Dehydrosteroid measurements in maternal urine or serum for the prenatal diagnosis of Smith–Lemli–Opitz syndrome (SLOS)

Biological Effects of CYP11A1-Derived Vitamin D and Lumisterol Metabolites in the Skin

Novel pathways of vitamin D3, lumisterol 3 (L3), and tachysterol 3 (T3) activation have been discovered, initiated by CYP11A1 and/or CYP27A1 in the case of L3 and T3. The resulting hydroxymetabolites enhance protection of skin against DNA damage and oxidative stress; stimulate keratinocyte differentiation; exert anti-inflammatory, antifibrogenic, and anticancer activities; and inhibit cell proliferation in a structure-dependent manner. They act on nuclear receptors, including vitamin D receptor, aryl hydrocarbon receptor, LXRα/β, RAR-related orphan receptor α/γ, and peroxisome proliferator-activated receptor-γ, with selectivity defined by their core structure and distribution of hydroxyl groups. They can activate NRF2 and p53 and inhibit NF-κB, IL-17, Shh, and Wnt/β-catenin signaling. Thus, they protect skin integrity and physiology.

Selective ability of rat 7-Dehydrocholesterol reductase (DHCR7) to act on some 7-Dehydrocholesterol metabolites but not on lumisterol metabolites

7-Dehydrocholesterol reductase (DHCR7) catalyses the final step of cholesterol biosynthesis in the Kandutsch-Russel pathway, the reduction of 7-dehydrocholesterol (7DHC) to cholesterol. 7DHC can be acted on by a range of other enzymes including CYP27A1 and CYP11A1, as well as by UVB radiation, producing a number of derivatives including hydroxy-metabolites, some of which retain the C7-C8 double bond and are biologically active. These metabolites include lumisterol (L3) which is a stereoisomer of 7DHC produced in the skin by UVB radiation of 7DHC, as well as vitamin D3. The aim of this study was to test whether these metabolites could act as substrates or inhibitors of DHCR7 in rat liver microsomes. To initially screen the ability of these metabolites to interact with the active site of DHCR7, their ability to inhibit the conversion of ergosterol to brassicasterol was measured. Sterols that significantly inhibited this reaction included 7DHC (as expected), 20S(OH)7DHC, 27(OH)DHC, 8DHC, 20S(OH)L3 and 22(OH)L3 but not 7-dehydropregnenolone (7DHP), 25(OH)7DHC, L3 or vitamin D3 and its hydroxyderivatives. Sterols that inhibited ergosterol reduction were directly tested as substrates for DHCR7. 20S(OH)7DHC, 27(OH)DHC and 7-dehydrodesmosterol were confirmed to be substrates, giving the expected product with the C7-C8 double bond removed. No products were observed from 8DHC or 20S(OH)L3 indicating that these sterols are inhibitors and not substrates of DHCR7. The resistance of lumisterol and 7DHP to reduction by DHCR7 in cells will permit other enzymes to metabolise these sterols to their active forms retaining the C7-C8 double bond, conferring specificity to their biological actions.

Fetal cardiac abnormalities: Genetic etiologies to be considered

Congenital heart diseases are a common prenatal finding. The prenatal identification of an associated genetic syndrome or a major extracardiac anomaly helps to understand the etiopathogenic diagnosis. Besides, it also assesses the prognosis, management, and familial recurrence risk while strongly influences parental decision to choose termination of pregnancy or postnatal care. This review article describes the most common genetic diagnoses associated with a prenatal finding of a congenital heart disease and a suggested diagnostic process.

GC/MS in Recent Years Has Defined the Normal and Clinically Disordered Steroidome: Will It Soon Be Surpassed by LC/Tandem MS in This Role?

