Polygenic Susceptibility to Hypertension and Cognitive Performance in Middle-aged Persons Without Stroke or Dementia

BACKGROUND AND OBJECTIVES

Mounting evidence indicates that hypertension leads to a higher risk of dementia. Hypertension is a highly heritable trait, and a higher polygenic susceptibility to hypertension (PSH) is known to associate with a higher risk of dementia. We tested the hypothesis that a higher PSH leads to worse cognitive performance in middle-aged persons without dementia. Confirming this hypothesis would support follow-up research focused on using hypertension-related genomic information to risk-stratify middle-aged adults before hypertension develops.

METHODS

We conducted a nested cross-sectional genetic study within the UK Biobank (UKB). Study participants with a history of dementia or stroke were excluded. We categorized participants as having low (≤20th percentile), intermediate, or high (≥80th percentile) PSH according to results of 2 polygenic risk scores for systolic and diastolic blood pressure (BP) generated with data on 732 genetic risk variants. A general cognitive ability score was calculated as the first component of an analysis that included the results of 5 cognitive tests. Primary analyses focused on Europeans, and secondary analyses included all race/ethnic groups.

RESULTS

Of the 502,422 participants enrolled in the UKB, 48,118 (9.6%) completed the cognitive evaluation, including 42,011 (8.4%) of European ancestry. Multivariable regression models using systolic BP-related genetic variants indicated that compared with study participants with a low PSH, those with intermediate and high PSH had reductions of 3.9% (β -0.039, SE 0.012) and 6.6% (β -0.066, SE 0.014), respectively, in their general cognitive ability score (p < 0.001). Secondary analyses including all race/ethnic groups and using diastolic BP-related genetic variants yielded similar results (p < 0.05 for all tests). Analyses evaluating each cognitive test separately indicated that reaction time, numeric memory, and fluid intelligence drove the association between PSH and general cognitive ability score (all individual tests, p < 0.05).

DISCUSSION

Among nondemented, community-dwelling, middle-aged Britons, a higher PSH is associated with worse cognitive performance. These findings suggest that genetic predisposition to hypertension influences brain health in persons who have not yet developed dementia. Because information on genetic risk variants for elevated BP is available long before the development of hypertension, these results lay the foundation for further research focused on using genomic data for the early identification of high-risk middle-aged adults.

A genome-wide association study of frailty identifies significant genetic correlation with neuropsychiatric, cardiovascular, and inflammation pathways

Frailty is an aging-related clinical phenotype defined as a state in which there is an increase in a person's vulnerability for dependency and/or mortality when exposed to a stressor. While underlying mechanisms leading to the occurrence of frailty are complex, the importance of genetic factors has not been fully investigated. We conducted a large-scale genome-wide association study (GWAS) of frailty, as defined by the five criteria (weight loss, exhaustion, physical activity, walking speed, and grip strength) captured in the Fried Frailty Score (FFS), in 386,565 European descent participants enrolled in the UK Biobank (mean age 57 [SD 8] years, 208,481 [54%] females). We identified 37 independent, novel loci associated with the FFS (p < 5 × 10-8), including seven loci without prior described associations with other traits. The variants associated with FFS were significantly enriched in brain tissues as well as aging-related pathways. Our post-GWAS bioinformatic analyses revealed significant genetic correlations between FFS and cardiovascular-, neurological-, and inflammation-related diseases/traits, and subsequent Mendelian Randomization analyses identified causal associations with chronic pain, obesity, diabetes, education-related traits, joint disorders, and depressive/neurological, metabolic, and respiratory diseases. The GWAS signals were replicated in the Health and Retirement Study (HRS, n = 9,720, mean age 73 [SD 7], 5,582 [57%] females), where the polygenic risk score built from UKB GWAS was significantly associated with the FFS in HRS individuals (OR per SD of the score 1.27, 95% CI 1.22-1.31, p = 1.3 × 10-11). These results provide new insight into the biology of frailty by comprehensively evaluating its genetic architecture.

Abstract 105: Polygenic Burden Of Hypertension-related Alleles Leads To Non-traumatic Subarachnoid Hemorrhage At Younger Ages

Introduction: Non-traumatic subarachnoid hemorrhage (SAH) is strongly linked to hypertension, a condition highly influenced by common genetic variants. For complex diseases influenced by genetic and environmental factors, genetic predisposition plays a key role in earlier onset. We tested the hypothesis that persons with a higher polygenic burden of hypertension-related alleles have SAH at younger ages.

Methods: We analyzed data from the UK Biobank, a large cohort study that enrolled over 500,000 Britons aged 40-69. We included participants of European descent. We constructed two polygenic risk scores (PRS) using 807 independent genetic variants known to associate with higher systolic and diastolic blood pressure (BP). We fitted linear regression to assess the relationship between these PRS and the age-of-onset of SAH, using product terms to test for interaction with sex. We subsequently implemented Mendelian Randomization analyses using the inverse variance weighted and weighted median methods to evaluate causality.

