Genetically predicted 17beta-estradiol, cognitive function and depressive symptoms in women: A Mendelian randomization in the Guangzhou Biobank Cohort Study

Age at menarche relates to depression in adolescent girls: Comparing a clinical sample to the general pediatric population

CONTEXT

The timing of puberty, physical features of pubertal development, and hormones are closely intertwined but may also individually contribute to the risk for depression and depression severity. Additionally, their effects on mood may depend on depression severity, but previously this has only been studied in mostly subclinical depression.

METHODS

In 184 girls from a single psychiatric hospital with significant depressive symptoms (Beck Depression Inventory-II score > 13), the relationship between depression severity and age at menarche (AAM), pubertal status, and gonadal/adrenal hormones (estradiol, progesterone, DHEA-S, androstenedione, testosterone, dihydrotestosterone) was investigated. Moreover, AAM in depressed girls was compared to that from a representative sample of German adolescents without a psychiatric disorder (N = 1674). Androgen levels were compared to those of age- and sex-matched controls (N = 59).

RESULTS

AAM but not pubertal stage or biochemical parameters related to depression. Girls with AAM at the lower normative range of pubertal development were 61 % more likely to develop depression and scored 4.9 points higher on the depression scale than girls experiencing menarche at the population average. Androstenedione levels were increased in the psychiatric sample, but neither androgen nor gonadal hormone levels were associated with depression severity.

LIMITATIONS

The study is cross-sectional.

CONCLUSIONS

These observations confirm previous studies in mostly subclinical depression and highlight the importance of AAM for adolescent depression. Thus, AAM could be considered a prognostic factor for a clinical risk score assessing the probability of adolescent depression. Moreover, these findings suggest fostering efforts that address risk factors that contribute to an earlier AAM.

Causal Effect of Age at Menarche on the Risk for Depression: Results From a Two-Sample Multivariable Mendelian Randomization Study

A fair number of epidemiological studies suggest that age at menarche (AAM) is associated with depression, but the reported effect sizes are small, and there is evidence of residual confounding. Moreover, previous Mendelian randomization (MR) studies to avoid inferential problems inherent to epidemiological studies have provided mixed findings. To clarify the causal relationship between age at menarche and broadly defined depression risk, we used 360 genome-wide significantly AAM-related single-nucleotide polymorphisms (SNPs) as instrumental variable and data from the latest GWAS for the broadly defined depression risk on 807,553 individuals (246,363 cases and 561,190 controls). Multiple methods to account for heterogeneity of the instrumental variable (penalized weighted median, MR Lasso, and contamination mixture method), systematic and idiosyncratic pleiotropy (MR RAPS), and horizontal pleiotropy (MR PRESSO and multivariable MR using three methods) were used. Body mass index, education attainment, and total white blood count were considered pleiotropic phenotypes in the multivariable MR analysis. In the univariable [inverse-variance weighted (IVW): OR = 0.96, 95% confidence interval = 0.94–0.98, p = 0.0003] and multivariable MR analysis (IVW: OR = 0.96, 95% confidence interval = 0.94–0.99, p = 0.007), there was a significant causal effect of AAM on depression risk. Thus, the present study supports conclusions from previous epidemiological studies implicating AAM in depression without the pitfalls of residual confounding and reverse causation. Considering the adverse consequences of an earlier AAM on mental health, this finding should foster efforts to address risk factors that promote an earlier AAM.

Which Risk Factors Causally Influence Dementia? A Systematic Review of Mendelian Randomization Studies

Background:

Numerous risk factors for dementia are well established, though the causal nature of these associations remains unclear.

Objective:

To systematically review Mendelian randomization (MR) studies investigating causal relationships between risk factors and global cognitive function or dementia.

Methods:

We searched five databases from inception to February 2017 and conducted citation searches including MR studies investigating the association between any risk factor and global cognitive function, all-cause dementia or dementia subtypes. Two reviewers independently assessed titles and abstracts, full-texts, and study quality.

Results:

We included 18 MR studies investigating education, lifestyle factors, cardiovascular factors and related biomarkers, diabetes related and other endocrine factors, and telomere length. Studies were of predominantly good quality, however eight received low ratings for sample size and statistical power. The most convincing causal evidence was found for an association of shorter telomeres with increased risk of Alzheimer’s disease (AD). Causal evidence was weaker for smoking quantity, vitamin D, homocysteine, systolic blood pressure, fasting glucose, insulin sensitivity, and high-density lipoprotein cholesterol. Well-replicated associations were not present for most exposures and we cannot fully discount survival and diagnostic bias, or the potential for pleiotropic effects.

Conclusions:

Genetic evidence supported a causal association between telomere length and AD, whereas limited evidence for other risk factors was largely inconclusive with tentative evidence for smoking quantity, vitamin D, homocysteine, and selected metabolic markers. The lack of stronger evidence for other risk factors may reflect insufficient statistical power. Larger well-designed MR studies would therefore help establish the causal status of these dementia risk factors.

Age at menarche and depressive symptoms in older Southern Chinese women: A Mendelian randomization study in the Guangzhou Biobank Cohort Study

To clarify the causal role of age at menarche in depressive symptoms we conducted a Mendelian randomization study using a large Southern Chinese cohort (n = 12,233). A genetic allele score was derived using stepwise regression with cross validation. Older age at menarche was not associated with geriatric depression scale score. Our findings suggest that higher rates of depression in women are likely attributable to other factors which require investigation.

Polymorphisms in sex steroid receptors: From gene sequence to behavior

Sex steroid receptors have received much interest as potential mediators of human behaviors and mental disorders. Candidate gene association studies have identified about 50 genetic variants of androgen and estrogen receptors that correlate with human behavioral phenotypes. Because most of these polymorphisms lie outside coding regions, discerning their effect on receptor function is not straightforward. Thus, although discoveries of associations improve our ability to predict risk, they have not greatly advanced our understanding of underlying mechanisms. This article is intended to serve as a starting point for psychologists and other behavioral biologists to consider potential mechanisms. Here, I review associations between polymorphisms in sex steroid receptors and human behavioral phenotypes. I then consider ways in which genetic variation can affect processes such as mRNA transcription, splicing, and stability. Finally, I suggest ways that hypotheses about mechanism can be tested, for example using in vitro assays and/or animal models.