Smith-Lemli-Opitz syndrome is caused by mutations in the 7-dehydrocholesterol reductase gene

Effect of DHCR7 on adipocyte differentiation in goats

Cholesterol is regarded as a signaling molecule in regulating the metabolism and function of fat cells, in which 7-Dehydrocholesterol reductase (DHCR7) is a key enzyme that catalyzes the conversion of 7-dehydrocholesterol to cholesterol, however, the exact function of DHCR7 in goat adipocytes remains unknown. Here, the effect of DHCR7 on the formation of subcutaneous and intramuscular fat in goats was investigated in vitro, and the result indicated that the mRNA level of DHCR7 showed a gradual downward trend in subcutaneous adipogenesis, but an opposite trend in intramuscular adipogenesis. In the process of subcutaneous preadipocytes differentiation, overexpression of DHCR7 inhibited the expression of adipocytes differentiation marker genes (CEBP/α, CEBP/β, SREBP1 and AP2), lipid metabolism-related genes (AGPAT6, FASN, SCD1 and LPL), and the lipid accumulation. However, in intramuscular preadipocyte differentiation, DHCR7 overexpression showed a promoting effect on adipocyte differentiation marker genes (CEBP/α, CEBP/β, PPARγ and SREBP1) and lipid metabolism-related genes (GPAM, AGPAT6, DGAT1 and SCD1) expression, and on lipid accumulation. In summary, our work demonstrated that DHCR7 played an important role in regulating adipogenic differentiation and lipid metabolism in preadipocytes in goats, which is of great significance for uncovering the underlying molecular mechanism of adipocyte differentiation and improving goat meat quality.

DHCR7 links cholesterol synthesis with neuronal development and axonal integrity

The DHCR7 enzyme converts 7-DHC into cholesterol. Mutations in DHCR7 can block cholesterol production, leading to abnormal accumulation of 7-DHC and causing Smith-Lemli-Opitz syndrome (SLOS). SLOS is an autosomal recessive disorder characterized by multiple malformations, including microcephaly, intellectual disability, behavior reminiscent of autism, sleep disturbances, and attention-deficit/hyperactivity disorder (ADHD)-like hyperactivity. Although 7-DHC affects neuronal differentiation in ex vivo experiments, the precise mechanism of SLOS remains unclear. We generated Dhcr7 deficient (dhcr7-/-) zebrafish that exhibited key features of SLOS, including microcephaly, decreased neural stem cell pools, and behavioral phenotypes similar to those of ADHD-like hyperactivity. These zebrafish demonstrated compromised myelination, synaptic anomalies, and neurotransmitter imbalances. The axons of the dhcr7-/- zebrafish showed increased lysosomes and attenuated autophagy, suggesting that autophagy-related neuronal homeostasis is disrupted.

Chemical Inhibition of Sterol Biosynthesis

Cholesterol is an essential molecule of life, and its synthesis can be inhibited by both genetic and nongenetic mechanisms. Hundreds of chemicals that we are exposed to in our daily lives can alter sterol biosynthesis. These also encompass various classes of FDA-approved medications, including (but not limited to) commonly used antipsychotic, antidepressant, antifungal, and cardiovascular medications. These medications can interfere with various enzymes of the post-lanosterol biosynthetic pathway, giving rise to complex biochemical changes throughout the body. The consequences of these short- and long-term homeostatic disruptions are mostly unknown. We performed a comprehensive review of the literature and built a catalogue of chemical agents capable of inhibiting post-lanosterol biosynthesis. This process identified significant gaps in existing knowledge, which fall into two main areas: mechanisms by which sterol biosynthesis is altered and consequences that arise from the inhibitions of the different steps in the sterol biosynthesis pathway. The outcome of our review also reinforced that sterol inhibition is an often-overlooked mechanism that can result in adverse consequences and that there is a need to develop new safety guidelines for the use of (novel and already approved) medications with sterol biosynthesis inhibiting side effects, especially during pregnancy.

History and highlights of the teratological collection in the Narrenturm, Vienna (Austria)

The collection of the Narrenturm in Vienna houses and maintains more than 50,000 objects including approximately 1200 teratological specimens; making it one of the biggest collections of specimens from human origin in Europe. The existence of this magnificent collection-representing an important resource for dysmorphology research, mostly awaiting contemporary diagnoses-is not widely known in the scientific community. Here, we show that the Narrenturm harbors a wealth of specimens with (exceptionally) rare congenital anomalies. These museums can be seen as physical repositories of human malformation, covering hundreds of years of dedicated collecting and preserving, thereby creating unique settings that can be used to expand our knowledge of developmental conditions that have to be preserved for future generations of scientists.

Smith-Lemli-Opitz syndrome: A pathophysiological manifestation of the Bloch hypothesis

The biosynthesis of cholesterol, an essential component of higher eukaryotic membranes, was worked out by Konrad Bloch (and Feodor Lynen) in the 1960s and they received the Nobel Prize around that time in recognition of their pioneering contributions. An elegant consequence of this was a hypothesis proposed by Konrad Bloch (the Bloch hypothesis) which suggests that each subsequent intermediate in the cholesterol biosynthesis pathway is superior in supporting membrane function in higher eukaryotes relative to its precursor. In this review, we discuss an autosomal recessive metabolic disorder, known as Smith-Lemli-Opitz syndrome (SLOS), associated with a defect in the Kandutsch-Russell pathway of cholesterol biosynthesis that results in accumulation of the immediate precursor of cholesterol in its biosynthetic pathway (7-dehydrocholesterol) and an altered cholesterol to total sterol ratio. Patients suffering from SLOS have several developmental, behavioral and cognitive abnormalities for which no drug is available yet. We characterize SLOS as a manifestation of the Bloch hypothesis and review its molecular etiology and current treatment. We further discuss defective Hedgehog signaling in SLOS and focus on the role of the serotonin_1A receptor, a representative neurotransmitter receptor belonging to the GPCR family, in SLOS. Notably, ligand binding activity and cellular signaling of serotonin_1A receptors are impaired in SLOS-like condition. Importantly, cellular localization and intracellular trafficking of the serotonin_1A receptor (which constitute an important determinant of a GPCR cellular function) are compromised in SLOS. We highlight some of the recent developments and emerging concepts in SLOS pathobiology and suggest that novel therapies based on trafficking defects of target receptors could provide new insight into treatment of SLOS.

