Common Genetic Variation Indicates Separate Causes for Periventricular and Deep White Matter Hyperintensities
Abstract
Background and Purpose:
Periventricular white matter hyperintensities (WMH; PVWMH) and deep WMH (DWMH) are regional classifications of WMH and reflect proposed differences in cause. In the first study, to date, we undertook genome-wide association analyses of DWMH and PVWMH to show that these phenotypes have different genetic underpinnings.
Methods:
Participants were aged 45 years and older, free of stroke and dementia. We conducted genome-wide association analyses of PVWMH and DWMH in 26,654 participants from CHARGE (Cohorts for Heart and Aging Research in Genomic Epidemiology), ENIGMA (Enhancing Neuro-Imaging Genetics Through Meta-Analysis), and the UKB (UK Biobank). Regional correlations were investigated using the genome-wide association analyses -pairwise method. Cross-trait genetic correlations between PVWMH, DWMH, stroke, and dementia were estimated using LDSC.
Results:
In the discovery and replication analysis, for PVWMH only, we found associations on chromosomes 2 (NBEAL), 10q23.1 (TSPAN14/FAM231A), and 10q24.33 (SH3PXD2A). In the much larger combined meta-analysis of all cohorts, we identified ten significant regions for PVWMH: chromosomes 2 (3 regions), 6, 7, 10 (2 regions), 13, 16, and 17q23.1. New loci of interest include 7q36.1 (NOS3) and 16q24.2. In both the discovery/replication and combined analysis, we found genome-wide significant associations for the 17q25.1 locus for both DWMH and PVWMH. Using gene-based association analysis, 19 genes across all regions were identified for PVWMH only, including the new genes: CALCRL (2q32.1), KLHL24 (3q27.1), VCAN (5q27.1), and POLR2F (22q13.1). Thirteen genes in the 17q25.1 locus were significant for both phenotypes. More extensive genetic correlations were observed for PVWMH with small vessel ischemic stroke. There were no associations with dementia for either phenotype.
Conclusions:
Our study confirms these phenotypes have distinct and also shared genetic architectures. Genetic analyses indicated PVWMH was more associated with ischemic stroke whilst DWMH loci were implicated in vascular, astrocyte, and neuronal function. Our study confirms these phenotypes are distinct neuroimaging classifications and identifies new candidate genes associated with PVWMH only.
Introduction
Radiological white matter hyperintensities (WMH) of presumed ischemic origin are the most prevalent sign of cerebral small vessel disease (SVD) and represent 40% of all SVD disease burden.1 They are detected as incidental lesions on T2-weighted magnetic resonance imaging.1 WMH are associated with increased risk for ischemic and hemorrhagic stroke, cognitive decline, and motor gait disorders.2–6 Two regional classifications, based on their anatomic relationship to the lateral ventricles in the brain, are periventricular WMH (PVWMH) and deep WMH (DWMH).5,7–9 PVWMH have been associated with declines in cognitive performance and increased systolic and arterial pressure, whereas DWMH are linked to body mass index, mood disorders, gait impairment, and arterial hypertension.10–12 This categorization reflects proposed differences in underlying pathophysiology.5,7,8 DWMH lesions occur in the subcortex, areas primarily supplied by long microvessels, with lower estimated blood pressures, possibly subject to damage secondary to hypertension and possibly with consequent hypoperfusion.1,8,13,14 PVWMH are related to alterations in short penetrating microvessels ending in close approximation to larger arterial blood vessels with different vascular architecture such as 2 leptomeningeal layers and enlarged perivascular spaces.1,15 They are hypothesized to be affected more directly by hypertension and risk factors associated with stroke.1,8,13,14
These subclassifications may also reflect differences in associated underlying genetic factors.16 Twin and family studies report that both PVWMH and DWMH have high heritability and genetic correlations.16,17 Recently, genome-wide association analyses (GWAS) for total WMH volume identified a major genetic risk locus on chromosome 17q25.118–21 and several other loci (eg, 10q24, 2p21, 2q33, 6q25.1).19,21,22 However, the genetic determinants of regional WMH burden, specifically DWMH and PVWMH, remain elusive.
