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

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.

Determination of the steroid profile in alternative matrices by liquid chromatography tandem mass spectrometry

The simultaneous determination of a broad panel of steroids provides more accurate information about the hormonal status than the detection of a single hormone. For that reason, the determination of the steroid profile, i.e. the endogenous steroid hormones and their main metabolites, has become the most powerful tool for the study of hormonal imbalances. The usefulness of the evaluation of the steroid profile in urine and plasma is widely accepted. However, despite its broad potential applicability, the evaluation of the whole steroid profile in alternative matrices such as amniotic fluid, saliva and breast milk remains almost unexplored. In this research we developed and validated a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of several steroids and their metabolites in amniotic fluid (28 analytes), saliva (15) and breast milk (12). Sample preparation, chromatographic conditions and mass spectrometric conditions (e.g. ionization species or ion source parameters) were optimized. The method was shown to be linear in the range of endogenous concentrations for all studied metabolites. Intra- and inter-assay accuracies were between 80% and 120% while intra- and inter-precisions were below 20% for all analytes in all matrices. The applicability of the method was evaluated by the comparison between the concentration ranges obtained in healthy volunteers (n = 30 per matrix) and the scarce data previously reported in literature. The concentration ranges for several analytes are reported for the first time. The present methodology represents a useful tool for the comprehensive evaluation of the steroid profile in alternative matrices and can be applicable for different clinical purposes.

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.

Differences between predicted and established diagnoses of Smith-Lemli-Opitz syndrome in the Polish population: underdiagnosis or loss of affected fetuses?

Smith-Lemli-Opitz syndrome (SLOS) is a metabolic disorder in which an error in cholesterol biosynthesis results in congenital anomalies/mental deficits. The results of our previous newborn screening, based on the carrier frequency of the two most common SLOS-causing mutations in Poland (p.W151X and p.V326L), would make SLOS one of the most frequent recessive disorders in our country (with an incidence of 1:2,300 - 1:3,937). This prompted us to carry out a 3-year (2006-2008) national surveillance program in which about 2,000 physicians were asked to identify potential SLOS patients pre- and postnatally based on clinical identification forms. The incidence of SLOS in Poland was estimated to be from 1:60,941 to 1:105,395 (1: 83,168 ± 22,227) live births, and its 3-year prevalence 1:866,273 ± 16,242. The mean carrier frequency was calculated to be from 1:123 to 1:165. The notable discrepancy between our previous carrier newborn screening and these prospective data may result from reduced fertility in SLOS carriers, intrauterine death of affected fetuses, or underdiagnosis in postnatal life. Since we did not notice significant data supporting the first two aspects, our study may support the suggestion that screening for the most frequent DHCR7 alleles does not reflect the true disease rates in the Polish population. Hence, further studies in which maternal urinary steroids (7-dehydroestriol/estriol and 8-dehydropregnanetriol/pregnanetriol ratios) would serve as screening markers in early pregnancies may be justified.

Smith-Lemli-Opitz syndrome and inborn errors of cholesterol synthesis: summary of the 2007 SLO/RSH Foundation scientific conference sponsored by the National Institutes of Health

In June 2007, the Smith-Lemli-Opitz/RSH Foundation held a scientific conference hosted jointly by Dr. Robert Steiner from Oregon Health & Science University and Dr. Forbes D. Porter from The Eunice Kennedy Shriver National Institute for Child Health and Human Development, National Institutes of Health. The main goal of this meeting was to promote interaction between scientists with expertise in cholesterol homeostasis, brain cholesterol metabolism, developmental biology, and oxysterol and neurosteroid biochemistry, clinicians researching and treating patients with Smith-Lemli-Opitz syndrome, the patient support organization and families. This report summarizes the presentations and discussions at the conference, represents the conference proceedings, and is intended to foster collaborative research and ultimately improve understanding and treatment of Smith-Lemli-Opitz syndrome and other inborn errors of cholesterol synthesis.

Pregnancy and life after preimplantation genetic diagnosis of Smith-Lemli-Opitz syndrome

OBJECTIVE

To use preimplantation genetic diagnosis to achieve Smith-Lemli-Opitz syndrome -free pregnancies in two couples at high risk of producing an affected child.

DESIGN

Case report.

SETTING

A private IVF unit.

PATIENT(S)

Two couples carrying the W151X mutation in the DHCR7 gene.

INTERVENTION(S)

Removal and testing for the W151X mutation in blastomeres from embryos after standard IVF.