Steroid hormones of the octopus self-destruct system

Among all invertebrates, soft-bodied cephalopods have the largest central nervous systems and the greatest brain-to-body mass ratios, yet unlike other big-brained animals, cephalopods are unusually short lived.^1-5 Primates and corvids survive for many decades, but shallow-water octopuses, such as the California two-spot octopus (Octopus bimaculoides), typically live for only 1 year.^6,7 Lifespan and reproduction are controlled by the principal neuroendocrine center of the octopus: the optic glands, which are functional analogs to the vertebrate pituitary gland.^8-10 After mating, females steadfastly brood their eggs, begin fasting, and undergo rapid physiological decline, featuring repeated self-injury and leading to death.¹¹ Removal of the optic glands completely reverses this life history trajectory,¹⁰ but the signaling factors underlying this major life transition are unknown. Here, we characterize the major secretions and steroidogenic pathways of the female optic gland using mass spectrometry techniques. We find that at least three pathways are mobilized to increase synthesis of select sterol hormones after reproduction. One pathway generates pregnane steroids, known in other animals to support reproduction.^12-16 Two other pathways produce 7-dehydrocholesterol and bile acid intermediates, neither of which were previously known to be involved in semelparity. Our results provide insight into invertebrate cholesterol pathways and confirm a remarkable unity of steroid hormone biology in life history processes across Bilateria.

Transcriptomic changes upon epoxiconazole exposure in a human stem cell-based model of developmental toxicity

Conazole fungicides such as epoxiconazole are mostly used on cereals of crops to inhibit fungal growth through direct inhibition of sterol 14α-demethylase (CYP51A1). However, this enzyme is highly conserved and in humans it is part of the steroid hormone biosynthesis pathway. Endocrine disrupting effects of epoxiconazole have been shown in rodents and have been substantiated by in vitro data, however, the underlying molecular mechanisms are not clear. We took advantage of a human stem cell based in vitro model for developmental toxicity to study the molecular effects of epoxiconazole. This model is based on 3D cultures of embryoid bodies and differentiation into cardiomyocytes, which mimics the early stages of embryonic development. We have previously shown that epoxiconazole impairs differentiation of these embryoid bodies and therefore has the potential to affect human embryonic development. We employed global transcriptome analysis using RNA sequencing and found that the steroid biosynthesis pathway including CYP51A1, the human sterol 14α-demethylase, was highly deregulated by epoxiconazole in our model. We confirmed that most genes of the steroid biosynthesis pathway were upregulated, including CYP51A1, suggesting a compensatory mechanism at the gene expression level. Our data suggest that epoxiconazole acts mainly by decreasing cholesterol biosynthesis in the cells. We conclude that epoxiconazole bears the potential to harm human embryonic development through inhibition of the steroid biosynthesis pathway. As this may be a common feature of compounds that target sterol 14α-demethylase, we add evidence to the assumption that conazole fungicides may be human developmental toxicants.

Sterol and lipid analyses identifies hypolipidemia and apolipoprotein disorders in autism associated with adaptive functioning deficits

An improved understanding of sterol and lipid abnormalities in individuals with autism spectrum disorder (ASD) could lead to personalized treatment approaches. Toward this end, in blood, we identified reduced synthesis of cholesterol in families with ≥2 children with ASD participating with the Autism Genetic Resource Exchange (AGRE), as well as reduced amounts of high-density lipoprotein cholesterol (HDL), apolipoprotein A1 (ApoA1) and apolipoprotein B (ApoB), with 19.9% of the subjects presenting with apolipoprotein patterns similar to hypolipidemic clinical syndromes and 30% with either or both ApoA1 and ApoB less than the fifth centile. Subjects with levels less than the fifth centile of HDL or ApoA1 or ApoA1 + ApoB had lower adaptive functioning than other individuals with ASD, and hypocholesterolemic subjects had apolipoprotein deficits significantly divergent from either typically developing individuals participating in National Institutes of Health or the National Health and Nutrition Examination Survey III.

Materno-fetal cholesterol transport during pregnancy

Cholesterol is a major nutrient required for fetal growth. It is also a precursor for the synthesis of steroid hormones and essential for the development and maturation of fetal organs. During pregnancy, the placenta controls the transport of cholesterol from the mother to the fetus and vice versa. Cholesterol originating from the maternal circulation has to cross two main membrane barriers to reach the fetal circulation: Firstly, cholesterol is acquired by the apical side of the syncytiotrophoblast (STB) from the maternal circulation as high-density lipoprotein (HDL)-, low-density lipoprotein (LDL)- or very-low-density lipoprotein (VLDL)-cholesterol and secreted at the basal side facing the villous stroma. Secondly, from the villous stroma cholesterol is taken up by the endothelium of the fetal vasculature and transported to the fetal vessels. The proteins involved in the uptake of HDL-, LDL-, VLDL- or unesterified-cholesterol are scavenger receptor type B class 1 (SR-B1), cubulin, megalin, LDL receptor (LDLR) or Niemann-Pick-C1 (NPC1) which are localized at the apical and/or basal side of the STB or at the fetal endothelium. Through interaction with apolipoproteins (e.g. apoA1) cholesterol is effluxed either to the maternal or fetal circulation via the ATP-binding-cassette (ABC)-transporter A1 and ABCG1 localized at the apical/basal side of the STB or the endothelium. In this mini-review, we summarize the transport mechanisms of cholesterol across the human placenta, the expression and localization of proteins involved in the uptake and efflux of cholesterol, and the expression pattern of cholesterol transport proteins in pregnancy pathologies such as pre-eclampsia, gestational diabetes mellitus and intrauterine growth retardation.

