The complex genetics of gait speed:Genome-wide meta-analysis approach

Emerging evidence suggests that the basis for variation in late-life mobility is attributable, in part, to genetic factors, which may become increasingly important with age. Our objective was to systematically assess the contribution of genetic variation to gait speed in older individuals. We conducted a meta-analysis of gait speed GWASs in 31,478 older adults from 17 cohorts of the CHARGE consortium, and validated our results in 2,588 older adults from 4 independent studies. We followed our initial discoveries with network and eQTL analysis of candidate signals in tissues. The meta-analysis resulted in a list of 536 suggestive genome wide significant SNPs in or near 69 genes. Further interrogation with Pathway Analysis placed gait speed as a polygenic complex trait in five major networks. Subsequent eQTL analysis revealed several SNPs significantly associated with the expression of PRSS16, WDSUB1 and PTPRT, which in addition to the meta-analysis and pathway suggested that genetic effects on gait speed may occur through synaptic function and neuronal development pathways. No genome-wide significant signals for gait speed were identified from this moderately large sample of older adults, suggesting that more refined physical function phenotypes will be needed to identify the genetic basis of gait speed in aging

GWAS analysis of handgrip and lower body strength in older adults in the CHARGE consortium

Decline in muscle strength with aging is an important predictor of health trajectory in the elderly. Several factors, including genetics, are proposed contributors to variability in muscle strength. To identify genetic contributors to muscle strength, a meta-analysis of genomewide association studies of handgrip was conducted. Grip strength was measured using a handheld dynamometer in 27 581 individuals of European descent over 65 years of age from 14 cohort studies. Genomewide association analysis was conducted on ~2.7 million imputed and genotyped variants (SNPs). Replication of the most significant findings was conducted using data from 6393 individuals from three cohorts. GWAS of lower body strength was also characterized in a subset of cohorts. Two genomewide significant (P-value< 5 × 10−8) and 39 suggestive (P-value< 5 × 10−5) associations were observed from meta-analysis of the discovery cohorts. After meta-analysis with replication cohorts, genomewide significant association was observed for rs752045 on chromosome 8 (β = 0.47, SE = 0.08, P-value = 5.20 × 10−10). This SNP is mapped to an intergenic region and is located within an accessible chromatin region (DNase hypersensitivity site) in skeletal muscle myotubes differentiated from the human skeletal muscle myoblasts cell line. This locus alters a binding motif of the CCAAT/enhancer-binding protein-β (CEBPB) that is implicated in muscle repair mechanisms. GWAS of lower body strength did not yield significant results. A common genetic variant in a chromosomal region that regulates myotube differentiation and muscle repair may contribute to variability in grip strength in the elderly. Further studies are needed to uncover the mechanisms that link this genetic variant with muscle strength

Cerebral small vessel disease genomics and its implications across the lifespan

White matter hyperintensities (WMH) are the most common brain-imaging feature of cerebral small vessel disease (SVD), hypertension being the main known risk factor. Here, we identify 27 genome-wide loci for WMH-volume in a cohort of 50,970 older individuals, accounting for modification/confounding by hypertension. Aggregated WMH risk variants were associated with altered white matter integrity (p = 2.5×10-7) in brain images from 1,738 young healthy adults, providing insight into the lifetime impact of SVD genetic risk. Mendelian randomization suggested causal association of increasing WMH-volume with stroke, Alzheimer-type dementia, and of increasing blood pressure (BP) with larger WMH-volume, notably also in persons without clinical hypertension. Transcriptome-wide colocalization analyses showed association of WMH-volume with expression of 39 genes, of which four encode known drug targets. Finally, we provide insight into BP-independent biological pathways underlying SVD and suggest potential for genetic stratification of high-risk individuals and for genetically-informed prioritization of drug targets for prevention trials.Peer reviewe

Novel genetic loci underlying human intracranial volume identified through genome-wide association

Intracranial volume reflects the maximally attained brain size during development, and remains stable with loss of tissue in late life. It is highly heritable, but the underlying genes remain largely undetermined. In a genome-wide association study of 32,438 adults, we discovered five novel loci for intracranial volume and confirmed two known signals. Four of the loci are also associated with adult human stature, but these remained associated with intracranial volume after adjusting for height. We found a high genetic correlation with child head circumference (ρgenetic=0.748), which indicated a similar genetic background and allowed for the identification of four additional loci through meta-analysis (Ncombined = 37,345). Variants for intracranial volume were also related to childhood and adult cognitive function, Parkinson’s disease, and enriched near genes involved in growth pathways including PI3K–AKT signaling. These findings identify biological underpinnings of intracranial volume and provide genetic support for theories on brain reserve and brain overgrowth

