Altered cerebrospinal fluid proteins in Smith-Lemli-Opitz syndrome patients.

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple malformation syndrome with neurocognitive impairment. SLOS arises from mutations in the 7-dehydrocholesterol reductase gene which results in impaired enzymatic conversion of 7-dehydrocholesterol to cholesterol. In the current work, we sought to measure proteins that were altered in the cerebrospinal fluid from SLOS patients compared to pediatric controls. Using a multi-analyte antibody-based assay, we found that 12 proteins are altered in SLOS patients. Validation studies were carried out and the findings from this study suggest alterations in extracellular matrix remodeling and further evidence of oxidative stress within the disease pathophysiology. The results of this study will be used to explore biological pathways altered in SLOS and identifies a set of CSF proteins that can be evaluated as biomarkers in future therapeutic trials. © 2016 Wiley Periodicals, Inc.

Free radical oxidation of cholesterol and its precursors: Implications in cholesterol biosynthesis disorders.

Free radical oxidation of cholesterol and its precursors contribute significantly to the pathophysiology of a number of human diseases. This review intends to summarize recent developments and provide a perspective on the reactivities of sterols toward free radical oxidation, the free radical reaction mechanism, and the biological consequences of oxysterols derived from the highly oxidizable cholesterol precursor, 7-dehydrocholesterol. We propose that the rigid structures, additional substituents on the double bonds, and the well-aligned reactive C-H bonds in sterols make them more prone to free radical oxidation than their acyclic analogs found in unsaturated fatty acids. The mechanism of sterol peroxidation follows some well-established reaction pathways found in the free radical peroxidation of polyunsaturated fatty acids, but sterols also undergo some reactions that are unique to these compounds. Peroxidation of 7-dehydrocholesterol gives arguably the most diverse set of oxysterol products that have been observed to date. The metabolism of these oxysterols in cells and the biological consequences of their formation will be discussed in the context of the pathophysiology of the human disease Smith-Lemli-Opitz syndrome. Considering the high reactivity of sterols, we propose that a number of other cholesterol biosynthesis disorders may be associated with oxidative stress.

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.

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.

A membrane defect in the pathogenesis of the Smith-Lemli-Opitz syndrome.

The Smith-Lemli-Opitz syndrome (SLOS) is an often lethal birth defect resulting from mutations in the gene responsible for the synthesis of the enzyme 3beta-hydroxy-steroid-Delta7-reductase, which catalyzes the reduction of the double bond at carbon 7 on 7-dehydrocholesterol (7-DHC) to form unesterified cholesterol. We hypothesize that the deficiency in cholesterol biosynthesis and subsequent accumulation of 7-DHC in the cell membrane leads to defective composition, organization, dynamics, and function of the cell membrane. Using skin fibroblasts obtained from SLOS patients, we demonstrate that the SLOS membrane has increased 7-DHC and reduced cholesterol content and abnormal membrane fluidity. X-ray diffraction analyses of synthetic membranes prepared to mimic SLOS membranes revealed atypical membrane organization. In addition, calcium permeability is markedly augmented, whereas membrane-bound Na+/K+ATPase activity, folate uptake, inositol-1,4,5-trisphosphate signaling, and cell proliferation rates are markedly suppressed. These data indicate that the disturbance in membrane sterol content in SLOS, likely at the level of membrane caveolae, directly contributes to the widespread tissue abnormalities in this disease.

Disruption of cholesterol homeostasis in the developing brain as a potential mechanism contributing to the developmental neurotoxicity of ethanol: an hypothesis.

While excess cholesterol may have deleterious consequences, as in the case of atherosclerosis, too little cholesterol may endanger the development of the brain. Different degrees of mental retardation are often observed in inborn errors of cholesterol synthesis, such as the Smith-Lemli-Opitz syndrome or in maternal phenylketonuria, where the metabolite of accumulating phenylalanine, phenylacetate, is an inhibitor of cholesterol synthesis. Lack of cholesterol during brain development as a consequence of these genetic defects leads to severe brain damage, microencephaly and mental retardation, which are also hallmarks of the fetal alcohol syndrome (FAS). The brain relies on the in situ synthesis of cholesterol, which occurs mostly in astrocytes. Astrocyte-produced cholesterol is utilized for cell proliferation, or is released, via astrocyte-secreted high density lipoprotein-like particles containing apolipoprotein E, outside the cell, where it is taken up and utilized by neurons for dendrite outgrowth and to form synapses. We propose the hypothesis that ethanol may disrupt cholesterol homeostasis during brain development, and that this effect may be responsible, at least in part, for the central nervous system dysfunctions observed in the FAS, which include altered astrocyte proliferation, neuronal death and diminished synaptic contacts.

Human malformation syndromes due to inborn errors of cholesterol synthesis.

PURPOSE OF REVIEW: This review covers a group of human malformation syndromes, which are caused by inborn errors of cholesterol synthesis. The Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive, multiple malformation, and mental retardation syndrome that is the prototypical example of this group of disorders. In the 10 years since the biochemical cause of SLOS was identified, other malformation syndromes have been shown to result from defects in this pathway. These include desmosterolosis, lathosterolosis, X-linked dominant chondrodysplasia punctata type 2 (CDPX2), congenital hemidysplasia with ichthyosiform erythroderma and limb defects (CHILD syndrome), hydrops-ectopic calcification-moth-eaten skeletal dysplasia (HEM dysplasia), and some cases of Antley-Bixler syndrome. These disorders represent the first true merging of dysmorphology with biochemical genetics. RECENT FINDINGS: Recent studies report the identification of human lathosterolosis patients, indicate that SLOS is a relatively common genetic disorder that may be a major unrecognized cause of fetal loss, suggest that correction of the biochemical defect can improve central nervous system function, and show that perturbed sonic hedgehog signaling due to decreased sterol levels likely underlies some of the malformations in SLOS and lathosterolosis. SUMMARY: Recognition of the biochemical defect in these syndromes has given insight into the role that cholesterol plays during normal development, into understanding the pathophysiological processes that underlie the clinical problems found in these disorders, and into developing therapeutic interventions.

