Prenatal diagnosis of Smith-Lemli-Opitz syndrome

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.

Fetal genital anomalies: an aid to diagnosis

OBJECTIVE

To report our experience with the prenatal diagnosis of fetal genital anomalies and suggest a protocol for management.

METHODS

A retrospective review of all the cases with fetal genital anomalies or phenotype and genotype discrepancy identified by prenatal ultrasound.

RESULTS

Twenty cases with abnormal fetal genitalia and four with a phenotype and genotype discrepancy were diagnosed prenatally. Genital anomalies were rarely found in isolation, most were found in combination with renal or multiple structural anomalies. The etiology of abnormal genitalia was broad and included metabolic, chromosomal and genetic syndromes.

CONCLUSION

Prenatal detection of genital anomalies should stimulate a detailed ultrasound examination and determination of genotypic sex. Measurement of 17-OHP and Delta(4)-androstenedione or metabolites of the cholesterol pathway in the amniotic fluid and/or maternal urine may be helpful in making a definitive diagnosis. Identification of genital anomalies in fetuses with renal or multiple abnormalities can aid prenatal diagnosis, thereby facilitating accurate counseling of parents who are then in a better position to make informed choices.

Maternal urinary steroid profiles in prenatal diagnosis of Smith-Lemli-Opitz syndrome: first patient series comparing biochemical and molecular studies

Smith-Lemli-Opitz syndrome (SLOS) is an autosomal recessive disorder caused by reduced activity of 7-dehydrocholesterol (7DHC) reductase, resulting in a decreased level of cholesterol and increased concentrations of 7DHC and 8DHC in body fluids and tissues. Ten pregnancies at 25% risk of SLOS underwent prenatal testing. Diagnostic studies included DHCR7 mutation analysis in chorionic villus samples, amniotic fluid sterol analysis and serial measurements of oestriol (E3), pregnanetriol (PT), 7-dehydropregnanetriol (7DHPT) and 8-dehydroesteriol (8DHE3) concentrations in maternal urine samples obtained between 9 and 20 weeks of gestation. All tests were diagnostic and revealed nine unaffected foetuses (two normal homozygotes and seven DHCR7 heterozygotes) and one affected foetus. In the affected pregnancy, 7DHC and 8DHC in amniotic fluid were 9.87 and 3.7 microg/ml, respectively [reference range (RR) 0.0026 +/- 0.0015 microg/ml and not detectable, respectively] and maternal urinary steroid analyses showed increased ratios of 7DHPT/PT and 8DHE3/E3 of 0.74 and 1.7, respectively (RR 0-0.0147 and 0-0.019). In the heterozygous foetuses, 7DHPT/PT and 8DHE3/E3 ratios did not exceed those found in 48 normal controls. This is the first series of prenatal diagnostic testing for SLOS where non-invasive biochemical testing was performed in tandem with invasive diagnostic testing. We conclude that steroid measurements in maternal urine are a reliable means of prenatal diagnosis for SLOS.

Molecular prenatal diagnosis of Smith-Lemli-Opitz syndrome is reliable and efficient

Smith-Lemli-Opitz (RSH) syndrome (SLOS, OMIM 270400) is a relatively common, autosomal recessive disorder of cholesterol biosynthesis with a broad spectrum of phenotypic abnormalities caused by mutations of the 7-dehydrocholesterol reductase gene (DHCR7) on chromosome 11. Prenatal diagnosis can be established by detection of elevated 7-dehydrocholesterol or of SLOS-causing mutations in the DHCR7 gene. We report here our experience with molecular prenatal diagnosis of SLOS. Mutation analysis of the DHCR7 gene was performed in chorionic villus samples of 13 pregnancies of couples with a family history of SLOS and known SLOS genotypes. This approach is accurate and reliable. If facilities for biochemical analysis are not available, or in cases with ambiguous biochemical patterns, molecular prenatal diagnosis is an attractive, alternative option.

The Smith-Lemli-Opitz syndrome: a novel metabolic way of understanding developmental biology, embryogenesis, and dysmorphology

The brief history of the Smith-Lemli-Opitz syndrome (SLOS) (MIM 270400) reflects that of latter 20th century dysmorphology and biochemical and molecular genetics: from its first description as a rare but characteristic multiple malformation syndrome known only to a handful of dysmorphologists, to a relatively common Garrodian defect with a complex molecular basis that has captured the attention of researchers and basic scientists from the fields as diverse as embryology, developmental biology, sterol biochemistry, epidemiology, and teratology. The discovery of the underlying biochemical defect - deficiency of 3beta-hydroxysteroid-Delta7-reductase (DHCR7), an enzyme catalyzing the last step of cholesterol biosynthesis, and the resultant generalized cholesterol deficiency - has led to an explosion of knowledge of this biochemical pathway and to a paradigm shift in the recognition of metabolic deficiencies as causes of dysmorphic syndromes. Characterization of the human DHCR7 gene and the identification of mutations in patients with SLOS have revealed a complex picture of molecular heterogeneity and provided insights into the structure and function of DHCR7. SLOS is the first metabolic malformation syndrome with profound effects on the body plan, and its discovery has paved the way to the discovery of a number of other defects of the cholesterol synthetic pathway.

