Genomic susceptibility Loci for brain atrophy, ventricular volume, and leukoaraiosis in hypertensive sibships

Interactive Association Between Intronic Polymorphism (rs10506151) of the LRRK2 Gene and Type 2 Diabetes on Neurodegenerative Diseases

PURPOSE

We investigated the interactive effect of rs10506151 polymorphism of the Leucine-rich repeat kinase 2 (LRRK2) gene and type 2 diabetes (T2D) on neurodegenerative disease (ND) risk.

MATERIALS AND METHODS

Data of 17, 927 participants in the Taiwan Biobank (TWB) assessed between 2008 and 2015 were linked to healthcare records in the National Health Insurance Research Database (NHIRD). The odd ratios (ORs) and 95% confidence intervals (CIs) for NDs were determined using logistic regression analysis.

RESULTS

There were 145 cases with NDs, and 28.28% (n = 41) of these individuals had T2D. Associations of neurodegenerative disorders with LRRK2 rs10506151 variant and T2D were not significant. The corresponding ORs (95% CI) for NDs were 1.06 (0.75-1.49) in CA/AA compared to CC individuals and 0.93 (0.63-1.39) in those with T2D compared to non-diabetic participants. However, we found evidence of a significant interaction between rs10506151 and T2D (p = 0.0073). After stratification by genotypes of rs10506151, the OR for NDs was 0.37 (CI, 0.17-0.82) in CA/AA individuals with T2D and 1.41 (0.88-2.27) in their CC counterparts. When CA/AA individuals with T2D represented the reference group, the OR (95% CI) was 1.74 (0.81-3.73) in CC individuals with no T2D, 2.47 (CI, 1.14-5.38) in CA/AA individuals with no T2D, and 2.34 (CI, 1.07-5.11) in CC individuals with T2D.

CONCLUSION

Our data indicated that the risk of NDs was significantly lower among diabetic individuals with combined CA/AA of the LRRK2 rs10506151 variant in Taiwan.

The metabolic network coherence of human transcriptomes is associated with genetic variation at the cadherin 18 locus

Metabolic coherence (MC) is a network-based approach to dimensionality reduction that can be used, for example, to interpret the joint expression of genes linked to human metabolism. Computationally, the derivation of 'transcriptomic' MC involves mapping of an individual gene expression profile onto a gene-centric network derived beforehand from a metabolic network (currently Recon2), followed by the determination of the connectivity of a particular, profile-specific subnetwork. The biological significance of MC has been exemplified previously in the context of human inflammatory bowel disease, among others, but the genetic architecture of this quantitative cellular trait is still unclear. Therefore, we performed a genome-wide association study (GWAS) of MC in the 1000 Genomes/ GEUVADIS data (n = 457) and identified a solitary genome-wide significant association with single nucleotide polymorphisms (SNPs) in the intronic region of the cadherin 18 (CDH18) gene on chromosome 5 (lead SNP: rs11744487, p = 1.2 × 10^- 8). Cadherin 18 is a transmembrane protein involved in human neural development and cell-to-cell signaling. Notably, genetic variation at the CDH18 locus has been associated with metabolic syndrome-related traits before. Replication of our genome-wide significant GWAS result was successful in another population study from the Netherlands (BIOS, n = 2661; lead SNP), but failed in two additional studies (KORA, Germany, n = 711; GENOA, USA, n = 411). Besides sample size issues, we surmise that these discrepant findings may be attributable to technical differences. While 1000 Genomes/GEUVADIS and BIOS gene expression profiles were generated by RNA sequencing, the KORA and GENOA data were microarray-based. In addition to providing first evidence for a link between regional genetic variation and a metabolism-related characteristic of human transcriptomes, our findings highlight the benefit of adopting a systems biology-oriented approach to molecular data analysis.

Genome-wide scan in Hispanics highlights candidate loci for brain white matter hyperintensities

Objective:

To investigate genetic variants influencing white matter hyperintensities (WMHs) in the understudied Hispanic population.

Methods:

Using 6.8 million single nucleotide polymorphisms (SNPs), we conducted a genome-wide association study (GWAS) to identify SNPs associated with WMH volume (WMHV) in 922 Hispanics who underwent brain MRI as a cross-section of 2 community-based cohorts in the Northern Manhattan Study and the Washington Heights–Inwood Columbia Aging Project. Multiple linear modeling with PLINK was performed to examine the additive genetic effects on ln(WMHV) after controlling for age, sex, total intracranial volume, and principal components of ancestry. Gene-based tests of association were performed using VEGAS. Replication was performed in independent samples of Europeans, African Americans, and Asians.

