Examination of patients’ responses to direct-to-consumer genetic susceptibility tests is needed to inform clinical practice. This study examined patients’ recall and interpretation of, and responses to, genetic susceptibility test results provided directly by mail.
This observational study had 3 prospective assessments (before testing; 10 days after receiving results; 3 months later). Participants were 199 patients aged 25–40 who received free genetic susceptibility testing for 8 common health conditions.
Over 80% correctly recalled their results for the 8 health conditions. Patients were unlikely to interpret genetic results as deterministic of health outcomes (mean=6.0, SD=0.8 on 1–7 scale, 1 indicating strongly deterministic). In multivariate analyses, patients with the least deterministic interpretations were White (p=.0098), more educated (p=.0093), and least confused by results (p=.001). Only 1% talked about their results with a provider.
Findings suggest that most patients will correctly recall their results and will not interpret genetics as the sole cause of diseases. The subset of those confused by results could benefit from consultation with a health care provider, which could emphasize that health habits currently are the best predictors of risk. Providers could leverage patients’ interest in genetic tests to encourage behavior changes to reduce disease risk.
Direct-to-consumer genetic tests; genetic testing; understanding; provider-patient communication; public health genomics
Individual studies of the genetics of neural tube defects (NTDs) contain results on a small number of genes in each report. To identify genetic risk factors for NTDs, we evaluated potentially functional single nucleotide polymorphisms (SNPs) that are biologically plausible risk factors for NTDs but that have never been investigated for an association with NTDs, examined SNPs that previously showed no association with NTDs in published studies, and tried to confirm previously reported associations in folate-related and non-folate-related genes. We investigated 64 SNPs in 34 genes for association with spina bifida in up to 558 case-families (520 cases, 507 mothers, 457 fathers) and 994 controls in Ireland. Case-control and mother-control comparisons of genotype frequencies, tests of transmission disequilibrium, and log-linear regression models were used to calculate effect estimates. Spina bifida was associated with over-transmission of the LEPR (leptin receptor) rs1805134 minor C allele (genotype relative risk (GRR): 1.5; 95% confidence interval (CI): 1.0, 2.1; P = 0.0264) and the COMT (catechol-O-methyltransferase) rs737865 major T allele (GRR: 1.4; 95% CI: 1.1, 2.0; P = 0.0206). After correcting for multiple comparisons, these individual test P-values exceeded 0.05. Consistent with previous reports, spina bifida was associated with MTHFR 677C>T, T (Brachyury) rs3127334, LEPR K109R, and PDGFRA promoter haplotype combinations. The associations between LEPR SNPs and spina bifida suggest a possible mechanism for the finding that obesity is a NTD risk factor. The association between a variant in COMT and spina bifida implicates methylation and epigenetics in NTDs.
congenital abnormalities; folic acid; neural tube defects; single nucleotide polymorphism; spina bifida
Suggestive, but not conclusive, studies implicate many genetic variants in oral cleft etiology. We used a large, ethnically homogenous study population to test whether reported associations between nonsyndromic oral clefts and 12 genes (CLPTM1, CRISPLD2, FGFR2, GABRB3, GLI2, IRF6, PTCH1, RARA, RYK, SATB2, SUMO1, TGFA) could be confirmed.
Thirty-one single nucleotide polymorphisms (SNPs) in exons, splice sites, and conserved non-coding regions were studied in 509 patients with cleft lip with or without cleft palate (CLP), 383 with cleft palate only (CP), 838 mothers and 719 fathers of patients with oral clefts, and 902 controls from Ireland. Case-control and family-based statistical tests were performed using isolated oral clefts for the main analyses.
In case-control comparisons, the minor allele of PTCH1 A562A (rs2066836) was associated with reduced odds of CLP (OR: 0.29, 95% CI: 0.13–0.64 for homozygotes) whereas the minor allele of PTCH1 L1315P (rs357564) was associated with increased odds of CLP (OR: 1.36, 95% CI: 1.07–1.74 for heterozygotes and OR: 1.56, 95% CI: 1.09–2.24 for homozygotes). The minor allele of one SUMO1 SNP, rs3769817 located in intron 2, was associated with increased odds of CP (OR: 1.45, 95% CI: 1.06–1.99 for heterozygotes). Transmission disequilibrium was observed for the minor allele of TGFA V159V (rs2166975) which was over-transmitted to CP cases (P=0.041).
