Phenotypic spectrum of fetal Smith–Lemli–Opitz syndrome

A Case Report of Donnai-Barrow Syndrome

BACKGROUND

A genetic disorder should be considered when an infant presents with multiple congenital anomalies. Because of the acute presentation of an infant with multiple life-threatening defects, a genetic diagnosis of a rare disorder took weeks to delineate.

CLINICAL FINDINGS

This case describes a late preterm infant who presented at birth with congenital diaphragmatic hernia, tetralogy of Fallot, cleft lip, low-set ears, and hypertelorism.

PRIMARY DIAGNOSIS

Donnai-Barrow syndrome was the final diagnosis confirmed by a defect observed on the LRP2 (2q31.1) gene using sequence analysis. This is a rare disorder that presents with a variety of phenotypic features in infants.

INTERVENTIONS

Initial neonatal resuscitation in the delivery room included intubation, positive pressure ventilation, and oxygen supplementation. Extracorporeal membrane oxygenation therapy was initiated from day of life 3 to 15. Initial surgery included correction of the congenital diaphragmatic hernia, and further surgical procedures included tracheostomy, gastrostomy tube, circumcision, ventricular septal defect repair, and cleft lip repair. Physical, occupational, and speech therapies were also initiated.

OUTCOMES

The infant was transported to a pediatric rehabilitation facility at 6 months of life for further management of his chronic lung disease requiring tracheostomy with ventilator dependence.

PRACTICE RECOMMENDATIONS

Early recognition and diagnosis of genetic syndromes can improve family education and guide treatment interventions. An underlying syndrome should be suspected when an infant presents with multiple congenital defects. Infants with Donnai-Barrow syndrome should have thorough cardiac, neurologic, ophthalmologic, audiologic, and renal examinations due to the gene mutation effects on those systems.

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

INTRODUCTION

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Genetic innovations and our understanding of stillbirth

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

Smith-Lemli-Opitz syndrome: what is the actual risk for couples carriers of the DHCR7:c.964-1G>C variant?

The founder variant DHCR7:c.964-1G>C causing autosomal recessive Smith-Lemli-Opitz (SLOS) was introduced into the Israeli preconception carrier program for Ashkenazi Jews in 2017 because of the high carrier frequency in this population (2.3%). Other disease-causing variants in DHCR7 are relatively rare in Israeli population. Discrepancy between the carrier frequency and disease prevalence raises the question of the actual risks for affected offspring for couples detected by the screening program. We performed a literature review of all relevant publications regarding homozygous DHCR7:c.964-1G>C fetuses/patients. We also collected clinical data about couples identified in the national screening program, including reproductive history. Out of 32 homozygous fetuses, six died in utero, 11 pregnancies were terminated during second trimester, and 15 children were born. All died between first days of life till 3 months of age. Reproductive history of SLOS-at-risk couples showed that after correction for ascertainment bias, out of 61 pregnancies, there was an absence of affected fetuses/children and an excess of miscarriages even if assumed that all the homozygous fetuses were miscarried. Out of these, eight families were Israelis, they had a total of one sick child, 21 healthy children, and 21 miscarriages. Our observations support the previous knowledge that homozygosity for c.964-1G>C in DHCR7 leads to a severe phenotype or early miscarriage. An unexpected observation was the excess of early miscarriages. This phenomenon is unclear and awaits further studies.

Birth defects in Brazil: Outcomes of a population-based study

Birth defects (BDs) are functional and structural alterations in embryonic or fetal development. With an incidence of approximately 3-5%, BDs are a leading cause of infant mortality and lifelong disability. A population-based prospective case-control study was conducted for one year with 5204 infants, between March 1st, 2011 and February 29th, 2012 in the city of São José do Rio Preto, State of São Paulo, Brazil. The incidence of BDs was 3.2% [95% confidence interval (95%CI): 2.8-3.8%]. The most common congenital anomalies were heart diseases in isolation (11.2%; 95%CI: 7.3-16.9%) followed by Down syndrome (9.5%; 95%CI: 5.9-14.8%), neural tube defects (8.9%; 95%CI: 5.4-14.1), urinary tract anomalies (7.7%; 95%CI: 4.4-12.7%), and polydactyly (7.0%; 95%CI: 4.0-12.0%). The majority of mothers with Down syndrome babies had advanced age. Family members with the same BD, maternal alcohol consumption, gestational diabetes, and previous miscarriages were the most frequent risk factors. The results were similar to published data from other countries except for the incidence of Down syndrome, which was twice as high as reported by other authors and is probably due to the high sociocultural level of the region where the current study was performed, leading to pregnancies at older maternal age.

