Deep sequencing study of the MTHFR gene to identify variants associated with myelomeningocele

Perspectives on urological care in spina bifida patients

Spina bifida (SB) is a neurogenetic disorder with a complex etiology that involves genetic and environmental factors. SB can occur in two major forms of open SB or SB aperta and closed SB or SB occulta. Myelomeningocele (MMC), the most common neural tube defects (NTDs), occurs in approximately 1 in 1,000 births. Considering non-genetic factors, diminished folate status is the best-known factor influencing NTD risk. The methylenetetrahydrofolate reductase (MTHFR) gene has been implicated as a risk factor for NTDs. The primary disorder in the pathogenesis of MMC is failed neural tube closure in the embryonic spinal region. The clinical manifestation of SB depends on clinical type and severity. SB can be detected in the second trimester using ultrasound which will reveal specific cranial signs. The management of MMC traditionally involves surgery within 48 h of birth. Prenatal repair of MMC is recommended for fetuses who meet maternal and fetal Management of Myelomeningocele Study (MOMS) specified criteria. Urological manifestations of SB include urinary incontinence, urolithiasis, sexual dysfunction, renal dysfunction, and urinary tract infection. Renal failure is among the most severe complications of SB. The most important role of the urologist is the management of neurogenic bladder. Medical management with clean intermittent catheterization and anticholinergic treatment is generally considered the gold standard of therapy. However, when this therapy fails surgical reconstruction become the only remaining option. This review will summarize the pathogenesis, risk factors, genetic contribution, diagnostic test, and management of SB. Lastly, the urologic outcomes and therapies are reviewed.

Guideline No. 410: Prevention, Screening, Diagnosis, and Pregnancy Management for Fetal Neural Tube Defects

OBJECTIVE

This revised guideline is intended to provide an update on the genetic aspects, prevention, screening, diagnosis, and management of fetal neural tube defects.

TARGET POPULATION

Women who are pregnant or may become pregnant. Neural tube defect screening should be offered to all pregnant women.

OPTIONS

For prevention: a folate-rich diet, and folic acid and vitamin B₁₂ supplementation, with dosage depending on risk level. For screening: second-trimester anatomical sonography; first-trimester sonographic screening; maternal serum alpha fetoprotein; prenatal magnetic resonance imaging. For genetic testing: diagnostic amniocentesis with chromosomal microarray and amniotic fluid alpha fetoprotein and acetylcholinesterase; fetal exome sequencing. For pregnancy management: prenatal surgical repair; postnatal surgical repair; pregnancy termination with autopsy. For subsequent pregnancies: prevention and screening options and counselling.

OUTCOMES

The research on and implementation of fetal surgery for prenatally diagnosed myelomeningocele has added a significant treatment option to the previous options (postnatal repair or pregnancy termination), but this new option carries an increased risk of maternal morbidity. Significant improvements in health and quality of life, both for the mother and the infant, have been shown to result from the prevention, screening, diagnosis, and treatment of fetal neural tube defects.

BENEFITS, HARMS, AND COSTS

The benefits for patient autonomy and decision-making are provided in the guideline. Harms include an unexpected fetal diagnosis and the subsequent management decisions. Harm can also result if the patient declines routine sonographic scans or if counselling and access to care for neural tube defects are delayed. Cost analysis (personal, family, health care) is not within the scope of this clinical practice guideline.

EVIDENCE

A directed and focused literature review was conducted using the search terms spina bifida, neural tube defect, myelomeningocele, prenatal diagnosis, fetal surgery, neural tube defect prevention, neural tube defect screening, neural tube defect diagnosis, and neural tube defect management in order to update and revise this guideline. A peer review process was used for content validation and clarity, with appropriate ethical considerations.

VALIDATION METHODS

The authors rated the quality of evidence and strength of recommendations using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. See online Appendix A (Tables A1 for definitions and A2 for interpretations of strong and weak recommendations).

INTENDED AUDIENCE

Maternity care professionals who provide any part of pre-conception, antenatal, delivery, and neonatal care. This guideline is also appropriate for patient education. RECOMMENDATIONS (GRADE RATINGS IN PARENTHESES).

Directive clinique no 410 : Anomalies du tube neural : Prévention, dépistage, diagnostic et prise en charge de la grossesse

OBJECTIF

La présente directive clinique révisée vise à fournir une mise à jour sur les aspects génétiques, la prévention, le dépistage, le diagnostic et la prise en charge des anomalies du tube neural.

