Risk Factors for Neural-Tube Defects Detected in Utero: A Prospective Community-Based Study from Addis Ababa

BACKGROUND

A recent community-based study from Addis Ababa identifying Neural Tube Defect (NTD) cases by ultrasound examination of pregnant women showed a higher prevalence of 17 per 1000 fetuses. The risk factors behind the high prevalence remain unclear.

METHODS

Altogether 891 of the 958 women participated in the ultrasound examination. Thirteen with unaffected twin pregnancies were excluded. Among 878 singleton pregnancies, 15 NTD cases were identified. Serum Folate, vitamin B12, and homocysteine levels were measured in case-mothers and a sub-set of 28 noncase mothers. Because of the modest sample size, exact logistic regression analysis was used to estimate associations between risk factors and NTDs.

RESULTS

Serum vitamin status was generally poor for participants in the study. Still, relatively higher values of folate or vitamin B12 in serum, appeared to be protective for NTD (odds ratio [OR] = 0.61 per ng/ml, 95% Confidence interval [CI]: 0.42-0.85 and OR = 0.67 per 100 pg/ml, 95% CI: 0.41-1.02, respectively). High serum homocysteine was associated with higher risk of NTD (OR = 1.3 per μmol/l, 95% CI: 1.02-1.8). Women aged 30 years or more had an OR of 3.5 (95% CI: 1.1-12) for having a NTD child, and families with NTD children had lower household income. Women in the NTD group also had more spontaneous abortions or stillbirths in previous pregnancies. Self-reported intake of folate did not appear to protect against NTDs.

CONCLUSIONS

Within this high-prevalence community, poor vitamin status was identified as a risk factor for NTDs detected at ultrasound examination. Improving food security and fortification of foods or food ingredients could be alternative measures.

Rare variants with large effects provide functional insights into the pathology of migraine subtypes, with and without aura

Migraine is a complex neurovascular disease with a range of severity and symptoms, yet mostly studied as one phenotype in genome-wide association studies (GWAS). Here we combine large GWAS datasets from six European populations to study the main migraine subtypes, migraine with aura (MA) and migraine without aura (MO). We identified four new MA-associated variants (in PRRT2, PALMD, ABO and LRRK2) and classified 13 MO-associated variants. Rare variants with large effects highlight three genes. A rare frameshift variant in brain-expressed PRRT2 confers large risk of MA and epilepsy, but not MO. A burden test of rare loss-of-function variants in SCN11A, encoding a neuron-expressed sodium channel with a key role in pain sensation, shows strong protection against migraine. Finally, a rare variant with cis-regulatory effects on KCNK5 confers large protection against migraine and brain aneurysms. Our findings offer new insights with therapeutic potential into the complex biology of migraine and its subtypes.

Prevalence of neural tube defects among pregnant women in Addis Ababa: a community-based study using prenatal ultrasound examination

PURPOSE

The primary aim of this study was to estimate the prevalence of NTDs at ultrasound examination in communities of Addis Ababa and secondarily to provide a description of the dysmorphology of the NTD cases.

METHODS

We enrolled 958 pregnant women from 20 randomly selected health centers in Addis Ababa during the period from October 1, 2018, to April 30, 2019. Of these 958 women, 891 had an ultrasound examination after enrollment, with a special focus on NTDs. We estimated the prevalence of NTDs and compared it with previously reported hospital-based birth prevalence estimates from Addis Ababa.

RESULTS

Among 891 women, 13 had twin pregnancies. We identified 15 NTD cases among 904 fetuses, corresponding to an ultrasound-based prevalence of 166 per 10,000 (95% CI: 100-274). There were no NTD cases among the 26 twins. Eleven had spina bifida (122 per 10,000, 95% CI: 67-219). Among the 11 fetuses with spina bifida, three had a cervical and one had a thoracolumbar defect while the anatomical site for 7 was not registered. Seven of the 11 spina bifida defects had skin covering, while two of the cervical lesions were uncovered.

CONCLUSION

We report a high prevalence of NTDs among pregnancies in communities of Addis Ababa based on screening by ultrasound. The prevalence was higher than in previous hospital-based studies in Addis, and the prevalence of spina bifida was particularly high.

Deficit of homozygosity among 1.52 million individuals and genetic causes of recessive lethality

Genotypes causing pregnancy loss and perinatal mortality are depleted among living individuals and are therefore difficult to find. To explore genetic causes of recessive lethality, we searched for sequence variants with deficit of homozygosity among 1.52 million individuals from six European populations. In this study, we identified 25 genes harboring protein-altering sequence variants with a strong deficit of homozygosity (10% or less of predicted homozygotes). Sequence variants in 12 of the genes cause Mendelian disease under a recessive mode of inheritance, two under a dominant mode, but variants in the remaining 11 have not been reported to cause disease. Sequence variants with a strong deficit of homozygosity are over-represented among genes essential for growth of human cell lines and genes orthologous to mouse genes known to affect viability. The function of these genes gives insight into the genetics of intrauterine lethality. We also identified 1077 genes with homozygous predicted loss-of-function genotypes not previously described, bringing the total set of genes completely knocked out in humans to 4785.

Genetic effects on the timing of parturition and links to fetal birth weight

The timing of parturition is crucial for neonatal survival and infant health. Yet, its genetic basis remains largely unresolved. We present a maternal genome-wide meta-analysis of gestational duration (n = 195,555), identifying 22 associated loci (24 independent variants) and an enrichment in genes differentially expressed during labor. A meta-analysis of preterm delivery (18,797 cases, 260,246 controls) revealed six associated loci and large genetic similarities with gestational duration. Analysis of the parental transmitted and nontransmitted alleles (n = 136,833) shows that 15 of the gestational duration genetic variants act through the maternal genome, whereas 7 act both through the maternal and fetal genomes and 2 act only via the fetal genome. Finally, the maternal effects on gestational duration show signs of antagonistic pleiotropy with the fetal effects on birth weight: maternal alleles that increase gestational duration have negative fetal effects on birth weight. The present study provides insights into the genetic effects on the timing of parturition and the complex maternal-fetal relationship between gestational duration and birth weight.

An examination of mediation by DNA methylation on birthweight differences induced by assisted reproductive technologies

BACKGROUND

Children born after assisted reproductive technologies (ART) differ in birthweight from those naturally conceived. It has been hypothesized that this might be explained by epigenetic mechanisms. We examined whether cord blood DNA methylation mediated the birthweight difference between 890 newborns conceived by ART (764 by fresh embryo transfer and 126 frozen thawed embryo transfer) and 983 naturally conceived newborns from the Norwegian Mother, Father, and Child Cohort Study (MoBa). DNA methylation was measured by the Illumina Infinium MethylationEPIC array. We conducted mediation analyses to assess whether differentially methylated CpGs mediated the differences in birthweight observed between: (1) fresh embryo transfer and natural conception and (2) frozen and fresh embryo transfer.

RESULTS

We observed a difference in birthweight between fresh embryo transfer and naturally conceived offspring of - 120 g. 44% (95% confidence interval [CI] 26% to 81%) of this difference in birthweight between fresh embryo transfer and naturally conceived offspring was explained by differences in methylation levels at four CpGs near LOXL1, CDH20, and DRC1. DNA methylation differences at two CpGs near PTGS1 and RASGRP4 jointly mediated 22% (95% CI 8.1% to 50.3%) of the birthweight differences between fresh and frozen embryo transfer.

CONCLUSION

Our findings suggest that DNA methylation is an important mechanism in explaining birthweight differences according to the mode of conception. Further research should examine how gene regulation at these loci influences fetal growth.