We combined all available participants aged 45 and above with both DWMH and PVWMH measurements from the CHARGE (Cohorts for Heart and Aging Research in Genomic Epidemiology) and the ENIGMA (Enhancing Neuro-Imaging Genetics Through Meta-Analysis) consortia, and the UKB (UK Biobank). This is the only GWAS to date examining WMH subclassifications. We hypothesized that separating the two WMH subclassifications would mitigate phenotype heterogeneity, allowing us to identify additional risk loci and show that DWMH and PVWMH have different genetic underpinnings and pathophysiology.
Methods
Summary data for this meta-analysis will be available through the database of Genotypes and Phenotypes Cohorts for Heart and Aging Research in Genomic Epidemiology Summary Results site, which can be downloaded via authorized access.
Study Cohorts
Study participants (total N=26 654) were drawn from cohorts in the CHARGE and ENIGMA consortia and the UKB. Detailed Methods are in the Data Supplement. All cohorts followed standardized procedures for participant inclusion, genotype calling, phenotype harmonization, covariate selection, and study-level analysis. Participants were included if they had phenotype, genotype, and covariate data available and were aged 45 years and over without stroke, dementia, or any neurological abnormality at the time of magnetic resonance imaging scanning. All participants provided written informed consent, and each study received ethical approval to undertake this work.
Phenotype and Covariates
The magnetic resonance imaging and WMH extraction methods for each study are detailed in the Data Supplement. In brief, PVWMH and DWMH volumetric data were extracted using automated methods for all studies except HUNT, LBC, and AGES, which used visual rating scales (Table I in the Data Supplement). Hypertension was defined as systolic blood pressure ≥140 mm Hg and diastolic blood pressure ≥90 mm Hg or on current antihypertensive treatment.
Statistical Analysis
Each study fitted linear regression models to test the association of DWMH and PVWMH (continuous measures) with individual single nucleotide polymorphisms (SNPs). Additive genetic effects were assumed, and the models were adjusted for age (years), sex, and intracranial volume (where applicable). In addition, principal components for population stratification and other covariates, such as familial structure, were included if necessary. Models were also fitted with hypertension as an additional covariate.
Fixed-effects, inverse variance–weighted meta-analysis was carried out in METAL,23 with correction for genomic control. Two meta-analyses were carried out: all cohorts excluding UKB (discovery, phase I) and all cohorts (phase II). Post meta-analysis QC was also performed (see in the Data Supplement).
Genetic Correlations With Stroke and Dementia
Cross-trait genetic correlation between the 2 subclassifications of WMH, stroke, and dementia was estimated using LDSC24 on the GWAS summary statistics from phase II, MEGASTROKE (European ancestry only).25 Linkage disequilibrium scores were based on the HapMap3 European reference panel. Regional level correlation was investigated using the GWAS-PW and HESS methods.26,27
Results
Detailed study descriptions are provided in Tables I through III in the Data Supplement. The discovery cohort was comprised of ≈18 234 older adults (≥45 years, 16 studies) and was primarily white, with 736 blacks and 658 Hispanics. The predominantly white UKB was used as the replication cohort (n=8428).
In the discovery analysis (phase I), genome-wide significant associations (P<5×10−8) were observed in the 17q25.1 region for both phenotypes (Tables IV and V in the Data Supplement). Only the PVWMH analysis found additional genome-wide significant associations on chromosomes 2 and 10 (2 regions). Two of these regions had previously been described for total WMH burden (chromosomes 2, NBEAL,19,21 10q24.33, SH3PXD2A21), whereas 10q23.1 had not been described. Adjusting for hypertension made little difference to our findings (Tables VI through VII in the Data Supplement). Replication of the majority of genome-wide significant results for both phenotypes was observed after adjustment for multiple testing (DWMH P<3.6×10−4, PVWMH P<2.76×10−4, Tables VIII and IX in the Data Supplement).