Gas chromatography/mass spectrometry (GC/MS) has been used for steroid analysis since the 1960s. The advent of protective derivatization, capillary columns, and inexpensive electron ionization bench-top single quadrupole soon made it the method of choice for studying disorders of steroid synthesis and metabolism. However, the lengthy sample workup prevented GC/MS from becoming routine for steroid hormone measurement, which was dominated by radioimmunoassay. It was the emergence of liquid chromatography/tandem MS (LC/MS/MS) that sparked a renewed interest in GC/MS for the multicomponent analysis of steroids. GC/MS is excellent at providing an integrated picture of a person's steroid metabolome, or steroidome, as we term it. We review the recent work on newly described disorders and discuss the technical advances such as GC coupling to triple quadrupole and ion trap analyzers, two-dimensional GC/MS, and alternative ionization and detection systems such as atmospheric pressure chemical ionization (APCI) and time of flight. We believe that no novel GC/MS-based technique has the power of GC(electron ionization)/MS/MS as a "discovery tool," although APCI might provide ultimate sensitivity, which might be required in tissue steroidomics. Finally, we discuss the role of LC/MS/MS in steroidomics. This remains a challenge but offers shorter analysis times and advantages in the detection and discovery of steroids with a known structure. We describe recent advances in LC/MS steroidomics of hydrolyzed and intact steroid conjugates and suggest the technique is catching up with GC/MS in this area. However, in the end, both techniques will likely remain complementary and both should be available in advanced analytical laboratories.

SULFATION PATHWAYS: Alternate steroid sulfation pathways targeted by LC-MS/MS analysis of disulfates: application to prenatal diagnosis of steroid synthesis disorders

The steroid disulfates (aka bis-sulfates) are a significant but minor fraction of the urinary steroid metabolome that have not been widely studied because major components are not hydrolyzed by the commercial sulfatases commonly used in steroid metabolomics. In early studies, conjugate fractionation followed by hydrolysis using acidified solvent (solvolysis) was used for the indirect detection of this fraction by GC-MS. This paper describes the application of a specific LC-MS/MS method for the direct identification of disulfates in urine, and their use as markers for the prenatal diagnosis of disorders causing reduced estriol production: STSD (steroid sulfatase deficiency), SLOS (Smith-Lemli-Opitz syndrome) and PORD (P450 oxidoreductase deficiency). Disulfates were detected by monitoring a constant ion loss (CIL) from the molecular di-anion. While focused on disulfates, our methodology included an analysis of intact steroid glucuronides and monosulfates because steroidogenic disorder diagnosis usually requires an examination of the complete steroid profile. In the disorders studied, a few individual steroids (as disulfates) were found particularly informative: pregn-5-ene-3β,20S-diol, pregn-5-ene-3β,21-diol (STSD, neonatal PORD) and 5α-pregnane-3β,20S-diol (pregnancy PORD). Authentic steroid disulfates were synthesized for use in this study as aid to characterization. Tentative identification of 5ξ-pregn-7-ene-3ξ,20S-diol and 5ξ-pregn-7-ene-3ξ,17,20S-triol disulfates was also obtained in samples from SLOS affected pregnancies. Seven ratios between the detected metabolites were applied to distinguish the three selected disorders from control samples. Our results show the potential of the direct detection of steroid conjugates in the diagnosis of pathologies related with steroid biosynthesis.

GC/MS in Recent Years Has Defined the Normal and Clinically Disordered Steroidome: Will It Soon Be Surpassed by LC/Tandem MS in This Role?

Gas chromatography/mass spectrometry (GC/MS) has been used for steroid analysis since the 1960s. The advent of protective derivatization, capillary columns, and inexpensive electron ionization bench-top single quadrupole soon made it the method of choice for studying disorders of steroid synthesis and metabolism. However, the lengthy sample workup prevented GC/MS from becoming routine for steroid hormone measurement, which was dominated by radioimmunoassay. It was the emergence of liquid chromatography/tandem MS (LC/MS/MS) that sparked a renewed interest in GC/MS for the multicomponent analysis of steroids. GC/MS is excellent at providing an integrated picture of a person's steroid metabolome, or steroidome, as we term it. We review the recent work on newly described disorders and discuss the technical advances such as GC coupling to triple quadrupole and ion trap analyzers, two-dimensional GC/MS, and alternative ionization and detection systems such as atmospheric pressure chemical ionization (APCI) and time of flight. We believe that no novel GC/MS-based technique has the power of GC(electron ionization)/MS/MS as a “discovery tool,” although APCI might provide ultimate sensitivity, which might be required in tissue steroidomics. Finally, we discuss the role of LC/MS/MS in steroidomics. This remains a challenge but offers shorter analysis times and advantages in the detection and discovery of steroids with a known structure. We describe recent advances in LC/MS steroidomics of hydrolyzed and intact steroid conjugates and suggest the technique is catching up with GC/MS in this area. However, in the end, both techniques will likely remain complementary and both should be available in advanced analytical laboratories.