Results: We evaluated a total of 1,178 SAH cases (mean age, 58; female sex, 722 [61.3%]). When evaluating all participants jointly, there was no association between the systolic BP PRS and age-of-onset for SAH (p=0.130). There was a significant interaction between the PRS and sex (p=0.002): each additional standard deviation of the systolic BP PRS was associated with an earlier onset of SAH in females (beta, -1.45; 95% CI, -2.31 to -0.58; p=0.001), but not in males (adjusted beta, 0.83; 95% CI, -0.37 to 2.02; p=0.176). In MR analyses, a 10mmHg increase in genetically determined systolic BP was associated with a 5-year earlier onset of SAH in female participants using both the inverse variance weighted (beta, -4.72; 95% CI, -7.34 to -2.10; p<0.001) and weighted median approaches (beta, -5.05; 95% CI, -9.19 to -0.90; p=0.017). Analyses with the diastolic BP SNPs yielded comparable results (all p<0.05).

Conclusions: Genetically determined hypertension is associated with earlier onset of non-traumatic SAH in women. These results indicate that genetic predisposition may play a more important causal role in younger patients and point to genetic information as possible tools for early identification of high-risk individuals.

Genetically Determined Smoking Behavior and Risk of Nontraumatic Subarachnoid Hemorrhage

BACKGROUND AND PURPOSE

Animal and observational studies indicate that smoking is a risk factor for aneurysm formation and rupture, leading to nontraumatic subarachnoid hemorrhage (SAH). However, a definitive causal relationship between smoking and the risk of SAH has not been established. Using Mendelian randomization (MR) analyses, we tested the hypothesis that smoking is causally linked to the risk of SAH.

METHODS

We conducted a 1-sample MR study using data from the UK Biobank, a large cohort study that enrolled over 500 000 Britons aged 40 to 69 from 2006 to 2010. Participants of European descent were included. SAH cases were ascertained using a combination of self-reported, electronic medical record, and death registry data. As the instrument, we built a polygenic risk score using independent genetic variants known to associate (P<5×10^-8) with smoking behavior. This polygenic risk score represents the genetic susceptibility to smoking initiation. The primary MR analysis utilized the ratio method. Secondary MR analyses included the inverse variance weighted and weighted median methods.

RESULTS

A total of 408 609 study participants were evaluated (mean age, 57 [SD 8], female sex, 220 937 [54%]). Among these, 132 566 (32%) ever smoked regularly, and 904 (0.22%) had a SAH. Each additional SD of the smoking polygenic risk score was associated with 21% increased risk of smoking (odds ratio [OR], 1.21 [95% CI, 1.20-1.21]; P<0.001) and a 10% increased risk of SAH (OR, 1.10 [95% CI, 1.03-1.17]; P=0.006). In the primary MR analysis, genetic susceptibility to smoking was associated with a 63% increase in the risk of SAH (OR, 1.63 [95% CI, 1.15-2.31]; P=0.006). Secondary analyses using the inverse variance weighted method (OR, 1.57 [95% CI, 1.13-2.17]; P=0.007) and the weighted median method (OR, 1.74 [95% CI, 1.06-2.86]; P=0.03) yielded similar results. There was no significant pleiotropy (MR-Egger intercept P=0.39; MR Pleiotropy Residual Sum and Outlier global test P=0.69).

CONCLUSIONS

These findings provide evidence for a causal link between smoking and the risk of SAH.

Genetically Elevated LDL Associates with Lower Risk of Intracerebral Hemorrhage

OBJECTIVE

Observational studies point to an inverse correlation between low-density lipoprotein (LDL) cholesterol levels and risk of intracerebral hemorrhage (ICH), but it remains unclear whether this association is causal. We tested the hypothesis that genetically elevated LDL is associated with reduced risk of ICH.

METHODS

We constructed one polygenic risk score (PRS) per lipid trait (total cholesterol, LDL, high-density lipoprotein [HDL], and triglycerides) using independent genomewide significant single nucleotide polymorphisms (SNPs) for each trait. We used data from 316,428 individuals enrolled in the UK Biobank to estimate the effect of each PRS on its corresponding trait, and data from 1,286 ICH cases and 1,261 matched controls to estimate the effect of each PRS on ICH risk. We used these estimates to conduct Mendelian Randomization (MR) analyses.

