Minyoung Kong

Klotho is a genetic risk factor for ischemic stroke caused by cardioembolism in Korean females.

An aging-suppressor gene, klotho, is a candidate factor for vascular disease because its deficiency leads to impaired endothelium-dependent vasodilation and impaired angiogenesis. We investigated the association of polymorphisms in klotho with ischemic stroke. We searched for sequence variants in promoter and exons of klotho gene. For the association study, selected variants were genotyped in control subjects and in patients with ischemic stroke and vascular dementia. The association with ischemic stroke was further investigated with its subtypes classified based on Trial of Org 10172 in Acute Stroke Treatment (TOAST). No significant association was observed for both G-395A and C1818T with ischemic stroke and vascular dementia (P>0.05). The analysis with subtypes of ischemic stroke revealed the associations that the A allele of G-395A increased the risk of cardioembolic stroke (CE, OR=2.60; P=0.006), and subjects carrying the A allele were susceptible to CE in both of dominant (AA+GA versus GG; OR=2.50; P=0.046) and recessive (AA versus GA+GG; OR=6.52; P=0.007) models. Further analysis of data partitioned by gender showed that the associations of G-395A with CE only existed in women (A versus G; OR=4.33; P=0.002), AA+GA versus GG; OR=5.68; P=0.014, and AA versus GA+GG; OR=9.07; P=0.012), but the significance disappeared in men (P>0.05). The sequence variant of G-395A in klotho might be a genetic risk factor for CE in females.

An Interactive Association of Common Sequence Variants in the Neuropeptide Y Gene With Susceptibility to Ischemic Stroke

Background and Purpose— Knowledge of the genetic architecture of ischemic stroke has been quite limited. Most significant associations of candidate genes with ischemic stroke have been difficult to replicate. This might be because the associations were not strong enough for results to be consistent, and testing a mixture of heterogeneous ischemic strokes might lead to confounded genetic associations. Methods— A preliminary association analysis with 28 sequence variants in 18 candidate genes (ACE, AGT, AGTR1, BDNF, CRP, F13B, LIF, MMP9, NPPA, NPY, PTGS2, SELP, SERPINE1, SREBF2, TFPI, THBD, VCAM1, and VEGF) revealed that NPY might be the most responsible for the susceptibility of ischemic stroke. Forty-five variants were discovered in the NPY gene by full sequencing, and 5 polymorphisms were selected based on their allele frequency and linkage disequilibrium estimates to conduct a thorough examination of their associations with ischemic stroke and its subtypes classified by TOAST. This study was conducted with 271 patients with ischemic stroke and 455 control subjects. Results— In contrast to a slight significance for an allelic association with ischemic stroke, remarkable discrepancies between haplotype frequencies of control subjects and patients were found. Especially, TA and CC of the haplotypes composed of C4112T and A6411C in the NPY gene were associated with increased risk (P=1.8×10−21, P=2.0×10−13). The interchanged haplotypes, TC and CA, were protective against the diseases (P=9.3×10−12, P=6.0×10−17). The associations were also shown in major subtypes of ischemic stroke. Conclusions— This remarkable haplotypic association suggested that the interaction between the 2 common sequence polymorphisms in NPY contributed to a great amount of phenotypic variability of ischemic stroke.

Genetic associations with C-reactive protein level and white blood cell count in the KARE study

C‐reactive protein (CRP) and white blood cell (WBC) have been utilized as critical markers contributing to acute and chronic inflammation. Genome‐wide associations were examined to identify nucleotide sequence variants associated with the two markers using 8842 individuals in the Korean Association REsource (KARE) study. A total of six and three nucleotide variants turned out to be associated with CRP and WBC (P < 1.42 × 10−7), and they were mutually exclusive. The only common variant associated with CRP was rs2393791 within hepatocyte nuclear factor 1 alpha (HNF1A) gene [minor allele frequency (MAF) = 0.478]. The only common variant associated with WBC [MAF = 0.468] was rs8078723, an intergenic single nucleotide polymorphism located between proteasome 26S subunits non‐ATPase 3 (PSMD3) and colony‐stimulating factor 3 (CSF3) in chromosome 17. The 2 variants were also associated with other inflammation‐related phenotypes (P < 0.05), and each phenotype was associated with the variant rs2393791 or with the variant rs8078723. We suggested that HNF1A gene was associated with CRP, and the region including PSMD3 and CSF3 genes was associated with WBC. The two inflammatory markers appeared to have distinct genetic components. Not only the functions of these two markers but also the functions of the corresponding genetic components might be largely complementary in determining inflammation process.