Auditory phenotype of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive multiple congenital malformation and intellectual disability syndrome resulting from variants in DHCR7. Auditory characteristics of persons with SLOS have been described in limited case reports but have not been systematically evaluated. The objective of this study is to describe the auditory phenotype in SLOS. Age- and ability-appropriate hearing evaluations were conducted on 32 patients with SLOS. A subset of 21 had auditory brainstem response testing, from which an auditory neural phenotype is described. Peripheral or retrocochlear auditory dysfunction was observed in at least one ear of 65.6% (21) of the patients in our SLOS cohort. The audiometric phenotype was heterogeneous and included conductive, mixed, and sensorineural hearing loss. The most common presentation was a slight to mild conductive hearing loss, although profound sensorineural hearing loss was also observed. Abnormal auditory brainstem responses indicative of retrocochlear dysfunction were identified in 21.9% of the patients. Many were difficult to test behaviorally and required objective assessment methods to estimate hearing sensitivity. Individuals with SLOS are likely to have hearing loss that may impact communication, including speech and language development. Routine audiologic surveillance should be conducted to ensure prompt management of hearing loss.

Visualisation of cholesterol and ganglioside GM1 in zebrafish models of Niemann-Pick type C disease and Smith-Lemli-Opitz syndrome using light sheet microscopy

Lysosomal storage diseases are the most common cause of neurodegeneration in children. They are characterised at the cellular level by the accumulation of storage material within lysosomes. There are very limited therapeutic options, and the search for novel therapies has been hampered as few good small animal models are available. Here, we describe the use of light sheet microscopy to assess lipid storage in drug and morpholino induced zebrafish models of two diseases of cholesterol homeostasis with lysosomal dysfunction: First, Niemann–Pick type C disease (NPC), caused by mutations in the lysosomal transmembrane protein NPC1, characterised by intralysosomal accumulation of cholesterol and several other lipids. Second, Smith–Lemli–Opitz syndrome (SLOS), caused by mutations in 7-dehydrocholesterol reductase, which catalyses the last step of cholesterol biosynthesis and is characterised by intralysosomal accumulation of dietary cholesterol. This is the first description of a zebrafish SLOS model. We find that zebrafish accurately model lysosomal storage and disease-specific phenotypes in both diseases. Increased cholesterol and ganglioside GM1 were observed in sections taken from NPC model fish, and decreased cholesterol in SLOS model fish, but these are of limited value as resolution is poor, and accurate anatomical comparisons difficult. Using light sheet microscopy, we were able to observe lipid changes in much greater detail and identified an unexpected accumulation of ganglioside GM1 in SLOS model fish. Our data demonstrate, for the first time in zebrafish, the immense potential that light sheet microscopy has in aiding the resolution of studies involving lysosomal and lipid disorders.

Maternal cholesterol levels during gestation: boon or bane for the offspring?

An increase in cholesterol levels is perceived during pregnancy and is considered as a normal adaptive response to the development of the fetus. In some pregnancies, excessive increase in total cholesterol with high levels of Low-Density Lipoprotein leads to maladaptation by the fetus to cholesterol demands, resulting in a pathological condition termed as maternal hypercholesterolemia (MH). MH is considered clinically irrelevant and therefore cholesterol levels are not routinely checked during pregnancy, as a consequence of which there is scarce information on its global prevalence in pregnant women. Studies have reported that MH during pregnancy can cause atherogenesis in adults emphasizing the concept of in utero programming of fetus. Moreover, Gestational Diabetes Mellitus, obesity and Polycystic Ovary Syndrome are potential risk factors which strengthen combined pathologies in placenta and fetuses of mothers with MH. However, lack of conclusive evidence on cholesterol transport and underlying programming demand substantial research to develop population-based life style strategies for women in their childbearing years. The current review focuses on the mechanisms and outcomes of MH from existing epidemiological as well as experimental data and presents a detailed insight on this novel risk factor of cardiovascular diseases.

TMEM147 interacts with lamin B receptor, regulates its localization and levels, and affects cholesterol homeostasis

The structurally and functionally complex endoplasmic reticulum (ER) hosts critical processes including lipid synthesis. Here, we focus on the functional characterization of transmembrane protein TMEM147, and report that it localizes at the ER and nuclear envelope in HeLa cells. Silencing of TMEM147 drastically reduces the level of lamin B receptor (LBR) at the inner nuclear membrane and results in mistargeting of LBR to the ER. LBR possesses a modular structure and corresponding bifunctionality, acting in heterochromatin organization via its N-terminus and in cholesterol biosynthesis via its sterol-reductase C-terminal domain. We show that TMEM147 physically interacts with LBR, and that the C-terminus of LBR is essential for their functional interaction. We find that TMEM147 also physically interacts with the key sterol reductase DHCR7, which is involved in cholesterol biosynthesis. Similar to what was seen for LBR, TMEM147 downregulation results in a sharp decline of DHCR protein levels and co-ordinate transcriptional decreases of LBR and DHCR7 expression. Consistent with this, lipidomic analysis upon TMEM147 silencing identified changes in cellular cholesterol levels, cholesteryl ester levels and profile, and in cellular cholesterol uptake, raising the possibility that TMEM147 is an important new regulator of cholesterol homeostasis in cells.This article has an associated First Person interview with the first author of the paper.

Discordant fetal sex on NIPT and ultrasound

Prenatal diagnosis of sex discordance is a relatively new phenomenon. Prior to cell-free DNA testing, the diagnosis of a disorder of sexual differentiation was serendipitous, either through identification of ambiguous genitalia at the midtrimester morphology ultrasound or discovery of genotype-phenotype discordance in cases where preimplantation genetic diagnosis or invasive prenatal testing had occurred. The widespread integration of cfDNA testing into modern antenatal screening has made sex chromosome assessment possible from 10 weeks of gestation, and discordant fetal sex is now more commonly diagnosed prenatally, with a prevalence of approximately 1 in 1500-2000 pregnancies. Early detection of phenotype-genotype sex discordance is important as it may indicate an underlying genetic, chromosomal or biochemical condition and it also allows for time-critical postnatal treatment. The aim of this article is to review cfDNA and ultrasound diagnosis of fetal sex, identify possible causes of phenotype-genotype discordance and provide a systematic approach for clinicians when counseling and managing couples in this circumstance.