Given the relatively large size of the replication cohort, a combined meta-analysis (phase II) was undertaken using all samples (N≈26 654). Removing either the small subsample of nonwhites or the cohorts with visual ratings did not substantially change the findings (beta value r2>0.93). The phase II GWAS meta-analyses identified 236 for DWMH and 513 genome-wide significant SNPs for PVWMH (Figure 1A, Table 1, Tables X and XI in the Data Supplement, respectively). Figure 1B shows the zoom plot of the single locus identified for DWMH on chr17q25.1. The associations of the identified genome-wide and suggestive associations for each phenotype for the alternate trait are also provided in Tables X and XI in the Data Supplement. The only SNPs genome-wide significant for both phenotypes (n=209) were located on 17q25.1 (Figure 2A).
WMH | rsID | CHR | POS | Nearest Gene | Function/Position | A1 | A2 | Freq (A1) | Beta (SE) | N | Direction | P Value |
---|---|---|---|---|---|---|---|---|---|---|---|---|
PV | rs3744020 | 17q25.1 | 73871773 | TRIM47 | Intronic | A | G | 0.1897 | 0.0899 (0.0073) | 26 438 | +++−+++?+++++++++++++ | 7.06×10−35 |
Deep | rs35392904 | 17q25.1 | 73883918 | TRIM65 | Intronic | T | C | 0.7981 | −0.0765 (0.0070) | 26 642 | −−−−−−−+−−−−−−−−+−−−− | 3.99×10−28 |
PV | rs3758575 | 10q24.33 | 105454881 | SH3PXD2A | Intronic | A | G | 0.4904 | 0.0388 (0.0058) | 26 654 | +++−++−++++++++++++++ | 2.00×10−11 |
PV* | rs12928520 | 16q24.2 | 87237568 | C16orf95 | Intergenic | T | C | 0.4252 | 0.0431 (0.0065) | 26 327 | +++++−?−+−−+++++++−++ | 4.22×10−11 |
PV | rs275350 | 6q25.1 | 151016058 | PLEKHG1 | Intronic | C | G | 0.4202 | 0.0374 (0.0057) | 26 654 | +−+−+++++−++++++−−−++ | 4.86×10−11 |
PV | rs7596872 | 2p16.1 | 56128091 | EFEMP1 | Intronic | A | C | 0.0975 | 0.0642 (0.0099) | 25 730 | −++++++−+−−+++???++++ | 8.66×10−11 |
PV | rs72934583 | 2q33.2 | 204009057 | NBEAL1 | Intronic | T | G | 0.8740 | 0.0529 (0.0087) | 25 730 | −+++++++++−+++???+−++ | 1.03×10−9 |
PV | rs57242328 | 2p21 | 43073247 | AC098824.6 | Intergenic | A | G | 0.3317 | −0.0368 (0.0061) | 25 730 | −−−−+−−−−+−−−−???−++− | 1.85×10−9 |
PV* | rs7213273 | 17q21.31 | 43155914 | NMT1 | Intronic | A | G | 0.6668 | 0.0341 (0.0059) | 26 111 | +++++−??++−++−+++++++ | 8.89×10−9 |
PV* | rs1993484 | 10q23.1 | 82222698 | TSPAN14 | Intronic | T | C | 0.2388 | 0.0378 (0.0067) | 26 654 | ++++−+−−++−++−+++++++ | 1.36×10−8 |
PV | rs11838776 | 13q34 | 111040681 | COL4A2 | Intronic | A | G | 0.2793 | 0.0350 | 26 654 | −+++++−++−+++++++−+−+ | 2.82×10−8 |
PV* | rs1799983 | 7q36.1 | 150696111 | NOS3 | Exonic | T | G | 0.3201 | 0.0373 | 26 654 | ++++++−−++−++−++−−−−+ | 3.68×10−8 |
Effect allele is A1. A1 indicates allele 1; A2, allele 2; Chr, chromosome; GWAS, genome-wide association analyses; POS, base pair position; PV, periventricular; and WMH, white matter hyperintensities.
