Intergenerational exchange and perinatal risks: a note on interpretation of generational recurrence risks

Clotting factor genes are associated with preeclampsia in high-altitude pregnant women in the Peruvian Andes

Preeclampsia is a multi-organ complication of pregnancy characterized by sudden hypertension and proteinuria that is among the leading causes of preterm delivery and maternal morbidity and mortality worldwide. The heterogeneity of preeclampsia poses a challenge for understanding its etiology and molecular basis. Intriguingly, risk for the condition increases in high-altitude regions such as the Peruvian Andes. To investigate the genetic basis of preeclampsia in a population living at high altitude, we characterized genome-wide variation in a cohort of preeclamptic and healthy Andean families (n = 883) from Puno, Peru, a city located above 3,800 meters of altitude. Our study collected genomic DNA and medical records from case-control trios and duos in local hospital settings. We generated genotype data for 439,314 SNPs, determined global ancestry patterns, and mapped associations between genetic variants and preeclampsia phenotypes. A transmission disequilibrium test (TDT) revealed variants near genes of biological importance for placental and blood vessel function. The top candidate region was found on chromosome 13 of the fetal genome and contains clotting factor genes PROZ, F7, and F10. These findings provide supporting evidence that common genetic variants within coagulation genes play an important role in preeclampsia. A selection scan revealed a potential adaptive signal around the ADAM12 locus on chromosome 10, implicated in pregnancy disorders. Our discovery of an association in a functional pathway relevant to pregnancy physiology in an understudied population of Native American origin demonstrates the increased power of family-based study design and underscores the importance of conducting genetic research in diverse populations.

Paternal Determinants in Preeclampsia

Preeclampsia is a condition associated with high rates of maternal-fetal morbidity and mortality. It usually occurs in 3–10% of nulliparous women and 18% of previously affected women. Different lines of evidence have demonstrated the role of the father in the onset of preeclampsia. The placenta is the cornerstone of preeclampsia and poses important paternal genetic determinants; in fact, the existence of a “paternal antigen” has been proposed. Nulliparity is a well-known risk factor. Change of partner to a woman without history of preeclampsia increases the risk; however, this change decreases in women with history of the condition. High interval between pregnancies, short sexual intercourse before pregnancy, and conception by intracytoplasmic sperm injection suggest a limited exposure to the so-called paternal antigen. A man who was born from a mother with preeclampsia also increases the risk to his partner. Not only maternal but also paternal obesity is a risk factor for preeclampsia. Fetal HLA-G variants from the father increased the immune incompatibility with the mother and are also significantly associated with preeclampsia in multigravida pregnancies. An analysis of a group of Swedish pregnant women showed that the risk for preeclampsia is attributable to paternal factors in 13% of cases, which could be related to genetic interactions with maternal genetic factors. This review aimed to evaluate the evidences of the father’s contribution to the onset of preeclampsia and determine the importance of including them in future studies.

The inherited risk of retained placenta: a population based cohort study

OBJECTIVE

To investigate whether retained placenta in the first generation is associated with an increased risk of retained placenta in the second generation.

DESIGN

Population-based cohort study.

SETTING

Sweden.

POPULATION

Using linked generational data from the Swedish Medical Birth Register 1973-2012, we identified 494 000 second-generation births with information on the birth of the mother (first-generation index birth). For 292 897 of these births there was information also on the birth of the father.

METHODS

Risk of retained placenta in the second generation was calculated as adjusted odds ratios (aOR) by unconditional logistic regression with 95% confidence intervals (95% CI) according to whether retained placenta occurred in a first generation birth or not.

MAIN OUTCOME

Retained placenta in the second generation.

RESULTS

The risk of retained placenta in a second-generation birth was increased if retained placenta had occurred at the mother's own birth (aOR 1.66, 95% CI 1.52-1.82), at the birth of one of her siblings (aOR 1.58, 95% CI 1.43-1.76) or both (aOR 2.75, 95% CI 2.18-3.46). The risk was slightly increased if retained placenta had occurred at the birth of the father (aOR 1.23, 95% CI 1.07-1.41). For preterm births in both generations, the risk of retained placenta in the second generation was increased six-fold if retained placenta had occurred at the mother's birth (OR 6.55, 95% CI 2.68-16.02).