For 10 of the 12 genes, this is the largest candidate gene study of nonsyndromic oral clefts to date. The findings provide further evidence that PTCH1, SUMO1, and TGFA contribute to nonsyndromic oral clefts.
cleft lip; cleft palate; congenital abnormalities
Advances in technology have made individual access to personal genetic information foreseeable in the near future. Policy makers and the media forecast that the ready availability of personal genetic profiles would benefit both the individual and the health care system by improving outcomes and decreasing cost. However, there is a significant gap between having access to genetic data and either wanting or understanding the information it provides. Objective: Our primary aim was to evaluate, using a population-based sample of healthy adults, whether gender, race and education status influences interest and participation in a multiplex genetic susceptibility test.
Healthy, insured individuals, 25–40 years of age, were approached via a large, integrated health system in which primary and specialty care is available. Study participants were offered personalized genetic risk information on 8 common chronic health conditions. Social groups historically known not to participate in genetic research (men, African Americans and those from lower education neighborhoods) were oversampled. We describe the recruitment outcomes and testing decisions of these social groups.
We found that even among those with access to health care, African Americans were less likely to participate in the multiplex genetic susceptibility test, while those from higher education neighborhoods were more likely to participate.
Our results suggest that large social groups will likely be underrepresented in research in personalized genomics even when robust population-based recruitment strategies are employed.
Multiplex genetic susceptibility test; Race; Gender; Education
Locus Specific Databases (LSDBs) are curated collections of sequence
variants in genes associated with disease. LSDBs of cancer-related genes often
serve as a critical resource to researchers, diagnostic laboratories,
clinicians, and others in the cancer genetics community. LSDBs are poised to
play an important role in disseminating clinical classification of variants. The
IARC Working Group on Unclassified Genetic Variants has proposed a new system of
five classes of variants in cancer susceptibility genes. However, standards are
lacking for reporting and analyzing the multiple data types that assist in
classifying variants. By adhering to standards of transparency and consistency
in the curation and annotation of data, LSDBs can be critical for organizing our
understanding of how genetic variation relates to disease. This article
discusses how LSDBs can accomplish these goals, using existing databases for
BRCA1, BRCA2, MSH2, MLH1, TP53, and
CDKN2A to illustrate the progress and remaining challenges
in this field. We recommend that: 1) LSDBs should only report a conclusion
related to pathogenicity if a consensus has been reached by an expert panel; 2)
The system used to classify variants should be standardized. The Working Group
encourages use of the five class system described in Plon et al (2008); 3) Evidence that supports a
conclusion should be reported in the database, including sources and criteria
used for assignment; 4) Variants should only be classified as pathogenic if more
than one type of evidence has been considered, and 5) All instances of all
variants should be recorded.
locus specific databases; LSDBs; BIC; mismatch repair; cancer; unclassified variant; variant of unknown significance; pathogenic
Deficiency of prolyl 3-hydroxylase 1, encoded by LEPRE1, causes recessive osteogenesis imperfecta. We previously identified a LEPRE1 mutation, exclusively in African Americans and contemporary West Africans. We hypothesized that this allele originated in West Africa and was introduced to the Americas with the Atlantic slave trade. We aimed to determine the frequency of carriers for this mutation among African Americans and West Africans, and the mutation origin and age.
Genomic DNA was screened for the mutation using PCR and restriction digestion, and a custom TaqMan genomic SNP assay. The mutation age was estimated using microsatellites and short tandem repeats spanning 4.2 Mb surrounding LEPRE1 in probands and carriers.
Approximately 0.4% of Mid-Atlantic African Americans carry this mutation, estimating recessive OI in 1/260,000 births in this population. In Nigeria and Ghana, 1.48% of unrelated individuals are heterozygous carriers, predicting 1/18,260 births will be affected with recessive OI, equal to the incidence of de novo dominant OI. The mutation was not detected in Africans from surrounding countries. All carriers shared a haplotype of 63-770 Kb, consistent with a single founder for this mutation. Using linkage disequilibrium analysis, the mutation was estimated to have originated between 650 and 900 years before present (1100-1350 C.E.).