Genetics and signaling mechanisms of orofacial clefts

Craniofacial development involves several complex tissue movements including several fusion processes to form the frontonasal and maxillary structures, including the upper lip and palate. Each of these movements are controlled by many different factors that are tightly regulated by several integral morphogenetic signaling pathways. Subject to both genetic and environmental influences, interruption at nearly any stage can disrupt lip, nasal, or palate fusion and result in a cleft. Here, we discuss many of the genetic risk factors that may contribute to the presentation of orofacial clefts in patients, and several of the key signaling pathways and underlying cellular mechanisms that control lip and palate formation, as identified primarily through investigating equivalent processes in animal models, are examined.

Smith-Lemli-Opitz syndrome - Fetal phenotypes with special reference to the syndrome-specific internal malformation pattern

Background

Autosomal‐recessive SLOS is caused by mutations in the DHCR7 gene. It is defined as a highly variable complex of microcephaly with intellectual disability, characteristic facies, hypospadias, and polysyndactyly. Syndrome diagnosis is often missed at prenatal ultrasound and fetal autopsy

Methods

We performed autopsies and DHCR7 gene analyses in eight fetuses suspected of having SLOS and measured cholesterol values in long‐term formalin‐fixed tissues of an additional museum exhibit

Results

Five of the nine fetuses presented classical features of SLOS, including four cases with atrial/atrioventricular septal defects and renal anomalies, and one with additional bilateral renal agenesis and a Dandy‐Walker cyst. These cases allowed for diagnosis at autopsy and subsequent SLOS diagnosis in two siblings. Two fetuses were mildly affected and two fetuses showed additional holoprosencephaly. These four cases and the exhibit had escaped diagnosis at autopsy. The case with bilateral renal agenesis presented a novel combination of a null allele and a putative C‐terminus missense mutation in the DHCR7 gene

Conclusions

In view of the discrepancy between the prevalence of SLOS among newborns and the carrier frequency of a heterozygous DHCR7 gene mutation, the syndrome‐specific internal malformation pattern may be helpful not to miss SLOS diagnosis in fetuses at prenatal ultrasound and fetal autopsy

Regulation of glucose and lipid metabolism in health and disease

Glucose and fatty acids are the major sources of energy for human body. Cholesterol, the most abundant sterol in mammals, is a key component of cell membranes although it does not generate ATP. The metabolisms of glucose, fatty acids and cholesterol are often intertwined and regulated. For example, glucose can be converted to fatty acids and cholesterol through de novo lipid biosynthesis pathways. Excessive lipids are secreted in lipoproteins or stored in lipid droplets. The metabolites of glucose and lipids are dynamically transported intercellularly and intracellularly, and then converted to other molecules in specific compartments. The disorders of glucose and lipid metabolism result in severe diseases including cardiovascular disease, diabetes and fatty liver. This review summarizes the major metabolic aspects of glucose and lipid, and their regulations in the context of physiology and diseases.

Cholesterol 24-Hydroxylation by CYP46A1: Benefits of Modulation for Brain Diseases

Cholesterol 24-hydroxylation is the major mechanism for cholesterol removal from the brain and the reaction catalyzed by cytochrome P450 46A1 (CYP46A1), a CNS-specific enzyme. This review describes CYP46A1 in the context of cholesterol homeostasis in the brain and summarizes available experimental data on CYP46A1 association with different neurologic diseases, including the mechanisms by which changes in the CYP46A1 activity in the brain could be beneficial for these diseases. The modulation of CYP46A1 activity by genetic and pharmacologic means is also presented along with a brief synopsis of the two clinical trials that evaluate CYP46A1 as a therapeutic target for Alzheimer's disease as well as Dravet and Lennox-Gastaut syndromes.

Liver Transplant and Improvements in Cholesterol Biosynthesis Defects: A Case Report of Smith-Lemli-Opitz Syndrome

Smith-Lemli-Opitz syndrome is an autosomal recessive metabolic disease characterized by mental retardation and multiple congenital anomalies. The main pathology is the lack of the enzyme 3β-hydroxysterol Δ7-reductase, which is the last enzymatic step in cholesterol synthesis, ending with a low cholesterol level. Cholesterol is vitally important in cell membranes and myelination of the nervous system. The cholesterol level affects many systems of the body, especially the nervous system. The cause of liver involvement in Smith-Lemli-Opitz syndrome is unclear, and many hypotheses have been suggested. Here, we present the early results of a patient with Smith-Lemli-Opitz syndrome who underwent living-donor liver transplant due to cirrhosis. As a result of liver transplant, normal cholesterol levels were shown, as well as improvements in the patient's neurodevelopment and behavior. Early liver transplant may be considered for patients with a defect of cholesterol biosynthesis, even in the absence of cirrhosis, and may be a future treatment option to prevent risks of neurologic deterioration.

Vitamin D levels in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive congenital malformation syndrome caused by mutations in the 7-dehydrocholesterol reductase gene. This inborn error of cholesterol synthesis leads to elevated concentrations of 7-dehydrocholesterol (7-DHC). 7-DHC also serves as the precursor for vitamin D synthesis. Limited data is available on vitamin D levels in individuals with SLOS. Due to elevated concentrations of 7-DHC, we hypothesized that vitamin D status would be abnormal and possibly reach toxic levels in patients with SLOS. Through a retrospective analysis of medical records between 1998 and 2006, we assessed markers of vitamin D and calcium metabolism from 53 pediatric SLOS patients and 867 pediatric patients who were admitted to the NIH Clinical Center (NIHCC) during the same time period. SLOS patients had significantly higher levels of 25(OH)D (48.06 ± 19.53 ng/ml, p < 0.01) across all seasons in comparison to the NIHCC pediatric patients (30.51 ± 16.14 ng/ml). Controlling for season and age of blood draw, 25(OH)D levels were, on average, 15.96 ng/ml (95%CI 13.95-17.90) higher in SLOS patients. Although, mean calcium values for both patient cohorts never exceeded the normal clinical reference range (8.6-10.2 mg/dl), the levels were higher in the SLOS cohort (9.49 ± 0.56 mg/dl, p < 0.01) compared to the NIHCC patients (9.25 ± 0.68 mg/dl). Overall, in comparison to the control cohort, individuals with SLOS have significantly higher concentrations of 25(OH)D that may be explained by elevated concentrations of serum 7-DHC. Despite the elevated vitamin D levels, there was no laboratory or clinical evidence of vitamin D toxicity.