Invited Commentary: Ionizing Radiation and Future Reproductive Health-Old Cohorts Still Deserve Attention

Radiation from nuclear weapons or power plants has caused great concern among the public-concern that needs to be addressed with the best available data. Among the concerns associated with ionizing radiation are possible serious and far-reaching effects on reproductive health. Relevant data that can be used to address these concerns are scarce. The Hiroshima and Nagasaki bombings of World War II and the 1986 Chernobyl disaster in Ukraine are probably among the most dramatic and important sources of information on health effects, but much of the information is historical, and the exposed cohorts are getting old. In their accompanying article, Yamada et al. (Am J Epidemiol. 2021;190(11):2323-2333) revisit data on reproductive health outcomes in survivors of the Hiroshima and Nagasaki bombings during the years after the blasts. Exposure levels were very high, but after Yamada et al.'s reanalysis, effect estimates were low, and the evidence for overall effects on birth defects and perinatal mortality is still weak. The authors acknowledge that their data have limitations and that the generalizability of the findings is limited by the devastating conditions that prevailed in the 2 Japanese cities after the blasts.

Wavelet Screening identifies regions highly enriched for differentially methylated loci for orofacial clefts

DNA methylation is the most widely studied epigenetic mark in humans and plays an essential role in normal biological processes as well as in disease development. More focus has recently been placed on understanding functional aspects of methylation, prompting the development of methods to investigate the relationship between heterogeneity in methylation patterns and disease risk. However, most of these methods are limited in that they use simplified models that may rely on arbitrarily chosen parameters, they can only detect differentially methylated regions (DMRs) one at a time, or they are computationally intensive. To address these shortcomings, we present a wavelet-based method called 'Wavelet Screening' (WS) that can perform an epigenome-wide association study (EWAS) of thousands of individuals on a single CPU in only a matter of hours. By detecting multiple DMRs located near each other, WS identifies more complex patterns that can differentiate between different methylation profiles. We performed an extensive set of simulations to demonstrate the robustness and high power of WS, before applying it to a previously published EWAS dataset of orofacial clefts (OFCs). WS identified 82 associated regions containing several known genes and loci for OFCs, while other findings are novel and warrant replication in other OFCs cohorts.

Variation in use of Caesarean section in Norway: An application of spatio-temporal Gaussian random fields

Aims:

Caesarean section (CS) is a medical intervention performed in Norway when a surgical delivery is considered more beneficial than a vaginal. Because deliveries with higher risk are centralized to larger hospitals, use of CS varies considerably between hospitals. We describe how the use of CS varies geographically by municipality. Since indications for CS should have little variation across the relatively homogenous population of Norway, we expect fair use of CS to be evenly distributed across the municipalities.

Methods:

Data from the Medical Birth Registry of Norway were used in our analyses (810,914 total deliveries, 133,746 CSs, 440 municipalities). We propose a spatial correlation model that takes the location into account to describe the variation in use of CS across the municipalities. The R packages R-INLA and TMB are used to estimate the yearly municipal CS rate and the spatial correlation between the municipalities. We also apply stratified models for different categories of delivering women (Robson groups). Estimated rates are displayed in maps and model parameters are shown in tables.

Results:

The CS rate varies substantially between the different municipalities. As expected, there was strong correlation between neighbouring municipalities. Similar results were found for different Robson groups.

Conclusions:

The substantial difference in CS use across municipalities in Norway is not likely to be due to specific medical reasons, but rather to hospitals’ different policies towards the use of CS. The policy to be either more or less restrictive to CS was not specific to any category of deliveries.

Heritability curves: A local measure of heritability in family models

Classical heritability models for family data split the phenotype variance into genetic and environmental components. For instance, the ACE model in twin studies assumes the phenotype variance decomposes as a²  + c²  + e² , representing (additive) genetic effects, common (shared) environment, and residual environment, respectively. However, for some phenotypes it is biologically plausible that the genetic and environmental components may vary over the range of the phenotype. For instance, very large or small values of the phenotype may be caused by "sporadic" environmental factors, whereas the mid-range phenotype variation may be more under the control of common genetic factors. This article introduces a "local" measure of heritability, where the genetic and environmental components are allowed to depend on the value of the phenotype itself. Our starting point is a general formula for local correlation between two random variables. For estimation purposes, we use a multivariate Gaussian mixture, which is able to capture nonlinear dependence and respects certain distributional constraints. We derive an analytical expression for the associated correlation curve, and show how to decompose the correlation curve into genetic and environmental parts, for instance, a² (y) + c² (y) + e² (y) for the ACE model, where we estimate the components as functions of the phenotype y. Furthermore, our model allows switching, for instance, from the ACE model to the ADE model within the range of the same phenotype. When applied to birth weight (BW) data on Norwegian mother-father-child trios, we conclude from the model that low and high BW are less heritable traits than medium BW. We also demonstrate switching between the ACE and ADE model when studying body mass index in adult monozygotic and dizygotic twins.

Gene-methylation interactions: discovering region-wise DNA methylation levels that modify SNP-associated disease risk

BACKGROUND

Current technology allows rapid assessment of DNA sequences and methylation levels at a single-site resolution for hundreds of thousands of sites in the human genome, in thousands of individuals simultaneously. This has led to an increase in epigenome-wide association studies (EWAS) of complex traits, particularly those that are poorly explained by previous genome-wide association studies (GWAS). However, the genome and epigenome are intertwined, e.g., DNA methylation is known to affect gene expression through, for example, genomic imprinting. There is thus a need to go beyond single-omics data analyses and develop interaction models that allow a meaningful combination of information from EWAS and GWAS.

RESULTS

We present two new methods for genetic association analyses that treat offspring DNA methylation levels as environmental exposure. Our approach searches for statistical interactions between SNP alleles and DNA methylation (G ×Me) and between parent-of-origin effects and DNA methylation (PoO ×Me), using case-parent triads or dyads. We use summarized methylation levels over nearby genomic region to ease biological interpretation. The methods were tested on a dataset of parent-offspring dyads, with EWAS data on the offspring. Our results showed that methylation levels around a SNP can significantly alter the estimated relative risk. Moreover, we show how a control dataset can identify false positives.

CONCLUSIONS

The new methods, G ×Me and PoO ×Me, integrate DNA methylation in the assessment of genetic relative risks and thus enable a more comprehensive biological interpretation of genome-wide scans. Moreover, our strategy of condensing DNA methylation levels within regions helps overcome specific disadvantages of using sparse chip-based measurements. The methods are implemented in the freely available R package Haplin ( https://cran.r-project.org/package=Haplin ), enabling fast scans of multi-omics datasets.

Design efficiency in genetic association studies

Selecting the best design for genetic association studies requires careful deliberation; different study designs can be used to scan for different genetic effects, and each design has its own set of strengths and limitations. A variety of family and unrelated control configurations are amenable to genetic association analyses, including the case-control design, case-parent triads, and case-parent triads in combination with unrelated controls or control-parent triads. Ultimately, the goal is to choose the design that achieves the highest statistical power using the lowest cost. For given parameter values and genotyped individuals, designs can be compared directly by computing the power. However, a more informative and general design comparison can be achieved by studying the relative efficiency, defined as the ratio of variances of two different parameter estimators, corresponding to two separate designs. Using log-linear modeling, we derive the relative efficiency from the asymptotic variance of the parameter estimators and relate it to the concept of Pitman efficiency. The relative efficiency takes into account the fact that different designs impose different costs relative to the number of genotyped individuals. We show that while optimal efficiency for analyses of regular autosomal effects is achieved using the standard case-control design, the case-parent triad design without unrelated controls is efficient when searching for parent-of-origin effects. Due to the potential loss of efficiency, maternal genes should generally not be adjusted for in an initial genome-wide association study scan of offspring genes but instead checked post hoc. The relative efficiency calculations are implemented in our R package Haplin.

Meta-analysis of epigenome-wide association studies in neonates reveals widespread differential DNA methylation associated with birthweight

Birthweight is associated with health outcomes across the life course, DNA methylation may be an underlying mechanism. In this meta-analysis of epigenome-wide association studies of 8,825 neonates from 24 birth cohorts in the Pregnancy And Childhood Epigenetics Consortium, we find that DNA methylation in neonatal blood is associated with birthweight at 914 sites, with a difference in birthweight ranging from -183 to 178 grams per 10% increase in methylation (PBonferroni < 1.06 x 10-7). In additional analyses in 7,278 participants, <1.3% of birthweight-associated differential methylation is also observed in childhood and adolescence, but not adulthood. Birthweight-related CpGs overlap with some Bonferroni-significant CpGs that were previously reported to be related to maternal smoking (55/914, p = 6.12 x 10-74) and BMI in pregnancy (3/914, p = 1.13x10-3), but not with those related to folate levels in pregnancy. Whether the associations that we observe are causal or explained by confounding or fetal growth influencing DNA methylation (i.e. reverse causality) requires further research.