POPULATION CIBLE

Les femmes enceintes ou qui pourraient le devenir. Il convient d'offrir le dépistage des anomalies du tube neural à toutes les femmes enceintes.

OPTIONS

Pour la prévention : un régime alimentaire riche en acide folique et des suppléments d'acide folique et de vitamine B₁₂ selon une posologie d'après le niveau de risque. Pour le dépistage : l'échographie obstétricale du deuxième trimestre, le dépistage échographique du premier trimestre, le dosage de l'alphafœtoprotéine sérique maternelle et l'imagerie par résonance magnétique prénatale. Pour les tests génétiques : l'amniocentèse diagnostique avec analyse chromosomique sur micropuce et le dosage de l'alphafœtoprotéine et de l'acétylcholinestérase dans le liquide amniotique et le séquençage de l'exome fœtal. Pour la prise en charge de la grossesse : la réparation chirurgicale prénatale, la réparation chirurgicale postnatale et l'interruption de grossesse avec autopsie. Pour les grossesses subséquentes : les options de prévention et de dépistage et les conseils. RéSULTATS: La recherche et la mise en œuvre du traitement chirurgical fœtal en cas de diagnostic prénatal de myéloméningocèle ont ajouté une option thérapeutique fœtale importante aux options précédentes (réparation postnatale ou interruption de grossesse), mais cette nouvelle option comporte un risque accru de morbidité maternelle. La prévention, le dépistage, le diagnostic et le traitement des anomalies du tube neural se révèlent entraîner des améliorations importantes à la mère et au nourrisson en matière de santé et de qualité de vie. BéNéFICES, RISQUES ET COûTS: Le type et l'ampleur des bénéfices, risques et coûts attendus pour les patientes grâce à la mise en œuvre de la présente directive clinique par un établissement de soins de santé intègrent un canal maternel préconception et prénatal adéquat comprenant l'accès des patientes aux soins, les conseils, les analyses et examens, l'imagerie, le diagnostic et l'interprétation. Les bénéfices relatifs à l'autonomie de la patiente et au processus décisionnel sont énoncés dans la présente directive clinique. Les risques comprennent un diagnostic fœtal inattendu et les décisions de prise en charge subséquentes. Le fait que la patiente refuse les échographies habituelles et le retard du conseil ou d'accès aux soins en cas d'anomalie du tube neural comportent également des risques. L'analyse des coûts (personnels, familiaux, santé publique) ne fait pas partie de la portée de la présente directive clinique. DONNéES PROBANTES: Afin de mettre à jour et réviser la présente directive, une revue de la littérature ciblée et dirigée a été effectuée à l'aide des termes de recherche suivants : spina bifida, neural tube defect, myelomeningocele, prenatal diagnosis, fetal surgery, neural tube defect prevention, neural tube defect screening, neural tube defect diagnosis et neural tube defect management. Un processus d'examen par les pairs a été utilisé pour la validation et la clarté du contenu, avec des considérations appropriées d'ordre éthique. MéTHODES DE VALIDATION: Les auteurs ont évalué la qualité des données probantes et la force des recommandations en utilisant l'approche d'évaluation, de développement et d'évaluation (GRADE). Consulter l'annexe A en ligne (le tableau A1 pour les définitions et le tableau A2 pour les interprétations des recommandations fortes et faibles). PROFESSIONNELS CONCERNéS: Professionnels des soins de maternité qui offrent des soins préconception, prénataux, obstétricaux ou néonataux. La présente directive clinique convient également aux fins d'éducation des patientes. RECOMMANDATIONS (CLASSEMENT GRADE ENTRE PARENTHèSES).