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.

Astrocyte lipid metabolism is critical for synapse development and function in vivo

The brain is considered to be autonomous in lipid synthesis with astrocytes producing lipids far more efficiently than neurons. Accordingly, it is generally assumed that astrocyte-derived lipids are taken up by neurons to support synapse formation and function. Initial confirmation of this assumption has been obtained in cell cultures, but whether astrocyte-derived lipids support synapses in vivo is not known. Here, we address this issue and determined the role of astrocyte lipid metabolism in hippocampal synapse formation and function in vivo. Hippocampal protein expression for the sterol regulatory element-binding protein (SREBP) and its target gene fatty acid synthase (Fasn) was found in astrocytes but not in neurons. Diminishing SREBP activity in astrocytes using mice in which the SREBP cleavage-activating protein (SCAP) was deleted from GFAP-expressing cells resulted in decreased cholesterol and phospholipid secretion by astrocytes. Interestingly, SCAP mutant mice showed more immature synapses, lower presynaptic protein SNAP-25 levels as well as reduced numbers of synaptic vesicles, indicating impaired development of the presynaptic terminal. Accordingly, hippocampal short-term and long-term synaptic plasticity were defective in mutant mice. These findings establish a critical role for astrocyte lipid metabolism in presynaptic terminal development and function in vivo. GLIA 2017;65:670-682.

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.

The Morbid Anatomy of the Dermatologic Genome: An Update for the Third Millennium

Background:

Much progress has been made in recent years in the identification of genes underlying many hereditary skin diseases.

Objective:

To provide an update on the status of the identification of genes involved in hereditary skin disorders and to compare the current standing with that in the last decade.

Methods:

A review of the literature is presented here in a series of lists describing the chromosomal location, specific gene, clinical relevance, and availability of molecular-based genetic tests for each genodermatosis.

Results:

Progress has been made in identifying the genes underlying many disorders of cornification, genodermatoses with malignant potential, bullous disorders, pigmentary disorders, disorders affecting the epidermal appendages and the dermis, and other miscellaneous genodermatoses.

Conclusion:

The great progress made toward the completion of the human gene sequence and the continued efforts of many clinical and molecular scientists to identify disease genes will make diagnosis of hereditary dermatological disorders more precise and allow accurate family counseling as well as possibly leading to more targeted therapies during this millennium.

A placebo-controlled trial of simvastatin therapy in Smith-Lemli-Opitz syndrome

Background

Smith-Lemli-Opitz syndrome (SLOS) is a multiple malformation/cognitive impairment syndrome characterized by the accumulation of 7-dehydrocholesterol (7DHC), a precursor sterol of cholesterol. Simvastatin, an HMG-CoA reductase inhibitor that crosses the blood-brain-barrier, has been proposed for treatment of SLOS based on in vitro and in vivo studies suggesting that simvastatin increases expression of hypomorphic DHCR7 alleles.

Methods

Safety and efficacy of simvastatin therapy in 23 mild to typical SLOS patients was evaluated in a randomized, double-blind, placebo-controlled trial. The cross-over trial consisted of two 12 month treatment phases separated by a 2 month wash-out period.

Results

No safety issues were identified in this study. Plasma dehydrocholesterol levels decreased significantly 8.9 ± 8.4% on placebo to 6.1 ± 5.5% on simvastatin (p<0.005) and we observed a trend toward decreased cerebral spinal fluid dehydrocholesterol levels. A significant improvement (p=0.017, paired t-test) was observed in the Aberrant Behavior Checklist-C Irritability when subjects were on simvastatin.

Conclusions

This paper reports the first randomized, placebo-controlled trial designed to test the safety and efficacy of simvastatin therapy in SLOS. Simvastatin appears to be relatively safe in SLOS patients, improves the serum dehydrocholesterol/total sterol ratio, and significantly improves irritability symptoms in mild to classical SLOS patients.

Investigation of 7-dehydrocholesterol reductase pathway to elucidate off-target prenatal effects of pharmaceuticals: a systematic review

Mendelian diseases contain important biological information regarding developmental effects of gene mutations that can guide drug discovery and toxicity efforts. In this review, we focus on Smith–Lemli–Opitz syndrome (SLOS), a rare Mendelian disease characterized by compound heterozygous mutations in 7-dehydrocholesterol reductase (DHCR7) resulting in severe fetal deformities. We present a compilation of SLOS-inducing DHCR7 mutations and the geographic distribution of those mutations in healthy and diseased populations. We observed that several mutations thought to be disease causing occur in healthy populations, indicating an incomplete understanding of the condition and highlighting new research opportunities. We describe the functional environment around DHCR7, including pharmacological DHCR7 inhibitors and cholesterol and vitamin D synthesis. Using PubMed, we investigated the fetal outcomes following prenatal exposure to DHCR7 modulators. First-trimester exposure to DHCR7 inhibitors resulted in outcomes similar to those of known teratogens (50 vs 48% born-healthy). DHCR7 activity should be considered during drug development and prenatal toxicity assessment.

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.

The p.Phe174Ser mutation is associated with mild forms of Smith Lemli Opitz Syndrome

Background

Smith Lemli Opitz syndrome (SLOS; OMIM #270400) is an autosomal recessive metabolic disorder caused by mutations in the DHCR7 gene. SLOS is characterized by a plethora of abnormalities involving mainly the brain and the genitalia but also the cardiac, skeletal and gastroenteric system, typical dysmorphic facial features, and variable degrees of developmental delay and intellectual disability (ID). SLOS has a broad phenotypic spectrum, ranging from multiple congenital malformation syndrome, to mild developmental delay and minor malformations. A large number of mutations have been described in the DHCR7 gene, with few common mutations accounting for the majority of mutated alleles found in patients and a large number of very rare or even private variants. Due to the wide variety of clinical presentations, diagnosis can be difficult, especially in the milder forms of the disorder. Furthermore, establishing a molecular diagnosis can be complicated by finding variants of unknown clinical significance in such cases.

