Maternal Polycystic Ovary Syndrome and Offspring Birth Weight: A Mendelian Randomization Study

Methodological approaches, challenges, and opportunities in the application of Mendelian randomisation to lifecourse epidemiology: A systematic literature review

Diseases diagnosed in adulthood may have antecedents throughout (including prenatal) life. Gaining a better understanding of how exposures at different stages in the lifecourse influence health outcomes is key to elucidating the potential benefits of disease prevention strategies. Mendelian randomisation (MR) is increasingly used to estimate causal effects of exposures across the lifecourse on later life outcomes. This systematic literature review explores MR methods used to perform lifecourse investigations and reviews previous work that has utilised MR to elucidate the effects of factors acting at different stages of the lifecourse. We conducted searches in PubMed, Embase, Medline and MedRXiv databases. Thirteen methodological studies were identified. Four studies focused on the impact of time-varying exposures in the interpretation of "standard" MR techniques, five presented methods for repeat measures of the same exposure, and four described methodological approaches to handling multigenerational exposures. A further 127 studies presented the results of an applied research question. Over half of these estimated effects in a single generation and were largely confined to the exploration of questions regarding body composition. The remaining mostly estimated maternal effects. There is a growing body of research focused on the development and application of MR methods to address lifecourse research questions. The underlying assumptions require careful consideration and the interpretation of results rely on select conditions. Whilst we do not advocate for a particular strategy, we encourage practitioners to make informed decisions on how to approach a research question in this field with a solid understanding of the limitations present and how these may be affected by the research question, modelling approach, instrument selection, and data availability.

Investigating the association of previously identified genome-wide significant loci (rs10739076 and rs1784692) with PCOS susceptibility and its related traits in Indian women

OBJECTIVE(S)

Polycystic ovary syndrome (PCOS) is a multifactorial endocrinopathy with an enigmatic etiology. Hallmark features include irregular menstrual cycles, insulin resistance and hyperandrogenemia and affected women are prone to development of adverse reproductive and cardiometabolic outcomes like anovulatory infertility, impaired glucose tolerance, type 2 diabetes, dyslipidemia, metabolic syndrome and cardiovascular disease. Genetic underpinnings of PCOS have been investigated extensively using genome-wide association studies, which have led to the identification of several novel susceptibility loci. However, as ethnic diversity contributes to phenotypic and genetic heterogeneity, we undertook the first genetic association study to determine the association of rs10739076 of PLGRKT and rs1784692 of ZBTB16 with PCOS susceptibility and its related traits in Indian women.

STUDY DESIGN

The present case-control study comprised 497 women with PCOS diagnosed according to the Rotterdam criteria and 233 age matched healthy women as controls. All participants were characterized in terms of anthropometric, hormonal and metabolic parameters and the variants were investigated by direct sequencing. Genotypic and genotype-phenotype association of these variants with PCOS susceptibility and its related biochemical and hormonal traits was analyzed with appropriate statistical tests.

RESULTS

The genotypic and allelic frequencies of rs1784692 of ZBTB16 were significantly decreased in lean women with PCOS only, and this variant was associated with lowered insulin levels, HOMA-IR, LH:FSH ratio along with increased ApoA1 levels and QUICKI in them. Although, the PLGRKT variant, rs10739076, showed similar frequency distribution in both lean and obese groups, it was found to be associated with reduced fasting glucose in all women with PCOS.

CONCLUSION(S)

To the best of our knowledge, this is the first study to demonstrate that ZBTB16 variant showed significant association with reduced PCOS susceptibility in lean rather than obese Indian women, highlighting the impact of obesity on determining genetic predisposition to PCOS in Indian women. In contrast, PLGRKT variant did not influence PCOS risk in lean or obese women. Importantly, both variants exerted a protective effect on glucose metabolism, insulin resistance, gonadotropin and lipid levels in women with PCOS. Determination of susceptibility variants for PCOS demand population specific replication studies to ascertain best candidate loci for PCOS.

Investigating the causal impact of polycystic ovary syndrome on gestational diabetes mellitus: a two-sample Mendelian randomization study

Introduction

Determining the causal relationship between polycystic ovary syndrome (PCOS) and gestational diabetes mellitus (GDM) holds significant implications for GDM prevention and treatment. Despite numerous observational studies suggesting an association between PCOS and GDM, it remains unclear whether a definitive causal relationship exists between these two conditions and which specific features of PCOS contribute to increased incidence of GDM.