Targeting human urinary metabolome by LC-MS/MS: a review

Urine is a biological matrix that contains hundreds of metabolic end products which constitute the urinary metabolome. The development and advances on LC-MS/MS have revolutionized the analytical study of biomolecules by enabling their accurate identification and quantification in an unprecedented manner. Nowadays, LC-MS/MS is helping to unveil the complexity of urine metabolome, and the results obtained have multiple biomedical applications. This review focuses on the targeted LC-MS/MS analysis of the urine metabolome. In the first part, we describe general considerations (from sample collection to quantitation) required for a proper targeted metabolic analysis. In the second part, we address the urinary analysis and recent applications of four relevant families: amino acids, catecholamines, lipids and steroids.

The utility of ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS) for clinically relevant steroid analysis

Liquid chromatography tandem mass spectrometry (LC-MS/MS) assays are considered the reference standard for serum steroid hormone analyses, while full urinary steroid profiles are only achievable by gas chromatography (GC-MS). Both LC-MS/MS and GC-MS have well documented strengths and limitations. Recently, commercial ultra-high performance supercritical fluid chromatography-tandem mass spectrometry (UHPSFC-MS/MS) systems have been developed. These systems combine the resolution of GC with the high-throughput capabilities of UHPLC. Uptake of this new technology into research and clinical labs has been slow, possibly due to the perceived increase in complexity. Here we therefore present fundamental principles of UHPSFC-MS/MS and the likely applications for this technology in the clinical research setting, while commenting on potential hurdles based on our experience to date.

Delivery of the 7-dehydrocholesterol reductase gene to the central nervous system using adeno-associated virus vector in a mouse model of Smith-Lemli-Opitz Syndrome

Smith Lemli Opitz syndrome (SLOS) is an inherited malformation and mental retardation metabolic disorder with no cure. Mutations in the last enzyme of the cholesterol biosynthetic pathway, 7-dehydrocholesterol reductase (DHCR7), lead to cholesterol insufficiency and accumulation of its dehyrdocholesterol precursors, and contribute to its pathogenesis. The central nervous system (CNS) constitutes a major pathophysiological component of this disorder and remains unamenable to dietary cholesterol therapy due to the impenetrability of the blood brain barrier (BBB). The goal of this study was to restore sterol homeostasis in the CNS. To bypass the BBB, gene therapy using an adeno-associated virus (AAV-8) vector carrying a functional copy of the DHCR7 gene was administered by intrathecal (IT) injection directly into the cerebrospinal fluid of newborn mice. Two months post-treatment, vector DNA and DHCR7 expression was observed in the brain and a corresponding improvement of sterol levels seen in the brain and spinal cord. Interestingly, sterol levels in the peripheral nervous system also showed a similar improvement. This study shows that IT gene therapy can have a positive biochemical effect on sterol homeostasis in the central and peripheral nervous systems in a SLOS animal model. A single dose delivered three days after birth had a sustained effect into adulthood, eight weeks post-treatment. These observations pave the way for further studies to understand the effect of biochemical improvement of sterol levels on neuronal function, to provide a greater understanding of neuronal cholesterol homeostasis, and to develop potential therapies.

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.

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.

Biochemical and Physiological Improvement in a Mouse Model of Smith-Lemli-Opitz Syndrome (SLOS) Following Gene Transfer with AAV Vectors

Smith-Lemli-Opitz syndrome (SLOS) is an inborn error of cholesterol synthesis resulting from a defect in 7-dehydrocholesterol reductase (DHCR7), the enzyme that produces cholesterol from its immediate precursor 7-dehydrocholesterol. Current therapy employing dietary cholesterol is inadequate. As SLOS is caused by a defect in a single gene, restoring enzyme functionality through gene therapy may be a direct approach for treating this debilitating disorder. In the present study, we first packaged a human DHCR7 construct into adeno-associated virus (AAV) vectors having either type-2 (AAV2) or type-8 (AAV2/8) capsid, and administered treatment to juvenile mice. While a positive response (assessed by increases in serum and liver cholesterol) was seen in both groups, the improvement was greater in the AAV2/8-DHCR7 treated mice. Newborn mice were then treated with AAV2/8-DHCR7 and these mice, compared to mice treated as juveniles, showed higher DHCR7 mRNA expression in liver and a greater improvement in serum and liver cholesterol levels. Systemic treatment did not affect brain cholesterol in any of the experimental groups. Both juvenile and newborn treatments with AAV2/8-DHCR7 resulted in increased rates of weight gain indicating that gene transfer had a positive physiological effect.