*
These loci have not been previously associated with total WMH.
Ten chromosomal regions containing 290 genome-wide significant SNPs for PVWMH only were identified on chromosomes 2 (3 regions), 6, 7, 10 (2 regions), 13, 16, and 17q23.1 (Results, Table XI, and Figures I and II in the Data Supplement). Four loci had not been previously reported for associations with total WMH at the genome-wide significant level: (1) 7q36.1 (7.2 kb) containing 2 exonic SNPs in the NOS3 gene; (2) 10q23.1 (50.5 kb) containing 4 intronic SNPs in TSPAN14 & FAM231A; (3) 16q24.2 (1.2 kb) containing 2 intergenic SNPs; (4) 17q21.31 (27.2 kb) containing 8 SNPs, most of which are intronic and in the NMT1 gene. Many of these are expression quantitative trait loci or participate in long-range chromatin interactions (Figure 2B). Further descriptions of the PVWMH findings are found in the Results in the Data Supplement.
As expected, the association of the 17q25.1 locus with both phenotypes was confirmed. The size of this region, including genome-wide significant SNPs only, was similar for both DWMH (236 SNPs, BP 73757836-74025656, Figure 1B) and PVWMH (223 SNPs, BP 73757836-74024711, Figure IA in the Data Supplement). The top results in this locus were rs3744020 for DWMH (P=7.06×10−35, TRIM47 intronic SNP) and rs35392904 for PVWMH (P=3.989×10−28, TRIM65 intronic SNP), which are in high linkage disequilibrium (R2=0.902; Table 1). Many of these SNPs are expression quantitative trait loci or have long-range chromatin interactions (Figure 2B and 2C). For further details, see the Results in the Data Supplement.
Using gene-based tests, 13 genes in the 17q25.1 locus reached genome-wide significance (P<2.66×10−6) with both phenotypes (Table 2, Figure 2D, Tables XII and XIII in the Data Supplement). For PVWMH, an additional 19 genes were identified, covering the majority of regions/loci found in the SNP-based analysis (Figure 2D, Table 2, Table XIII in the Data Supplement). Four genes were located in previously unidentified regions: CALCRL (2q32.1), KLHL24 (3q27.1), VCAN (5q27.1), and POLR2F (22q13.1).
Gene | CHR | START | STOP | N SNPs | N | P PVWMH | P DWMH |
---|---|---|---|---|---|---|---|
WBP2 | 17 | 73841780 | 73852588 | 28 | 24 682 | 3.19×10−26 | 1.16×10−21* |
TRIM65 | 17 | 73876416 | 73893084 | 52 | 24 555 | 7.73×10−24 | 9.12×10−19* |
TRIM47 | 17 | 73870242 | 73874656 | 13 | 24 185 | 1.70×10−23 | 9.04×10−19* |
RP11-552F3.12 | 17 | 73894726 | 73926210 | 53 | 24 351 | 2.15×10−20 | 1.76×10−15* |
FBF1† | 17 | 73905655 | 73937221 | 55 | 24 338 | 3.98×10−17 | 1.23×10−13* |
GALK1† | 17 | 73747675 | 73761792 | 36 | 24 307 | 6.34×10−16 | 3.23×10−14* |
MRPL38 | 17 | 73894724 | 73905899 | 21 | 24 481 | 7.62×10−15 | 1.18×10−13* |