Haplin power analysis: a software module for power and sample size calculations in genetic association analyses of family triads and unrelated controls

Background

Log-linear and multinomial modeling offer a flexible framework for genetic association analyses of offspring (child), parent-of-origin and maternal effects, based on genotype data from a variety of child-parent configurations. Although the calculation of statistical power or sample size is an important first step in the planning of any scientific study, there is currently a lack of software for genetic power calculations in family-based study designs. Here, we address this shortcoming through new implementations of power calculations in the R package Haplin, which is a flexible and robust software for genetic epidemiological analyses. Power calculations in Haplin can be performed analytically using the asymptotic variance-covariance structure of the parameter estimator, or else by a straightforward simulation approach. Haplin performs power calculations for child, parent-of-origin and maternal effects, as well as for gene-environment interactions. The power can be calculated for both single SNPs and haplotypes, either autosomal or X-linked. Moreover, Haplin enables power calculations for different child-parent configurations, including (but not limited to) case-parent triads, case-mother dyads, and case-parent triads in combination with unrelated control-parent triads.

Results

We compared the asymptotic power approximations to the power of analysis attained with Haplin. For external validation, the results were further compared to the power of analysis attained by the EMIM software using data simulations from Haplin. Consistency observed between Haplin and EMIM across various genetic scenarios confirms the computational accuracy of the inference methods used in both programs. The results also demonstrate that power calculations in Haplin are applicable to genetic association studies using either log-linear or multinomial modeling approaches.

Conclusions

Haplin provides a robust and reliable framework for power calculations in genetic association analyses for a wide range of genetic effects and etiologic scenarios, based on genotype data from a variety of child-parent configurations.

Electronic supplementary material

The online version of this article (10.1186/s12859-019-2727-3) contains supplementary material, which is available to authorized users.

A comparison of DNA methylation in newborn blood samples from infants with and without orofacial clefts

Background

Isolated orofacial clefts are among the most common congenital birth defects. Although the underlying biological mechanisms remain largely unknown, clefts are thought to be complex disorders influenced by genetic, environmental, and potentially epigenetic factors.

Methods

In blood samples from 2- to 3-day-old infants (n = 747) collected in a nationwide population-based study of orofacial clefts in Norway, we measured DNA methylation profiles for more than 450,000 CpGs and then conducted epigenome-wide association analyses (EWAS). We tested methylation profile difference at each CpG between controls (n = 436) and each of the cleft subtypes (92 cleft lip only, CLO; 84 cleft palate only, CPO; 132 cleft lip and palate, CLP). We also compared controls to various combinations of case groups and compared case subtypes to each other. Finally, using the EWAS results, we searched for larger differentially methylated regions (DMRs) associated with orofacial clefts.

Results

In EWAS comparing controls to individual cleft subtypes, we found no significant associations at a Bonferroni P value threshold of 10⁻⁷. After pooling case groups, we found two significantly differentially methylated CpGs: cg09696939 near gene BICC1 is associated with CLO+CLP (P = 9.58 × 10⁻⁸); cg26985354 in gene CLASRP is associated with CPO+CLP (P = 7.38 × 10⁻⁸). In DMR analysis, we identified a total of 56 significant regions when comparing controls to individual cleft subtypes (10 for CLO, 6 for CPO, 41 for CLP). Only one DMR is shared among the three cleft groups. In combined case group analysis, we found 26 DMRs for CLP+CLO, 31 for CLP+CPO, and 37 when all subtypes are combined. Finally, in case-case comparisons of subtypes, we identified 10 DMRs when comparing CLP to CPO, 9 in CLP compared to CLO, and 13 in CLP compared to CPO.

Conclusions

We identified two individual CpGs and multiple DMRs that differ between controls and cleft case subtypes. Although we find some evidence for the possible role of DNA methylation in etiology of orofacial clefts, our study does not support previous reports of widespread differences in blood DNA methylation between babies with and without facial clefts.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0638-9) contains supplementary material, which is available to authorized users.

Microbubble-Induced Serotonin Secretion in Human Platelets

The effect of nitrogen (N2) microbubbles on platelets resembles that of common platelet agonists with respect to aggregation (Thorsen T et al., Undersea Biomed Res 1986; 13:289-303). In the present study we examined the effect of microbubbles on platelet secretion of preloaded 14C-serotonin. We demonstrate that stirring of platelet-rich plasma with N2-microbubbles causes a loss of single platelets that is associated with secretion. However, secretion did not increase above baseline values until after 20 min of microbubble exposure, when platelet aggregation had reached 40%. After that time the secretion rate increased. There was no correlation between secreted serotonin and the degree of platelet aggregation. Although no 14C-serotonin secretion occurred in presence of acetylsalicylic acid (ASA), microbubble-induced platelet aggregation was only marginally reduced. Epinephrine alone caused significant platelet aggregation but no 14C-serotonin secretion and it enhanced N2-microbubble-induced platelet aggregation and secretion; ASA completely prevented secretion under these circumstances but failed to abolish the enhancement of aggregation compared with microbubbles alone. Earlier studies have shown that platelets adhere to the bubble surfaces (Thorsen T et al., Undersea Biomed Res 1987; 14:45-59). The results in the present study indicate that non-adhering platelets in the bulk phase are not activated by means of autocrine stimulation through dense granule material.

Maternal underweight and obesity and risk of orofacial clefts in a large international consortium of population-based studies

Background

Evidence on association of maternal pre-pregnancy weight with risk of orofacial clefts is inconsistent.

Methods

Six large case-control studies of orofacial clefts from Northern Europe and the USA were included in analyses pooling individual-level data. Cases included 4943 mothers of children with orofacial clefts (cleft lip only: 1135, cleft palate with cleft lip: 2081, cleft palate only: 1727) and controls included 10 592 mothers of unaffected children. Association of orofacial cleft risk with pre-pregnancy maternal weight classified by level of body mass index (BMI, kg/m 2 ) was evaluated using logistic regression adjusting for multiple covariates.

Results

Cleft palate, both alone and with cleft lip (CP+/-CL), was associated with maternal class II+ pre-pregnancy obesity (≥ 35)compared with normal weight [adjusted odds ratio (aOR) = 1.36; 95% confidence interval (CI) = 1.16, 1.58]. CP+/-CL was marginally associated with maternal underweight (aOR = 1.16; 95% CI = 0.98, 1.36). Cleft lip alone was not associated with BMI.

Conclusions

In this largest population-based study to date, we found an increased risk of cleft palate, with or without cleft lip, in class II+ obese mothers compared with normal-weight mothers; underweight mothers may also have an increased risk, but this requires further study. These results also suggest that extremes of weight may have a specific effect on palatal development.