Prenatal presentation and diagnostic evaluation of suspected Smith-Lemli-Opitz (RSH) syndrome

Smith-Lemli-Opitz (SLOS), or RSH syndrome, is an autosomal recessive deficiency of 7-dehydrocholesterol reductase (DHCR7) resulting in an accumulation of 7- and 8-dehydrocholesterol (7- and 8-DHC) in tissues and body fluids. At birth patients have variable malformations of CNS, heart, kidney, genitalia, and limbs, which may be life-limiting. In later course, psychomotor and mental retardation and behavior abnormalities become evident. Prenatally SLOS can be suspected on the basis of malformations and intrauterine growth retardation (IUGR) in prenatal ultrasonography and reduced maternal free estriol in serum. The diagnosis is confirmed by sterol analysis in a chorionic villus biopsy or amniotic fluid (AF). In this study, we evaluated the predictive value of the above mentioned criteria in combination with family history by quantification of sterols in AF in pregnancies with either a family history, ultrasonographical abnormalities typical for SLOS, or reduced maternal serum unconjugated estriol (MSuE3). The relative frequency of SLOS in fetuses with an affected sibling was 0.23, as to be expected for an autosomal recessive disease. The probability for SLOS was <0.6% when neither an affected sib nor more than one typical SLOS malformation was present. For safety reasons and for cost-effectiveness we recommend careful evaluation of history, MSuE3, and clinical presentation before determining sterols in AF.

Prenatal diagnosis of congenital adrenal hyperplasia caused by P450 oxidoreductase deficiency

CONTEXT

Mutations in the electron donor enzyme P450 oxidoreductase (POR) result in congenital adrenal hyperplasia with apparent combined 17α-hydroxylase/17,20 lyase and 21-hydroxylase deficiencies, also termed P450 oxidoreductase deficiency (PORD). Major clinical features present in PORD are disordered sex development in affected individuals of both sexes, glucocorticoid deficiency, and multiple skeletal malformations.

OBJECTIVE

The objective of the study was to establish a noninvasive approach to prenatal diagnosis of PORD including assessment of malformation severity to facilitate optimized prenatal diagnosis and timely treatment.

DESIGN

We analyzed 20 pregnancies with children homozygous or compound heterozygous for disease-causing POR mutations and 1 pregnancy with a child carrying a heterozygous POR mutation by recording clinical and biochemical presentations and fetal ultrasound findings. In 4 of the pregnancies (3 homozygous and 1 heterozygous for disease-causing POR mutations), prenatal analysis of steroid metabolite excretion in maternal urine was carried out by gas chromatography/mass spectrometry during gestational weeks 11-23.

RESULTS

Pregnancy complications in our cohort included maternal virilization (6 of 20) with onset in the second trimester. Seven pregnant women presented with low unconjugated estriol at prenatal screening (triple or quadruple antenatal screening test). Overt dysmorphic features were noted in 19 of the 20 babies at birth but observed in only 5 by prenatal ultrasound. These 5 had the most severe malformation phenotypes and poor outcome, whereas the other babies showed normal development. Steroid profiling of maternal urine revealed significantly increased steroids of fetal origin, namely the pregnenolone metabolite epiallopregnanediol and the androgen metabolite androsterone, with concomitant low values for estriol. Diagnostic steroid ratios conclusively indicated PORD as early as gestational week 12. In the heterozygous pregnancy, steroid ratios were only slightly elevated and estriol excretion was normal.

CONCLUSION

Prenatal diagnosis in PORD is readily established via urinary steroid metabolite analysis of maternal urine. Visible malformations at prenatal ultrasound predict a severe malformation phenotype.

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.