UNC13D | 17 | 73823306 | 73840798 | 73 | 23 788 | 3.10×10−14 | 1.22×10−13* |
UNK | 17 | 73780681 | 73821886 | 120 | 22 768 | 3.28×10−13 | 4.85×10−10* |
H3F3B | 17 | 73772515 | 73781974 | 23 | 24 009 | 4.43×10−12 | 1.41×10−10* |
SH3PXD2A | 10 | 105348285 | 105615301 | 788 | 24 847 | 8.43×10−12 | 0.21731 |
ACOX1 | 17 | 73937588 | 73975515 | 151 | 24 198 | 7.72×10−11 | 1.1×10−9* |
EVPL | 17 | 74000583 | 74023533 | 67 | 24 582 | 1.26×10−10 | 2.82×10−14* |
PLEKHG1 | 6 | 150920999 | 151164799 | 1022 | 24 922 | 1.59×10−10 | 0.011765 |
WDR12† | 2 | 203739505 | 203879521 | 322 | 23 753 | 2.53×10−10 | 0.00104 |
ICA1L† | 2 | 203640690 | 203736708 | 224 | 23 843 | 8.44×10−10 | 0.001301 |
CARF† | 2 | 203776937 | 203851786 | 157 | 24 076 | 2.41×10−9 | 0.001763 |
NMT1† | 17 | 43128978 | 43186384 | 221 | 24 766 | 7.18×10−8 | 0.00034 |
CDK3† | 17 | 73996987 | 74002080 | 12 | 24 433 | 8.54×10−8 | 1.82×10−8* |
OBFC1† | 10 | 105642300 | 105677963 | 99 | 25 461 | 1.41×10−7 | 0.054127 |
NOS3† | 7 | 150688083 | 150711676 | 58 | 24 608 | 1.73×10−7 | 0.000371 |
DCAKD† | 17 | 43100708 | 43138473 | 111 | 25 229 | 2.60×10−7 | 0.000363 |
DYDC2† | 10 | 82104501 | 82127829 | 91 | 25 050 | 2.88×10−7 | 0.003460 |
NBEAL1 | 2 | 203879602 | 204091101 | 367 | 23 413 | 3.83×10−7 | 0.040539 |
NEURL1 | 10 | 105253736 | 105352309 | 296 | 25 038 | 4.84×10−7 | 0.098303 |
MAT1A† | 10 | 82031576 | 82049440 | 66 | 25 295 | 4.90×10−7 | 0.002421 |
TSPAN14† | 10 | 82213922 | 82292879 | 213 | 24 731 | 6.73×10−7 | 0.006605 |
CALCRL† | 2 | 188207856 | 188313187 | 278 | 24 309 | 7.87×10−7 | 0.000574 |
KLHL24† | 3 | 183353356 | 183402265 | 207 | 24 356 | 1.29×10−6 | 0.002571 |
POLR2F† | 22 | 38348614 | 38437922 | 105 | 23 525 | 1.94×10−6 | 0.252540 |
VCAN† | 5 | 82767284 | 82878122 | 316 | 24 248 | 2.52×10−6 | 0.065044 |
COL4A2 | 13 | 110958159 | 111165374 | 1140 | 24 876 | 2.61×10−6 | 0.365300 |
Chr indicates chromosome; DWMH, deep white matter hyperintensities; and PVWMH, periventricular white matter hyperintensities.
*
Thirteen of these genes (chr17) were also significant for DWMH.
†
Those loci bolded have not been previously associated with total WMH.
Heritability analyses revealed low to moderate heritability for both traits (see Results in the Data Supplement). A high genetic correlation between DWMH and PVWMH was observed (rg=0.927, P=1.1×10−65), indicating a shared genetic architecture. Figure 3 shows the genetic correlations with DWMH, PVWMH, stroke, and Alzheimer disease. Positive genetic correlations with both phenotypes were found for all stroke, ischemic stroke, and SVD. Intracerebral hemorrhage (all types) was correlated with DWMH only. No significant correlations were found with Alzheimer disease (Table XIV in the Data Supplement).