Results:

From the SNP analysis, a total of 17 independent SNPs in 7 genes had suggestive evidence of association with WMHV in Hispanics (p < 1 × 10⁻⁵) and 5 genes from the gene-based analysis with p < 1 × 10⁻³. One SNP (rs9957475 in GATA6) and 1 gene (UBE2C) demonstrated evidence of association (p < 0.05) in the African American sample. Four SNPs with p < 1 × 10⁻⁵ were shown to affect binding of SPI1 using RegulomeDB.

Conclusions:

This GWAS of 2 community-based Hispanic cohorts revealed several novel WMH-associated genetic variants. Further replication is needed in independent Hispanic samples to validate these suggestive associations, and fine mapping is needed to pinpoint causal variants.

Associations of Brain Structure With Adiposity and Changes in Adiposity in a Middle-Aged and Older Biracial Population

Background

Studies of adiposity and brain pathology in African Americans (AA) are sparse despite higher rates of obesity, dementia, and dementia-associated brain pathology in AA. This study examined relations of adiposity to white matter hyperintensities (WMH) and total brain volume (TBV) in AA and non-Hispanic whites (NHW).

Methods

Waist circumference (WC) and body mass index (BMI) were measured in the Genetic Epidemiology Network of Arteriopathy study at Visits 1 (mean age 57 [±11]) and 2 (mean age 61 [±10], mean 5.2 years later). Brain MRIs were obtained shortly after Visit 2 in 1,702 participants (64% women, 48% AA). Multilevel linear regression using generalized estimating equation estimated associations of adiposity (cross-sectional) or adiposity changes with WMH (accounting for intracranial size) or TBV adjusting for demographics, cardiovascular risk factors, and incorporating adiposity-by-race interactions. Adiposity-by-age interactions were examined.

Results

Concurrent TBV was inversely associated with BMI (β = -2.76 [95% confidence interval (CI): -4.99, -0.53]) and WC (β = -2.19 [CI: -4.04, -0.34]). Concurrent WMH were negatively associated with BMI (β = -0.04 [CI: -0.06, -0.01]) and, among NHW, with WC (β = -0.04 [CI: -0.06, -0.02]) but not with changes in BMI or WC. BMI increases were associated with lower TBV (β = -16.20, [CI: -30.34, -2.06]) in AA but not in NHW (β = -2.76 [CI: -14.02, 8.51]), although race-by-adiposity interactions were not supported. WC increases were not associated with MRI outcomes.

Conclusion

Greater measures of obesity and increases in measures of obesity, which are common in mid-life, could be detrimental to brain health, particularly in AA.

Multiple Factors Involved in the Pathogenesis of White Matter Lesions

White matter lesions (WMLs), also known as leukoaraiosis (LA) or white matter hyperintensities (WMHs), are characterized mainly by hyperintensities on T2-weighted or fluid-attenuated inversion recovery (FLAIR) images. With the aging of the population and the development of imaging technology, the morbidity and diagnostic rates of WMLs are increasing annually. WMLs are not a benign process. They clinically manifest as cognitive decline and the subsequent development of dementia. Although WMLs are important, their pathogenesis is still unclear. This review elaborates on the advances in the understanding of the pathogenesis of WMLs, focusing on anatomy, cerebral blood flow autoregulation, venous collagenosis, blood brain barrier disruption, and genetic factors. In particular, the attribution of WMLs to chronic ischemia secondary to venous collagenosis and cerebral blood flow autoregulation disruption seems reasonable. With the development of gene technology, the effect of genetic factors on the pathogenesis of WMLs is gaining gradual attention.

White Matter Hyperintensities Are Under Strong Genetic Influence

BACKGROUND AND PURPOSE

The genetic basis of white matter hyperintensities (WMH) is still unknown. This study examines the heritability of WMH in both sexes and in different brain regions, and the influence of age.

METHODS

Participants from the Older Australian Twins Study were recruited (n=320; 92 monozygotic and 68 dizygotic pairs) who volunteered for magnetic resonance imaging scans and medical assessments. Heritability, that is, the ratio of the additive genetic variance to the total phenotypic variance, was estimated using the twin design.

RESULTS

Heritability was high for total WMH volume (0.76), and for periventricular WMH (0.64) and deep WMH (0.77), and varied from 0.18 for the cerebellum to 0.76 for the occipital lobe. The genetic correlation between deep and periventricular WMH regions was 0.85, with one additive genetics factor accounting for most of the shared variance. Heritability was consistently higher in women in the cerebral regions. Heritability in deep but not periventricular WMH declined with age, in particular after the age of 75.