Case presentation

We report a case of SLOS at the mild end of the clinical spectrum, presenting with bilateral pelvis ectasia, mild dysmorphic features and mild intellectual disability. The case is compound heterozygous for a known pathogenic mutation (c.724C > T, p.Arg242Cys) and a mutation that has only been reported once in a Portuguese patient (c.521 T > C, p.Phe174Ser) whose pathogenicity has not been yet assessed. We compared the two patients carrying the p.Phe174Ser variant and concluded that this variant is associated with mild forms of SLOS.

Conclusion

We report a patient with a mild case of SLOS, highlighting the importance of recognizing subtle anomalies of the genitourinary system, associated with mild dysmorphic features and mild intellectual disability in establishing the diagnosis of mild forms of SLOS. With this report, we confirm the pathogenicity of the p.Phe174Ser variant and we also provide evidence of its association with mild forms of SLOS. This finding further facilitates the establishment of a genotype–phenotype correlation for SLOS. This helps in counselling for this disorder and in predicting therapeutic responses.

Identification of Environmental Quaternary Ammonium Compounds as Direct Inhibitors of Cholesterol Biosynthesis

In this study, we aim to identify environmental molecules that can inhibit cholesterol biosynthesis, potentially leading to the same biochemical defects as observed in cholesterol biosynthesis disorders, which are often characterized by congenital malformations and developmental delay. Using the Distributed Structure-Searchable Toxicity (DSSTox) Database Network developed by EPA, we first carried out in silico screening of environmental molecules that display structures similar to AY9944, a known potent inhibitor of 3β-hydroxysterol-Δ(7)-reductase (DHCR7)-the last step of cholesterol biosynthesis. Molecules that display high similarity to AY9944 were subjected to test in mouse and human neuroblastoma cells for their effectiveness in inhibiting cholesterol biosynthesis by analyzing cholesterol and its precursor using gas chromatography-mass spectrometry. We found that a common disinfectant mixture, benzalkonium chlorides (BACs), exhibits high potency in inhibiting DHCR7, as suggested by greatly elevated levels of the cholesterol precursor, 7-dehydrocholesterol (7-DHC). Subsequent structure-activity studies suggested that the potency of BACs as Dhcr7 inhibitors decrease with the length of their hydrocarbon chain: C10 > C12 ≫ C14 > C16. Real-time qPCR analysis revealed upregulation of the genes related to cholesterol biosynthesis and downregulation of the genes related to cholesterol efflux, suggesting a feedback response to the inhibition. Furthermore, an oxidative metabolite of 7-DHC that was previously identified as a biomarker in vivo was also found in cells exposed to BACs by liquid chromatography-mass spectrometry. Our findings suggest that certain environmental molecules could potently inhibit cholesterol biosynthesis, which could be a new link between environment and developmental disorders.

Perspectives in Pediatric Pathology, Chapter 6. Male Undermasculinization

Normal male development requires three conditions: (1) adequate differentiation of the fetal testis; (2) synthesis and secretion of testicular hormones; and (3) effective action of these hormones on target organs. This requires the combined action of the inhibitory anti-müllerian hormone (AMH, secreted by Sertoli cells) to block the development of the uterus and fallopian tubes from the müllerian duct, together with the trophic stimulus of testosterone (a Leydig cell product), which leads to virilization of the wolffian ducts. Additionally, the development of external genitalia depends on the conversion of testosterone to dihydrotestosterone by the enzyme 5-α-reductase. Failure of any of these mechanisms leads to deficient virilization or the so-called "male pseudohermaphroditism" syndromes.

Disorders of cholesterol metabolism and their unanticipated convergent mechanisms of disease

Cholesterol plays a key role in many cellular processes, and is generated by cells through de novo biosynthesis or acquired from exogenous sources through the uptake of low-density lipoproteins. Cholesterol biosynthesis is a complex, multienzyme-catalyzed pathway involving a series of sequentially acting enzymes. Inherited defects in genes encoding cholesterol biosynthetic enzymes or other regulators of cholesterol homeostasis result in severe metabolic diseases, many of which are rare in the general population and currently without effective therapy. Historically, these diseases have been viewed as discrete disorders, each with its own genetic cause and distinct pathogenic cascades that lead to its specific clinical features. However, studies have recently shown that three of these diseases have an unanticipated mechanistic convergence. This surprising finding is not only shedding light on details of cellular cholesterol homeostasis but also suggesting novel approaches to therapy.

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.

Brothers with Smith-Lemli-Opitz syndrome

Abnormal cholesterol metabolism is the cause of SLOS, with low cholesterol levels and elevated levels of cholesterol precursors thought to contribute to the clinical findings in this syndrome. Management of SLOS involves early intervention with appropriate therapies for identified disabilities, genetic counseling for families, nutritional consultations, educational interventions, and behavioral management. Although no randomized dietary studies have been conducted, cholesterol supplementation continues to be a common recommendation for persons with SLOS, because it may result in clinical improvement and has few adverse effects (Nowaczyk, 2013). Even with early detection and treatment (e.g., sibling B in this case report), persons with SLOS often have significant behavioral issues and cognitive and developmental delays that require a team approach by parents, educators, specialists, and primary care providers.

Sleep and sleep disorders in rare hereditary diseases: a reminder for the pediatrician, pediatric and adult neurologist, general practitioner, and sleep specialist

Although sleep abnormalities in general and sleep-related breathing disorders (SBD) in particular are quite common in healthy children; their presence is notably under-recognized. Impaired sleep is a frequent problem in subjects with inborn errors of metabolism as well as in a variety of genetic disorders; however, they are commonly either missed or underestimated. Moreover, the complex clinical presentation and the frequently life-threatening symptoms are so overwhelming that sleep and its quality may be easily dismissed. Even centers, which specialize in rare genetic-metabolic disorders, are expected to see only few patients with a particular syndrome, a fact that significantly contributes to the under-diagnosis and treatment of impaired sleep in this particular population. Many of those patients suffer from reduced life quality associated with a variable degree of cognitive impairment, which may be worsened by poor sleep and abnormal ventilation during sleep, abnormalities which can be alleviated by proper treatment. Even when such problems are detected, there is a paucity of publications on sleep and breathing characteristics of such patients that the treating physician can refer to. In the present paper, we provide an overview of sleep and breathing characteristics in a number of rare genetic–metabolic disorders with the hope that it will serve as a reminder for the medical professional to look for possible impaired sleep and SBD in their patients and when present to apply the appropriate evaluation and treatment options.

