Estimating the causal effect of frailty index on vestibular disorders: A two-sample Mendelian randomization

A multi-ancestry genetic study of pain intensity in 598,339 veterans

Chronic pain is a common problem, with more than one-fifth of adult Americans reporting pain daily or on most days. It adversely affects the quality of life and imposes substantial personal and economic costs. Efforts to treat chronic pain using opioids had a central role in precipitating the opioid crisis. Despite an estimated heritability of 25-50%, the genetic architecture of chronic pain is not well-characterized, in part because studies have largely been limited to samples of European ancestry. To help address this knowledge gap, we conducted a cross-ancestry meta-analysis of pain intensity in 598,339 participants in the Million Veteran Program, which identified 126 independent genetic loci, 69 of which are new. Pain intensity was genetically correlated with other pain phenotypes, level of substance use and substance use disorders, other psychiatric traits, education level and cognitive traits. Integration of the genome-wide association studies findings with functional genomics data shows enrichment for putatively causal genes (n = 142) and proteins (n = 14) expressed in brain tissues, specifically in GABAergic neurons. Drug repurposing analysis identified anticonvulsants, β-blockers and calcium-channel blockers, among other drug groups, as having potential analgesic effects. Our results provide insights into key molecular contributors to the experience of pain and highlight attractive drug targets.

Investigating causal relationships between extensive peripheral immune cell phenotypes and preeclampsia: A bi-directional Mendelian randomization analysis

PROBLEM

Preeclampsia, a multifaceted condition during pregnancy characterized by hypertension and organ dysfunction, poses significant risks to both maternal and fetal health. This study aims to investigate the bidirectional causal relationship between peripheral immune cell phenotypes and preeclampsia using a two-sample Mendelian randomization (MR) approach.

METHOD OF STUDY

Genetic data from two sizable cohorts were utilized: 3757 individuals from Sardinia, providing information on 731 immune traits, and 200 929 Finnish adult females, encompassing 6663 preeclampsia cases. Single-nucleotide polymorphisms served as instrumental variables. The MR analyses employed the inverse variance-weighted (IVW) method as the primary tool, supplemented by MR-Egger, weighted median, and weighted mode methods to enhance reliability and address potential heterogeneity and horizontal pleiotropy.

RESULTS

Among the 731 immune cell phenotypes studied, 18 displayed a suggestive positive association (IVW p < .05) with heightened preeclampsia risk, while 20 exhibited a suggestive negative association linked to reduced risk. Following false discovery rate (FDR) adjustment, four immune phenotypes showed significant associations with decreased preeclampsia risk: CD27 on CD24+ CD27+ B cells (B-cell panel) (odds ratio [OR] = 0.927, PFDR = 0.061), CD33+ HLA DR+ CD14- absolute count (OR = 0.963, PFDR = 0.061), CD80 on plasmacytoid dendritic cells (OR = 0.923, PFDR = 0.061); and CD80 on CD62L+ plasmacytoid dendritic cells (OR = 0.923, PFDR = 0.061). In the reverse-direction MR analysis, no significant causal effects of preeclampsia on immune cell phenotypes were observed.

CONCLUSIONS

This study provides quantifiable evidence linking specific immune cell phenotypes to the risk of developing preeclampsia. This novel understanding of the immunological aspects underlying preeclampsia's pathogenesis could lead to innovative therapeutic strategies centered on immune modulation.

Genetic liability to frailty in relation to functional outcome after ischemic stroke

BACKGROUND

Frailty appears to be associated with unfavorable prognosis after stroke in observational studies, but the causality remains largely unknown.

AIMS

The aim of this study is to investigate the potential causal effect of frailty on functional outcome at 3 months after ischemic stroke using the Mendelian randomization (MR) framework.

METHODS

Genetic instruments for frailty index were identified in a genome-wide association study meta-analysis including 175,226 individuals of European descent. Corresponding genetic association estimates for functional outcome after ischemic stroke at 90 days were taken from the Genetic of Ischemic Stroke Functional Outcome (GISCOME) network of 6021 patients. We performed inverse-variance weighted MR as the main analyses, followed by several alternate methods and sensitivity analyses.