Using GWAS-PW,26 we observed several regions with high probability (>90%) for harboring a shared genetic variant between PVWMH and DWMH (Table XV in the Data Supplement). These regions encompass several genome-wide significant loci that were identified for PVWMH (2p16.1 [EFEMP1], 2q33.2 [CARF and NBEAL], 6q25.1 [PLEKHGI22], 16q24.2 [C16orf95], and 17q25.1 [TRIM47, TRIM65]). Additionally, by using HESS,27 regional level correlation estimates were derived for those regions identified by the Bayesian approach (GWAS-PW).
Finally, we investigated local regions of a shared genetic variant between the WMH subtypes and stroke (Table XV in the Data Supplement). A region on chromosome 7 (encompassing the PVWMH NOS3 exonic SNP) exhibited shared genetic influence of all stroke with both phenotypes. Other regions of shared influence with all stroke were observed for PVWMH only. For the subtypes of stroke, significant regions were identified for DWMH and PVWMH, but none were found for both phenotypes except the chromosome 7 region for ischemic stroke (also identified for all stroke). Similar to the GW level correlation, a positive regional level genetic correlation was observed between the WMH subtypes and stroke (all stroke, all-ischemic, cardio-embolic and small vessel), by using HESS.27
Discussion
In our meta-analyses using all available individuals (N=26 654, phase II), PVWMH had significant independent associations with loci containing genes implicated in large and SVD, as well as ischemic and deep hemorrhagic stroke suggesting a unique genetic and pathophysiological underpinning. Although our phase II GWAS were only slightly larger than the previous biggest GWAS on total WMH burden with 21 079 participants,21 our detection rate of significant SNPs was substantially higher.18,19,21 This improved detection may be the result of reduced heterogeneity by separately analyzing the DWMH and PVWMH phenotypes.
We identified 11 independent loci for PVWMH and one locus for DWMH. Significant genes associated with WMH for the first time in PVWMH include CALCRL, VCAN, TSPAN, and NOS3. Most genes and loci previously reported as significant in total WMH.28–32 were now found to be associated with PVWMH alone, including PLEKHG1,22 SH3PXD2A,25,28,33 and COL4A2.33. Similarly, genes viewed as potential candidates18,19,21 in prior studies we now find to be significantly associated only with PVWMH, including DYDC2 and NEURL1, as well as NMT1, GALK1, H3F3B, UNK, UNC13D, EVPL, ICAL1, WDR12/CARF, NBEAL1, and EFEMP1.
Many of these genes associated with PVWMH affect vascular function or vascular diseases, such as ischemic stroke or coronary artery disease. The NOS3 gene is associated with coronary artery disease, migraine, vascular dysfunction, SVD, and ischemic stroke.22,29,30,34 PLEKHG1 is associated with dementia and ischemic stroke,35 and SH3PXD2A has been previously associated with total WMH and ischemic stroke.19,25
The most notable associated vascular gene is COL4A2 that encodes for a subunit of type IV collagen, which has been associated with SVD, ischemic stroke, intracranial hemorrhage, and coronary artery disease.31,35–38 It is a proposed therapeutic target for the prevention of intracranial hemorrhage.32,39 The association of this vascular gene with PVWMH and deep intracerebral hemorrhage is suggestive of underlying regional gene effects of the COL4A2 gene on the microvasculature affecting the risk of vascular injury in the periventricular region. These include potential weakening of the structural integrity of the regional microvasculature by altered collagen type 4 structural integrity, dysregulated gene expression of COL4A1 and COL4A2, and toxic cytosolic accumulations of COL4A2 within microvascular structural cells.40 When comparing PVWMH and DWMH anatomy, these mechanisms may enhance the direct mechanical effects of hypertension, or the other stroke risk factors, on the unique microvascular structure of the PVWMH region that also has predicted higher ambient blood pressure.1,6,13
We also discovered a new set of putative PVWMH genes. These include: TSPAN14, which encodes one of the tetraspanins which organize a network of interactions referred to as the tetraspanin web, ADAM10, a metalloprotease that cleaves the precursor of cell surface proteins,41 KLHL24 encodes a ubiquitin ligase substrate receptor,42 VCAN encodes a large chondroitin sulfate proteoglycan that is found in the extracellular matrix. In a recent meta-analysis, VCAN was associated with white matter microstructural integrity.43 These candidate genes for PVWMH may influence the immediate tissues surrounding microvessels and may contribute to SVD-associated biological changes.