A Genome-Wide Search for Gene-Environment Effects in Isolated Cleft Lip with or without Cleft Palate Triads Points to an Interaction between Maternal Periconceptional Vitamin Use and Variants in ESRRG

Background: It is widely accepted that cleft lip with or without cleft palate (CL/P) results from the complex interplay between multiple genetic and environmental factors. However, a robust investigation of these gene-environment (GxE) interactions at a genome-wide level is still lacking for isolated CL/P. Materials and Methods: We used our R-package Haplin to perform a genome-wide search for GxE effects in isolated CL/P. From a previously published GWAS, genotypes and information on maternal periconceptional cigarette smoking, alcohol intake, and vitamin use were available on 1908 isolated CL/P triads of predominantly European or Asian ancestry. A GxE effect is present if the relative risk estimates for gene-effects in the offspring are different across exposure strata. We tested this using the relative risk ratio (RRR). Besides analyzing all ethnicities combined ("pooled analysis"), separate analyses were conducted on Europeans and Asians to investigate ethnicity-specific effects. To control for multiple testing, q-values were calculated from the p-values. Results: We identified significant GxVitamin interactions with three SNPs in "Estrogen-related receptor gamma" (ESRRG) in the pooled analysis. The RRRs (95% confidence intervals) were 0.56 (0.45-0.69) with rs1339221 (q = 0.011), 0.57 (0.46-0.70) with rs11117745 (q = 0.011), and 0.62 (0.50-0.76) with rs2099557 (q = 0.037). The associations were stronger when these SNPs were analyzed as haplotypes composed of two-SNP and three-SNP combinations. The strongest effect was with the "t-t-t" haplotype of the rs1339221-rs11117745-rs2099557 combination [RRR = 0.50 (0.40-0.64)], suggesting that the effects observed with the other SNP combinations, including those in the single-SNP analyses, were mainly driven by this haplotype. Although there were potential GxVitamin effects with rs17734557 and rs1316471 and GxAlcohol effects with rs9653456 and rs921876 in the European sample, respectively, none of the SNPs was located in or near genes with strong links to orofacial clefts. GxAlcohol and GxSmoke effects were not assessed in the Asian sample because of a lack of observations for these exposures. Discussion/Conclusion: We identified significant interactions between vitamin use and variants in ESRRG in the pooled analysis. These GxE effects are novel and warrant further investigations to elucidate their roles in orofacial clefting. If validated, they could provide prospects for exploring the impact of estrogens and vitamins on clefting, with potential translational applications.

Analysis of Parent-of-Origin Effects on the X Chromosome in Asian and European Orofacial Cleft Triads Identifies Associations with DMD, FGF13, EGFL6, and Additional Loci at Xp22.2

Background: Although both the mother's and father's alleles are present in the offspring, they may not operate at the same level. These parent-of-origin (PoO) effects have not yet been explored on the X chromosome, which motivated us to develop new methods for detecting such effects. Orofacial clefts (OFCs) exhibit sex-specific differences in prevalence and are examples of traits where a search for various types of effects on the X chromosome might be relevant. Materials and Methods: We upgraded our R-package Haplin to enable genome-wide analyses of PoO effects, as well as power simulations for different statistical models. 14,486 X-chromosome SNPs in 1,291 Asian and 1,118 European case-parent triads of isolated OFCs were available from a previous GWAS. For each ethnicity, cleft lip with or without cleft palate (CL/P) and cleft palate only (CPO) were analyzed separately using two X-inactivation models and a sliding-window approach to haplotype analysis. In addition, we performed analyses restricted to female offspring. Results: Associations were identified in "Dystrophin" (DMD, Xp21.2-p21.1), "Fibroblast growth factor 13" (FGF13, Xq26.3-q27.1) and "EGF-like domain multiple 6" (EGFL6, Xp22.2), with biologically plausible links to OFCs. Unlike EGFL6, the other associations on chromosomal region Xp22.2 had no apparent connections to OFCs. However, the Xp22.2 region itself is of potential interest because it contains genes for clefting syndromes [for example, "Oral-facial-digital syndrome 1" (OFD1) and "Midline 1" (MID1)]. Overall, the identified associations were highly specific for ethnicity, cleft subtype and X-inactivation model, except for DMD in which associations were identified in both CPO and CL/P, in the model with X-inactivation and in Europeans only. Discussion/Conclusion: The specificity of the associations for ethnicity, cleft subtype and X-inactivation model underscores the utility of conducting subanalyses, despite the ensuing need to adjust for additional multiple testing. Further investigations are needed to confirm the associations with DMD, EGF16, and FGF13. Furthermore, chromosomal region Xp22.2 appears to be a hotspot for genes implicated in clefting syndromes and thus constitutes an exciting direction to pursue in future OFCs research. More generally, the new methods presented here are readily adaptable to the study of X-linked PoO effects in other outcomes that use a family-based design.

Parent-of-origin-environment interactions in case-parent triads with or without independent controls

With case–parent triad data, one can frequently deduce parent of origin of the child's alleles. This allows a parent‐of‐origin (PoO) effect to be estimated as the ratio of relative risks associated with the alleles inherited from the mother and the father, respectively. A possible cause of PoO effects is DNA methylation, leading to genomic imprinting. Because environmental exposures may influence methylation patterns, gene–environment interaction studies should be extended to allow for interactions between PoO effects and environmental exposures (i.e., PoOxE). One should thus search for loci where the environmental exposure modifies the PoO effect.

We have developed an extensive framework to analyze PoOxE effects in genome‐wide association studies (GWAS), based on complete or incomplete case–parent triads with or without independent control triads. The interaction approach is based on analyzing triads in each exposure stratum using maximum likelihood estimation in a log‐linear model. Interactions are then tested applying a Wald‐based posttest of parameters across strata. Our framework includes a complete setup for power calculations. We have implemented the models in the R software package Haplin.

To illustrate our PoOxE test, we applied the new methodology to top hits from our previous GWAS, assessing whether smoking during the periconceptional period modifies PoO effects on cleft palate only.

Maternal BMI at the start of pregnancy and offspring epigenome-wide DNA methylation: findings from the pregnancy and childhood epigenetics (PACE) consortium

Pre-pregnancy maternal obesity is associated with adverse offspring outcomes at birth and later in life. Individual studies have shown that epigenetic modifications such as DNA methylation could contribute. Within the Pregnancy and Childhood Epigenetics (PACE) Consortium, we meta-analysed the association between pre-pregnancy maternal BMI and methylation at over 450,000 sites in newborn blood DNA, across 19 cohorts (9,340 mother-newborn pairs). We attempted to infer causality by comparing the effects of maternal versus paternal BMI and incorporating genetic variation. In four additional cohorts (1,817 mother-child pairs), we meta-analysed the association between maternal BMI at the start of pregnancy and blood methylation in adolescents. In newborns, maternal BMI was associated with small (<0.2% per BMI unit (1 kg/m2), P < 1.06 × 10-7) methylation variation at 9,044 sites throughout the genome. Adjustment for estimated cell proportions greatly attenuated the number of significant CpGs to 104, including 86 sites common to the unadjusted model. At 72/86 sites, the direction of the association was the same in newborns and adolescents, suggesting persistence of signals. However, we found evidence for acausal intrauterine effect of maternal BMI on newborn methylation at just 8/86 sites. In conclusion, this well-powered analysis identified robust associations between maternal adiposity and variations in newborn blood DNA methylation, but these small effects may be better explained by genetic or lifestyle factors than a causal intrauterine mechanism. This highlights the need for large-scale collaborative approaches and the application of causal inference techniques in epigenetic epidemiology.

A Population-Based Study of Effects of Genetic Loci on Orofacial Clefts

Prior genome-wide association studies for oral clefts have focused on clinic-based samples with unclear generalizability. Prior samples were also small for investigating effects by cleft type and exclusively studied isolated clefts (those occurring without other birth defects). We estimated the effects of 17 top loci on cleft types in both isolated and nonisolated cases in the largest consortium to date of European-descent population-based studies. Our analytic approach focused on a mother-child dyad case-control design, but it also allowed analyzing mother-only or child-only genotypes to maximize power. Our total sample included 1,875 cases with isolated clefts, 459 cases with nonisolated clefts, and 3,749 controls. After correcting for multiple testing, we observed significant associations between fetal single-nucleotide polymorphisms (SNPs) at IRF6, PAX7, 8q21.3, 8q24, KIAA1598-VAX1, and MAFB and isolated cleft lip only (CLO) and cleft lip and palate (CLP). Significant associations were observed between isolated CLO and fetal SNPs near TPM1 and NOG1 and between CLP and fetal SNPs at ABCA4-ARHGAP29, THADA, FOXE1, and SPRY2. Overall, effects were similar for isolated CLO and CLP, except for ABCA4-ARHGAP29. A protective effect was observed for the fetal NOG1 SNP on cleft palate only, opposite in direction to the effect on CLO. For most fetal SNPs, a dose-response allelic effect was observed. No evidence of parent-of-origin or maternal genome effects was observed. Overall, effect direction and magnitude were similar between isolated and nonisolated clefts, suggesting that several loci are modifiers of cleft risk in both isolated and nonisolated forms. Our results provide reliable estimates of the effects of top loci on risks of oral clefts in a population of European descent.