CONCLUSION

There is an intergenerational recurrence of retained placenta on the maternal and most likely also on the paternal side. The recurrence risk seems strongest in preterm pregnancies.

TWEETABLE ABSTRACT

A population-based cohort study suggests that there is an intergenerational recurrence of retained placenta.

Familial Factors, Low Birth Weight, and Development of ESRD: A Nationwide Registry Study

BACKGROUND

Previous studies have demonstrated that low birth weight (LBW) is associated with higher risk for end-stage renal disease (ESRD). However, both LBW and ESRD cluster in families. The present study investigates whether familial factors explain the association between LBW and ESRD.

STUDY DESIGN

Retrospective registry-based cohort study.

SETTING & PARTICIPANTS

Since 1967, the Medical Birth Registry of Norway has recorded medical data for all births in the country. Sibling data are available through the Norwegian Population Registry. Since 1980, all patients with ESRD in Norway have been registered in the Norwegian Renal Registry. Individuals registered in the Medical Birth Registry with at least 1 registered sibling were included.

PREDICTOR

LBW in the participant and/or LBW in at least 1 sibling.

OUTCOME

ESRD.

RESULTS

Of 1,852,080 included individuals, 527 developed ESRD. Compared with individuals without LBW and with no siblings with LBW, individuals without LBW but with a sibling with LBW had an HR for ESRD of 1.20 (95% CI, 0.91-1.59), individuals with LBW but no siblings with LBW had an HR of 1.59 (95% CI, 1.18-2.14), and individuals with LBW and a sibling with LBW had an HR of 1.78 (95% CI, 1.26-2.53). Similar results were observed for individuals who were small for gestational age (SGA). Separate analyses for the association of age 18 to 42 years and noncongenital ESRD showed stronger associations for SGA than for LBW, and the associations were not statistically significant for age 18 to 42 years for LBW.

LIMITATIONS

Follow-up only until 42 years of age.

CONCLUSIONS

LBW and SGA are associated with higher risk for ESRD during the first 40 years of life, and the associations were not explained by familial factors. Our results support the hypothesis that impaired intrauterine nephron development may be a causal risk factor for progressive kidney disease.

Transgenerational developmental programming

BACKGROUND

The concept of developmental programming suggests that the early life environment influences offspring characteristics in later life, including the propensity to develop diseases such as the metabolic syndrome. There is now growing evidence that the effects of developmental programming may also manifest in further generations without further suboptimal exposure. This review considers the evidence, primarily from rodent models, for effects persisting to subsequent generations, and evaluates the mechanisms by which developmental programming may be transmitted to further generations. In particular, we focus on the potential role of the intrauterine environment in contributing to a developmentally programmed phenotype in subsequent generations.

METHODS

The literature was systematically searched at http://pubmed.org and http://scholar.google.com to identify published findings regarding transgenerational (F2 and beyond) developmental programming effects in human populations and animal models.

RESULTS

Transmission of programming effects is often viewed as a form of epigenetic inheritance, either via the maternal or paternal line. Evidence exists for both germline and somatic inheritance of epigenetic modifications which may be responsible for phenotypic changes in further generations. However, there is increasing evidence for the role of both extra-genomic components of the zygote and the interaction of the developing conceptus with the intrauterine environment in propagating programming effects.

CONCLUSIONS

The contribution of a suboptimal reproductive tract environment or maternal adaptations to pregnancy may be critical to inheritance of programming effects via the maternal line. As the effects of age exacerbate the programmed metabolic phenotype, advancing maternal age may increase the likelihood of developmental programming effects being transmitted to further generations. We suggest that developmental programming effects could be propagated through the maternal line de novo in generations beyond F2 as a consequence of development in a suboptimally developed intrauterine tract and not necessarily though directly transmitted epigenetic mechanisms.

Familial risk of obstetric anal sphincter injuries: registry-based cohort study

OBJECTIVE

To investigate the aggregation of obstetric anal sphincter injuries (OASIS) in relatives.

DESIGN

Population-based cohort study.

SETTING

The Medical Birth Registry of Norway from 1967 to 2008.

POPULATION

All singleton, vertex-presenting infants weighing 500 g or more. Through linkage by national identification numbers, 393 856 mother-daughter pairs, 264 675 mother-son pairs, 134 889 mothers whose sisters later became mothers, 132 742 fathers whose brothers later became fathers, 131 702 mothers whose brothers later became fathers and 88 557 fathers whose sisters later became mothers were provided.