CONCLUSIONS

WMH have a strong genetic influence but this is not uniform through the brain, being higher for deep than periventricular WMH and in the cerebral regions. The genetic influence is higher in women, and there is an age-related decline, most markedly for deep WMH. The data suggest some heterogeneity in the pathogenesis of WMH for different brain regions and for men and women.

Blood and CSF biomarkers in brain subcortical ischemic vascular disease: Involved pathways and clinical applicability

Vascular dementia is the second most common type of dementia after Alzheimer’s disease (AD). Subcortical ischemic vascular disease refers to a form of vascular cognitive impairment characterized by the presence of diffuse white matter hyperintensities (WMHs) and multiple lacunar infarcts. These neuroimaging findings are mainly caused by cerebral small-vessel disease (cSVD) and relate to aging and cognitive impairment, but they can also be silent and highly prevalent in otherwise healthy individuals. We aimed to review studies on blood and cerebrospinal fluid (CSF) markers related to the presence of WMHs and lacunar infarcts that have been conducted in the past in large population-based studies and in high-risk selected patients (such as those with vascular risk factors, vascular cognitive impairment, or AD). Relevant associations with the presence and progression of cSVD have been described in the blood for markers related to inflammatory processes, endothelial damage and coagulation/fibrinolysis processes, etc. Also, different combinations of CSF markers might help to differentiate between etiologic types of dementia. In the future, to translate these findings into clinical practice and use biomarkers to early diagnosis and monitoring vascular cognitive impairment would require the replication of candidate markers in large-scale, multicenter, and prospectively designed studies.

Renin-angiotensin system genetic polymorphisms and brain white matter lesions in older Australians

BACKGROUND

White matter lesions (WMLs), seen as hyperintensities on T2-weighted magnetic resonance imaging brain scans, are common in the brains of healthy older individuals. They are thought to be related to cerebral small vessel disease and to have a genetic component to their aetiology, and hypertension is thought to be an important risk factor. Genetic polymorphisms in hypertension-related genes may therefore be associated with the formation of WMLs.

METHODS

In this study, a sample of 445 Australians aged 60-65 years was drawn from a larger longitudinal epidemiological study, the Personality and Total Health Through Life Project. The associations of single nucleotide polymorphisms (SNPs) in the genes encoding angiotensinogen (AGT, rs699), angiotensin-converting enzyme (ACE, rs4362), and angiotensin II receptor type 1 (AGTR1, rs5182) with WMLs were examined.

RESULTS

No individual SNPs showed a significant association with WMLs for the whole sample. When the cohort was stratified by sex, ACE rs4362 and AGT rs699 showed significant associations with WMLs in men only (P = 0.01 and P = 0.03, respectively), and remained significant after controlling for hypertension. Although the AGTR1 SNP did not show any association with WMLs, the interaction of the AGT rs699 and AGTR1 rs5182 SNPs with WMLs was significant before (P = 0.03) and after adjustment for hypertension (P = 0.045).

CONCLUSIONS

The results provide evidence for association of polymorphisms in the renin-angiotensin system genes with WMLs, independent of hypertension. Male-only associations with WMLs were found for the AGT rs699 and ACE rs362 polymorphisms. Moreover, for the entire sample an interaction between AGT and AGTR1 rs5182 genotypes on WMLs was observed.

Genetic profiles in ischaemic stroke

Stroke represents a clinical syndrome rather than a single disease. A number of stroke subtypes can be distinguished based on careful phenotyping, with each of these having distinct and overlapping risk factor profiles. Recent evidence has suggested that genetics plays an important part in stroke risk, with at least 2 genes specific to stroke risk directly now having been identified. This review will explore our current understanding of the genetics underlying stroke risk and whether this information is currently useful in a clinical setting for patient benefit.

Increased cerebral arterial pulsatility in patients with leukoaraiosis: arterial stiffness enhances transmission of aortic pulsatility

BACKGROUND AND PURPOSE

Arterial stiffening reduces damping of the arterial waveform and hence increases pulsatility of cerebral blood flow, potentially damaging small vessels. In the absence of previous studies in patients with recent transient ischemic attack or stroke, we determined the associations between leukoaraiosis and aortic and middle cerebral artery stiffness and pulsatility.

