Cerebral small vessel disease genomics and its implications across the lifespan

The BS variant of C4 protects against age-related loss of white matter microstructural integrity

Age-related loss of white matter microstructural integrity is a major determinant of cognitive decline, dementia, and gait disorders. However, the mechanisms and molecular pathways that contribute to this loss of integrity remain elusive. We performed a GWAS of white matter microstructural integrity as quantified by diffusion MRI metrics (mean diffusivity, MD; and fractional anisotropy, FA) in up to 31,128 individuals from UK Biobank (age 45-81 years) based on a 2 degrees of freedom (2df) test of single nucleotide polymorphism (SNP) and SNP x age effects. We identified 18 loci that were associated at genome-wide significance with either MD (N = 16) or FA (N = 6). Among the top loci was a region on chromosome 6 encoding the human major histocompatibility complex (MHC). Variants in the MHC region were strongly associated with both MD (best SNP: 6:28866209_TTTTG_T, beta(SE)=-0.069(0.009); 2df p = 6.5x10-15) and FA (best SNP: rs3129787, beta(SE)=-0.056(0.008); 2df p = 3.5x10-12). Of the imputed HLA alleles and complement component 4 (C4) structural haplotype variants in the human MHC, the strongest association was with the C4-BS variant (for MD: beta(SE)=-0.070(0.010); p = 2.7x10-11; for FA: beta(SE)=-0.054(0.011); p = 1.6x10-7). After conditioning on C4-BS no associations with HLA alleles remained significant. The protective influence of C4-BS was stronger in older subjects (age ≥ 65; interaction p = 0.0019 (MD), p = 0.015 (FA)) and in subjects without a history of smoking (interaction p = 0.00093 (MD), p = 0.021 (FA)). Taken together, our findings demonstrate a role of the complement system and of gene-environment interactions in age-related loss of white matter microstructural integrity.

Stroke Genetics: Turning Discoveries into Clinical Applications

The field of medical and population genetics in stroke is moving at a rapid pace and has led to unanticipated opportunities for discovery and clinical applications. Genome-wide association studies have highlighted the role of specific pathways relevant to etiologically defined subtypes of stroke and to stroke as a whole. They have further offered starting points for the exploration of novel pathways and pharmacological strategies in experimental systems. Mendelian randomization studies continue to provide insights in the causal relationships between exposures and outcomes and have become a useful tool for predicting the efficacy and side effects of drugs. Additional applications that have emerged from recent discoveries include risk prediction based on polygenic risk scores and pharmacogenomics. Among the topics currently moving into focus is the genetics of stroke outcome. While still at its infancy, this field is expected to boost the development of neuroprotective agents. We provide a brief overview on recent progress in these areas.

Cerebral Small-Vessel Disease in Individuals with a Family History of Coronary Heart Disease: The Atherosclerosis Risk in Communities Study

INTRODUCTION

The degree to which a family history of coronary heart disease (FHCHD) is associated with silent cerebral small-vessel disease (cSVD) among healthy adults, independent of prevalent CHD and traditional risk factors, is unknown.

METHODS

The Atherosclerosis Risk in Communities (ARIC) study is a community-based cohort study with self-reported family history data and brain magnetic resonance imaging (ages 68-88). The association between markers of cSVD (lacunar infarcts and cerebral microbleeds), or log-transformed white matter hyperintensity (WMH) volume, and FHCHD, or the number of affected relatives was examined using separate adjusted logistic or linear regression models, respectively. Race interaction terms were evaluated.

RESULTS

Of 1,639 participants without prevalent CHD (76 ± 5 years, 62% female, 29% black), 686 (42%) had FHCHD. There were higher odds of lacunar infarct (OR 1.40, 95% CI 1.07-1.84) among those with parental FHCHD and higher odds of microhemorrhages (lobar OR 1.86, 95% CI 1.13-3.06; subcortical OR 1.47, 95% CI 1.01-2.15) among those with sibling FHCHD. A greater number of any relative affected was associated with higher odds of lacunar infarct (OR 1.24, 95% CI 1.04-1.47) and lobar microhemorrhages (OR 1.31, 95% CI 1.05-1.64) but not subcortical microhemorrhages (OR 1.09, 95% CI 0.92-1.28). Odds of having a lacunar infarct were higher among blacks (p-interaction 0.04) with paternal FHCHD (OR 2.20, CI 1.35-3.58) than whites with paternal FHCHD (OR 1.17, CI 0.87-1.56). There was no association with WMH.

DISCUSSION/CONCLUSION

Markers of cSVD, specifically lacunar infarcts and microhemorrhages, appear to be associated with FHCHD, potentially representing shared mechanisms in different vascular beds, and perhaps a genetic propensity for vascular disease.

ESO Guideline on covert cerebral small vessel disease

'Covert' cerebral small vessel disease (ccSVD) is common on neuroimaging in persons without overt neurological manifestations, and increases the risk of future stroke, cognitive impairment, dependency, and death. These European Stroke Organisation (ESO) guidelines provide evidence-based recommendations to assist with clinical decisions about management of ccSVD, specifically white matter hyperintensities and lacunes, to prevent adverse clinical outcomes. The guidelines were developed according to ESO standard operating procedures and Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) methodology. We prioritised the clinical outcomes of stroke, cognitive decline or dementia, dependency, death, mobility and mood disorders, and interventions of blood pressure lowering, antiplatelet drugs, lipid lowering, lifestyle modifications, glucose lowering and conventional treatments for dementia. We systematically reviewed the literature, assessed the evidence, formulated evidence-based recommendations where feasible, and expert consensus statements. We found little direct evidence, mostly of low quality. We recommend patients with ccSVD and hypertension to have their blood pressure well controlled; lower blood pressure targets may reduce ccSVD progression. We do not recommend antiplatelet drugs such as aspirin in ccSVD. We found little evidence on lipid lowering in ccSVD. Smoking cessation is a health priority. We recommend regular exercise which may benefit cognition, and a healthy diet, good sleep habits, avoiding obesity and stress for general health reasons. In ccSVD, we found no evidence for glucose control in the absence of diabetes or for conventional Alzheimer dementia treatments. Randomised controlled trials with clinical endpoints are a priority for ccSVD.