RESULTS

We identified 410, 339, 393, and 317 lipid-related SNPs for total cholesterol, LDL, HDL, and triglycerides, respectively. All four PRSs were strongly associated with their corresponding trait (all p < 1.00 × 10-100 ). While one SD increase in the PRSs for total cholesterol (odds ratio [OR] = 0.92; 95% confidence interval [CI] = 0.85-0.99; p = 0.03) and LDL cholesterol (OR = 0.88; 95% CI = 0.81-0.95; p = 0.002) were inversely associated with ICH risk, no significant associations were found for HDL and triglycerides (both p > 0.05). MR analyses indicated that 1mmol/L (38.67mg/dL) increase of genetically instrumented total and LDL cholesterol were associated with 23% (OR = 0.77; 95% CI = 0.65-0.98; p = 0.03) and 41% lower risks of ICH (OR = 0.59; 95% CI = 0.42-0.82; p = 0.002), respectively.

INTERPRETATION

Genetically elevated LDL levels were associated with lower risk of ICH, providing support for a potential causal role of LDL cholesterol in ICH. ANN NEUROL 2020 ANN NEUROL 2020;88:56-66.

Abstract 156: Recurrent Stroke in Middle-Aged Lacunar Stroke Survivors: Understanding Risk Factors and Vulnerability in an Important Target Population

Background: The precise role of stroke risk factors in middle-aged people remains a significant knowledge gap. Confounding risk factors conferred by young and elderly stroke are largely avoided, providing a unique opportunity to understand the relationship between traditional risk factors and stroke. We aimed to determine the predictors of stroke and myocardial infarction (MI) in a unique middle-aged cohort with MRI-defined lacunar stroke.

Methods: We conducted a reanalysis of data from the Secondary Prevention of Small, Subcortical Strokes (SPS3) clinical trial. We focused on middle-aged study participants, defined as those aged 40-60 years at study entry. We used multivariate Cox regression models to estimate the risk of recurrent stroke or MI.

Results: Out of 3,020 total subjects from SPS3, 1,312 (mean age 53 [SD 5], 445 females [34%]) were in the middle-aged category and were included in this analysis. Of these, there were 619 (47%) white, 297 (23%) black, and 283 (22%) Hispanic subjects. Over a mean follow-up time of 3.90 years, there were 123 strokes (2.6% per patient-year) and 33 MIs (0.7% per patient-year). The rates (% per patient-year) of having a stroke or MI differed significantly across white (n=59, 2.7%), black (n=54, 5.1%), and Hispanic (n=27, 2.8%) ethnic groups (p=0.006). Significant risk factors for recurrent stroke or MI are described for middle-aged and all SPS3 subjects in the table.

Conclusions: In middle-aged individuals with prior stroke, diabetes, greater white matter disease severity, black race, and family history were potent predictors of recurrent stroke. Male sex, diabetes, and heart disease were potent predictors of MI. Compared to the entire SPS3 cohort, these predictors confer a greater risk for recurrent stroke or MI in the middle-aged. These data identify modifiable risk factors and target populations that are especially vulnerable to vascular events or complications.

Abstract 66: Causal Associations Between Genetically-determined Smoking and Risk of Subarachnoid Hemorrhage

Introduction: Animal and observational studies indicate that smoking is a risk factor for aneurysm formation and rupture, leading to subarachnoid hemorrhage (SAH). However, a definitive causal relationship between smoking and SAH has not been established. We leveraged the causal properties of mutation-disease associations to test the hypothesis that smoking is causally linked to SAH.

Methods: We conducted a one-sample Mendelian Randomization (MR) study within the UK Biobank, a prospective, population-based observational study. We restricted the analysis to study participants with genetically-confirmed European ancestry. SAH cases were ascertained using previously validated codes. As the instrument, we built a polygenic risk score (PRS) using independent (R2<0.1) genetic variants known to be associated (p<5x10-8) with smoking. For the primary MR analysis, we implemented the ratio method using the estimates obtained from testing the PRS for association with risk of SAH and smoking. In secondary analyses, we implemented the inverse-variance weighted (IVW) and weighted median (WM) methods. Pleiotropy was assessed via the MR-Egger approach.

Results: We included a total of 408,622 individuals in this study (mean age 57 [SD 8], female sex 220,944 [54%]). Of these, 132,568 (32%) ever smoked regularly and 904 (0.22%) had an SAH. Each additional standard deviation of the smoking PRS was associated with a 9% increased risk of SAH (OR 1.09, 95%CI 1.03-1.17; p=0.006) and 21% increased risk of smoking (OR 1.21, 95%CI 1.2-1.21; p=1x10-16). In the primary analysis, genetically-determined smoking was associated with a 63% increase in risk of SAH (OR 1.63, 95%CI 1.15-2.30; p=0.006). Secondary analyses using the IVW method (OR 1.57, 95%CI 1.13-2.17; p=0.007) and the WM method (OR 1.74, 95%CI 1.06-2.86; p=0.028) yielded comparable results. There was no significant pleiotropy (MR-Egger intercept p=0.38).

