levels in humans and this polymorphic gene has been found to be associated with cardiovascular as well as neurological disorders. This locus has recently been implicated in accounting for some of the variations in SLOS. To address whether maternal hypercholesterolemia can affect fetal outcome, we tested the ability of maternal hypercholesterolemia to rescue the neonatal lethality in a mouse model of SLOS. Maternal hypercholesterolemia, induced by ApoE or Ldl-r deficiency not only failed to ameliorate the postnatal lethality, it increased the prenatal mortality of Dhcr7 deficient pups. Thus the murine data suggest that maternal loss of ApoE or Ldl-r function further exacerbates the neonatal lethality, suggesting they may play a role in maternal transfer of cholesterol to the embryo.

Role of apolipoprotein E4 in protecting children against early childhood diarrhea outcomes and implications for later development

Our group and others have reported a series of studies showing that heavy burdens of diarrheal diseases in the formative first two years of life in children in urban shantytowns have profound consequences of impaired physical and cognitive development lasting into later childhood and schooling. Based on these previous studies showing that apolipoprotein E4 (APOE4) is relatively common in favela children, we review recent data suggesting a protective role for the APOE4 allele in the cognitive and physical development of children with heavy burdens of diarrhea in early childhood. Despite being a marker for cognitive decline with Alzheimer's and cardiovascular diseases later in life, APOE4 appears to be important for cognitive development under the stress of heavy diarrhea. The reviewed findings provide a potential explanation for the survival advantage in evolution of the thrifty APOE4 allele and raise questions about its implications for human development under life-style changes and environmental challenges.