Allison M. Momany

Genetic Associations with Gestational Duration and Spontaneous Preterm Birth

BACKGROUND Despite evidence that genetic factors contribute to the duration of gestation and the risk of preterm birth, robust associations with genetic variants have not been identified. We used large data sets that included the gestational duration to determine possible genetic associations. METHODS We performed a genomewide association study in a discovery set of samples obtained from 43,568 women of European ancestry using gestational duration as a continuous trait and term or preterm (<37 weeks) birth as a dichotomous outcome. We used samples from three Nordic data sets (involving a total of 8643 women) to test for replication of genomic loci that had significant genomewide association (P<5.0×10‐8) or an association with suggestive significance (P<1.0×10‐6) in the discovery set. RESULTS In the discovery and replication data sets, four loci (EBF1, EEFSEC, AGTR2, and WNT4) were significantly associated with gestational duration. Functional analysis showed that an implicated variant in WNT4 alters the binding of the estrogen receptor. The association between variants in ADCY5 and RAP2C and gestational duration had suggestive significance in the discovery set and significant evidence of association in the replication sets; these variants also showed genomewide significance in a joint analysis. Common variants in EBF1, EEFSEC, and AGTR2 showed association with preterm birth with genomewide significance. An analysis of mother–infant dyads suggested that these variants act at the level of the maternal genome. CONCLUSIONS In this genomewide association study, we found that variants at the EBF1, EEFSEC, AGTR2, WNT4, ADCY5, and RAP2C loci were associated with gestational duration and variants at the EBF1, EEFSEC, and AGTR2 loci with preterm birth. Previously established roles of these genes in uterine development, maternal nutrition, and vascular control support their mechanistic involvement. (Funded by the March of Dimes and others.)

Genetic Associations of Surfactant Protein D and Angiotensin-Converting Enzyme with Lung Disease in Preterm Neonates

Objective:To replicate genetic associations with respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD) in genes related to surfactant deficiency, inflammation and infection, and the renin–angiotensin system.Study Design:We examined eight candidate genes for associations with RDS and BPD in 433 preterm birth (PTB—<37 weeks) infants (251 with RDS and 134 with BPD). Both case–control and family-based analyses were performed in preterm (<37 weeks) and very preterm birth (VPTB—<32 weeks) infants.Result:We replicated a previous finding that rs1923537, a marker downstream of surfactant protein D (SFTPD) is associated with RDS in VPTB infants in that the T allele was overtransmitted from parents to offspring with RDS (P=8.4 × 10−3). We also observed the A allele of rs4351 in the angiotensin-converting enzyme (ACE) gene was overtransmitted from parents to VPTB offspring with BPD (P=9.8 × 10−3).Conclusion:These results give further insight into the genetic risk factors for complex neonatal respiratory diseases and provide more evidence of the importance of SFTPD and ACE in the etiology of RDS and BPD, respectively.

Sequence variants in oxytocin pathway genes and preterm birth: a candidate gene association study

BackgroundPreterm birth (PTB) is a complex disorder associated with significant neonatal mortality and morbidity and long-term adverse health consequences. Multiple lines of evidence suggest that genetic factors play an important role in its etiology. This study was designed to identify genetic variation associated with PTB in oxytocin pathway genes whose role in parturition is well known.MethodsTo identify common genetic variants predisposing to PTB, we genotyped 16 single nucleotide polymorphisms (SNPs) in the oxytocin (OXT), oxytocin receptor (OXTR), and leucyl/cystinyl aminopeptidase (LNPEP) genes in 651 case infants from the U.S. and one or both of their parents. In addition, we examined the role of rare genetic variation in susceptibility to PTB by conducting direct sequence analysis of OXTR in 1394 cases and 1112 controls from the U.S., Argentina, Denmark, and Finland. This study was further extended to maternal triads (maternal grandparents-mother of a case infant, N=309). We also performed in vitro analysis of selected rare OXTR missense variants to evaluate their functional importance.ResultsMaternal genetic effect analysis of the SNP genotype data revealed four SNPs in LNPEP that show significant association with prematurity. In our case–control sequence analysis, we detected fourteen coding variants in exon 3 of OXTR, all but four of which were found in cases only. Of the fourteen variants, three were previously unreported novel rare variants. When the sequence data from the maternal triads were analyzed using the transmission disequilibrium test, two common missense SNPs (rs4686302 and rs237902) in OXTR showed suggestive association for three gestational age subgroups. In vitro functional assays showed a significant difference in ligand binding between wild-type and two mutant receptors.ConclusionsOur study suggests an association between maternal common polymorphisms in LNPEP and susceptibility to PTB. Maternal OXTR missense SNPs rs4686302 and rs237902 may have gestational age-dependent effects on prematurity. Most of the OXTR rare variants identified do not appear to significantly contribute to the risk of PTB, but those shown to affect receptor function in our in vitro study warrant further investigation. Future studies with larger sample sizes are needed to confirm the findings of this study.

Replication of genetic associations in the inflammation, complement, and coagulation pathways with intraventricular hemorrhage in LBW preterm neonates.