Role of a disordered steroid metabolome in the elucidation of sterol and steroid biosynthesis

In 1937 Butler and Marrian found large amounts of the steroid pregnanetriol in urine from a patient with the adrenogenital syndrome, a virilizing condition known to be caused by compromised adrenal secretion even in this pre-cortisol era. This introduced the concept of the study of altered excretion of metabolites as an in vivo tool for understanding sterol and steroid biosynthesis. This approach is still viable and has experienced renewed significance as the field of metabolomics. From the first cyclized sterol lanosterol to the most downstream product estradiol, there are probably greater than 30 steps. Based on a distinctive metabolome clinical disorders have now been attributed to about seven post-squalene cholesterol (C) biosynthetic steps and around 15 en-route to steroid hormones or needed for further metabolism of such hormones. Forty years ago it was widely perceived that the principal steroid biosynthetic defects were known but interest rekindled as novel metabolomes were documented. In his career this investigator has been involved in the study of many steroid disorders, the two most recent being P450 oxidoreductase deficiency and apparent cortisone reductase deficiency. These are of interest as they are due not to mutations in the primary catalytic enzymes of steroidogenesis but in ancillary enzymes needed for co-factor oxido-reduction A third focus of this researcher is Smith-Lemli-Opitz syndrome (SLOS), a cholesterol synthesis disorder caused by 7-dehydrocholesterol reductase mutations. The late George Schroepfer, in whose honor this article has been written, contributed greatly to defining the sterol metabolome of this condition. Defining the cause of clinically severe disorders can lead to improved treatment options. We are now involved in murine gene therapy studies for SLOS which, if successful could in the future offer an alternative therapy for this severe condition.

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.

Prevalence of steroid sulfatase deficiency in California according to race and ethnicity

OBJECTIVE

Estimate steroid sulfatase deficiency (STSD) prevalence among California's racial/ethnic groups using data from a previous study focused on prenatal detection of Smith-Lemli-Opitz syndrome (SLOS). SLOS and STSD both have low maternal serum unconjugated estriol (uE3) levels.

METHODS

Prevalence was estimated using three steps: listing clinically identified cases; modeling STSD frequency at three uE3 intervals using diagnostic urine steroid measurements; applying this model to determine frequency in pregnancies not providing urine.

RESULTS

Overall, 2151 of 777 088 pregnancies (0.28%) were screen positive; 1379 of these were explained and excluded. Fifty-four cases were diagnosed clinically among 707 remaining pregnancies with a male fetus. Urine steroid testing identified 74 additional STSD cases: 66 (89.2%) at uE3 values < 0.15 MoM, 8 (10.8%) at 0.15-0.20 MoM, and 0 (0%) at > 0.20 MoM. Modeling estimated 107.5 STSD cases among 370 pregnancies without urine samples. In males, STSD prevalence was highest among non-Hispanic Whites (1:1230) compared to Hispanics (1:1620) and Asians (1:1790), but differences were not significant. No STSD pregnancies were found among 65 screen positive Black women.

CONCLUSION

The overall prevalence estimate of 1:1500 males is consistent with published estimates and is reasonable for counseling, except among Black pregnancies where no reliable estimate could be made.

Increasing cholesterol synthesis in 7-dehydrosterol reductase (DHCR7) deficient mouse models through gene transfer

Smith-Lemli-Opitz syndrome (SLOS) is caused by deficiency in the terminal step of cholesterol biosynthesis: the conversion of 7-dehydrocholesterol (7DHC) to cholesterol (C), catalyzed by 7-dehydrocholesterol reductase (DHCR7). This disorder exhibits several phenotypic traits including dysmorphia and mental retardation with a broad range of severity. There are few proven treatment options. That most commonly used is a high cholesterol diet that seems to enhance the quality of life and improve behavioral characteristics of patients, although these positive effects are controversial. The goal of our study was to investigate the possibility of restoring DHCR7 activity by gene transfer. We constructed an adeno-associated virus (AAV) vector containing the DHCR7 gene. After we infused this vector into affected mice, the introduced DHCR7 gene could be identified in liver, mRNA was expressed and a functional enzyme was produced. Evidence of functionality came from the ability to partially normalize the serum ratio of 7DHC/C in treated animals, apparently by increasing cholesterol production with concomitant decrease in 7DHC precursor. By 5 weeks after treatment the mean ratio (for 7 animals) had fallen to 0.05 while the ratio for untreated littermate controls had risen to 0.14. This provides proof of principle that gene transfer can ameliorate the genetic defect causing SLOS and provides a new experimental tool for studying the pathogenesis of this disease. If effective in humans, it might also offer a possible alternative to exogenous cholesterol therapy. However, it would not offer a complete cure for the disorder as many of the negative implications of defective synthesis are already established during prenatal development.