Dehydro-oestriol and dehydropregnanetriol are candidate analytes for prenatal diagnosis of Smith-Lemli-Opitz syndrome

Gas chromatographic/mass spectrometric (GC/MS) analysis of maternal urine and serum steroids from 13 pregnancies at 25% risk for Smith-Lemli-Opitz syndrome (SLOS) was undertaken. All patients were between 12 and 31 weeks' gestational age. From dehydrocholesterol/cholesterol ratios determined in amniotic fluid and chorionic villus cells, five patients were shown to carry SLOS affected fetuses and eight patients were negative for the condition. Because it had previously been shown that dehydro-oestriol and dehydropregnanetriol were novel steroids produced in SLOS, these compounds were measured in the serum and urine samples of the 13 mothers. All five urine samples from SLOS affected pregnancies had high levels of both dehydrosteroid metabolites, which were below the detection limit in the non-affected pregnancies. The ratios of dehydro-oestriol/oestriol (DHE(3)/E(3)) were between 0.073 and 1.42 for the affected patients and less than 0.01 for unaffected patients. Corresponding values for dehydropregnanetriol/pregnanetriol (DHPT/PT) were 0.037-1.02 for affected and less than 0.01 for unaffected. In the positive serum sample available for analysis, the DHE(3)/E(3) ratio was 0.20 [unaffected (n=5), <0.014]. It is proposed that the measurement of DHE(3) and DHPT in maternal urine and serum may allow non-invasive antenatal diagnosis of SLOS.

The Smith-Lemli-Opitz syndrome

The Smith-Lemli-Opitz syndrome (SLOS) is one of the archetypical multiple congenital malformation syndromes. The recent discovery of the biochemical cause of SLOS and the subsequent redefinition of SLOS as an inborn error of cholesterol metabolism have led to important new treatment possibilities for affected patients. Moreover, the recent recognition of the important role of cholesterol in vertebrate embryogenesis, especially with regard to the hedgehog embryonic signalling pathway and its effects on the expression of homeobox genes, has provided an explanation for the abnormal morphogenesis in the syndrome. The well known role of cholesterol in the formation of steroid hormones has also provided a possible explanation for the abnormal behavioural characteristics of SLOS.

RSH (so-called Smith-Lemli-Opitz) syndrome

Now known as a Garrodian inborn error caused by the homozygous state of many different autosomal recessive mutations of the 7-dehydrocholesterol reductase gene leading to deficient conversion of 7-dehydrocholesterol to cholesterol, the RSH (so-called Smith-Lemli-Opitz) syndrome has become a paradigmatic metabolic malformation syndrome in a pathway that also involves cause and pathogenesis of desmosterolosis, two forms of the Conradi-Hünermann-Happle type chondodysplasia punctata and its mouse homologs, and the Greenberg "moth-eaten" skeletal dysplasia and the CHILD syndrome. Many other defects in this pathway remain to be discovered.

[Smith-Lemli-Opitz syndrome]

BACKGROUND

Smith-Lemli-Opitz syndrome (SLOS) is an autosomic recessive metabolic affection. Children affected by SLOS exhibit a defect in cholesterol biosynthesis associated with a high concentration of cholesterol precursor 7 dehydrocholesterol (7 DHC) and its isomers, which is due to an enzymatic block at the level of delta-7-DHC reductase. SLOS has been subdivided into two types on the basis of clinical severity: type I is the classic and type II is the severe one.

CASE REPORT

A full term female was born from a pregnancy complicated by oligoamniosis and intra-uterine growth retardation. The neurologic status was immediately impaired with severe hypotonia, absence of reflexes, and abnormal crying. She exhibited multiple congenital anomalies with a facial dysmorphia, anomalies of members, unicornus uterus and a pyloric stenosis. Plasmatic concentration exhibited a normal cholesterolemia contrasting with an elevated level of 7 and 8 DHC. Major alimentary tract defect led to enteral and parenteral nutrition. The severe neurological defect led to death on the 16th day of life.

CONCLUSION

Despite normal blood cholesterol levels that can be attributed to enteral and parenteral nutrition, the severity of clinical findings and the lethal course permit to classify this case as type II.