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

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.

Smith-Lemli-Opitz Mutations in Unexplained Stillbirths

OBJECTIVE

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive syndrome caused by a defect in cholesterol biosynthesis with mutations in 7-dehydrocholesterol reductase (DHCR7). A total of 3% of Caucasians carry DHCR7 mutations, theoretically resulting in a homozygote frequency of 1/4000. However, SLOS occurs in only 1/20,000 to 60,000 live births. Our objective was to assess DHCR7 mutations in unexplained stillbirths.

STUDY DESIGN

Prospective, multicenter, population-based case-control study of all stillbirths and a representative sample of live births enrolled in five geographic areas. Cases with stillbirth due to obstetric complications, infection, or aneuploidy, and those with poor quality deoxyribonucleic acid (DNA) were excluded. DNA was extracted from placental tissue stored at -80°C, and exons 3 to 9 of the DCHR7 gene were amplified, purified, and subjected to bidirectional sequencing to identify mutations.

RESULTS

One-hundred forty four stillbirths were unexplained and had adequate DNA for analysis. Nine stillbirths of 139 (6.5%) had a single mutation in one allele in coding exons 3 to 9 of DHCR7 (Table 1). One case (0.7%) was a compound heterozygote for mutations in exons 3 to 9 of DHCR7; this fetus had no clinical or histologic features of SLOS.

CONCLUSION

We detected SLOS mutations in only 0.7% of stillbirths. This does not support a strong association between unrecognized DHCR7 mutations and stillbirth.

Smith-Lemli-Opitz syndrome: clinical and biochemical correlates

BACKGROUND

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder caused by mutations in the DHCR7 gene that result in reduced cholesterol biosynthesis. The aim of the study was to examine the biochemical and clinical features of SLOS in the context of the emerging evidence of the importance of cholesterol in morphogenesis and steroidogenesis.

METHODS

We retrospectively reviewed the records of 18 patients (including four fetuses) with confirmed SLOS and documented their clinical and biochemical features.

RESULTS

Seven patients had branchial arch abnormalities, including micrognathia, immune dysfunction and hypocalcemia. Thymic abnormalities were found in three fetuses. All four patients with a cholesterol level of ≤0.35 mmol/L died. They all had electrolyte abnormalities (hyperkalemia, hyponatremia, hypocalcemia), necrotizing enterocolitis, sepsis-like episodes and midline defects including the branchial and cardiac defects. Patients with cholesterol levels ≥1.7 mmol/L had milder features and were diagnosed at 9 months to 25 years of age. All 10 patients had intellectual disability. One patient was found to have a novel mutation, c.1220A>G (p.Asn407Ser).

CONCLUSIONS

We suggest that screening for adrenal insufficiency and for hypoparathyroidism, hypothyroidism and immunodeficiency, should be done routinely in infants diagnosed early with SLOS. Early diagnosis and intervention to correct these biochemical consequences may decrease mortality and improve long-term outcome in these patients.

Pulmonary vein stenosis in patients with Smith-Lemli-Opitz syndrome

OBJECTIVE

To describe a group of children with co-incident pulmonary vein stenosis and Smith-Lemli-Opitz syndrome and to generate hypotheses as to the shared pathogenesis of these disorders.

DESIGN

Retrospective case series.

PATIENTS

Five subjects in a pulmonary vein stenosis cohort of 170 subjects were diagnosed with Smith-Lemli-Opitz syndrome soon after birth.

RESULTS

All five cases were diagnosed with Smith-Lemli-Opitz syndrome within 6 weeks of life, with no family history of either disorder. All cases had pathologically elevated 7-dehydrocholesterol levels and two of the five cases had previously reported pathogenic 7-dehydrocholesterol reductase mutations. Smith-Lemli-Opitz syndrome severity scores ranged from mild to classical (2-7). Gestational age at birth ranged from 35 to 39 weeks. Four of the cases were male by karyotype. Pulmonary vein stenosis was diagnosed in all cases within 2 months of life, earlier than most published cohorts. All cases progressed to bilateral disease and three cases developed atresia of at least one vein. Despite catheter and surgical interventions, all subjects' pulmonary vein stenosis rapidly recurred and progressed. Three of the subjects died, at 2 months, 3 months, and 11 months. Survival at 16 months after diagnosis was 43%.