We identified a West African founder mutation for recessive OI in LEPRE1. Nearly 1.5% of Ghanians and Nigerians are carriers. The age of this allele is consistent with introduction to North America via the Atlantic slave trade (1501 – 1867 C.E).
LEPRE1; osteogenesis imperfecta; founder mutation; West Africa
Patients with biallelic mutations in BRCA2 are in Fanconi anaemia group D1. We analysed the severity of the mutations in 27 cases, classified according to their association with breast cancer in heterozygotes, and their predicted functional effect. Twenty mutations were frameshifts or truncations, three involved splice sites, five were missense variants of unknown severity and two were benign polymorphisms. Five patients had VACTERL‐H association. Leukaemia was reported in 13 patients, and solid tumours in 15; 6 patients had two or more malignancies. The cumulative probability of any malignancy was 97% by age 5.2 years. IVS7+1G→A and IVS7+2T→G were associated with AML, and 886delGT and 6174delT with brain tumours. However, patients with other alleles remained at very high risk of these events. Missense mutations formed a distinct cluster in a highly conserved region of the BRCA2 protein.
The small group of patients with biallelic mutations in BRCA2 is distinctive in the severity of the phenotype, and early onset and high rates of leukaemia and specific solid tumours, and may comprise an extreme variant of Fanconi anaemia. Several of the alleles were not associated with cancer in presumed carriers, and thus counselling presents more uncertainties than usual.
Both taking folic acid-containing vitamins around conception and consuming food fortified with folic acid have been reported to reduce omphalocele rates. Genetic factors are etiologically important in omphalocele as well; our pilot study showed a relationship with the folate metabolic enzyme gene methylenetetrahydrofolate reductase (MTHFR). We studied 169 non-aneuploid omphalocele cases and 761 unaffected, matched controls from all New York State births occurring between 1998 and 2005 to look for associations with single nucleotide polymorphisms (SNPs) known to be important in folate, vitamin B12, or choline metabolism. In the total study population, variants in the transcobalamin receptor gene (TCblR), rs2232775 (Q8R), and the MTHFR gene, rs1801131 (1298A>C), were significantly associated with omphalocele. In African-Americans significant associations were found with SNPs in genes for the vitamin B12 transporter (TCN2) and the vitamin B12 receptor (TCblR). A SNP in the homocysteine-related gene, betaine-homocysteine S-methyltransferase (BHMT), rs3733890 (R239Q), was significantly associated with omphalocele in both African-Americans and Asians. Only the TCblR association in the total population remained statistically significant if Bonferroni correction was applied. The finding that transcobalamin receptor (TCblR) and transporter (TCN2) SNPs and a BHMT SNP were associated with omphalocele suggests that disruption of methylation reactions, in which folate, vitamin B12, and homocysteine play critical parts, may be a risk factor for omphalocele. Our data, if confirmed, suggest that supplements containing both folic acid and vitamin B12 may be beneficial in preventing omphaloceles.
omphalocele; folate; vitamin B12; homocysteine; transcobalamin; transcobalamin receptor
Periconceptional use of folic acid prevents most neural tube defects (NTDs). Whether folic acid and/or multivitamins can prevent other congenital anomalies is not clear. This study tested whether maternal blood levels of folate and vitamin B12 in pregnancies affected by congenital malformations excluding NTDs are lower when compared to non-affected pregnancies.
We measured pregnancy red cell folate (RCF), vitamin B12, and homocysteine (tHcy) concentrations in blood samples taken at the first antenatal clinic in Dublin maternity hospitals in 1986–1990 when vitamin supplementation was rare. The cases were mothers who delivered a baby with a congenital malformation other than NTD identified by the Dublin EUROCAT Registry; controls were a systematic sample of mothers of offspring without congenital malformations from the same hospitals in the same time period.