Conclusion: Genetically-determined smoking is strongly associated with the risk of SAH. These findings provide evidence for a causal link between smoking and the occurrence of this often-debilitating condition. Interventions aimed at reducing smoking behavior could offer significant benefits, especially to those at high risk of SAH.

Abstract 71: Sex and Genetic Predisposition Synergistically Influence Risk of Stroke and Myocardial Infarction in Middle-Aged Persons Without Risk Factors

Background and Hypothesis: Driven by aging-related physiological changes, the incidence of stroke and myocardial infarction rises rapidly in persons aged >40 years. A significant proportion of these acute vascular events (AVE) take place in persons without vascular risk factors. We tested the hypothesis that sex and genetic predisposition synergistically increase the risk of AVE in middle-aged persons without vascular risk factors.

Methods: We analyzed data from the UK Biobank, a prospective longitudinal study that enrolled persons aged 40 to 69 years. Our analysis was restricted to middle-aged participants, defined as those aged 40 to 60 years. Prevalent and incident cases of stroke (ischemic and hemorrhagic) and myocardial infarction were included. To quantify the genetic predisposition to sustain an AVE, we constructed a polygenic risk score using 68 independent (R 2 <0.1) genetic variants known to associate (p<5x10 -8 ) with AVE. Participants were classified as having low, intermediate or high genetic risk according to tertiles of the score. We used Cox models for association and interaction testing.

Results: Of the 502,536 study participants enrolled in the UK Biobank, 303,295 (60%) did not have any vascular risk factors. During the follow-up period, there were 5,746 AVEs, including 1,954 strokes and 3,792 myocardial infarctions. The cumulative risk of AVE was 0.12% (n=352), 0.46% (n = 1,386) and 1.32% (n = 4,008) at ages 40, 50 and 60 years (test-for-trend p<0.001). The risk of AVE was 3 times greater in men than women (HR 3.30, 95%CI 3.08 - 3.53). Compared to persons with low genetic risk, those with intermediate and high genetic risk had a 22% (HR 1.22, 95%CI 1.13 - 1.32) and 52% (HR 1.52, 95%CI 1.41 - 1.65) increase in risk of AVE, respectively. There was significant synergy (interaction) between sex and genetic predisposition: compared to females with low genetic risk, males with high genetic risk had 4 times (HR 3.91, 95%CI 3.58 - 4.26) the risk of AVE (interaction analysis p<0.001).

Conclusion: Genetic information constitutes a promising tool to risk stratify middle-aged persons without vascular risk factors. The synergistic effect of sex and genetic predisposition points to specific subgroups that could benefit from aggressive preventive interventions.

Deep Learning for Automated Measurement of Hemorrhage and Perihematomal Edema in Supratentorial Intracerebral Hemorrhage

Background and Purpose- Volumes of hemorrhage and perihematomal edema (PHE) are well-established biomarkers of primary and secondary injury, respectively, in spontaneous intracerebral hemorrhage. An automated imaging pipeline capable of accurately and rapidly quantifying these biomarkers would facilitate large cohort studies evaluating underlying mechanisms of injury. Methods- Regions of hemorrhage and PHE were manually delineated on computed tomography scans of patients enrolled in 2 intracerebral hemorrhage studies. Manual ground-truth masks from the first cohort were used to train a fully convolutional neural network to segment images into hemorrhage and PHE. The primary outcome was automated-versus-human concordance in hemorrhage and PHE volumes. The secondary outcome was voxel-by-voxel overlap of segmentations, quantified by the Dice similarity coefficient (DSC). Algorithm performance was validated on 84 scans from the second study. Results- Two hundred twenty-four scans from 124 patients with supratentorial intracerebral hemorrhage were used for algorithm derivation. Median volumes were 18 mL (interquartile range, 8-43) for hemorrhage and 12 mL (interquartile range, 5-30) for PHE. Concordance was excellent (0.96) for automated quantification of hemorrhage and good (0.81) for PHE, with DSC of 0.90 (interquartile range, 0.85-0.93) and 0.54 (0.39-0.65), respectively. External validation confirmed algorithm accuracy for hemorrhage (concordance 0.98, DSC 0.90) and PHE (concordance 0.90, DSC 0.55). This was comparable with the consistency observed between 2 human raters (DSC 0.90 for hemorrhage, 0.57 for PHE). Conclusions- We have developed a deep learning-based imaging algorithm capable of accurately measuring hemorrhage and PHE volumes. Rapid and consistent automated biomarker quantification may accelerate powerful and precise studies of disease biology in large cohorts of intracerebral hemorrhage patients.