CONCLUSIONS

Patients with pulmonary vein stenosis who have a suggestive syndromic presentation should be screened for Smith-Lemli-Opitz syndrome with easily obtainable serum sterol tests. Echocardiograms should be obtained in all newly diagnosed patients with Smith-Lemli-Opitz syndrome, with a low threshold for repeating the study if new respiratory symptoms of uncertain etiology arise. Further studies into the pathophysiology of pulmonary vein stenosis should consider the role of cholesterol-based signaling pathways in the promotion of intimal proliferation.

Antenatal manifestations of inborn errors of metabolism: autopsy findings suggestive of a metabolic disorder

This review highlights the importance of performing an autopsy when faced with fetal abortion or termination of pregnancy with suspicion of an inborn error of metabolism. Radiological, macroscopic and microscopic features found at autopsy as well as placental anomalies that can suggest such a diagnosis are detailed. The following metabolic disorders encountered in fetuses are discussed: lysosomal storage diseases, peroxisomal disorders, cholesterol synthesis disorders, congenital disorders of glycosylation, glycogenosis type IV, mitochondrial respiratory chain disorders, transaldolase deficiency, generalized arterial calcification of infancy, hypophosphatasia, arylsulfatase E deficiency, inborn errors of serine metabolism, asparagine synthetase deficiency, hyperphenylalaninemia, glutaric aciduria type I, non-ketotic hyperglycinemia, pyruvate dehydrogenase deficiency, pyruvate carboxylase deficiency, glutamine synthase deficiency, sulfite oxidase and molybdenum cofactor deficiency.

Etiologies of uterine malformations

Ranging from aplastic uterus (including Mayer-Rokitansky-Kuster-Hauser syndrome) to incomplete septate uterus, uterine malformations as a group are relatively frequent in the general population. Specific causes remain largely unknown. Although most occurrences ostensibly seem sporadic, familial recurrences have been observed, which strongly implicate genetic factors. Through the study of animal models, human syndromes, and structural chromosomal variation, several candidate genes have been proposed and subsequently tested with targeted methods in series of individuals with isolated, non-isolated, or syndromic uterine malformations. To date, a few genes have garnered strong evidence of causality, mainly in syndromic presentations (HNF1B, WNT4, WNT7A, HOXA13). Sequencing of candidate genes in series of individuals with isolated uterine abnormalities has been able to suggest an association for several genes, but confirmation of a strong causative effect is still lacking for the majority of them. We review the current state of knowledge about the developmental origins of uterine malformations, with a focus on the genetic variants that have been implicated or associated with these conditions in humans, and we discuss potential reasons for the high rate of negative results. The evidence for various environmental and epigenetic factors is also reviewed. © 2016 Wiley Periodicals, Inc.

Radiographic features of the skeleton in disorders of post-squalene cholesterol biosynthesis

Disorders of post-squalene cholesterol biosynthesis are inborn errors of metabolism characterised by multiple congenital abnormalities, including significant skeletal involvement. The most frequent and best-characterised example is the Smith-Lemli-Opitz syndrome. Nine other disorders are known, namely autosomal-recessive Antley-Bixler syndrome, Greenberg dysplasia, X-linked dominant chondrodysplasia punctata, X-linked recessive male emopamil-binding protein deficiency, CHILD syndrome, CK syndrome, sterol C4 methyloxidase-like deficiency, desmosterolosis and lathosterolosis. This study provides an overview of the radiologic features observed in these diseases. A common pattern of limb abnormalities is recognisable, including polydactyly, which is typically post-axial and rarely interdigital and can involve all four limbs, and syndactyly of the toes. Chondrodysplasia punctata is specifically associated with a subgroup of disorders of cholesterol biosynthesis (Greenberg dysplasia, CHILD syndrome, X-linked dominant chondrodysplasia punctata, male emopamil-binding protein deficiency). The possible occurrence of epiphyseal stippling in the Smith-Lemli-Opitz syndrome, initially reported, does not appear to be confirmed. Stippling is also associated with other congenital disorders such as chromosomal abnormalities, brachytelephalangic chondrodysplasia punctata (X-linked recessive chondrodysplasia punctata, disruptions of vitamin K metabolism, maternal autoimmune diseases), rhizomelic chondrodysplasia punctata (peroxisomal disorders) and lysosomal storage disorders. In the differential diagnosis of epiphyseal stippling, a moth-eaten appearance of bones, asymmetry, or presence of a common pattern of limb abnormalities indicate inborn errors of cholesterol biosynthesis. We highlight the specific differentiating radiologic features of disorders of post-squalene cholesterol biosynthesis.