The median maternal levels of RCF and tHcy did not differ significantly between cases and controls for any of the congenital malformation groups examined (RCF: all malformations 275.9 ug/L v controls 271.2; p=0.77; tHcy: all malformations 7.5 umol/L v controls 7.6; p=0.57). In an unadjusted analysis vitamin B12 was significantly higher in case-mothers whose babies had cleft palate only (p=0.006), musculoskeletal malformations (p=0.034) and midline defects (p=0.039) but not after adjustment for multiple testing.
Our data suggest that low maternal folate and B12 levels or high tHcy levels in early pregnancy are not associated with all congenital malformations excluding NTDs. Fortification with folic acid or B12 may not have a beneficial effect in the prevention of these anomalies.
To evaluate what psychological and behavioral factors predict who is likely to seek SNP-based genetic test for multiple common health conditions where feedback can be used to motivate primary prevention.
Adults aged 25 to 40, who were enrolled in a large managed care organization were surveyed. Those eligible could log on to a secure study Web site to review information about the risks and benefits of a SNP-based genetic test and request free testing. Two primary outcomes are addressed: Accessing the Web (yes, no) and deciding to be tested (completed a blood draw at the clinic)
Those considering genetic susceptibility testing did hold genetically deterministic beliefs (0.42 on scale of 0-behavior to 1-genetic), but believed genetic information to be valuable and were confident they could understand such information. Individuals who believed it important to learn about genetics (OR=1.28), were confident they could understand genetics (OR=1.26), and reported the most health habits to change (OR=1.39) were most likely to get tested.
Physician-patient interactions could benefit if physicians develop “net friendly” strategies to capitalize on patients’ interest in online genetics information and leverage the interaction as a teachable moment to encourage family health history assessment and improved health behaviors.
personalized genomics; risk assessment; internet; psychosocial predictors
Despite improved outcomes in the past 30 years, less than half of all women diagnosed with epithelial ovarian cancer live five years beyond their diagnosis. Although typically treated as a single disease, epithelial ovarian cancer includes several distinct histological subtypes, such as papillary serous and endometrioid carcinomas. To address whether the morphological differences seen in these carcinomas represent distinct characteristics at the molecular level we analyzed DNA methylation patterns in 11 papillary serous tumors, 9 endometrioid ovarian tumors, 4 normal fallopian tube samples and 6 normal endometrial tissues, plus 8 normal fallopian tube and 4 serous samples from TCGA. For comparison within the endometrioid subtype we added 6 primary uterine endometrioid tumors and 5 endometrioid metastases from uterus to ovary. Data was obtained from 27,578 CpG dinucleotides occurring in or near promoter regions of 14,495 genes. We identified 36 locations with significant increases or decreases in methylation in comparisons of serous tumors and normal fallopian tube samples. Moreover, unsupervised clustering techniques applied to all samples showed three major profiles comprising mostly normal samples, serous tumors, and endometrioid tumors including ovarian, uterine and metastatic origins. The clustering analysis identified 60 differentially methylated sites between the serous group and the normal group. An unrelated set of 25 serous tumors validated the reproducibility of the methylation patterns. In contrast, >1,000 genes were differentially methylated between endometrioid tumors and normal samples. This finding is consistent with a generalized regulatory disruption caused by a methylator phenotype. Through DNA methylation analyses we have identified genes with known roles in ovarian carcinoma etiology, whereas pathway analyses provided biological insight to the role of novel genes. Our finding of differences between serous and endometrioid ovarian tumors indicates that intervention strategies could be developed to specifically address subtypes of epithelial ovarian cancer.
While germline mutations in the adenomatous polyposis coli (APC) gene cause the hereditary colon cancer syndrome (Familial Adenomatous Polyposis), the role of common germline APC variants in sporadic adenomatous polyposis remains unclear. We studied the association of eight APC SNPs, possibly associated with functional consequences, and previously identified gene-environment (dietary fat intake and hormone replacement therapy (HRT) use) interactions, in relation to advanced colorectal adenoma in 758 cases and 767 sex- and race-matched controls, randomly selected from the screening arm of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Cases had at least one verified advanced adenoma of the distal colon; controls, a negative sigmoidoscopy. We did not observe an association between genotypes for any of the eight APC SNPs and advanced distal adenoma risk (Pglobal gene-based =0.92). Frequencies of identified common haplotypes did not differ between cases and controls (Pglobal haplotype test =0.97). However, the risk for advanced distal adenoma was three-fold higher for one rare haplotype (cases:2.7%;controls:1.6%) (odds ratio = 3.27; 95 percent confidence interval =1.08–9.88). The genetic association between D1822V and advanced distal adenoma was confined to persons consuming a high-fat diet (Pinteraction=0.03). Similar interactions were not observed with HRT use. In our large, nested case-control study of advanced distal adenoma and clinically-verified adenoma-free controls, we observed no association between specific APC SNPs and advanced adenoma. Fat intake modified the APC D1822V-adenoma association, but further studies are warranted.
