Although the differences in dementia incidence were nonsignificant, our study suggests that dementia incidence has decreased between 1990 and 2005.

Background The burden of cerebral white matter hyperintensities (WMH) is associated with an increased risk of stroke, dementia, and death. WMH are highly heritable, but their genetic underpinnings are incompletely characterized. To identify novel genetic variants influencing WMH burden, we conducted a meta-analysis of multi-ethnic genome-wide association studies. Methods and Results We included 21,079 middle-aged to elderly individuals from 29 population-based cohorts, who were free of dementia and stroke and were of European (N=17,936), African (N=1,943), Hispanic (N=795), and Asian (N=405) descent. WMH burden was quantified on MRI either by a validated automated segmentation method or a validated visual grading scale. Genotype data in each study were imputed to the 1000 Genomes reference. Within each ethnic group, we investigated the relationship between each SNP and WMH burden using a linear regression model adjusted for age, sex, intracranial volume, and principal components of ancestry. A meta-analysis was conducted for each ethnicity separately and for the combined sample. In the European descent samples, we confirmed a previously known locus on chr17q25 (p=2.7×10−19) and identified novel loci on chr10q24 (p=1.6×10−9) and chr2p21 (p=4.4×10−8). In the multi-ethnic meta-analysis, we identified two additional loci, on chr1q22 (p=2.0×10−8) and chr2p16 (p=1.5×10−8). The novel loci contained genes that have been implicated in Alzheimer’s disease (chr2p21, chr10q24), intracerebral hemorrhage (chr1q22), neuroinflammatory diseases (chr2p21), and glioma (chr10q24, chr2p16). Conclusions We identified four novel genetic loci that implicate inflammatory and glial proliferative pathways in the development of white matter hyperintensities in addition to previously-proposed ischemic mechanisms.

Background and Purpose— It is unknown whether white matter lesions (WML) develop abruptly in previously normal brain areas, or whether tissue changes are already present before WML become apparent on MRI. We therefore investigated whether development of WML is preceded by quantifiable changes in normal-appearing white matter (NAWM). Methods— In 689 participants from the general population (mean age 67 years), we performed 2 MRI scans (including diffusion tensor imaging and Fluid Attenuation Inversion Recovery [FLAIR] sequences) 3.5 years apart using the same 1.5-T scanner. Using automated tissue segmentation, we identified NAWM at baseline. We assessed which NAWM regions converted into WML during follow-up and differentiated new WML into regions of WML growth and de novo WML. Fractional anisotropy, mean diffusivity, and FLAIR intensity of regions converting to WML and regions of persistent NAWM were compared using 3 approaches: a whole-brain analysis, a regionally matched approach, and a voxel-wise approach. Results— All 3 approaches showed that low fractional anisotropy, high mean diffusivity, and relatively high FLAIR intensity at baseline were associated with WML development during follow-up. Compared with persistent NAWM regions, NAWM regions converting to WML had significantly lower fractional anisotropy (0.337 vs 0.387; P <0.001), higher mean diffusivity (0.910×10 –3 mm 2 /s vs 0.729×10 –3 mm 2 /s; P <0.001), and relatively higher normalized FLAIR intensity (1.233 vs –0.340; P <0.001). This applied to both NAWM developing into growing and de novo WML. Conclusions— White matter changes in NAWM are present and can be quantified on diffusion tensor imaging and FLAIR before WML develop. This suggests that WML develop gradually, and that visually appreciable WML are only the tip of the iceberg of white matter pathology.

C erebral white matter lesions (WMLs) are highly prevalent in the elderly population and increase the risk of dementia and stroke.1 Although believed to be vascular in origin, the exact etiology of WMLs is still unknown. On the basis of pathological and epidemiological studies, blood pressure is considered to be one of the most important factors by damaging the cerebral small vessels.2,3 Because blood pressure is modifiable, blood pressure control seems an important candidate for the prevention of WML progression.The earliest studies demonstrating an association between high blood pressure and WMLs were cross-sectional by design, which limits causal inferences. [4][5][6][7][8][9][10][11][12][13] More recently, studies have used longitudinal designs and found similar results.14-23 Yet, because WML progression is strongly influenced by the WML load at baseline, 15 it is unknown to what extent associations of blood pressure with WML progression are affected by the baseline WML load. Moreover, to provide stronger evidence for a temporal relationship, blood pressure should preferably be measured before the window in which WML progression is determined, instead of during this window. In addition, the use of different MRI scanners or scanning protocols when measuring WML progression can possibly lead to systematic biases. Previous studies have addressed 1 or 2 of these issues, but none of them addressed all.It is also unknown whether the associations between blood pressure and WML progression are present for systolic, diastolic, and pulse pressure. Moreover, the influence of medication use and control of hypertension on WML progression remains unclear. We hypothesized that blood pressure would relate to WML progression even when taking baseline WML load into account and that medication use and adequate control of hypertension would reduce this progression.We tested this hypothesis in a population-based longitudinal MRI study in which we measured systolic, diastolic, and pulse pressure before MRI scanning; evaluated the influence of the WML load at baseline; and used exactly the same scanners and scanning protocol at baseline and follow-up.Abstract-High blood pressure is considered an important risk factor for cerebral white matter lesions (WMLs) in the aging population. In a longitudinal population-based study of 665 nondemented persons, we investigated the longitudinal relationship of systolic blood pressure, diastolic blood pressure, and pulse pressure with annual progression of WMLs.Means of blood pressure were calculated over a 5-year period before longitudinal MRI scanning. WML progression was subsequently measured on 2 scans 3.5 years apart. We performed analyses with linear regression models and evaluated adjustments for age, sex, cardiovascular risk factors, and baseline WML volume. In addition, we evaluated whether treatment of hypertension is related to less WML progression. Continuing medical education (CME) credit is available for this article. Go to http://cme.ahajournals.org to take the quiz.

One Sentence Summary: In cerebral small vessel disease, endothelial dysfunction leads to white matter vulnerability which is reversible in a rat model with endothelial stabilizing drugs.Abstract: Dementia is a major social and economic problem for our ageing population. One of the commonest causes of dementia in the elderly is cerebral small vessel disease (SVD).Magnetic resonance scans of SVD patients typically show white matter abnormalities, but we do not understand the mechanistic pathological link between blood vessels and white matter myelin damage. Hypertension is suggested as the cause of sporadic SVD, but a recent alternative hypothesis invokes dysfunction of the blood brain barrier as the primary cause. Here, in a rat model of SVD, we show that endothelial cell (EC) dysfunction is the first change in development of the disease. Dysfunctional ECs secrete heat shock protein 90-alpha, which blocks oligodendroglial differentiation, contributing to impaired myelination. Treatment with ECstabilizing drugs reversed these EC and oligodendroglial pathologies in the rat model. EC and oligodendroglial dysfunction were also observed in humans with early, asymptomatic SVD pathology. We identified a loss-of-function mutation in ATPase11B which caused the EC dysfunction in the rat SVD model, and a single nucleotide polymorphism (SNP) in ATPase11B that was associated with white matter abnormalities in humans with SVD. We show that EC dysfunction is a cause of SVD white matter vulnerability and provide a therapeutic strategy to treat and reverse SVD in the rat model which may also be of relevance to human SVD.