Antioxidant supplementation ameliorates molecular deficits in Smith-Lemli-Opitz syndrome

BACKGROUND

Smith-Lemli-Opitz syndrome (SLOS) is an inborn error of cholesterol biosynthesis characterized by diminished cholesterol and increased 7-dehydrocholesterol (7-DHC) levels. 7-Dehydrocholesterol is highly reactive, giving rise to biologically active oxysterols.

METHODS

7-DHC-derived oxysterols were measured in fibroblasts from SLOS patients and an in vivo SLOS rodent model using high-performance liquid chromatography tandem mass spectrometry. Expression of lipid biosynthesis genes was ascertained by quantitative polymerase chain reaction and Western blot. The effects of an antioxidant mixture of vitamin A, coenzyme Q10, vitamin C, and vitamin E were evaluated for their potential to reduce formation of 7-DHC oxysterols in fibroblast from SLOS patients. Finally, the effect of maternal feeding of vitamin E enriched diet was ascertained in the brain and liver of newborn SLOS mice.

RESULTS

In cultured human SLOS fibroblasts, the antioxidant mixture led to decreased levels of the 7-DHC-derived oxysterol, 3β,5α-dihydroxycholest-7-en-6-one. Furthermore, gene expression changes in SLOS human fibroblasts were normalized with antioxidant treatment. The active ingredient appeared to be vitamin E, as even at low concentrations, it significantly decreased 3β,5α-dihydroxycholest-7-en-6-one levels. In addition, analyzing a mouse SLOS model revealed that feeding a vitamin E enriched diet to pregnant female mice led to a decrease in oxysterol formation in brain and liver tissues of the newborn Dhcr7-knockout pups.

CONCLUSIONS

Considering the adverse effects of 7-DHC-derived oxysterols in neuronal and glial cultures and the positive effects of antioxidants in patient cell cultures and the transgenic mouse model, we believe that preventing formation of 7-DHC oxysterols is critical for countering the detrimental effects of DHCR7 mutations.

Role of microsomal steroid hydroxylases in Δ7-steroid biosynthesis

CYP17 (steroid 17α-hydroxylase/17,20-lyase) is a key enzyme in steroid hormone biosynthesis. It catalyzes two independent reactions at the same active center and has a unique ability to differentiate Δ(4)-steroids and Δ(5)-steroids in the 17,20-lyase reaction. The present work presents a complex experimental analysis of the role of CYP17 in the metabolism of 7-dehydrosteroids. The data indicate the existence of a possible alternative pathway of steroid hormone biosynthesis using 7-dehydrosteroids. The major reaction products of CYP17 catalyzed hydroxylation of 7-dehydropregnenolone have been identified. Catalytic activity of CYP17 from different species with 7-dehydropregnenolone has been estimated. It is shown that CYP21 cannot use Δ(5)-Δ(7) steroids as a substrate.

Relation between biomarkers and clinical severity in patients with Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS), a multiple congenital anomaly with severe mental retardation, is caused by decreased activity of 7-dehydrocholesterol reductase. Fifteen Hungarian patients were diagnosed with SLOS on the basis of clinical symptoms, serum cholesterol, 7-dehydrocholesterol, and molecular genetic testing. Their age at the time of diagnosis in mild SLOS (n = 4, clinical score <20) was 0.5-18 years, cholesterol was 2.37 ± 0.8 mmol/L, and 7DHC was 0.38 ± 0.14 mmol/L. In the group of typical SLOS (n = 7, score 20-50), the diagnosis was set up earlier (age of 0.1-7 years); t-cholesterol was 1.47 ± 0.7 mmol/L, and 7DHC was 0.53 ± 0.20 mmol/L. Patients with severe SLOS (n = 4, clinical score > 50) died as newborns and had the lowest t-cholesterol (0.66 ± 0.27 mmol/L), and 7DHC was 0.47 ± 0.14 mmol/L. Correlation coefficient with clinical severity was 0.74 for initial t-cholesterol and 0.669 for Cho/7DHC. Statistically significant difference was between the initial t-cholesterol of mild and severe SLOS (p = 0.01), and between the Cho/7DHC ratios of groups (p = 0.004). In severe SLOS, the percentage of α-lipoprotein was significantly lower than in typical (p = 0.003) and mild SLOS (p = 0.004). Although serum albumin, total bilirubin, and hemostasis parameters remained in the reference range during cholesterol supplementation (n = 10) combined with statin therapy (n = 9), increase of aspartate aminotransferase and alanine aminotransferase in 50 % of the patients probably refers to a reversible alteration of liver function; therefore, statin therapy was suspended.

CONCLUSION

life expectancy is fundamentally determined by the initial t-cholesterol, but dehydrocholesterol and α-lipoprotein have prognostic value. Accumulation of hepatotoxic DHC may inhibit the synthesis of α-lipoproteins, decreasing the reverse cholesterol transport. During statin therapy, we suggest monitoring of lipid parameters and liver function.