adenomatous polyposis coli; SNPs; advanced adenoma
A roundtable to discuss the measurement of folate status biomarkers in NHANES took place in July 2010. NHANES has measured serum folate since 1974 and red blood cell (RBC) folate since 1978 with the use of several different measurement procedures. Data on serum 5-methyltetrahydrofolate (5MTHF) and folic acid (FA) concentrations in persons aged ≥60 y are available in NHANES 1999–2002. The roundtable reviewed data that showed that folate concentrations from the Bio-Rad Quantaphase II procedure (Bio-Rad Laboratories, Hercules, CA; used in NHANES 1991–1994 and NHANES 1999–2006) were, on average, 29% lower for serum and 45% lower for RBC than were those from the microbiological assay (MA), which was used in NHANES 2007–2010. Roundtable experts agreed that these differences required a data adjustment for time-trend analyses. The roundtable reviewed the possible use of an isotope-dilution liquid chromatography–tandem mass spectrometry (LC-MS/MS) measurement procedure for future NHANES and agreed that the close agreement between the MA and LC-MS/MS results for serum folate supported conversion to the LC-MS/MS procedure. However, for RBC folate, the MA gave 25% higher concentrations than did the LC-MS/MS procedure. The roundtable agreed that the use of the LC-MS/MS procedure to measure RBC folate is premature at this time. The roundtable reviewed the reference materials available or under development at the National Institute of Standards and Technology and recognized the challenges related to, and the scientific need for, these materials. They noted the need for a commutability study for the available reference materials for serum 5MTHF and FA.
A roundtable to discuss the measurement of vitamin B-12 (cobalamin) status biomarkers in NHANES took place in July 2010. NHANES stopped measuring vitamin B-12–related biomarkers after 2006. The roundtable reviewed 3 biomarkers of vitamin B-12 status used in past NHANES—serum vitamin B-12, methylmalonic acid (MMA), and total homocysteine (tHcy)—and discussed the potential utility of measuring holotranscobalamin (holoTC) for future NHANES. The roundtable focused on public health considerations and the quality of the measurement procedures and reference methods and materials that past NHANES used or that are available for future NHANES. Roundtable members supported reinstating vitamin B-12 status measures in NHANES. They noted evolving concerns and uncertainties regarding whether subclinical (mild, asymptomatic) vitamin B-12 deficiency is a public health concern. They identified the need for evidence from clinical trials to address causal relations between subclinical vitamin B-12 deficiency and adverse health outcomes as well as appropriate cutoffs for interpreting vitamin B-12–related biomarkers. They agreed that problems with sensitivity and specificity of individual biomarkers underscore the need for including at least one biomarker of circulating vitamin B-12 (serum vitamin B-12 or holoTC) and one functional biomarker (MMA or tHcy) in NHANES. The inclusion of both serum vitamin B-12 and plasma MMA, which have been associated with cognitive dysfunction and anemia in NHANES and in other population-based studies, was preferable to provide continuity with past NHANES. Reliable measurement procedures are available, and National Institute of Standards and Technology reference materials are available or in development for serum vitamin B-12 and MMA.