Methods

The causal relationship between polycystic ovary syndrome (PCOS), its characteristic indices, and gestational diabetes mellitus (GDM) was investigated using a two-sample Mendelian randomization study based on publicly available statistics from genome-wide association studies (GWAS). The inverse-variance weighted method was employed as the primary analytical approach to examine the association between PCOS, its characteristic indices, and GDM. MR Egger intercept was used to assess pleiotropy, while Q values and their corresponding P values were utilized to evaluate heterogeneity. It is important to note that this study adopts a two-sample MR design where PCOS and its characteristic indices are considered as exposures, while GDM is treated as an outcome.

Results

The study results indicate that there is no causal relationship between PCOS and GDM (all methods P > 0.05, 95% CI of OR values passed 1). The IVW OR value was 1.007 with a 95% CI of 0.906 to 1.119 and a P value of 0.904. Moreover, the MR Egger Q value was 8.141 with a P value of 0.701, while the IVW Q value was also 8.141 with a P value of 0.774, indicating no significant heterogeneity. Additionally, the MR Egger intercept was 0.0004, which was close to zero with a P value of 0.988, suggesting no pleiotropy. However, the study did find a causal relationship between several other factors such as testosterone, high-density lipoprotein, sex hormone-binding globulin, body mass index, waist-hip ratio, apolipoprotein A-I, number of children, diabetes illnesses of mother, father and siblings, hemoglobin A1c, fasting insulin, fasting blood glucose, years of schooling, and GDM based on the IVW method.

Conclusion

We observed no association between genetically predicted PCOS and the risk of GDM, implying that PCOS itself does not confer an increased susceptibility to GDM. The presence of other PCOS-related factors such as testosterone, high-density lipoprotein, and sex hormone-binding globulin may elucidate the link between PCOS and GDM. Based on these findings, efforts aimed at preventing GDM in individuals with PCOS should prioritize those exhibiting high-risk features rather than encompassing all women with PCOS.

Polycystic ovary syndrome and adverse pregnancy outcomes: potential role of decidual function

Polycystic ovary syndrome (PCOS) is a common endocrine disorder affecting fertility and mental health among women of reproductive age. In addition to anovulation and hyperandrogenism, patients also experience metabolic issues, such as insulin resistance, obesity, and dyslipidemia, as well as chronic low-grade inflammation throughout the body. Recent studies have shown that even with assisted reproductive technology to treat anovulatory issues, patients with PCOS still have higher rates of adverse pregnancy outcomes and abortion compared to normal pregnancies. These findings suggest that PCOS may impair the endometrium and disrupt the onset and maintenance of healthy pregnancies. Decidualization is a crucial step in the process of healthy pregnancy, during which endometrial stromal cells (ESCs) differentiate into secretory decidual stromal cells (DSCs) regulated by hormones and local metabolism. This article comprehensively reviews the pathological processes of PCOS and the mechanisms involved in its impaired decidualization. In addition, we explore how PCOS increases the incidence of adverse pregnancy outcomes (APO). By gaining a better understanding of the adverse effects of PCOS on pregnancy and its specific mechanisms, we hope to provide a theoretical basis for reducing APO and improving the live birth rate among women with PCOS.

Maternal Testosterone and Offspring Birth Weight: A Mendelian Randomization Study

CONTEXT

Evidence has shown maternal androgen levels in both the general population and populations with hyperandrogenic disorders are inversely associated with offspring birth weight.

CONTEXT

We aimed to investigate the causal effect of maternal testosterone levels in the general population on offspring birth weight and preterm delivery risk using a two-sample Mendelian randomization (MR) method.

METHODS

We obtained independent genetic instruments from a sex-specific genome-wide association study with up to 230 454 females of European descent from the UK Biobank. Genetic instruments with consistent testosterone effects but no aggregate effect on sex hormone-binding globulin were used to perform the main analysis. Summary-level data of offspring birth weight adjusted for genotype were obtained from a study with 210 406 females of European descent. Summary-level data of preterm delivery were obtained from the FinnGen study (6736 cases and 116 219 controls).

RESULTS

MR analysis showed that each SD (0.62 nmol/L) increase in testosterone levels could reduce the offspring birth weight by 37.26 g (95% CI, 19.59-54.94 g; P = 3.62 × 10-5). Each SD increase in testosterone levels was also associated with an increased risk of preterm delivery (odds ratio = 1.329; 95% CI, 1.161-1.520; P = 3.57 × 10-5). Similar results were found using different MR methods and multivariable MR analyses.

CONCLUSION

This two-sample MR study showed genetically determined higher circulating testosterone levels in females from the general population were associated with low birth weight of offspring and increased risk of preterm delivery.