Intraventricular hemorrhage (IVH) is a significant morbidity seen in very LBW infants. Genes related to the inflammation, infection, complement, or coagulation pathways have been implicated as risk factors for IVH. We examined 10 candidate genes for associations with IVH in 271 preterm infants (64 with IVH grades I–IV and 207 without IVH) weighing <1500 g. The heterozygous genotype OR = 8.1, CI = 2.5–26.0, p = 4 × 10−4) and the A allele (OR = 7.3, CI = 2.4–22.5, p = 1 × 10−4) of the coagulation factor V (FV) Leiden mutation (rs6025) were associated with an increased risk of developing IVH grade I or II but not grade III or IV after correction for multiple testing with Bonferroni. Lack of association in the severe grades of IVH may be a result of lack of power to detect an effect given the small sample size (n = 8). However, this result is consistent with previous research that demonstrates that the heterozygous genotype of the FV mutation is associated with increased risk for the development of IVH but a decreased risk for the progression or extension to more severe grades of IVH.

Genetic Variants Associated With Severe Retinopathy of Prematurity in Extremely Low Birth Weight Infants

PURPOSE To determine genetic variants associated with severe retinopathy of prematurity (ROP) in a candidate gene cohort study of US preterm infants. METHODS Preterm infants in the discovery cohort were enrolled through the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network, and those in the replication cohort were from the University of Iowa. All infants were phenotyped for ROP severity. Because of differences in the durations of enrollment between cohorts, severe ROP was defined as threshold disease in the discovery cohort and as threshold disease or type 1 ROP in the replication cohort. Whole genome amplified DNA from stored blood spot samples from the Neonatal Research Network biorepository was genotyped using an Illumina GoldenGate platform for candidate gene single nucleotide polymorphisms (SNPs) involving angiogenic, developmental, inflammatory, and oxidative pathways. Three analyses were performed to determine significant epidemiologic variables and SNPs associated with levels of ROP severity. Analyses controlled for multiple comparisons, ancestral eigenvalues, family relatedness, and significant epidemiologic variables. Single nucleotide polymorphisms significantly associated with ROP severity from the discovery cohort were analyzed in the replication cohort and in meta-analysis. RESULTS Eight hundred seventeen infants in the discovery cohort and 543 in the replication cohort were analyzed. Severe ROP occurred in 126 infants in the discovery and in 14 in the replication cohort. In both cohorts, ventilation days and seizure occurrence were associated with severe ROP. After controlling for significant factors and multiple comparisons, two intronic SNPs in the gene BDNF (rs7934165 and rs2049046, P < 3.1 × 10(-5)) were associated with severe ROP in the discovery cohort and were not associated with severe ROP in the replication cohort. However, when the cohorts were analyzed together in an exploratory meta-analysis, rs7934165 increased in associated significance with severe ROP (P = 2.9 × 10(-7)). CONCLUSIONS Variants in BDNF encoding brain-derived neurotrophic factor were associated with severe ROP in a large candidate gene study of infants with threshold ROP.

Polymorphisms in the fetal progesterone receptor and a calcium-activated potassium channel isoform are associated with preterm birth in an Argentinian population

Objective:To investigate genetic etiologies of preterm birth (PTB) in Argentina through evaluation of single-nucleotide polymorphisms (SNPs) in candidate genes and population genetic admixture.Study Design:Genotyping was performed in 389 families. Maternal, paternal and fetal effects were studied separately. Mitochondrial DNA (mtDNA) was sequenced in 50 males and 50 females. Y-chromosome anthropological markers were evaluated in 50 males.Result:Fetal association with PTB was found in the progesterone receptor (PGR, rs1942836; P=0.004). Maternal association with PTB was found in small conductance calcium activated potassium channel isoform 3 (KCNN3, rs883319; P=0.01). Gestational age associated with PTB in PGR rs1942836 at 32–36 weeks (P=0.0004). MtDNA sequencing determined 88 individuals had Amerindian consistent haplogroups. Two individuals had Amerindian Y-chromosome consistent haplotypes.Conclusion:This study replicates single locus fetal associations with PTB in PGR, maternal association in KCNN3, and demonstrates possible effects for divergent racial admixture on PTB.

Maternal and neonatal epidemiological features in clinical subtypes of preterm birth

Abstract Objective: This study was designed to characterize and compare the maternal and newborn epidemiological characteristics through analysis of environmental factors, sociodemographic characteristics and clinical characteristics between the different clinical subtypes of preterm birth (PTB): Idiopathic (PTB-I), premature rupture of the membranes (PTB-PPROM) and medically indicated (PTB-M). The two subtypes PTB-I and PTB-PPROM grouped are called spontaneous preterm births (PTB-S). Methods: A retrospective, observational study was conducted in 1.291 preterm nonmalformed singleton live-born children to nulliparous and multiparous mother’s in Tucumán-Argentina between 2005 and 2010. Over 50 maternal variables and 10 newborn variables were compared between the different clinical subtypes. The comparisons were done to identify heterogeneity between subtypes of preterm birth: (PTB-S) versus (PTB-M), and within spontaneous subtype: (PTB-I) versus (PTB-PPROM). In the same way, two conditional logistic multivariate regressions were used to compare the odds ratio (OR) between PTB-S and PTB-M, as well as PTB-I and PTB-PPROM. We matched for maternal age when comparing maternal variables and gestational age when comparing infant variables. Results: The PTB-I subtype was characterized by younger mothers of lower socio-economic status, PTB-PPROM was characterized by environmental factors resulting from inflammatory processes, and PTB-M was characterized by increased maternal or fetal risk pregnancies. Conclusions: The main risk factor for PTB-I and PTB-M was having had a prior preterm delivery; however, previous spontaneous abortion was not a risk factor, suggesting a reproductive selection mechanism.