Polymorphisms in folate-related genes have emerged as important risk factors in a range of diseases including neural tube defects (NTDs), cancer and coronary artery disease (CAD). Having previously identified a polymorphism within the cytoplasmic folate enzyme, MTHFD1, as a maternal risk factor for NTDs; we considered the more recently identified mitochondrial paralogue, MTHFD1L as a candidate gene for NTD association. We identified a common deletion/insertion polymorphism, rs3832406, c.781-6823ATT(7-9), that influences splicing efficiency and is strongly associated with NTD risk. Three alleles of rs3832406 were detected in the Irish population with varying number of ATT repeats; Allele 1 consists of ATT7, while Alleles 2 and 3 consist of ATT8 and ATT9 respectively. Allele 2 of this triallelic polymorphism showed a decreased case risk as demonstrated by case-control logistic regression (P= 0.002) and by transmission disequilibrium test (TDT) (P= 0.001); while Allele 1 showed an increased case risk. Allele 3 showed no influence on NTD risk and represents the lowest frequency allele (0.15). Additional SNP genotyping in the same genomic region provides additional supportive evidence of an association. We demonstrate that two of the three alleles of rs3832406 are functionally different and influence the splicing efficiency of the alternate MTHFD1L mRNA transcripts.
MTHFD1L; NTD; Splicing; Polymorphism; Association; Folate; Mitochondria
Genetic variants in MTHFD1 (5,10-methylenetetrahydrofolate dehydrogenase/ 5,10-methenyltetrahydrofolate cyclohydrolase/ 10-formyltetrahydrofolate synthetase), an important folate metabolic enzyme, are associated with a number of common diseases, including neural tube defects (NTDs). This study investigates the promoter of the human MTHFD1 gene in a bid to understand how this gene is controlled and regulated. Following a combination of in silico and molecular approaches, we report that MTHFD1 expression is controlled by a TATA-less, Initiator-less promoter and transcription is initiated at multiple start sites over a 126bp region. We confirmed the presence of three database polymorphisms (dbSNP) by direct sequencing of the upstream region (rs1076991 C>T, rs8010584 G>A, rs4243628 G>T), with a fourth (dbSNP rs746488 A>T) not found to be polymorphic in our population and no novel polymorphisms identified. We demonstrate that a common SNP rs1076991 C>T within the window of transcriptional initiation exerts a significant effect on promoter activity in vitro. We investigated this SNP as a potential risk factor for NTDs in a large homogenous Irish population and determined that it is not an independent risk factor, but, it does increase both case (χ2 = 11.06, P = 0.001) and maternal (χ2 = 6.68, P = 0.01) risk when allele frequencies were analysed in combination with the previously identified disease-associated p.R653Q (c.1958 G>A; dbSNP rs2236225) polymorphism. These results provide the first insight into how MTHFD1 is regulated and further emphasise its importance during embryonic development.
MTHFD1; NTD; Functional; SNP; R653Q; Promoter
Genetic and environmental factors contribute to the etiology of neural tube defects (NTDs). While periconceptional folic acid supplementation is known to significantly reduce the risk of NTDs, folate metabolic pathway related factors do not account for all NTDs. Evidence from mouse models indicates that the tumor protein p53 (TP53) is involved in implantation and normal neural tube development. To determine whether genetic variation in the TP53 might contribute to NTD risk in humans, we constructed a high resolution linkage disequilibrium (LD) map of the TP53 genomic region based on genotyping 21 markers in an Irish population. We found that nine of these variants can be used to capture the majority of common variation in the TP53 genomic region. In contrast, the 3-marker haplotype commonly reported in the TP53 literature offers limited coverage of the variation in the gene. We used the expanded set of polymorphisms to measure the influence of TP53 on NTDs using both case-control and family-based tests of association. We also assayed a functional variant in the p53 regulator MDM2 (rs2279744). Alleles of three noncoding TP53 markers were associated with NTD risk. A case effect was seen with the GG genotype of rs1625895 in intron 6 (OR = 1.37 [1.04-1.79], p=0.02). A maternal effect was seen with the 135/135 genotype of the intron 1 VNTR (OR = 1.86 [1.16-2.96], p=0.01) and the TT genotype of rs1614984 (RR = 0.58 [0.37-0.91], p=0.02). As multiple comparisons were made, these cannot be considered definitive positive findings and additional investigation is required.
neural tube defects; spina bifida; p53; TP53; MDM2; linkage disequilibrium
Both environmental and genetic factors are involved in the etiology of neural tube defects (NTDs). Inadequate folate intake and obesity are important environmental risk factors. Several folate-related genetic variants have been identified as risk factors; however, little is known about how genetic variants relate to the increased risk seen in obese women. Uncoupling Protein 2 (UCP2) is an attractive candidate to screen for NTD risk because of its possible role in obesity as well as energy metabolism, type-2 diabetes, and the regulation of reactive oxygen species. Interestingly, a previous study found that a common UCP2 compound homozygous genotype was associated with a threefold increase in NTD risk.