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.

Gas chromatography/mass spectrometry (GC/MS) remains a pre-eminent discovery tool in clinical steroid investigations even in the era of fast liquid chromatography tandem mass spectrometry (LC/MS/MS)

Liquid chromatography tandem mass spectrometry (LC/MS/MS) is replacing classical methods for steroid hormone analysis. It requires small sample volumes and has given rise to improved specificity and short analysis times. Its growth has been fueled by criticism of the validity of steroid analysis by older techniques, testosterone measurements being a prime example. While this approach is the gold-standard for measurement of individual steroids, and panels of such compounds, LC/MS/MS is of limited use in defining novel metabolomes. GC/MS, in contrast, is unsuited to rapid high-sensitivity analysis of specific compounds, but remains the most powerful discovery tool for defining steroid disorder metabolomes. Since the 1930s almost all inborn errors in steroidogenesis have been first defined through their urinary steroid excretion. In the last 30 years, this has been exclusively carried out by GC/MS and has defined conditions such as AME syndrome, glucocorticoid remediable aldosteronism (GRA) and Smith-Lemli-Opitz syndrome. Our recent foci have been on P450 oxidoreductase deficiency (ORD) and apparent cortisone reductase deficiency (ACRD). In contrast to LC/MS/MS methodology, a particular benefit of GC/MS is its non-selective nature; a scanned run will contain every steroid excreted, providing an integrated picture of an individual's metabolome. The "Achilles heel" of clinical GC/MS profiling may be data presentation. There is lack of familiarity with the multiple hormone metabolites excreted and diagnostic data are difficult for endocrinologists to comprehend. While several conditions are defined by the absolute concentration of steroid metabolites, many are readily diagnosed by ratios between steroid metabolites (precursor metabolite/product metabolite). Our work has led us to develop a simplified graphical representation of quantitative urinary steroid hormone profiles and diagnostic ratios.

Steroid production and excretion by the pregnant mouse, particularly in relation to pregnancies with fetuses deficient in Delta7-sterol reductase (Dhcr7), the enzyme associated with Smith-Lemli-Opitz syndrome

This study has shown that the mouse has a great increase in steroid production during pregnancy in similar fashion to the human. Many steroids were provisionally identified in maternal urine of the wild-type mouse. The major progesterone metabolites appear to be hydroxylated pregnanolones, particularly with hydroxyl groups in the 16alpha position. Rather than estriol being the major end-product of feto-placental steroid synthesis as in the human, the pregnant mouse produces and excretes large amounts of androgen metabolites, ranging in polarity from androstanetriols to androstanepentols. These steroids have 15alpha- or 18-hydroxyl groups with additional hydroxylation at uncharacterized positions. From metabolite data the peak of pregnancy progesterone production appears to be between 7.5 and 14.5 gestational days, while for C(19) metabolites peak excretion is later. The starting-point of the studies was to study pregnancy steroid production by a mouse model for Smith-Lemli-Opitz syndrome, 7-dehydrosterol reductase (DHCR7) deficiency. In human pregnancies with DHCR7 deficient fetuses large amounts of 7- and 8-dehydrosteroids are excreted, products secondary to high fetal 7- and 8-dehydrocholesterol (DHC) accumulation. This agrees with existing evidence that human feto-placental steroid synthesis utilizes little maternal cholesterol as precursor. In contrast, this study has shown that pregnant mice carrying dhcr7 deficient fetuses with relatively high DHC production had essentially undetectable maternal excretions of steroids with Delta(7)- and Delta(8)-unsaturation. As mutant mouse mothers have essentially normal cholesterol production (little or no DHC build-up), this suggests maternal cholesterol is primarily utilized for pregnancy steroid synthesis in the mouse.

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.