Behavioral and serotonergic response changes in the Dhcr7-HET mouse model of Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a developmental disorder resulting from mutations to the Dhcr7 gene, which is required for cholesterol synthesis. Patients with SLOS typically exhibit a number of severe behavioral deficits and many are diagnosed with autistic spectrum disorder. Although the molecular pathophysiology underlying behavioral changes in SLOS and autism spectrum disorders is poorly understood, there is evidence for the involvement of the serotonergic system in SLOS and autism in general. Behavioral testing was undertaken to ascertain the basal behavioral differences between Dhcr7-heterozygous (HET) and wild-type control mice and explore the utility of a Dhcr7-HET mouse line in the development of new treatments for this disorder. Dhcr7-HET mice did not differ from wild-type control mice on basic measures of locomotor activity, anxiety and neuromuscular ability. However, female Dhcr7-HET mice at 6 months of age or older were significantly more likely to win on the social dominance tube test against an unfamiliar mouse. Pharmacological testing, using the 5-HT2A agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), showed increased head-twitch response in Dhcr7-HET mice, which was apparent from 6 months of age. No differences were found between the genotypes in testing for 5-HT1A agonist 8-OH-DPAT-induced hypothermia. These data indicate an underlying dysfunction of the 5-HT2A receptors in Dhcr7-HET mice that warrants further investigation to establish how this may relate to behavioral disturbances in human patients carrying Dhcr7 mutations.

Challenging behavior in Smith-Lemli-Opitz syndrome: initial test of biobehavioral influences

OBJECTIVE

To study challenging behavior (destruction, aggression, self-injury, stereotypy) in children with Smith-Lemli-Opitz syndrome (SLOS) using a biobehavioral model that helps distinguish biological from socially mediated variables influencing the behavior.

BACKGROUND

SLOS is an autosomal-recessive syndrome of multiple malformations and intellectual disability resulting from a genetic error in cholesterol synthesis in all cells and tissues, including brain. The exact cause of the challenging behavior in SLOS is unclear, but defective brain cholesterol synthesis may contribute. Because the precise genetic and biochemical etiology of SLOS is known, this disorder is a good model for studying biological causes of challenging behavior.

METHOD

In a preliminary application of a biobehavioral model, we studied the association between cholesterol levels (as a biochemical indicator of disease severity) and behavior subtype ("biological" vs "learned") in 13 children with SLOS. Parents completed a questionnaire that categorized challenging behavior as influenced primarily by social or nonsocial (thus, presumably biological) factors.

RESULTS

The severity of the cholesterol synthesis defect correlated significantly with behavior subtype classification for 1 of 2 challenging behaviors. Greater severity of the cholesterol synthesis defect was associated with behavior being classified as primarily influenced by biological factors.

CONCLUSION

The interplay between challenging behavior and defective cholesterol synthesis in SLOS may help explain biological influences on the behavior. Our findings have implications for research on the effectiveness of behavioral and medical treatments for behavioral difficulties in SLOS and other neurodevelopmental disorders.

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.

A physiologically based in silico kinetic model predicting plasma cholesterol concentrations in humans

Increased plasma cholesterol concentration is associated with increased risk of cardiovascular disease. This study describes the development, validation, and analysis of a physiologically based kinetic (PBK) model for the prediction of plasma cholesterol concentrations in humans. This model was directly adapted from a PBK model for mice by incorporation of the reaction catalyzed by cholesterol ester transfer protein and contained 21 biochemical reactions and eight different cholesterol pools. The model was calibrated using published data for humans and validated by comparing model predictions on plasma cholesterol levels of subjects with 10 different genetic mutations (including familial hypercholesterolemia and Smith-Lemli-Opitz syndrome) with experimental data. Average model predictions on total cholesterol were accurate within 36% of the experimental data, which was within the experimental margin. Sensitivity analysis of the model indicated that the HDL cholesterol (HDL-C) concentration was mainly dependent on hepatic transport of cholesterol to HDL, cholesterol ester transfer from HDL to non-HDL, and hepatic uptake of cholesterol from non-HDL-C. Thus, the presented PBK model is a valid tool to predict the effect of genetic mutations on cholesterol concentrations, opening the way for future studies on the effect of different drugs on cholesterol levels in various subpopulations in silico.

No evidence for mevalonate shunting in moderately affected children with Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is caused by a genetic deficiency in 7-dehydrocholesterol (7-DHC) reductase (EC 1.3.1.21), the last enzyme of the cholesterol synthetic pathway. In SLOS, plasma cholesterol concentration is reduced and immediate precursor concentration (7-DHC) is elevated. Surprisingly, total sterol synthesis is reduced but HMG-CoA reductase activity, a rate-limiting enzyme in cholesterol synthesis is unaltered as judged by normal urinary excretion of mevalonic acid (MVA) (Pappu et al. J Lipid Res 43:1661-1669, 2002). These findings raise the possibility of increased diversion of MVA into the MVA shunt pathway away from sterol synthesis, by activation of the shunt pathway enzymes. To test this hypothesis, we measured the urinary excretion of 3-methylglutaconic acid (U-3MGC), a by-product of the shunt pathway, in 19 mildly to moderately severely affected SLOS subjects (ten males, nine females) receiving either a cholesterol-free or a high cholesterol diet, and in 20 age- and sex-matched controls. U-3MGC was similar in SLOS and controls, and was unaffected by dietary cholesterol intake. Further, no change in U-3MGC was observed in a subset of SLOS subjects (n = 9) receiving simvastatin. In contrast, U-MVA was reduced by cholesterol supplementation (~54%, p < 0.05) and by simvastatin (~50%, p < 0.04). There was no correlation between U-3MGC and either plasma sterol concentrations, urinary isoprenoids, or the subjects' clinical severity score. However U-3MGC was inversely correlated with age (p < 0.04) and body weight (p < 0.02), and higher in females than in males (~65%, p < 0.025). The data show that DHCR7 deficiency does not result in 3MGC accumulation in SLOS and suggest that the MVA shunt pathway is not activated in patients with the condition.

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.

Growth charts for individuals with Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a rare multiple congenital anomaly neurodevelopmental syndrome of impaired cholesterol synthesis. Growth restriction and developmental delay are very common clinical manifestations of SLOS. The degree, etiology, and consequences of growth restriction in SLOS remain an area of limited knowledge to the scientific community. There have been no studies describing the growth parameters and providing reference growth charts for individuals with SLOS. Our longitudinal data from 78 patients between the ages of 0.1 and 16 years with SLOS show a growth restriction of about two standard deviations below the Centers for Disease Control (CDC) norms for age. This study represents comprehensive anthropometric data from the largest cohort available, and proposes growth charts for widespread use in the management and study of individuals with SLOS.