Health Status Among Adults Born With an Oral Cleft in Norway

IMPORTANCE

Parents regularly express concern about long-term health outcomes for children who are born with an oral cleft.

OBJECTIVE

To assess whether oral clefts affect the health and ability to work of young adults.

DESIGN, SETTING, AND PARTICIPANTS

A population-based cohort study was conducted on all individuals born in Norway between calendar years 1967 and 1992 (n = 1 490 401). All patients treated for clefts in Norway during the study period were invited to participate (n = 2860). This study used population-based, long-term follow-up data from national registries to focus on the future health outcomes of individuals with cleft and no additional chronic medical conditions or congenital anomalies. A total of 523 individuals were excluded from the study cohort because they declined participation, could not be reached by mail, or had birth defects other than clefts. The final cohort, consisting of 2337 cases with isolated clefts and 1 413 819 unaffected individuals, was followed up until December 31, 2010, using compulsory national registries and clinical data. Data analysis was conducted from February 13, 2014, to April 18, 2016.

EXPOSURES

Oral clefts.

MAIN OUTCOMES AND MEASURES

Death, intellectual disability, schizophrenia, mood affective disorders, anxiety disorders, autism spectrum disorders, attention deficit/hyperactivity disorder, severe learning disability, cerebral palsy, epilepsy, muscle or skeletal disorders, trauma, and episodes of reduced health.

RESULTS

Of 2860 individuals born with an oral cleft, 2337 were included in the analysis; of these, 1401 were male (59.9%). Mean (SD) age in 2010 was 30.6 (7.7) years. Compared with unaffected individuals, no increased risks were found regarding morbidity or mortality among persons with isolated cleft lip only. Among individuals with isolated cleft lip and cleft palate, increased risks of intellectual disability (relative risk [RR], 2.2; 95% CI, 1.2-4.1) and cerebral palsy (RR, 2.6; 95% CI, 1.1-6.2) were found. Individuals with isolated cleft palate (ie, without cleft lip) had increased mortality (hazard ratio, 3.4; 95% CI, 2.1-5.7) in addition to an increased risk of intellectual disability (RR, 11.5; 95% CI, 8.5-15.6), anxiety disorders (RR, 2.9; 95% CI, 1.3-6.5), autism spectrum disorders (RR, 6.6; 95% CI, 2.8-15.7), severe learning disabilities (RR, 10.6; 95% CI, 5.5-20.2), cerebral palsy (RR, 4.8; 95% CI, 2.3-10.0), epilepsy (RR, 4.9; 95% CI, 2.2-10.8), and muscle or skeletal disorders (RR, 2.7; 95% CI, 1.4-5.4).

CONCLUSIONS AND RELEVANCE

Young adults who were born with isolated cleft lip only did not differ significantly from unaffected individuals in their risk of health problems. However, individuals with isolated cleft palate had increased health risks and mortality. This information should be provided to genetic counselors, parents of children with clefts, and health care workers involved in the treatment or follow-up of these children.

Variations in the risk of disability pension in Norway 1970 - 99

Aims: A study was undertaken to investigate whether cohort or period effects could explain the varying and generally increasing incidence of disability pension in Norway between 1970 and 1999. Methods: The study used data from a complete national register of new disability cases in Norway, including all cases of disability pension in the 16 - 60 age group categorized according to age and gender for each year from 1970 to 1999. The population at risk was defined for each year from census data and number of individuals already receiving disability pension. Data were organized in five-year age groups, five-year time periods and corresponding overlapping nine-year birth cohorts. Age- and gender-specific rates were displayed graphically for periods and cohorts. Separate Poisson regression models were fitted for age periods and age cohorts. Finally a combined age, period, and cohort model was applied. Results: The overall incidence was 7.4/1,000 non-disabled persons per year for women and 6.0/1,000 for men. For women 52.1% of the cases were in the 51 - 60 age group, whereas the corresponding figure for men was 57.6%. Statistical analysis showed an increasing trend for both genders, more pronounced for women than men. All time periods deviated significantly from the trend, either upwards or downwards. Age-cohort models showed less variation, but recent cohorts had higher than expected rates, especially for men. Conclusions: Further studies should investigate why Norwegian women were more affected by the period effects than men. An increasing incidence of disability pension among recent cohorts is a major challenge for the Norwegian welfare system.

Neurodevelopmental Disorders or Early Death in Siblings of Children With Cerebral Palsy

OBJECTIVES

To explore the presence of shared underlying causes of cerebral palsy (CP) and other neurodevelopmental disorders, by examining risks of other disorders in siblings of children with CP.

METHODS

We used Norwegian national registries to identify 1.4 million pairs of full siblings (singletons) and 28 000 sets of twins born from 1967 to 2006, identify stillbirths and neonatal deaths, and find individuals with CP, epilepsy, intellectual disability, autism spectrum disorders, attention-deficit/hyperactivity disorder, blindness, deafness, schizophrenia, and bipolar disorder. Associations between CP in 1 sibling and neurodevelopmental disorders or early death in other siblings were estimated using logistic regression models.

RESULTS

There were 5707 neonatal survivors (beyond 28 days) with CP (2.5/1000). These children had substantial comorbidity (eg, 29% had epilepsy). Singleton siblings of (singleton) children with CP had increased risks of neurodevelopmental problems, including epilepsy (odds ratio [OR], 1.8 [95% confidence interval (CI), 1.5-2.5]), intellectual disability (OR, 2.3 [95% CI, 1.8-2.9]), autism spectrum disorders (OR, 1.6 [95% CI, 1.1-2.2]), attention-deficit/hyperactivity disorder (OR 1.3 [95% CI, 1.1-1.6]), blindness (OR 2.4 [95% CI, 1.1-5.4]), and schizophrenia (OR 2.0 [95% CI, 1.2-3.2]). There was no increase in risk of bipolar disorder (OR 1.0 [95% CI, 0.6-1.6]). Families with children with CP also had increased risk of losing another child in the perinatal period (stillbirth OR, 1.8 [95% CI, 1.5- 2.3]; neonatal death OR, 1.7 [95% CI, 1.3-2.2]). Associations were stronger within sets of twins.

CONCLUSIONS

Siblings of a child with CP were at increased risk for a variety of other neurodevelopmental morbidities, as well as early death, indicating the presence of shared underlying causes.

Maternal Age at Delivery Is Associated with an Epigenetic Signature in Both Newborns and Adults

Offspring of older mothers are at increased risk of adverse birth outcomes, childhood cancers, type 1 diabetes, and neurodevelopmental disorders. The underlying biologic mechanisms for most of these associations remain obscure. One possibility is that maternal aging may produce lasting changes in the epigenetic features of a child’s DNA. To test this, we explored the association of mothers’ age at pregnancy with methylation in her offspring, using blood samples from 890 Norwegian newborns and measuring DNA methylation at more than 450,000 CpG sites across the genome. We examined replication of a maternal-age finding in an independent group of 1062 Norwegian newborns, and then in 200 US middle-aged women. Older maternal age was significantly associated with reduced methylation at four adjacent CpGs near the 2^nd exon of KLHL35 in newborns (p-values ranging from 3x10^-6 to 8x10^-7). These associations were replicated in the independent set of newborns, and replicated again in women 40 to 60 years after their birth. This study provides the first example of parental age permanently affecting the epigenetic profile of offspring. While the specific functions of the affected gene are unknown, this finding opens the possibility that a mother’s age at pregnancy could affect her child’s health through epigenetic mechanisms.