Cerebral small vessel disease genomics and its implications across the lifespan

White matter hyperintensities (WMH) are the most common brain-imaging feature of cerebral small vessel disease (SVD), hypertension being the main known risk factor. Here, we identify 27 genome-wide loci for WMH-volume in a cohort of 50,970 older individuals, accounting for modification/confounding by hypertension. Aggregated WMH risk variants were associated with altered white matter integrity (p = 2.5×10-7) in brain images from 1,738 young healthy adults, providing insight into the lifetime impact of SVD genetic risk. Mendelian randomization suggested causal association of increasing WMH-volume with stroke, Alzheimer-type dementia, and of increasing blood pressure (BP) with larger WMH-volume, notably also in persons without clinical hypertension. Transcriptome-wide colocalization analyses showed association of WMH-volume with expression of 39 genes, of which four encode known drug targets. Finally, we provide insight into BP-independent biological pathways underlying SVD and suggest potential for genetic stratification of high-risk individuals and for genetically-informed prioritization of drug targets for prevention trials.</p

Prevalence of brain MRI markers of hemorrhagic risk in patients with stroke and atrial fibrillation

Background and Purpose: Cerebral microbleeds, cortical superficial siderosis, white matter lesions and cerebral atrophy may signify greater bleeding risk particularly in patients in whom anticoagulation is to be considered. We investigated their prevalence and associations with stroke type in patients with stroke and atrial fibrillation. Material and Methods: Cross-sectional sample, Monash Medical Centre (Melbourne, Australia) between 2010 and 2013, with brain MRI. MRI abnormalities were rated using standardized methods. Logistic regression was used to study associations adjusting for age and sex.Results: There were 170 patients, mean age 78 years (SD 9.8), 154 (90.6%) with ischemic stroke. Prevalence of MRI markers were: any microbleed 49%, multiple (≥2) microbleeds 30%, confluent white matter lesions 18.8%, siderosis 8.9%, severe cerebral atrophy 37.7%. Combinations of the severe manifestations of these markers were much less prevalent (2.9% to 12.4%). Compared with ischemic stroke, those with hemorrhagic stroke were more likely to have ≥10 microbleeds (OR 5.50 95% CI 1.46-20.77, p=0.012) and siderosis (OR 6.24, 95% CI 1.74-22.40, p=0.005). Siderosis was associated with multiple microbleeds (OR 8.14, 95% CI 2.38 - 27.86, p = 0.001). Patients admitted with hemorrhagic stroke and multiple microbleeds were more frequently anticoagulated prior to stroke (6/7, 85.7%) than in those with single (1/2, 50%) or no microbleeds (4/7, 57%). Conclusion: Multiple CMBs, severe WML, and severe cerebral atrophy were common individually in hospitalized patients with stroke and AF, but less so in combination. A higher burden of CMBs may be associated with ICH in stroke patients with AF

Methylglyoxal, cognitive function and cerebral atrophy in older people

Background.The effects of advanced glycation endproducts on cognition and brain structure are poorly understood. We studied associations of the advanced glycation endproduct precursor methylglyoxal (MGO) with cognitive function and brain volumes in older people.Methods.Nondemented participants in the Tasmanian Study of Cognition and Gait underwent cognitive testing and brain magnetic resonance imaging scans. Brain volumes were obtained by magnetic resonance imaging scan segmentation and statistical parametric mapping procedures. Serum MGO was measured after derivatization to methylquinoxaline by high pressure liquid chromatography and UV detection. Linear regression was used to examine associations of log-transformed MGO with cognitive scores and brain volumes adjusting for potential confounding by age, sex, education, mood, insulin resistance, history of stroke, vascular risk factors, alcohol intake, and psychoactive medication use.Results.There were 378 participants, mean age 72.1 years (SD 7.1), 55% male. Greater MGO was associated with poorer memory (β =-.12, 95% confidence interval:-0.22,-0.02, p =. 02) and executive function, the latter being greater among those with a history of stroke (MGO × stroke β =. 48, 95% confidence interval: 0.17, 0.79, p =. 002). Greater MGO was associated with lower grey matter volume (β =-6.42, 95% confidence interval-11.82,-1.11, p =. 02) but not with white matter volume, white matter lesion volume, or hippocampal volume.Conclusions.These results support the investigation of the role of the advanced glycation endproduct precursor methylglyoxal in cognitive decline and neurodegeneration in older people

Vascular cognitive impairment and Alzheimer's disease: role of cerebral hypoperfusion and oxidative stress

Cerebrovascular disease may lead to a wide range of cognitive changes, referred to collectively as vascular cognitive impairment. Stroke increases the risk of cognitive impairment and dementia, and may contribute to the progression of Alzheimer's disease (AD). Apart from clinical stroke itself, vascular risk factors are associated with the development of cognitive impairment and dementia. Animal models involving a temporary or permanent interruption of blood flow in the common carotid arteries develop nonprogressive cognitive impairment. Oxidative stress during cerebral hypoperfusion in animal models plays a key role in neuronal death and may thus contribute to the development of cognitive impairment in cerebrovascular disease. Genetic and pharmacological interventions to inhibit the major source of reactive oxygen species, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, are neuroprotective in experimental cerebral ischemia. Recent studies have demonstrated that inhibition of NADPH oxidase activity can mitigate cognitive impairment in rodent models of cerebral hypoperfusion. In this article, we review the evidence linking cognitive impairment and/or AD with NADPH oxidase-dependent oxidative stress, including the renin-angiotensin system