METHODS

Patients were recruited from the Oxford Vascular Study within 6 weeks of a transient ischemic attack or minor stroke. Leukoaraiosis was categorized on MRI by 2 independent observers with the Fazekas and age-related white matter change scales. Middle cerebral artery (MCA) stiffness (transit time) and pulsatility (Gosling's index: MCA-PI) were measured with transcranial ultrasound and aortic pulse wave velocity and aortic systolic, diastolic, and pulse pressure with applanation tonometry (Sphygmocor).

RESULTS

In 100 patients, MCA-PI was significantly greater in patients with leukoaraiosis (0.91 versus 0.73, P<0.0001). Severity of leukoaraiosis was associated with MCA-PI and aortic pulse wave velocity (Fazekas: χ(2)=0.39, MCA-PI P=0.01, aortic pulse wave velocity P=0.06; age-related white matter change: χ(2)=0.38, MCA-PI P=0.015; aortic pulse wave velocity P=0.026) for periventricular and deep white matter lesions independent of aortic systolic blood pressure, diastolic blood pressure, and pulse pressure and MCA transit time with MCA-PI independent of age. In a multivariate model (r(2)=0.68, P<0.0001), MCA-PI was independently associated with aortic pulse wave velocity (P=0.016) and aortic pulse pressure (P<0.0001) and inversely associated with aortic diastolic blood pressure (P<0.0001) and MCA transit time (P=0.001).

CONCLUSIONS

MCA pulsatility was the strongest physiological correlate of leukoaraiosis, independent of age, and was dependent on aortic diastolic blood pressure and pulse pressure and aortic and MCA stiffness, supporting the hypothesis that large artery stiffening results in increased arterial pulsatility with transmission to the cerebral small vessels resulting in leukoaraiosis.

Genetics of age-related white matter lesions from linkage to genome wide association studies

White matter lesions are a frequent phenomenon in the elderly and contribute to the development of disability. The mechanisms underlying these brain lesions are still not fully understood with age and hypertension being the most well established risk factors. The heritability of white matter lesions is consistently high in different populations. Candidate gene studies strongly support the role of genes involved in the renin–angiotensin system, as well as Notch3 signaling. The recent genome wide association study by the CHARGE consortium identified a novel locus on chromosome 17q25 harboring several genes such as TRIM65 and TRIM47 which pinpoint to possible novel mechanisms leading to white matter lesions.

Genetics of subcortical vascular dementia

Subcortical vascular dementia or cerebral small vessel disease is a common cause of disability in the elderly. On magnetic resonance imaging the disease is manifested as white matter lesions, lacunes and microbleeds. Its etiology is complex, with age and hypertension as established risk factors. The heritability of white matter lesions is constantly high over different populations. Linkage studies identified several loci for these lesions however no genes responsible for the linkage signals had been identified so far. Results from genetic association studies using the candidate gene approach support the role of APOE, the renin-angiotensin system, as well as the Notch3 signaling pathway in the development of subcortical vascular dementia. The recent genomegenome wide association study on white matter lesions identified a novel locus on chromosome 17q25 harboring several genes such as TRIM65 and TRIM47 which pinpoints to possible novel mechanisms leading to these lesions.

Genetics of ischemic stroke, stroke-related risk factors, stroke precursors and treatments

Stroke remains a leading cause of death worldwide and the first cause of disability in the western world. Ischemic stroke (IS) accounts for almost 80% of the total cases of strokes and is a complex and multifactorial disease caused by the combination of vascular risk factors, environment and genetic factors. Investigations of the genetics of atherosclerosis and IS has greatly enhanced our knowledge of this complex multifactorial disease. In this article we sought to review common single-gene disorders relevant to IS, summarize candidate gene and genome-wide studies aimed at discovering genetic stroke risk factors and subclinical phenotypes, and to briefly discuss pharmacogenetics related to stroke treatments. Genetics of IS is, in fact, one of the most promising research frontiers and genetic testing may be helpful for novel drug discoveries as well as for appropriate drug and dose selection for treatment of patients with cerebrovascular disease.