The only significant locus observed for DWMH was the previously reported total WMH 17q25.1 locus,18,19,21,22 which was also found for PVWMH. This locus contained the SNPs with the largest effect sizes for both phenotypes. The top genome-wide significant hits for DWMH and PVWMH (17q25.1) were either identical with the SNP recently reported by Traylor et al22 for total WMH (PVWMH rs3744020) or in high linkage disequilibrium (R2>0.9) with the previously identified top ranked SNPs in the same locus (rs3744028, Fornage et al,18 rs7214628, Verhaaren et al21). Our identified SNPs were only in moderate linkage disequilibrium (R2≤0.396) with the top SNP (rs3760128) identified in a recent exome association analysis.19 All of these SNPs fall within or between the previously reported TRIM47 and TRIM65 genes.18,21,22,35 This gene-rich locus contains genes that influence glial cell proliferation and have been hypothesized to influence gliosis, which is a histological and magnetic resonance imaging marker of microvascular injury.1 It includes previously identified total WMH genes, such as TRIM47/TRIM65 (glial proliferation, astrocytoma’s),18,21 ACOX1 (cell replication, hepatic cancer)18,19,21 and MRPL38 (protein synthesis).19 Genes associated with neuronal injury or neurodegenerative disorders are also found in the 17q25.1 locus, including CDK3 (neuronal cell death in stroke),44 H3F3B (schizophrenia pathogenesis) and GALK1 (galactosemia).45 Interestingly, 2 genome-wide significant intronic UNC13D SNPs identified in this study and reported previously for total WMH burden,21 rs9894244 and rs7216615, have been reported as expression quantitative trait loci for GALK1 and H3F3B, respectively.46 The PVWMH specific loci also contained genes that potentially influence astrocytic function and gliosis, several previously reported for total WMH. These include NBEAL1,19,21 WDR12,19 NEURL1,18,19,21 CARF,47 and EFEMP1.37 Newly identified PVWMH genes potentially affecting astrocytic functioning include NMT1,48 ICA1L,49 POLR2F, OBFC1, and DYDC2.
Shortcomings of this study include the potential variability due to the different WMH extraction algorithms used, with a minority of samples using visual ratings. However, this is a common problem encountered in this type of study.18,19,21 Although our results suggest improved power and reduction in potential bias through the discrimination of PVWMH from DWMH, the Euclidean methodology used by the majority of studies undoubtedly missed PVWMH lesions outside this boundary. The majority of the participants in this study were white, and hence these results may not apply to other ethnicities. Sex differences have been previously reported but were not examined in the current study.50 For the phase II meta-analysis, we did not have an independent replication cohort. Older adults were included in this study, and the majority of participants had both DWMH and PVWMH and not one or the other. However, selection of individuals with only one subtype of these lesions present may be more appropriate to identify differences but would only be possible in younger cohorts. Future studies should aim to address these shortcomings, including continuing to improve and harmonize WMH measurement methods but also using consistent DWMH and PVWMH measurement methods across studies.
Conclusions
Our study confirms PVWMH and DWMH have distinct and shared genetic architecture. Genetic analyses indicated PVWMH was more associated with ischemic stroke and vascular function (PLEKHG1, SH3PXD2, COL4A2, CALCRL, VCAN, NOS3), whereas DWMH loci were implicated in vascular, astrocyte and neuronal function (TRIM47/TRIM 65, ACOX1, MRPL38, H3F3B, GALK, UNC13D, GALK1). New genes for PVWMH, potentially affecting the extravascular connective tissue, were also identified (TSPAN14, ADAM10, KLHL24, VCAN). Our study confirms that PVWMH and DWMH are distinct neuroimaging classifications and identifies new candidate genes associated with PVWMH only.