Maternal alcohol binge-drinking in the first trimester and the risk of orofacial clefts in offspring: a large population-based pooling study

Using individual participant data from six population-based case–control studies, we conducted pooled analyses to examine maternal alcohol consumption and the risk of clefts among >4600 infants with cleft lip only, cleft lip with cleft palate, or cleft palate only and >10,000 unaffected controls. We examined two first-trimester alcohol measures: average number of drinks/sitting and maximum number of drinks/sitting, with five studies contributing to each analysis. Study-specific odds ratios (ORs) were estimated using logistic regression and pooled to generate adjusted summary ORs. Across studies, 0.9–3.2 % of control mothers reported drinking an average of 5+ drinks/sitting, while 1.4–23.5 % reported drinking a maximum of 5+ drinks/sitting. Compared with non-drinkers, mothers who drank an average of 5+ drinks/sitting were more likely to deliver an infant with cleft lip only (pooled OR 1.48; 95 % confidence intervals 1.01, 2.18). The estimate was higher among women who drank at this level 3+ times (pooled OR 1.95; 1.23, 3.11). Ever drinking a maximum of 5+ drinks/sitting and non-binge drinking were not associated with cleft risk. Repeated heavy maternal alcohol consumption was associated with an increased risk of cleft lip only in offspring. There was little evidence of increased risk for other cleft types or alcohol measures.

Passive Smoke Exposure as a Risk Factor for Oral Clefts-A Large International Population-Based Study

Maternal cigarette smoking is a well-established risk factor for oral clefts. Evidence is less clear for passive (secondhand) smoke exposure. We combined individual-level data from 4 population-based studies (the Norway Facial Clefts Study, 1996-2001; the Utah Child and Family Health Study, 1995-2004; the Norwegian Mother and Child Cohort Study, 1999-2009; and the National Birth Defects Prevention Study (United States), 1999-2007) to obtain 4,508 cleft cases and 9,626 controls. We categorized first-trimester passive and active smoke exposure. Multivariable logistic models adjusted for possible confounders (maternal alcohol consumption, use of folic acid supplements, age, body size, education, and employment, plus study fixed effects). Children whose mothers actively smoked had an increased risk of oral clefts (odds ratio (OR) = 1.27, 95% confidence interval (CI): 1.11, 1.46). Children of passively exposed nonsmoking mothers also had an increased risk (OR = 1.14, 95% CI: 1.02, 1.27). Cleft risk was further elevated among babies of smoking mothers who were exposed to passive smoke (OR = 1.51, 95% CI: 1.35, 1.70). Using a large pooled data set, we found a modest association between first-trimester passive smoking and oral clefts that was consistent across populations, diverse study designs, and cleft subtypes. While this association may reflect subtle confounding or bias, we cannot rule out the possibility that passive smoke exposure during pregnancy is teratogenic.

A multi-ethnic genome-wide association study identifies novel loci for non-syndromic cleft lip with or without cleft palate on 2p24.2, 17q23 and 19q13

Orofacial clefts (OFCs), which include non-syndromic cleft lip with or without cleft palate (CL/P), are among the most common birth defects in humans, affecting approximately 1 in 700 newborns. CL/P is phenotypically heterogeneous and has a complex etiology caused by genetic and environmental factors. Previous genome-wide association studies (GWASs) have identified at least 15 risk loci for CL/P. As these loci do not account for all of the genetic variance of CL/P, we hypothesized the existence of additional risk loci. We conducted a multiethnic GWAS in 6480 participants (823 unrelated cases, 1700 unrelated controls and 1319 case-parent trios) with European, Asian, African and Central and South American ancestry. Our GWAS revealed novel associations on 2p24 near FAM49A, a gene of unknown function (P = 4.22 × 10^-8), and 19q13 near RHPN2, a gene involved in organizing the actin cytoskeleton (P = 4.17 × 10^-8). Other regions reaching genome-wide significance were 1p36 (PAX7), 1p22 (ARHGAP29), 1q32 (IRF6), 8q24 and 17p13 (NTN1), all reported in previous GWASs. Stratification by ancestry group revealed a novel association with a region on 17q23 (P = 2.92 × 10^-8) among individuals with European ancestry. This region included several promising candidates including TANC2, an oncogene required for development, and DCAF7, a scaffolding protein required for craniofacial development. In the Central and South American ancestry group, significant associations with loci previously identified in Asian or European ancestry groups reflected their admixed ancestry. In summary, we have identified novel CL/P risk loci and suggest new genes involved in craniofacial development, confirming the highly heterogeneous etiology of OFCs.

Reproduction and marriage among male survivors of cancer in childhood, adolescence and young adulthood: a national cohort study

BACKGROUND

Increased survival after cancer in young age has made long-term follow-up studies of high external validity important. In this national cohort study, we explored the impact of cancer in young age on reproduction and marital status in male survivors.

METHODS

Hazard ratios (HRs) and relative risks (RRs) of reproductive and marital outcomes were studied for male survivors of cancer in young age (<25 years) and cancer-free male comparisons, born during 1965-1985, by linking compulsory national registries in Norway.

RESULTS

Male cancer survivors (n=2687) had reduced paternity (HR: 0.72, 95% confidence interval (CI): 0.68-0.76). This was most apparent in survivors of testicular cancer, brain tumours, lymphoma, leukemia and bone tumours, and when diagnosed with cancer before 15 years of age. Male cancer survivors were more likely to avail of assisted reproduction (RR: 3.32, 95% CI: 2.68-4.11). There was no increased risk of perinatal death, congenital malformations, being small for gestational age, of low birth weight or preterm birth in their first offspring. Male cancer survivors were less likely to marry (HR: 0.93, 95% CI: 0.86-1.00), in particular brain tumour survivors.

CONCLUSIONS

In this national cohort study, we demonstrated reduced paternity and increased use of assisted reproduction among male cancer survivors, but no adverse outcome for their first offspring at birth.

Exposure to household air pollution from wood combustion and association with respiratory symptoms and lung function in nonsmoking women: results from the RESPIRE trial, Guatemala

BACKGROUND

With 40% of the world's population relying on solid fuel, household air pollution (HAP) represents a major preventable risk factor for COPD (chronic obstructive pulmonary disease). Meta-analyses have confirmed this relationship; however, constituent studies are observational, with virtually none measuring exposure directly.

OBJECTIVES

We estimated associations between HAP exposure and respiratory symptoms and lung function in young, nonsmoking women in rural Guatemala, using measured carbon monoxide (CO) concentrations in exhaled breath and personal air to assess exposure.

METHODS

The Randomized Exposure Study of Pollution Indoors and Respiratory Effects (RESPIRE) Guatemala study was a trial comparing respiratory outcomes among 504 women using improved chimney stoves versus traditional cookstoves. The present analysis included 456 women with data from postintervention surveys including interviews at 6, 12, and 18 months (respiratory symptoms) and spirometry and CO (ppm) in exhaled breath measurements. Personal CO was measured using passive diffusion tubes at variable times during the study. Associations between CO concentrations and respiratory health were estimated using random intercept regression models.

RESULTS

Respiratory symptoms (cough, phlegm, wheeze, or chest tightness) during the previous 6 months were positively associated with breath CO measured at the same time of symptom reporting and with average personal CO concentrations during the follow-up period. CO in exhaled breath at the same time as spirometry was associated with lower lung function [average reduction in FEV1 (forced expiratory volume in 1 sec) for a 10% increase in CO was 3.33 mL (95% CI: -0.86, -5.81)]. Lung function measures were not significantly associated with average postintervention personal CO concentrations.

CONCLUSIONS

Our results provide further support for the effects of HAP exposures on airway inflammation. Further longitudinal research modeling continuous exposure to particulate matter against lung function will help us understand more fully the impact of HAP on COPD.

Identification of DNA methylation changes in newborns related to maternal smoking during pregnancy

BACKGROUND

Maternal smoking during pregnancy is associated with significant infant morbidity and mortality, and may influence later disease risk. One mechanism by which smoking (and other environmental factors) might have long-lasting effects is through epigenetic modifications such as DNA methylation.

OBJECTIVES

We conducted an epigenome-wide association study (EWAS) investigating alterations in DNA methylation in infants exposed in utero to maternal tobacco smoke, using the Norway Facial Clefts Study.