RESULTS

In univariable MR, we found evidence that genetically predicted higher frailty index (odds ratio (OR) = 5.12; 95% confidence interval (CI) = 1.31-20.09; p = 0.019) was associated with worse functional outcome (modified Rankin Scale score ⩾3) after ischemic stroke. In further multivariable MR adjusting for potential confounding traits including body mass index, C-reactive protein, inflammatory bowel disease, and smoking initiation, the overall patterns between genetic liability to frailty and poor functional outcome status remained. Sensitivity analyses with complementary methods and with model unadjusted for baseline stroke severity (OR = 4.19; 95% CI = 1.26-13.90; p = 0.019) yielded broadly concordant results.

CONCLUSIONS

The present MR study suggested a possible causal effect of frailty on poor functional outcome after ischemic stroke. Frailty might represent a potential target for intervention to improve recovery after ischemic stroke.

Assessment of the bidirectional causal association between frailty and depression: A Mendelian randomization study

BACKGROUND

Observational studies have demonstrated a strong bidirectional association between frailty and depression, but it remains unclear whether this association reflects causality. This study aimed to examine the bidirectional causal relationship between frailty and depression.

METHODS

Using genome-wide association study summary data, two-sample Mendelian randomization was performed to test for the potential bidirectional causality between frailty, as defined by both the frailty index and the frailty phenotype, and depression. Several frailty-related traits were additionally investigated, including weaker hand grip strength, slower walking pace and physical inactivity. Findings were replicated using an independent depression data source and verified using multiple sensitivity analyses.

RESULTS

Genetically predicted higher frailty index (odds ratio [OR], 1.86; P < 0.001), higher frailty phenotype score (OR, 2.79; P < 0.001), lower grip strength (OR, 1.23; P = 0.003), slower walking pace (OR, 1.55; P = 0.027) and physical inactivity (OR, 1.44; P = 0.003) all were associated with a higher risk of depression. As for the reverse direction, genetic liability to depression showed consistent associations with a higher frailty index (beta, 0.167; P < 0.001) and a higher frailty phenotype score (beta, 0.067; P = 0.001), but not with other frailty-related traits that were investigated. The results were stable across sensitivity analyses and across depression datasets.

CONCLUSIONS

Our findings add novel evidence supporting the bidirectional causal association between frailty and depression. Improving balance and muscle strength and increasing physical activity may be beneficial in both depression and frailty.

Can Intelligence Affect Alcohol-, Smoking-, and Physical Activity-Related Behaviors? A Mendelian Randomization Study

People with high levels of intelligence are more aware of risk factors, therefore choosing a healthier lifestyle. This assumption seems reasonable, but is it true? Previous studies appear to agree and disagree. To cope with the uncertainty, we designed a mendelian randomization (MR) study to examine the causal effects of genetically proxied intelligence on alcohol-, smoking-, and physical activity (PA)-related behaviors. We obtained genome-wide association study (GWAS) datasets concerning these variables from separate studies or biobanks and used inverse-variance weighted (IVW) or MR-Egger estimator to evaluate the causal effects according to an MR protocol. The MR-Egger intercept test, MR-PRESSO, and funnel plots were employed for horizontal pleiotropy diagnosis. The Steiger test (with reliability test), Cochran's Q test, MR-PRESSO, and leave-one-out method were employed for sensitivity analysis. We found significant or potential effects of intelligence on alcohol dependence (OR = 0.749, p = 0.003), mental and behavioral disorders due to alcohol (OR = 0.814, p = 0.009), smoking (OR = 0.585, p = 0.005), and smoking cessation (OR = 1.334, p = 0.001). Meanwhile, we found significant or potential effects on walking duration (B = -0.066, p < 0.001), walking frequency (B = -0.055, p = 0.031), moderate PA frequency (B = -0.131, p < 0.001), and vigorous PA frequency (B = -0.070, p = 0.001), but all in a negative direction. In conclusion, our findings reinforce some existing knowledge, indicate the complexity of the health impacts of human intelligence, and underline the value of smoking and alcohol prevention in less intelligent populations. Given the existing limitations in this study, particularly the potential reverse causality in some estimations, re-examinations are warranted in future research.