Disorders of post-squalene cholesterol biosynthesis leading to human dysmorphogenesis.

Insights in molecular developmental biology in animals and humans are facilitating the understanding of pathophysiologic mechanisms in dysmorphogenesis or abnormalities in normal embryologic structural development. A milestone was recognition of the role of shh in morphogenesis of craniofacial structures, especially the development of holoprosencephaly. The dependence of hedgehog morphogens on cholesterol modification for normal hedgehog signaling function has particular relevance to disorders of cholesterol synthesis which manifest dysmorphogenesis. Four human disorders of morphogenesis (Smith-Lemli-Opitz syndrome, desmosterolosis, X-linked chondrodysplasia punctata, CHILD syndrome) have recently been shown to be caused by sterol abnormalities resulting from cholesterol biosynthesis enzyme deficiencies. This review summarizes the clinical, biochemical and molecular data in these disorders with an emphasis on understanding the pathophysiology of dysmorphogenesis.

Bile acid synthesis in the Smith-Lemli-Opitz syndrome: effects of dehydrocholesterols on cholesterol 7alpha-hydroxylase and 27-hydroxylase activities in rat liver.

The Smith-Lemli-Opitz syndrome (SLOS) is a congenital birth defect syndrome caused by a deficiency of 3beta-hydroxysterol Delta(7)-reductase, the final enzyme in the cholesterol biosynthetic pathway. The patients have reduced plasma and tissue cholesterol concentrations with the accumulation of 7-dehydrocholesterol and 8-dehydrocholesterol. Bile acid synthesis is reduced and unnatural cholenoic and cholestenoic acids have been identified in some SLOS patients. To explore the mechanism of the abnormal bile acid production, the activities of key enzymes in classic and alternative bile acid biosynthetic pathways (microsomal cholesterol 7alpha-hydroxylase and mitochondrial sterol 27-hydroxylase) were measured in liver biopsy specimens from two mildly affected SLOS patients. The effects of 7- and 8-dehydrocholesterols on these two enzyme activities were studied by using liver from SLOS model rats that were treated with the Delta(7)-reductase inhibitor (BM15.766) for 4 months and were comparable with more severe SLOS phenotype in plasma and hepatic sterol compositions. In the SLOS patients, cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase were not defective. In BM15.766-treated rats, both enzyme activities were lower than those in control rats and they were competitively inhibited by 7- and 8-dehydrocholesterols. Rat microsomal cholesterol 7alpha-hydroxylase did not transform 7-dehydrocholesterol or 8-dehydrocholesterol into 7alpha-hydroxylated sterols. In contrast, rat mitochondrial sterol 27-hydroxylase catalyzed 27-hydroxylation of 7- and 8-dehydrocholesterols, which were partially converted to 3beta-hydroxycholestadienoic acids. Addition of microsomes to the mitochondrial 27-hydroxylase assay mixture reduced 27-hydroxydehydrocholesterol concentrations, which suggested that 27-hydroxydehydrocholesterols were further metabolized by microsomal enzymes. These results suggest that reduced normal bile acid production is characteristic of severe SLOS phenotype and is caused not only by depletion of hepatic cholesterol but also by competitive inhibition of cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities by accumulated 7- and 8-dehydrocholesterols. Unnatural bile acids are synthesized mainly by the alternative pathway via mitochondrial sterol 27-hydroxylase in SLOS.

Síndromes de Smith-Lemli-Optiz en dos hermanos. Presentación del caso / Smith-Lemli-Optiz Syndrome in two brothers. Case presentation

El síndrome de Smith-Lemli-Opitz es una entidad de etiología autosómica recesiva, que cursa con malformaciones congénitas, retraso del crecimiento y desarrollo pre y posnatal y es causa de muerte a temprana edad. No se conoce tratamiento, por lo que solamente se cuenta con el asesoramiento genético para evitar la aparición de nuevos casos.Se presenta el caso de dos hermanos, hijos de padres consanguíneos. Ambos fueron detectados desde el nacimiento y aun cuando se diagnosticaron al mes de vida, el asesoramiento genético proporcionando a los padres no fue efectivo, ya que después del primer hijo afectado tuvieron dos embarazos más, resultando afectado el producto del segundo de éstos. Se ha encontrado una deficiencia en la síntesis de colesterol, por lo que es posible hacer el diagnóstico prenatal en las mujeres que tienen antecedentes de gestas previas con esta enfermedad

Molecular genetics of the Smith-Lemli-Opitz syndrome and postsqualene sterol metabolism.

The Smith-Lemli-Opitz syndrome is a disorder of morphogenesis resulting from an enzymatic defect in the last step of cholesterol metabolism (reduction of 7-dehydrocholesterol). Analysis of the defective gene and identification of mutations therein have paved the way for the study of the molecular genetics of the disorder which is caused by numerous different mutations. Future efforts should identify a postulated intracellular signalling activity of sterol intermediates, isolate proteins that govern the sterol traffic between intracellular compartments, structurally characterize the enzyme delta 7-sterol reductase defective in the Smith-Lemli-Opitz syndrome and investigate the pathomechanism of sterol depletion-induced dysmorphogenesis.