We evaluated three polymorphisms, −866G>A, A55V, and the 3′UTR 45bp insertion/deletion, as risk factors for NTDs in Irish NTD cases (N=169), their mothers (N=163), their fathers (N=167) and normal control subjects (N=332).
Allele and genotype frequencies were not significantly different when comparing NTD mothers, NTD fathers, or affected children to controls. Additionally, the previously reported risk genotype (combined homozygosity of 55VV and 3′UTR 45bp deletion/deletion) was not present at a higher frequency in any NTD group when compared to controls.
In our Irish study population, UCP2 polymorphisms do not influence NTD risk. Moreover, the prevalence of this allele in other populations was similar to the Irish prevalence but far lower than reported in the previous NTD study, suggesting that this previous finding of an association with NTDs might have been due to an unrepresentative study sample.
neural tube defects; spina bifida; UCP2; obesity
Cleft lip with or without cleft palate (CLP) and cleft palate only (CPO) have an inherited component and, many studies suggest, a relationship with folate. Attempts to find folate-related genes associated with clefts have, however, often been inconclusive. This study examined four SNPs related to folate metabolism (MTHFR 677 C→T, MTHFR 1298 A→C, MTHFD1 1958 G→A, and TC II 776 C→G) in a large Irish population to clarify their relationship with clefts.
Cases and their parents were recruited from major surgical centers performing cleft repairs in Ireland and a support organization. Data on risk factors, medical history, and DNA were collected. Controls were pregnant women from the greater Dublin area (n = 1,599).
CLP cases numbered 536 and CPO cases 426 after exclusions. CPO mothers were significantly more likely than controls to be MTHFR 677 TT, OR 1.50 (95% CI: 1.05–2.16; p = .03). Log-linear analysis showed a borderline association (p = .07). Isolated CPO case mothers were significantly more likely than controls to be homozygous for the MTHFD1 1958 G→A variant, OR 1.50 (95%CI: 1.08–2.09; p = .02). When multiple cases were added, both CPO cases and case mothers were significantly more likely to be AA (p = .02 and p = .007, respectively). The CLP case-control and mother-control analyses also showed significant effects, ORs 1.38 (95% CI: 1.05–1.82; p = .03) and 1.39 (95% CI: 1.04–1.85; p = .03), respectively.
Associations were found for both CPO and CLP and MTHFD1 1958 G→A in cases and case mothers. MTHFR 677 C→T could be a maternal risk factor for clefts but the association was not strong. Because multiple comparisons were made, these findings require additional investigation. Given the known association between MTHFD1 1958 G→A and NTDs, these findings should be explored in more detail.
cleft lip; cleft palate; oral clefts; folate; folate genes; vitamin B12; transcobalamin gene
Alterations in homocysteine, methionine, folate, and/or B12 homeostasis have been associated with neural tube defects, cardiovascular disease, and cancer. Methionine synthase, one of only two mammalian enzymes known to require vitamin B12 as a cofactor, lies at the intersection of these metabolic pathways. This enzyme catalyzes the transfer of a methyl group from 5-methyl-tetrahydrofolate to homocysteine, generating tetrahydrofolate and methionine. Human patients with methionine synthase deficiency exhibit homocysteinemia, homocysteinuria, and hypomethioninemia. They suffer from megaloblastic anemia with or without some degree of neural dysfunction and mental retardation. To better study the pathophysiology of methionine synthase deficiency, we utilized gene-targeting technology to inactivate the methionine synthase gene in mice. On average, heterozygous knockout mice from an outbred background have slightly elevated plasma homocysteine and methionine compared to wild-type mice but seem to be otherwise indistinguishable. Homozygous knockout embryos survive through implantation but die soon thereafter. Nutritional supplementation during pregnancy was unable to rescue embryos that were completely deficient in methionine synthase. Whether any human patients with methionine synthase deficiency have a complete absence of enzyme activity is unclear. These results demonstrate the importance of this enzyme for early development in mice and suggest either that methionine synthase-deficient patients have residual methionine synthase activity or that humans have a compensatory mechanism that is absent in mice.