Acknowledgments
See in the Data Supplement.
Supplemental Material
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Received: 11 September 2019
Revision received: 30 March 2020
Accepted: 27 April 2020
Published online: 10 June 2020
Published in print: July 2020
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Dr Marchini is an employee of, and owns stock and stock options for, Regeneron Pharmaceuticals; Dr Sachdev received personal fees from Biogen; Henry Brodaty, Advisory Board member, Nutricia Australia; Philippe Amouyel, advisor for Foundation Alzheimer non-profit organization and for Genoscreen Biotech company; Christine Fennema-Notestine, received finding from National Institutes of Health Grants R01AG022381; Dr Gottesman, American Academy of Neurology, Associate Editor, Neurology; Drs Thompson and Jahanshad received grant support from Biogen Inc for work unrelated to the contents of this manuscript. Dr DeCarli, consultant to Novartis; Markus Scholz disclosed Pfizer, Inc, grants; Ralph Sacco, grant support from Boehringer Ingelheim, National Institute of Neurological Disorders and Stroke Grants; Dr Wardlaw, grant support from the Medical Research Council, Age UK, Scottish Funding Council, and Row Fogo Trust during the conduct of the study and grant support from Fondation Leducq, Wellcome Trust, Engineering and Physical Sciences Research Council, Chest Heart Stroke Scotland, British Heart Foundation, Stroke Association, Alzheimer’s Society and Alzheimer’s Research UK outside the submitted work. The other authors report no conflicts.
Sources of Funding
This work is supported by the National Institute of Neurological Disorders and Stroke, National Institutes of Health, R01AG059874, P41EB015922, R56AG058854, U54 EB020403, R01AG022381, U54EB020403, R01AG059874, and R01NS115845. Medical Research Council, Age UK, Scottish Funding Council, Row Fogo Trust, The Welcome Trust, Age UK, Cross Council Lifelong Health and Wellbeing Initiative, Leverhulme Trust, National Institute for Health Research, Biotechnology and Biological Sciences Research Council, UK Medical Research Council, Icelandic Heart Association, and the Althingi, Austrian Science Fund (FWF), Australian National Health and Medical Research Council, Austrian National Bank, Anniversary Fund, European Commission FP6 STRP, European Community’s 5th and 7th Framework Program, Netherlands Organization for Scientific Research, Netherlands Consortium for Healthy Aging, Russian Foundation for Basic Research, Russian Federal Agency of Scientific Organizations, Liaison Committee between the Central Norway Regional Health Authority and the Norwegian University of Science and Technology, Norwegian National Advisory Unit for functional magnetic resonance imaging (MRI), Leipzig Research Center for Civilization Diseases (LIFE), Bristol-Myers Squibb, Netherlands Heart Foundation, French National Research Agency (ANR), Foundation Leducq, Joint Programme of Neurodegenerative Disease research, Bordeaux University, Institut Pasteur de Lille, the labex DISTALZ and the Centre National de Génotypage. Deutsche Forschungsgesellschaft (DFG) no. WI 3342/3-1 and grants from European Union, European Regional Development Fund, Free State of Saxony within the framework of the excellence initiative, LIFE-Leipzig Research Center for Civilization Diseases no. 100329290, 713-241202, 14505/2470, 14575/2470. Max Planck Society, State of Saxony, Brain Foundation, Bristol-Myers Squibb, National Health and Medical Research Council (NHMRC) of Australia, NHMRC of Australia, Parkinson’s UK; Medical Research Council - Dementias Platform UK, National Institute on Aging, Bethesda, MD, P30 AG 010129 Full details of funding support for each cohort are detailed in the Data Supplement.
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