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.

Neu-Laxova syndrome is a heterogeneous metabolic disorder caused by defects in enzymes of the L-serine biosynthesis pathway

Neu-Laxova syndrome (NLS) is a rare autosomal-recessive disorder characterized by a recognizable pattern of severe malformations leading to prenatal or early postnatal lethality. Homozygous mutations in PHGDH, a gene involved in the first and limiting step in L-serine biosynthesis, were recently identified as the cause of the disease in three families. By studying a cohort of 12 unrelated families affected by NLS, we provide evidence that NLS is genetically heterogeneous and can be caused by mutations in all three genes encoding enzymes of the L-serine biosynthesis pathway. Consistent with recently reported findings, we could identify PHGDH missense mutations in three unrelated families of our cohort. Furthermore, we mapped an overlapping homozygous chromosome 9 region containing PSAT1 in four consanguineous families. This gene encodes phosphoserine aminotransferase, the enzyme for the second step in L-serine biosynthesis. We identified six families with three different missense and frameshift PSAT1 mutations fully segregating with the disease. In another family, we discovered a homozygous frameshift mutation in PSPH, the gene encoding phosphoserine phosphatase, which catalyzes the last step of L-serine biosynthesis. Interestingly, all three identified genes have been previously implicated in serine-deficiency disorders, characterized by variable neurological manifestations. Our findings expand our understanding of NLS as a disorder of the L-serine biosynthesis pathway and suggest that NLS represents the severe end of serine-deficiency disorders, demonstrating that certain complex syndromes characterized by early lethality could indeed be the extreme end of the phenotypic spectrum of already known disorders.

New insights into genotype-phenotype correlation for GLI3 mutations

The phenotypic spectrum of GLI3 mutations includes autosomal dominant Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS). PHS was first described as a lethal condition associating hypothalamic hamartoma, postaxial or central polydactyly, anal atresia and bifid epiglottis. Typical GCPS combines polysyndactyly of hands and feet and craniofacial features. Genotype-phenotype correlations have been found both for the location and the nature of GLI3 mutations, highlighting the bifunctional nature of GLI3 during development. Here we report on the molecular and clinical study of 76 cases from 55 families with either a GLI3 mutation (49 GCPS and 21 PHS), or a large deletion encompassing the GLI3 gene (6 GCPS cases). Most of mutations are novel and consistent with the previously reported genotype-phenotype correlation. Our results also show a correlation between the location of the mutation and abnormal corpus callosum observed in some patients with GCPS. Fetal PHS observations emphasize on the possible lethality of GLI3 mutations and extend the phenotypic spectrum of malformations such as agnathia and reductional limbs defects. GLI3 expression studied by in situ hybridization during human development confirms its early expression in target tissues.

Brain magnetic resonance imaging findings in Smith-Lemli-Opitz syndrome

Smith-Lemli-Opitz syndrome (SLOS) is a neurodevelopmental disorder caused by inborn errors of cholesterol metabolism resulting from mutations in 7-dehydrocholesterol reductase (DHCR7). There are only a few studies describing the brain imaging findings in SLOS. This study examines the prevalence of magnetic resonance imaging (MRI) abnormalities in the largest cohort of patients with SLOS to date. Fifty-five individuals with SLOS (27 M, 28 F) between age 0.17 years and 25.4 years (mean = 6.2, SD = 5.8) received a total of 173 brain MRI scans (mean = 3.1 per subject) on a 1.5T GE scanner between September 1998 and December 2003, or on a 3T Philips scanner between October 2010 and September 2012; all exams were performed at the Clinical Center of the National Institutes of Health. We performed a retrospective review of these imaging studies for both major and minor brain anomalies. Aberrant MRI findings were observed in 53 of 55 (96%) SLOS patients, with abnormalities of the septum pellucidum the most frequent (42/55, 76%) finding. Abnormalities of the corpus callosum were found in 38 of 55 (69%) patients. Other findings included cerebral atrophy, cerebellar atrophy, colpocephaly, white matter lesions, arachnoid cysts, Dandy-Walker variant, and type I Chiari malformation. Significant correlations were observed when comparing MRI findings with sterol levels and somatic malformations. Individuals with SLOS commonly have anomalies involving the midline and para-midline structures of the brain. Further studies are required to examine the relationship between structural brain abnormalities and neurodevelopmental disability in SLOS.

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.