Neural tube defects (NTDs) are common birth defects (~1 in 1000 pregnancies in the US and Europe) that have complex origins, including environmental and genetic factors. A low level of maternal folate is one well-established risk factor, with maternal periconceptional folic acid supplementation reducing the occurrence of NTD pregnancies by 50-70%. Gene variants in the folate metabolic pathway (e.g., MTHFR rs1801133 (677 C > T) and MTHFD1 rs2236225 (R653Q)) have been found to increase NTD risk. We hypothesized that variants in additional folate/B12 pathway genes contribute to NTD risk.
A tagSNP approach was used to screen common variation in 82 candidate genes selected from the folate/B12 pathway and NTD mouse models. We initially genotyped polymorphisms in 320 Irish triads (NTD cases and their parents), including 301 cases and 341 Irish controls to perform case–control and family based association tests. Significantly associated polymorphisms were genotyped in a secondary set of 250 families that included 229 cases and 658 controls. The combined results for 1441 SNPs were used in a joint analysis to test for case and maternal effects.
Nearly 70 SNPs in 30 genes were found to be associated with NTDs at the p < 0.01 level. The ten strongest association signals (p-value range: 0.0003–0.0023) were found in nine genes (MFTC, CDKN2A, ADA, PEMT, CUBN, GART, DNMT3A, MTHFD1 and T (Brachyury)) and included the known NTD risk factor MTHFD1 R653Q (rs2236225). The single strongest signal was observed in a new candidate, MFTC rs17803441 (OR = 1.61 [1.23-2.08], p = 0.0003 for the minor allele). Though nominally significant, these associations did not remain significant after correction for multiple hypothesis testing.
To our knowledge, with respect to sample size and scope of evaluation of candidate polymorphisms, this is the largest NTD genetic association study reported to date. The scale of the study and the stringency of correction are likely to have contributed to real associations failing to survive correction. We have produced a ranked list of variants with the strongest association signals. Variants in the highest rank of associations are likely to include true associations and should be high priority candidates for further study of NTD risk.
Neural tube defects; Spina bifida; Folic acid; One-carbon metabolism; Candidate gene
Folic acid supplementation reduces the risk of neural tube defects and congenital heart defects. The biological mechanisms through which folate prevents birth defects are not well understood. We explore the use of zebrafish as a model system to investigate the role of folate metabolism during development.
We first identified zebrafish orthologs of 12 human folate metabolic genes. RT-PCR and in situ analysis indicated maternal transcripts supply the embryo with mRNA so that the embryo has an intact folate pathway. To perturb folate metabolism we exposed zebrafish embryos to methotrexate (MTX), a potent inhibitor of dihydrofolate reductase (Dhfr) an essential enzyme in the folate metabolic pathway. Embryos exposed to high doses of MTX exhibited developmental arrest prior to early segmentation. Lower doses of MTX resulted in embryos with a shortened anterior-posterior axis and cardiac defects: linear heart tubes or incomplete cardiac looping. Inhibition of dhfr mRNA with antisense morpholino oligonucleotides resulted in embryonic lethality. One function of the folate pathway is to provide essential one-carbon units for dTMP synthesis, a rate-limiting step of DNA synthesis. After 24 hours of exposure to high levels of MTX, mutant embryos continue to incorporate the thymidine analog BrdU. However, additional experiments indicate that these embryos have fewer mitotic cells, as assayed with phospho-histone H3 antibodies, and that treated embryos have perturbed cell cycles.
Our studies demonstrate that human and zebrafish utilize similar one-carbon pathways. Our data indicate that folate metabolism is essential for early zebrafish development. Zebrafish studies of the folate pathway and its deficiencies could provide insight into the underlying etiology of human birth defects and the natural role of folate in development.