Objective-To analyze the extent and spatial distribution of white matter hyperintensities (WMH) in brain regions from cognitively normal older individuals (CN) and patients with mild cognitive impairment (MCI) and Alzheimer disease (AD).Methods-We studied 26 mild AD, 28 MCI, and 33 CN. MRI analysis included quantification of WMH volume, nonlinear mapping onto a common anatomic image, and spatial localization of each WMH voxel to create an anatomically precise frequency distribution map. Areas of greatest frequency of WMH from the WMH composite map were used to identify 10 anatomic regions involving periventricular areas and the corpus callosum (CC) for group comparisons.Results-Total WMH volumes were associated with age, extent of concurrent vascular risk factors, and diagnosis. After correcting for age, total WMH volumes remained significantly associated with diagnosis and extent of vascular risk. Regional WMH analyses revealed significant differences in WMH across regions that also differed significantly according to diagnosis. In post-hoc analyses, significant differences were seen between CN and AD in posterior periventricular regions and the splenium of the CC. MCI subjects had intermediate values at all regions. Repeated measures analysis including vascular risk factors in the model found a significant relationship between periventricular WMH and vascular risk that differed by region, but regional differences according to diagnosis remained significant and there was no interaction between diagnosis and vascular risk.Conclusions-Differences in white matter hyperintensities (WMH) associated with increasing cognitive impairment appear related to both extent and spatial location. Multiple regression analysis of regional WMH, vascular risk factors, and diagnosis suggest that these spatial differences may result from the additive effects of vascular and degenerative injury. Posterior periventricular and corpus callosum extension of WMH associated with mild cognitive impairment and Alzheimer disease indicate involvement of strategic white matter bundles that may contribute to the cognitive deficits seen with these syndromes.White matter hyperintensities (WMH) are areas of increased signal on T2-weighted and fluid-attenuated inversion recovery (FLAIR) MRI sequences of the brain. In this study, we applied image segmentation and nonlinear image mapping techniques to determine the extent and spatial location of WMH among CN, MCI, and AD. We then tested whether differences in anatomic distribution were associated with cognitive status and vascular risk. The CDR score was determined independently of neuropsychological information according to published protocol. In addition, participants received a standardized MRI scan of the brain at the baseline evaluation. Methods SubjectsThe institutional review boards at all participating institutions approved this study, and subjects or their legal representatives gave written informed consent. Vascular risk factorsThe presence or absence of six cerebrovascular risk fact...

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (r g ¼ À 0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness.

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.

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 An international Delphi panel has defined a harmonized protocol (HarP) for the manual segmentation of the hippocampus on MR. The aim of this study is to study the concurrent validity of the HarP toward local protocols, and its major sources of variance. Methods Fourteen tracers segmented 10 Alzheimer's Disease Neuroimaging Initiative (ADNI) cases scanned at 1.5 T and 3T following local protocols, qualified for segmentation based on the HarP through a standard web-platform and resegmented following the HarP. The five most accurate tracers followed the HarP to segment 15 ADNI cases acquired at three time points on both 1.5 T and 3T. Results The agreement among tracers was relatively low with the local protocols (absolute left/right ICC 0.44/0.43) and much higher with the HarP (absolute left/right ICC 0.88/0.89). On the larger set of 15 cases, the HarP agreement within (left/right ICC range: 0.94/0.95 to 0.99/0.99) and among tracers (left/right ICC range: 0.89/0.90) was very high. The volume variance due to different tracers was 0.9% of the total, comparing favorably to variance due to scanner manufacturer (1.2), atrophy rates (3.5), hemispheric asymmetry (3.7), field strength (4.4), and significantly smaller than the variance due to atrophy (33.5%, P < .001), and physiological variability (49.2%, P < .001). Conclusions The HarP has high measurement stability compared with local segmentation protocols, and good reproducibility within and among human tracers. Hippocampi segmented with the HarP can be used as a reference for the qualification of human tracers and automated segmentation algorithms.