MAIN OUTCOME MEASURE(S)

DNA analysis of blastomeres indicating whether corresponding embryos were mutation-free, for the purpose of transferring only unaffected embryos.

RESULT(S)

Delivery of healthy children without the W151X mutation in the DHCR7 gene.

CONCLUSION(S)

This is the first report of preimplantation genetic diagnosis for Smith-Lemli-Opitz syndrome, allowing transfer of mutation-free embryos and successful pregnancies.

Prenatal diagnosis of Smith-Lemli-Opitz syndrome (SLOS) by DHCR7 mutation analysis

OBJECTIVES

We review our experience using mutation analysis of the DHCR7 gene for prenatal diagnosis of Smith-Lemli-Opitz syndrome (SLOS), an autosomal recessive disorder of endogenous cholesterol biosynthesis caused by deficiency of 7-dehydrocholesterol reductase (DHCR7).

METHODS AND RESULTS

Prenatal diagnosis of SLOS was conducted for 21 pregnancies involving 15 families. DNA was isolated directly from amniotic fluid cells or chorionic villus samples (CVS), and the DHCR7 gene was screened for the parental mutations using PCR-ARMS and nucleotide sequencing. Sixteen of the pregnancies were unaffected and five were affected. There have been no incidences of misdiagnosed pregnancies.

CONCLUSIONS

DHCR7 mutation is a rapid and reliable method for prenatal diagnosis of SLOS, and provides an alternative to specialized biochemical tests for elevated 7DHC in amniotic fluid or CVS.

High-throughput urine screening for Smith-Lemli-Opitz syndrome and cerebrotendinous xanthomatosis using negative electrospray tandem mass spectrometry

BACKGROUND

Smith-Lemli-Opitz syndrome (SLOS) and cerebrotendinous xanthomatosis (CTX) are disorders affecting cholesterol metabolism. Currently, diagnosis relies on clinical recognition and specific and complex biochemical testing.

METHODS

A rapid, high-throughput urine test, suitable for mass screening for these two disorders, was developed using flow injection negative electrospray tandem mass spectrometry with multiple reaction monitoring. Cholestane-pentol glucuronide, a known marker for CTX, was measured and a steroid sulfate with a proposed keto-pregnadien-diol structure was identified and measured for SLOS. Measurement of the two markers was readily incorporated into an existing tandem mass spectrometry method for diagnosing inborn errors of amino and organic acid metabolism.

RESULTS

Levels in affected patients were well separated from 1738 controls, ranging from 6.7 to 100 times the 99.7th percentile of controls in SLOS patients (n=3) and 7.3 to 24 times the 99.7th percentile of controls in CTX patients (n=4).

CONCLUSIONS

The addition of testing for SLOS and CTX to a routine tandem mass spectrometry urine screening program simplifies the diagnosis of these two disorders and further extends the range of inborn errors of metabolism detected by this technique.

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

In a large multi-center trial involving prenatal screening for Smith-Lemli-Opitz syndrome (SLOS), we evaluated maternal urine and serum steroid analysis as a non-invasive diagnostic alternative to amniotic fluid sterol analysis. Candidate steroid ratios included: 7-dehydropregnanetriol/pregnanetriol (7-PT/PT), 8-dehydropregnanetriol/PT (8-PT/PT), the sum of these two (7 + 8-PT/PT), and dehydroestriol/estriol (DHE3/E3). Results are presented from 19 SLOS pregnancies, and 732 reference pregnancies that were screen positive for SLOS but negative on testing in amniotic fluid. Steroid ratios are expressed as multiples of the 75th centile (MoS), rather than multiples of the median, as most reference measurements were undetectable. All four urine ratios were available in 12 SLOS pregnancies; the median 7-PT/PT MoS was 94, with no overlap between affected and reference pregnancies in the second trimester. The separation between these groups increased by 27% per week. The other three ratios performed similarly in urine, with (7 + 8)-PT/PT ratios being marginally superior, due to fewer high reference outliers. All four steroid ratios in urine were diagnostic for SLOS between 14 and 22 weeks' gestation. In six SLOS pregnancies in which all serum analytes were measured, the median 7-PT/PT MoS was 71, and there was slight overlap in the second trimester. The separation increased by 28% per week. Steroid ratios in serum were less definitive than in urine but might be useful in certain circumstances, at 14 weeks gestation or later. Urine testing performance prior to 14 weeks gestation appears promising, but reference data are sparse.