Mutations in folate transporter genes and risk for human myelomeningocele

The molecular mechanisms linking folate deficiency and neural tube defect (NTD) risk in offspring remain unclear. Folate transporters (SLC19A1, SLC46A1, SLC25A32, and FOLH1) and folate receptors (FOLR1, FOLR2, and FOLR3) are suggested to play essential roles in transporting folate from maternal intestinal lumen to the developing embryo. Loss of function variants in these genes may affect folate availability and contribute to NTD risk. This study examines whether variants within the folate transporter and receptor genes are associated with an increased risk for myelomeningocele (MM). Exons and their flanking intron sequences of 348 MM subjects were sequenced using the Sanger sequencing method and/or next generation sequencing to identify variants. Frequencies of alleles of single nucleotide polymorphisms (SNPs) in MM subjects were compared to those from ethnically matched reference populations to evaluate alleles' associated risk for MM. We identified eight novel variants in SLC19A1 and twelve novel variants in FOLR1, FOLR2, and FOLR3. Pathogenic variants include c.1265delG in SLC19A1 resulting in an early stop codon, four large insertion deletion variants in FOLR3, and a stop_gain variant in FOLR3. No new variants were identified in SLC46A1, SLC25A32, or FOLH1. In SLC19A1, c.80A>G (rs1051266) was not associated with our MM cohort; we did observe a variant allele G frequency of 61.7%, higher than previously reported in other NTD populations. In conclusion, we discovered novel loss of function variants in genes involved in folate transport in MM subjects. Our results support the growing evidence of associations between genes involved in folate transport and susceptibility to NTDs.

Genetic Risk Factors for Folate-Responsive Neural Tube Defects

Neural tube defects (NTDs) are the most severe congenital malformations of the central nervous system. The etiology is complex, with both genetic and environmental factors having important contributions. Researchers have known for the past two decades that maternal periconceptional use of the B vitamin folic acid can prevent many NTDs. Though this finding is arguably one of the most important recent discoveries in birth defect research, the mechanism by which folic acid exerts this benefit remains unknown. Research to date has focused on the hypothesis that an underlying genetic susceptibility interacts with folate-sensitive metabolic processes at the time of neural tube closure. Little progress has been made searching for risk-causative variants in candidate genes; therefore, more complex genetic and epigenetic methodologies are now being considered. This article reviews the research to date that has been targeted on this important gene-nutrient locus.

A duplex polymerase chain reaction-restriction fragment length polymorphism for rapid screening of methylenetetrahydrofolate reductase gene variants: Genotyping in acute leukemia

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR; NM_005957.4) is the key enzyme for folate metabolism which plays in DNA biosynthesis and the epigenetic process of DNA methylation. MTHFR gene polymorphisms, the c. 677C>T and c. 1298A>C have been implicated as risk factors for several types of cancers as the acute leukemia.

AIM

We have optimized a duplex polymerase chain reaction-restriction fragment length polymorphism assay (PCR-RFLP) for the simultaneous detection of both variants in acute leukemia patients, from Tunisia.

METHODS

Genomic DNA was extracted from EDTA-anticoagulant blood samples from a total of 50 patients suffering from acute leukemia (AL). After DNA extraction, the polymerase chain reaction using specific primers, designed using Primer 3 Software. Restriction Fragment Length Polymorphism (RFLP) was performed in two separate tubes followed by agarose gel electrophoresis.

CONCLUSION

This new method has proved to be a rapid, simple, and reliable method that should facilitate high throughput genotyping of MTHFR polymorphisms in acute leukemia.

Genetic association of the glycine cleavage system genes and myelomeningocele

BACKGROUND

Neural tube defects (NTDs) are one of the most common congenital birth defects, with myelomeningocele (MM) being the most severe form compatible with life. Recent studies show a link between mitochondrial folate one carbon metabolism and NTDs by means of the glycine cleavage system (GCS). We hypothesize that single nucleotide polymorphisms and novel variants in the coding regions of the GCS genes increase the risk for MM.

METHODS

DNA was obtained from 96 subjects with MM born before the United States mandated folic acid fortification of grains in 1998. Primers were designed for polymerase chain reaction amplification and sequencing of all exons in the AMT gene, one of four genes in the GCS, followed by identification of single nucleotide polymorphisms and novel variants. An additional 252 MM subjects underwent whole exome sequencing to examine all four GCS genes (aminomethyltransferase, glycine dehydrogenase, glycine cleavage system protein-H, and dihydrolipoamide dehydrogenase).

RESULTS

We identified six novel, heterozygous variants in the AMT gene with three predicted to be deleterious to AMT function (p.Val7Leu, p.Pro251Arg, and p.Val380Met). Five extremely rare, known heterozygous variants were found in the AMT gene and one in the GLDC gene. No novel variants in the exons of the other two GCS genes (DLD and GCSH) were identified.

CONCLUSION

We identified novel and rare, known variants in two of the four GCS genes that may contribute to the development of MM. Consistent with previous findings, the current study provides additional support that genetic variations in GCS genes contribute to the risk of NTDs. Birth Defects Research (Part A) 106:847-853, 2016. © 2016 Wiley Periodicals, Inc.