METHODS

The Illumina HumanMethylation450 BeadChip was used to assess DNA methylation in whole blood from 889 infants shortly after delivery. Of 889 mothers, 287 reported smoking-twice as many smokers as in any previous EWAS of maternal smoking. CpG sites related to maternal smoking during the first trimester were identified using robust linear regression.

RESULTS

We identified 185 CpGs with altered methylation in infants of smokers at genome-wide significance (q-value < 0.05; mean Δβ = ± 2%). These correspond to 110 gene regions, of which 7 have been previously reported and 10 are newly confirmed using publicly available results. Among these 10, the most noteworthy are FRMD4A, ATP9A, GALNT2, and MEG3, implicated in processes related to nicotine dependence, smoking cessation, and placental and embryonic development.

CONCLUSIONS

Our study identified 10 genes with newly established links to maternal smoking. Further, we note differences between smoking-related methylation changes in newborns and adults, suggesting possible distinct effects of direct versus indirect tobacco smoke exposure as well as potential differences due to age. Further work would be needed to determine whether these small changes in DNA methylation are biologically or clinically relevant. The methylation changes identified in newborns may mediate the association between in utero maternal smoking exposure and later health outcomes.

Familial risk of cerebral palsy: population based cohort study

OBJECTIVE

To investigate risks of recurrence of cerebral palsy in family members with various degrees of relatedness to elucidate patterns of hereditability.

DESIGN

Population based cohort study.

SETTING

Data from the Medical Birth Registry of Norway, linked to the Norwegian social insurance scheme to identify cases of cerebral palsy and to databases of Statistics Norway to identify relatives.

PARTICIPANTS

2,036,741 Norwegians born during 1967-2002, 3649 of whom had a diagnosis of cerebral palsy; 22,558 pairs of twins, 1,851,144 pairs of first degree relatives, 1,699,856 pairs of second degree relatives, and 5,165,968 pairs of third degree relatives were identified.

MAIN OUTCOME MEASURE

Cerebral palsy.

RESULTS

If one twin had cerebral palsy, the relative risk of recurrence of cerebral palsy was 15.6 (95% confidence interval 9.8 to 25) in the other twin. In families with an affected singleton child, risk was increased 9.2 (6.4 to 13)-fold in a subsequent full sibling and 3.0 (1.1 to 8.6)-fold in a half sibling. Affected parents were also at increased risk of having an affected child (6.5 (1.6 to 26)-fold). No evidence was found of differential transmission through mothers or fathers, although the study had limited power to detect such differences. For people with an affected first cousin, only weak evidence existed for an increased risk (1.5 (0.9 to 2.7)-fold). Risks in siblings or cousins were independent of sex of the index case. After exclusion of preterm births (an important risk factor for cerebral palsy), familial risks remained and were often stronger.

CONCLUSIONS

People born into families in which someone already has cerebral palsy are themselves at elevated risk, depending on their degree of relatedness. Elevated risk may extend even to third degree relatives (first cousins). The patterns of risk suggest multifactorial inheritance, in which multiple genes interact with each other and with environmental factors. These data offer additional evidence that the underlying causes of cerebral palsy extend beyond the clinical management of delivery.

First-trimester nonsystemic corticosteroid use and the risk of oral clefts in Norway

PURPOSE

Exposure of pregnant mice to corticosteroids can produce oral clefts in offspring. Although data in humans are more mixed, recent reports have suggested that dermatologic steroids are associated with oral clefts.

METHODS

We investigated maternal first-trimester exposure to corticosteroids (focusing on dermatologic uses) and oral clefts in offspring using two population-based studies. The Norway Cleft Study (1996-2001) is a national case-control study including 377 infants with cleft lip ± palate (CLP), 196 infants with cleft palate only (CPO), and 763 controls. The Norwegian Mother and Child Cohort Study (MoBa, 1998-2008) is a national birth cohort including 123 infants with CLP, 61 infants with CPO, and 551 controls.

RESULTS

In the case-control study, there was the suggestion of an association of dermatologic corticosteroids with both CLP (adjusted OR [aOR], 2.3; 95% confidence interval [CI], 0.71-7.7) and CPO (aOR, 3.4; CI, 0.87-13). There was no evidence of this association in the cohort data (odds ratio for CLP, 1.2; CI, 0.50-2.8 and odds ratio for CPO, 1.0; CI, 0.30-3.4), although exposure to dermatologic steroids was less specifically ascertained. There were no associations with other types of corticosteroids.

CONCLUSIONS

Our data add to the suggestive but inconsistent findings for this association.

Recurrence of preeclampsia in northern Tanzania: a registry-based cohort study

OBJECTIVE

Preeclampsia occurs in about 4 per cent of pregnancies worldwide, and may have particularly serious consequences for women in Africa. Studies in western countries have shown that women with preeclampsia in one pregnancy have a substantially increased risk of preeclampsia in subsequent pregnancies. We estimate the recurrence risks of preeclampsia in data from Northern Tanzania.

METHODS

A prospective cohort study was designed using 19,811 women who delivered singleton infants at a hospital in Northern Tanzania between 2000 and 2008. A total of 3,909 women were recorded with subsequent deliveries in the hospital with follow up through 2010. Adjusted recurrence risks of preeclampsia were computed using regression models.

RESULTS

The absolute recurrence risk of preeclampsia was 25%, which was 9.2-fold (95% CI: 6.4 - 13.2) compared with the risk for women without prior preeclampsia. When there were signs that the preeclampsia in a previous pregnancy had been serious either because the baby was delivered preterm or had died in the perinatal period, the recurrence risk of preeclampsia was even higher. Women who had preeclampsia had increased risk of a series of adverse pregnancy outcomes in future pregnancies. These include perinatal death (RR= 4.3), a baby with low birth weight (RR= 3.5), or a preterm birth (RR= 2.5). These risks were only partly explained by recurrence of preeclampsia.

CONCLUSIONS

Preeclampsia in one pregnancy is a strong predictor for preeclampsia and other adverse pregnancy outcomes in subsequent pregnancies in Tanzania. Women with previous preeclampsia may benefit from close follow-up during their pregnancies.

X-linked markers in the Duchenne muscular dystrophy gene associated with oral clefts

As part of an international consortium, case-parent trios were collected for a genome-wide association study of isolated, non-syndromic oral clefts, including cleft lip (CL), cleft palate (CP), and cleft lip and palate (CLP). Non-syndromic oral clefts have a complex and heterogeneous etiology. Risk is influenced by genes and environmental factors, and differs markedly by gender. Family-based association tests (FBAT) were used on 14,486 single nucleotide polymorphisms (SNPs) spanning the X chromosome, stratified by type of cleft and racial group. Significant results, even after multiple-comparisons correction, were obtained for the Duchenne muscular dystrophy (DMD) gene, the largest single gene in the human genome, among CL/P (i.e., both CL and CLP combined) trios. When stratified into groups of European and Asian ancestry, stronger signals were obtained for Asian subjects. Although conventional sliding-window haplotype analysis showed no increase in significance, selected combinations of the 25 most significant SNPs in the DMD gene identified four SNPs together that attained genome-wide significance among Asian CL/P trios, raising the possibility of interaction between distant SNPs within the DMD gene.

Recurrence of perinatal death in Northern Tanzania: a registry based cohort study

Background

Perinatal mortality is known to be high in Sub-Saharan Africa. Some women may carry a particularly high risk which would be reflected in a high recurrence risk. We aim to estimate the recurrence risk of perinatal death using data from a hospital in Northern Tanzania.

Methods

We constructed a cohort study using data from the hospital based KCMC Medical Birth Registry. Women who delivered a singleton for the first time at the hospital between 2000 and 2008 were followed in the registry for subsequent deliveries up to 2010 and 3,909 women were identified with at least one more delivery within the follow-up period. Recurrence risk of perinatal death was estimated in multivariate models analysis while adjusting for confounders and accounting for correlation between births from the same mother.