METHODS

Comparison of women with and without a history of OASIS in their relatives.

MAIN OUTCOME MEASURE

Relative risk of OASIS after a previous OASIS in the family.

RESULTS

The risk of OASIS was increased if the woman's mother or sister had OASIS in a delivery (aRR 1.9, 95% CI 1.6-2.3; aRR 1.7, 95% CI 1.6-1.7, respectively). If OASIS occurred in one brother's partner at delivery, the risk of OASIS in the next brother's partner was modestly increased (aRR 1.2, 95% CI 1.1-1.4). If OASIS occurred in one sister at delivery, the risk of OASIS in the brother's partner was also increased a little (aRR 1.2, 95% CI 1.1-1.4). However, there was no excess occurrence in sisters whose brothers' partners had previously had OASIS (aRR 1.1, 95% CI 0.9-1.3).

CONCLUSIONS

There appears to be increased familial aggregation of OASIS. These risks are stronger through the maternal rather than the paternal line of transmission, suggesting a strong genetic role that shapes aggregation of OASIS within families. These observations must be cautiously interpreted because of bias from unmeasured confounding factors may have impacted the findings.

Familial factors in the association between preeclampsia and later ESRD

BACKGROUND AND OBJECTIVES

Women with preeclampsia have increased risk of developing ESRD. This study assessed whether this can be explained by preeclampsia itself or by familial aggregation of common risk factors.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Since 1967, the Medical Birth Registry of Norway has registered data on all births in the country. By linkage with the Norwegian Population Registry, different, but overlapping, cohorts were defined: the first and second cohorts included women and a sibling (first cohort) or child (second cohort) with a registered first birth between 1967 and 2008. Similar cohorts were defined for men. The Norwegian Renal Registry provided data on ESRD from 1980 to June 2009.

RESULTS

Cohort 1 was used for the main analyses and included 570,675 women, 291 of whom developed ESRD after a median 18.2 years. Compared with women without preeclampsia and no siblings with preeclampsia, women without preeclampsia but a sibling with preeclampsia had a relative risk (RR) of ESRD of 0.96 (95% confidence interval, 0.59-1.6), women with preeclampsia but no siblings with preeclampsia had a RR of 6.0 (4.4-8.1), and women with preeclampsia and a sibling with preeclampsia had a RR of 2.8 (0.88-8.6). Further analyses of women showed no increased risk of ESRD if a child had preeclampsia in first pregnancy.

CONCLUSIONS

Familial aggregation of risk factors does not seem to explain increased ESRD risk after preeclampsia. These findings support the hypothesis that preeclampsia per se may lead to kidney damage.

Recurrence of placental dysfunction disorders across generations

OBJECTIVE

Knowledge about the causes of placental dysfunction disorders is limited. We performed an intergenerational study, focusing on the risks of placental dysfunction disorders in mothers and fathers who had been born small for gestational age (SGA).

STUDY DESIGN

Using linked generational data from the Swedish Medical Birth Register from 1973-2006, we identified 321,383 mother-offspring units and 135,637 mother-father-offspring units.

RESULTS

Compared with mothers who had not been born SGA, mothers who had been born SGA had the following adjusted odds ratios: late preeclampsia, 1.41 (95% confidence interval [CI], 1.26-1.57); early preeclampsia, 1.87 (95% CI, 1.38-2.35); placental abruption, 1.60 (95% CI, 1.23-2.09); spontaneous preterm birth, 1.11 (95% CI, 1.00-1.23); and stillbirth, 1.24 (95% CI, 0.84-1.82). Compared with parents who had not been born SGA, the risk of preeclampsia was more than 3-fold increased if both parents had been born SGA, whereas if only the mother had been born SGA, the corresponding risk was increased by only 50%.

CONCLUSION

There is an intergenerational recurrence of placental dysfunction disorders on the maternal side and most likely also on the paternal side.