Use of selective serotonin reuptake inhibitors (SSRIs) during pregnancy and disorganized infant-mother attachment

Objective: To examine the quality of infant–mother attachment in a prospective case series of infants whose mothers took selective serotonin reuptake inhibitors (SSRIs) during pregnancy. Background: SSRIs are prescribed to 2–6% of pregnant women. Recent articles on the use of SSRIs during pregnancy note the increased risk for problematic infant–mother relationships among mothers with untreated postpartum depression. However, little is known about the quality of infant–mother relationships among mothers who took SSRIs during pregnancy. Methods: Five mothers who took SSRIs during pregnancy were recruited from a community study of infant development. Mothers completed ratings of postpartum depression symptoms (Beck Depression Inventory) 4–6 times between 1 month and 1 year following the infant’s birth. At 1 year postpartum, quality of infant–mother attachment was assessed using the strange situation procedure. Results: Four of the five infant–mother dyads (80%) were classified as disorganised, a rate considerably higher than in postpartum depression samples. Conclusion: These results are used to raise questions about the clinical implications of research on in utero exposure to SSRIs, perinatal depression, and disorganised attachment. Specifically, this case series raises questions about using research on the link between postpartum depression and infant–mother attachment as a rationale for the use of SSRIs during pregnancy. Current research indicates use of SSRIs during pregnancy may: (1) increase risk for disorganised attachment, (2) decrease risk for disorganised attachment, or (3) have no effect on disorganised attachment.

A Meta-Analysis of the Association Between Birth Weight and Attention Deficit Hyperactivity Disorder

A large body of work has investigated the association between birth weight and ADHD and has resulted in mixed findings with regard to the direction and magnitude of this association. Despite the vast amount of research on this topic, a comprehensive and systematic quantification of the association between birth weight and ADHD has yet to be undertaken. A meta-analysis of 88 unique studies (N = 4,645,482) was conducted to quantify the overall effect size of birth weight on ADHD symptoms. Several variables were examined as moderators that may contribute to systematic variation in effect sizes. Overall, birth weight was found to have a small, but significant, association with ADHD symptoms such that individuals born at lower birth weights manifested greater symptoms of ADHD (r = −0.15). Sample type, mean birth weight of the sample, geographic region, the informant of ADHD symptoms, ADHD symptom measurement method, and race were all found to contribute significantly to heterogeneity in effect sizes. Notably, several early life risk factors previously found to be associated with both ADHD and birth weight, gestational age and prenatal smoking exposure, were not found to contribute to heterogeneity in effect sizes. The findings of the current analyses align with the growing recognition that early life adversity contributes to neurodevelopmental difficulties, and the findings highlight the importance of a better understanding of the mechanisms underlying the association between early life risk factors and adverse neurodevelopmental sequela, such as that observed in ADHD.

DRD4 Variants Moderate the Impact of Parental Characteristics on Child Attention-Deficit Hyperactivity Disorder: Exploratory Evidence from a Multiplex Family Design

Parental ADHD symptomatology and related impairments have been robustly associated with youth ADHD across decades of work. Notably, these factors may impede typical development of child self-regulation capabilities through both neurobiological and interpersonal processes. High heritability of estimates for the disorder further suggest that these effects are likely genetically-mediated, at least in part. Variation within the dopamine D4 receptor gene (DRD4) has been shown to moderate parental influences on youth ADHD. Use of a multiplex family design (i.e., samples of families that included multiple affected members) may facilitate identification of additional gene variants of interest and advance understanding of gene-environment interplay in regard to parenting. Thirty multiplex families consisting of 114 individuals (66 youth, 48 parents) completed a multi-stage, multi-informant diagnostic and neurocognitive assessment, measures of parenting, and provided saliva samples for DNA analyses. Sanger sequencing of the DRD4 gene yielded 16 rare variants; a polygenic risk score was computed for both parents and youth. Generalized estimating equations (GEE) examined the predictive effects of parental ADHD symptoms, parental neurocognitive functioning, and poor parenting dimensions on youth ADHD as well as moderation of these effects by parental and youth DRD4 variants. Findings indicated that parental DRD4 variants moderated the impact of parental ADHD and neurocognitive functioning on youth ADHD symptoms. Youth DRD4 variants moderated the impact of parental inconsistent discipline on child ADHD. In all cases, stronger associations were observed for those individuals with more risk variants. These exploratory findings highlight the potential utility of a multiplex family design for examining the interplay between parent and child characteristics in predicting youth outcomes.