Risk factor profile for chronic kidney disease is similar to risk factor profile for small artery disease

BACKGROUND AND METHOD

We investigated whether chronic kidney disease detected by increased serum creatinine (S(Cr)) or urine albumin-to-creatinine ratio (U(ACR)) may reflect arteriosclerosis involving the kidneys. The sample consisted of 1585 members of sibships (804 non-Hispanic whites and 781 non-Hispanic blacks) in which at least two siblings had primary hypertension. We first evaluated the correlations of increased S(Cr) and U(ACR) with the presence of cerebral small vessel arteriosclerosis, which was determined by increased subcortical white matter hyperintensity (WMH) volume on brain magnetic resonance imaging; and with peripheral large vessel arteriosclerosis, which was determined by decreased ankle-brachial index (ABI). After age adjustment, increased S(Cr) and U(ACR) correlated with increased WMH volume (0.54 and 0.52, respectively) and with decreased ABI (0.50 and 0.54, respectively; all P < 0.001). We then used logistic regression to evaluate the dependency of each measure of disease on conventional risk factors for arteriosclerosis to assess whether the risk factors' effects were proportional across different measures of disease.

RESULTS

Age, race, sex, hypertension, diabetes, total cholesterol, and smoking made similar overall contributions to the prediction of each measure of disease, as judged by the model C-statistics, which varied in a narrow range from 0.84 to 0.85 (all P < 0.001). However, the relative contributions that the modifiable risk factors, including hypertension, diabetes, total cholesterol, and smoking made to prediction of increased S(Cr) and U(ACR) were disproportionate to their relative contributions to prediction of decreased ABI (P < 0.0001).

CONCLUSION

The findings support the view that chronic kidney disease detected by increased S(Cr) or U(ACR) primarily reflects small vessel arteriosclerosis involving the kidneys.

Genetics of common polygenic ischaemic stroke: current understanding and future challenges

Stroke is the third commonest cause of death and the major cause of adult neurological disability worldwide. While much is known about conventional risk factors such as hypertension, diabetes and incidence of smoking, these environmental factors only account for a proportion of stroke risk. Up to 50% of stroke risk can be attributed to genetic risk factors, although to date no single risk allele has been convincingly identified as contributing to this risk. Advances in the field of genetics, most notably genome wide association studies (GWAS), have revealed genetic risks in other cardiovascular disease and these techniques are now being applied to ischaemic stroke. This paper covers previous genetic studies in stroke including candidate gene studies, discusses the genome wide association approach, and future techniques such as next generation sequencing and the post-GWAS era. The review also considers the overlap from other cardiovascular diseases and whether findings from these may also be informative in ischaemic stroke.

Genetic susceptibility to ischemic stroke

Clinicians who treat patients with stroke need to be aware of several single-gene disorders that have ischemic stroke as a major feature, including sickle cell disease, Fabry disease, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, and retinal vasculopathy with cerebral leukodystrophy. The reported genome-wide association studies of ischemic stroke and several related phenotypes (for example, ischemic white matter disease) have shown that no single common genetic variant imparts major risk. Larger studies with samples numbering in the thousands are ongoing to identify common variants with smaller effects on risk. Pharmacogenomic studies have uncovered genetic determinants of response to warfarin, statins and clopidogrel. Despite increasing knowledge of stroke genetics, incorporating this new knowledge into clinical practice remains a challenge. The goals of this article are to review common single-gene disorders relevant to ischemic stroke, summarize the status of candidate gene and genome-wide studies aimed at discovering genetic stroke risk factors, and to briefly discuss pharmacogenomics related to stroke treatment.

The genetics of white matter lesions

White matter lesions (WMLs), commonly seen as hyperintensities on T2-weighted MRI scans of healthy elderly individuals, are considered to be related to small vessel disease in the brain, and are often associated with subtle cognitive and functional impairments. WMLs also show a strong correlation with a wide range of neurodegenerative and neuropsychiatric disorders. Although a number of vascular risk factors for WMLs have been identified, genetic factors are also important with twin and family studies reporting high heritability. Mutations in several genes have been described that lead to monogenic disorders manifesting WMLs, such as Fabry disease and CADASIL. Because most individuals with WMLs do not have Mendelian disorders, most of the focus has been on single nucleotide polymorphisms as genetic risk markers for WMLs, either directly or through their interactions with other genes or medical risk factors. Candidate genes examined to date include those involved in cholesterol regulation and atherosclerosis, hypertension, neuronal repair, homocysteine levels, and oxidative stress pathways. In addition, although there have been a few genome-wide linkage studies, only one genome-wide association study has been performed. The majority of the genetic findings need independent replication, and studies need to be extended to other candidate genes. Collaborative efforts to examine genome-wide associations in large samples of both sexes of a broad age range using longitudinal studies are necessary. The identification of individuals genetically at risk of developing white matter lesions will have important implications for recognizing the etiology of WMLs and thereby developing clinical intervention strategies for their prevention.