Mothers' and fathers' birth characteristics and perinatal mortality in their offspring: a population-based cohort study

There is increasing interest in the associations between parental birthweight and gestational age with their perinatal outcomes. We investigated perinatal mortality risk in offspring in relation to maternal and paternal gestational age and birthweight. We used population-based generational data from the Medical Birth Registry of Norway, 1967-2006. Singletons in both generations were included, forming 520,794 mother-offspring and 376,924 father-offspring units. Perinatal mortality in offspring was not significantly associated with paternal gestational age or birthweight, whereas it was inversely associated with maternal gestational age. A threefold increased risk in perinatal mortality was found among offspring of mothers born at 28-30 weeks of gestation relative to offspring of mothers born at term (37-43 weeks) (relative risk: 2.9, 95% CI 1.9, 4.6). There was also an overall association between maternal birthweight and offspring perinatal mortality. Relative risk for mothers whose birthweight was <2000 g was 1.5 (95% CI 1.1, 1.9), relative to mothers whose birthweight was 3500-3999 g. However, confined to mothers born at >or=34 weeks of gestation, the birthweight association was not significant. Weight-specific perinatal mortality in offspring was dependent on the birthweight of the mother and the father, that is, offspring who were small relative to their mother's or father's birthweight had increased perinatal mortality. In conclusion, a mother's gestational age, and not her birthweight, was significantly associated with perinatal mortality in the offspring, while there was no such association for the father.

Maternal and paternal contribution to intergenerational recurrence of breech delivery: population based cohort study

OBJECTIVE

To investigate intergenerational recurrence of breech delivery, with a hypothesis that both women and men delivered in breech presentation contribute to increased risk of breech delivery in their offspring.

DESIGN

Population based cohort study for two generations.

SETTING

Data from the medical birth registry of Norway, based on all births in Norway 1967-2004 (2.2 million births).

PARTICIPANTS

Generational data were provided through linkage by national identification numbers, forming 451,393 mother-offspring units and 295,253 father-offspring units. We included units where both parents and offspring were singletons and offspring were first born, forming 232,704 mother-offspring units and 154,851 father-offspring units for our analyses.

MAIN OUTCOME MEASURE

Breech delivery in the second generation.

RESULTS

Men and women who themselves were delivered in breech presentation had more than twice the risk of breech delivery in their own first pregnancies compared with men and women who had been cephalic presentations (odds ratios 2.2, 95% confidence interval 1.8 to 2.7, and 2.2, 1.9 to 2.5, for men and women, respectively). The strongest risks of recurrence were found for vaginally delivered offspring and were equally strong for men and women. Increased risk of recurrence of breech delivery in offspring was present only for parents delivered at term.

CONCLUSION

Intergenerational recurrence risk of breech delivery in offspring was equally high when transmitted through fathers and mothers. It seems reasonable to attribute the observed pattern of familial predisposition to term breech delivery to genetic inheritance, predominantly through the fetus.

Familial risk of oral clefts by morphological type and severity: population based cohort study of first degree relatives

OBJECTIVE

To estimate the relative risk of recurrence of oral cleft in first degree relatives in relation to cleft morphology.

DESIGN

Population based cohort study.

SETTING

Data from the medical birth registry of Norway linked with clinical data on virtually all cleft patients treated in Norway over a 35 year period.

PARTICIPANTS

2.1 million children born in Norway between 1967 and 2001, 4138 of whom were treated for an oral cleft.

MAIN OUTCOME MEASURE

Relative risk of recurrence of isolated clefts from parent to child and between full siblings, for anatomic subgroups of clefts.

RESULTS

Among first degree relatives, the relative risk of recurrence of cleft was 32 (95% confidence interval 24.6 to 40.3) for any cleft lip and 56 (37.2 to 84.8) for cleft palate only (P difference=0.02). The risk of clefts among children of affected mothers and affected fathers was similar. Risks of recurrence were also similar for parent-offspring and sibling-sibling pairs. The "crossover" risk between any cleft lip and cleft palate only was 3.0 (1.3 to 6.7). The severity of the primary case was unrelated to the risk of recurrence.

CONCLUSIONS

The stronger family recurrence of cleft palate only suggests a larger genetic component for cleft palate only than for any cleft lip. The weaker risk of crossover between the two types of cleft indicates relatively distinct causes. The similarity of mother-offspring, father-offspring, and sibling-sibling risks is consistent with genetic risk that works chiefly through fetal genes. Anatomical severity does not affect the recurrence risk in first degree relatives, which argues against a multifactorial threshold model of causation.