Results

The recurrence risk of perinatal death for women who had lost a previous baby was 9.1%. This amounted to a relative risk of 3.2 (95% CI: 2.2 - 4.7) compared to the much lower risk of 2.8% for women who had had a surviving baby. Recurrence contributed 21.2% (31/146) of perinatal deaths in subsequent pregnancies. Preeclampsia, placental abruption, placenta previa, induced labor, preterm delivery and low birth weight in a previous delivery with a surviving baby were also associated with increased perinatal mortality in the next pregnancy.

Conclusions

Some women in Tanzanian who suffer a perinatal loss in one pregnancy are at a particularly high risk of also losing the baby of a subsequent pregnancy. Strategies of perinatal death prevention that target pregnant women who are particularly vulnerable or already have experienced a perinatal loss should be considered in future research.

Recurrence of preterm birth and perinatal mortality in northern Tanzania: registry-based cohort study

OBJECTIVES

To estimate the recurrence risk of preterm delivery and estimate the perinatal mortality in repeated preterm deliveries.

METHODS

Prospective study in Tanzania of 18 176 women who delivered a singleton between 2000 and 2008 at KCMC hospital. The women were followed up to 2010 for consecutive births. A total of 3359 women were identified with a total of 3867 subsequent deliveries in the follow-up period. Recurrence risk of preterm birth and perinatal mortality was estimated using log-binomial regression and adjusted for potential confounders.

RESULTS

For women with a previous preterm birth, the risk of preterm birth in a subsequent pregnancy was 17%. This recurrence risk was estimated to be 2.7-fold (95% CI: 2.1-3.4) of the risk of women with a previous term birth. The perinatal mortality of babies in a second preterm birth of the same woman was 15%. Babies born at term who had an older sibling that was born preterm had a perinatal mortality of 10%. Babies born at term who had an older sibling who was also born at term had a perinatal mortality of 1.7%.

CONCLUSION

Previous delivery of a preterm infant is a strong predictor of future preterm births in Tanzania. Previous or repeated preterm births increase the risk of perinatal death substantially in the subsequent pregnancy.

The Impact of Cigarette Quitting during Pregnancy on Other Prenatal Health Behaviors

Several economic studies have evaluated the effects of cigarette smoking and quitting on other health behaviors such as alcohol use and weight gain. However, there is little research that evaluates the effects of cigarette quitting during pregnancy on other health behaviors such as caloric intake, alcohol consumption, multivitamin use, and caffeine intake. In this paper, we evaluate these effects and employ a genetic variant that predicts cigarette quitting to aid in identification. We find some evidence that cigarette quitting during pregnancy may increase multivitamin use and caloric intake and reduce caffeine consumption.

X-linked genes and risk of orofacial clefts: evidence from two population-based studies in Scandinavia

BACKGROUND

Orofacial clefts are common birth defects of complex etiology, with an excess of males among babies with cleft lip and palate, and an excess of females among those with cleft palate only. Although genes on the X chromosome have been implicated in clefting, there has been no association analysis of X-linked markers.

METHODOLOGY/PRINCIPAL FINDINGS

We added new functionalities in the HAPLIN statistical software to enable association analysis of X-linked markers and an exploration of various causal scenarios relevant to orofacial clefts. Genotypes for 48 SNPs in 18 candidate genes on the X chromosome were analyzed in two population-based samples from Scandinavia (562 Norwegian and 235 Danish case-parent triads). For haplotype analysis, we used a sliding-window approach and assessed isolated cleft lip with or without cleft palate (iCL/P) separately from isolated cleft palate only (iCPO). We tested three statistical models in HAPLIN, allowing for: i) the same relative risk in males and females, ii) sex-specific relative risks, and iii) X-inactivation in females. We found weak but consistent associations with the oral-facial-digital syndrome 1 (OFD1) gene (formerly known as CXORF5) in the Danish iCL/P samples across all models, but not in the Norwegian iCL/P samples. In sex-specific analyses, the association with OFD1 was in male cases only. No analyses showed associations with iCPO in either the Norwegian or the Danish sample.

CONCLUSIONS

The association of OFD1 with iCL/P is plausible given the biological relevance of this gene. However, the lack of replication in the Norwegian samples highlights the need to verify these preliminary findings in other large datasets. More generally, the novel analytic methods presented here are widely applicable to investigations of the role of X-linked genes in complex traits.

Genome wide study of maternal and parent-of-origin effects on the etiology of orofacial clefts

We performed a genome wide association analysis of maternally-mediated genetic effects and parent-of-origin (POO) effects on risk of orofacial clefting (OC) using over 2,000 case-parent triads collected through an international cleft consortium. We used log-linear regression models to test individual SNPs. For SNPs with a P-value <10(-5) for maternal genotypic effects, we also applied a haplotype-based method, TRIMM, to extract potential information from clusters of correlated SNPs. None of the SNPs were significant at the genome wide level. Our results suggest neither maternal genome nor POO effects play major roles in the etiology of OC in our sample. This finding is consistent with previous genetic studies and recent population-based cohort studies in Norway and Denmark, which showed no apparent difference between mother-to-offspring and father-to-offspring recurrence of clefting. We, however, cannot completely rule out maternal genome or POO effects as risk factors because very small effects might not be detectable with our sample size, they may influence risk through interactions with environmental exposures or may act through a more complex network of interacting genes. Thus, the most promising SNPs identified by this study may still be worth further investigation.

Smoking and body weight: evidence using genetic instruments

Several studies have evaluated whether the high and rising obesity rates over the past three decades may be due to the declining smoking rates. There is mixed evidence across studies - some find negative smoking effects and positive cigarette cost effects on body weight, while others find opposite effects. This study applies a unique approach to identify the smoking effects on body weight and to evaluate the heterogeneity in these effects across the body mass index (BMI) distribution by utilizing genetic instruments for smoking. Using a data sample of 1057 mothers from Norway, the study finds heterogeneous effects of cigarette smoking on BMI - smoking increases BMI at low/moderate BMI levels and decreases BMI at high BMI levels. The study highlights the potential advantages and challenges of employing genetic instrumental variables to identify behavior effects including the importance of qualifying the instruments and the need for large samples.

Assessing the impact of nicotine dependence genes on the risk of facial clefts: An example of the use of national registry and biobank data

BACKGROUND

Maternal smoking during pregnancy has been associated with risk of facial clefts in offspring, but causation has not yet been established. It is possible that the effect of maternal smoking on facial clefts is mediated through genes that are involved in nicotine dependence. Gamma-aminobutyric acid B receptor 2 (GABBR2), dopa decarboxylase (DDC), and cholinergic receptor nicotinic alpha 4 (CHRNA4) are three examples of genes that have previously shown strong associations with nicotine dependence.

METHODS

We used a population-based sample of 377 case-parent trios of cleft lip with or without cleft palate (CL/P) and 762 control-parent trios from Norway (1996-2001) to investigate whether variants in GABBR2, DDC and CHRNA4 are associated with maternal first-trimester smoking and with clefting risk. We used HAPLIN (Gjessing et al. 2006), a statistical software tailored for family-based association tests, to perform haplotype-based analyses on 12 SNPs in these genes (rs10985765, rs1435252, rs3780422, rs2779562, and rs3750344 in GABBR2; rs2060762, rs3757472, rs1451371, rs3735273, and rs921451 in DDC; rs4522666 and rs1044393 in CHRNA4).

RESULTS

When analyzed one at a time, there was little evidence of association between any of the 12 SNPs and maternal first-trimester smoking. In haplotype analyses, however, one copy of the maternal G-G-c-G-c haplotype in DDC was linked with smoking prevalence (odds ratio: 1.5; 95% confidence interval: 1.0-2.1). This same haplotype also increased the risk of isolated CL/P in offspring by 1.5-fold with one copy and 2.4-fold with two copies (P_trend = 0.06). No statistically significant associations were detected with GABBR2 and CHRNA4.

CONCLUSIONS

Despite strong associations previously reported between nicotine dependence and variants in GABBR2, DDC and CHRNA4, these genes were poor predictors of maternal first-trimester smoking in our data. The direct association of the DDC haplotype with CL/P suggests that this haplotype may either have direct effects on clefts or it may influence clefting risks through other yet unexplored risk behavior(s).