Smith-Lemli-Opitz syndrome presenting with persisting nuchal oedema and non-immune hydrops

Smith-Lemli-Opitz syndrome (SLO) is a recognized clinical entity with distinctive anomalies. Recently it has been shown that a specific defect in cholesterol metabolism, 7-dehydroxycholesterol reductase deficiency, causes the multiple abnormalities seen in SLO. There have been two reports of first-trimester nuchal translucency associated with SLO. We report two cases of SLO in the third trimester, one with persisting nuchal oedema and the other presenting with hydrops. These findings may explain a proportion of the perinatal loss associated with this syndrome.

Smith-Lemli-Opitz syndrome: a variable clinical and biochemical phenotype

We have reviewed all known UK cases of Smith-Lemli-Opitz syndrome. Among 49 cases with proven 7-dehydrocholesterol reductase deficiency, half had been terminated or had died in infancy. The minimum incidence is 1 in 60,000. The frequent occurrence of hypospadias may account for 71% of recognised cases being male. Important common features which emerged include short thumbs, severe photosensitivity, aggressive behaviour, and atrioventricular septal defect. The typical facial appearance becomes less obvious with age and 20% of cases did not have 2/3 toe syndactyly. Biochemical measurements of serum 7-dehydrocholesterol did not correlate with clinical severity.

Craniofacial developmental abnormalities

Major advances have been made in the elucidation of the molecular basis of a number of human dysmorphic syndromes involving abnormalities of craniofacial development. This will lead, in turn, to a greater understanding of the mechanisms that underlie normal craniofacial development.

RSH (Smith-Lemli-Opitz) syndrome: "severe" phenotype with ectrodactyly

We describe the antenatal ultrasound findings of growth retardation, oligohydramnios, mesomelic limb shortness, and cardiac, renal, and hand defects in a fetus who was postnatally diagnosed as having RSH ("Smith-Lemli-Opitz") syndrome. An unusual finding was ectrodactyly of both hands.

First trimester prenatal diagnosis of Smith-Lemli-Opitz syndrome (7-dehydrocholesterol reductase deficiency)

In Smith-Lemli-Opitz syndrome (SLOs), 7-dehydrocholesterol (7-DHC) accumulated because there is a block in the pathway for synthesis of cholesterol via 7-DHC. Prenatal diagnosis of SLOs has been achieved by analysis of 7-DHC in amniotic fluid obtained at 16-18 wk from pregnancies at risk. The purpose of this study was to investigate 7-DHC and cholesterol concentrations in chorionic villus (CV) samples with a view to performing first trimester prenatal diagnosis. Using a sensitive gas chromatography-mass spectrometry assay it was possible to detect 7-DHC in CV samples obtained as early as 7 wk of gestation. The ration of 7-DHC to cholesterol in placental tissue was shown to be relatively constant over the gestational period of 7-18 wk. We therefore proceeded to analyze the 7-DHC/cholesterol ration in CV samples taken at 10-12 wk of gestation from three pregnancies at risk for SLOs. The results were as follows: patient A, 1.10 x 10(-3); patient B, 1.80 x 10(-3); patient C, 0.091; control range for CVS (8-12 wk), 3.10 x 10(-4) to 1.62 x 10(-3) (mean +/- 2SD; n = 5). The fetus of patient C was diagnosed as affected by SLOs, and the parents requested termination. Analysis of cultured skin fibroblasts confirmed the diagnosis. Pregnancies A and B were diagnosed unaffected, and this was confirmed first by amniocentesis and then by the birth of normal infants at term. We conclude that synthesis of cholesterol via 7-DHC is occurring in the placenta and/or fetus at 10 wk of gestation and that prenatal diagnosis by CV biopsy is possible.

Quantification of 7-dehydrocholesterol in plasma and amniotic fluid by liquid chromatography/particle beam-mass spectrometry as a biochemical diagnostic marker for the Smith-Lemli-Opitz syndrome

The qualitative and quantitative determination of cholesterol and 7-dehydrocholesterol (7-DHC) in plasma as a biochemical diagnostic marker for the Smith-Lemli-Opitz syndrome by liquid chromatography/particle beam interface-mass spectrometry (LC/PB-MS) is presented. Baseline separation of cholesterol and 7-DHC is achieved on a silica column with hexane+ethanol (99: 1 v/v) as mobile phase within a 10 min analysis. Recoveries of cholesterol and 7-DHC in a simple two-phase extraction system are nearly 100%. The absolute limit of detection using LC/PB-MS is approximately 10 ng. The method presented allows extraction, analysis and quantification of cholesterol and 7-DHC within 15 min without the necessity of sample derivatization.