Association of intronic sequence variant in the gene encoding spleen tyrosine kinase with susceptibility to vascular dementia.

Abstract Objectives. This study was aimed to identify a novel strong candidate gene for the susceptibility to vascular dementia (VaD) with comprehensive evidences. Methods. A preliminary genome-wide association study (GWAS) was conducted to identify nucleotide sequence variants susceptible to VaD. Literature-based analysis and network analysis were conducted to single out the best candidate gene, and its association was thoroughly examined over its whole sequences. Functions of the most probable variant were predicted by in silico alternative splicing analysis and evaluated by minigene assay. Results. The GWAS showed the most significant variant in spleen tyrosine kinase (SYK) gene. This concurred with the suggestions from both literature-based analysis and network analysis. Further association analysis over the whole SYK gene revealed that rs290227 in intron 8 was the most significant (P = 7.38 × 10−11). The subsequent in silico analysis showed that the intronic variant played potential roles in alternative splicing by skipping exon 8 or by truncating exon 9. It was validated by in vivo minigene assay that the G allele of rs290227 induced the delayed splicing. Conclusions. We suggested a novel association of the VaD susceptibility with an intronic variant of rs290227 in the SYK gene. Its G allele could render mature transcripts inappropriately by intron retention and thus lead to a genetic risk for VaD.

Genetic dissection of susceptibility to vascular dementia.

Vascular dementia (VD) is the dementia induced by cerebrovascular lesions with a variety of pathophysiological subtypes. Our knowledge of the genetic mechanism of VD was restricted to a few Mendelian forms of VD. The complexity of sporadic VD caused by individual and interactive genetic effects under various environmental exposures renders it difficult to uncover genetic determinants. Much more effort has been made to identify associations of various candidate genes and to explain the variability of the complex VD than the Mendelian VD. The identified genes, however, explain a small portion of the heritability of VD, and the associations are often controversial in different populations. This makes understanding the genetic architecture of VD more complicated. We studied the genes and their sequence variants associated with susceptibility to VD, and many of the genes were involved in lipid metabolism, angiotensin, and inflammation. We also discussed future directions for the association analysis. Endeavors with various approaches would eventually show the genetic architecture of VD and provide a valuable tool in stratifying patients according to their genotypes. This is the first review to introduce a variety of primary studies that may offer some foundation for the genetics of VD.

Genetic architecture for susceptibility to gout in the KARE cohort study

This study aimed to identify functional associations of cis-regulatory regions with gout susceptibility using data resulted from a genome-wide association study (GWAS), and to show a genetic architecture for gout with interaction effects among genes within each of the identified functions. The GWAS was conducted with 8314 control subjects and 520 patients with gout in the Korea Association REsource cohort. However, genetic associations with any individual nucleotide variants were not discovered by Bonferroni multiple testing in the GWAS (P>1.42 × 10−7). Genomic regions enrichment analysis was employed to identify functional associations of cis-regulatory regions. This analysis revealed several biological processes associated with gout susceptibility, and they were quite different from those with serum uric acid level. Epistasis for susceptibility to gout was estimated using entropy decomposition with selected genes within each biological process identified by the genomic regions enrichment analysis. Some epistases among nucleotide sequence variants for gout susceptibility were found to be larger than their individual effects. This study provided the first evidence that genetic factors for gout susceptibility greatly differed from those for serum uric acid level, which may suggest that research endeavors for identifying genetic factors for gout susceptibility should not be heavily dependent on pathogenesis of uric acid. Interaction effects between genes should be examined to explain a large portion of phenotypic variability for gout susceptibility.

Lack of common genetic factors for susceptibility to vascular dementia and Alzheimer's disease.

Since vascular risk factors commonly act for susceptibility to Alzheimers disease (AD) and vascular dementia (VaD) by declining cognitive abilities, we conducted a genetic association study to identify their common underlying genetic factors. We selected single nucleotide polymorphisms (SNPs) which had been previously discovered for association with AD, and case and control associations of VaD were examined with the individual SNPs using 207 patients with VaD and 207 sex- and age-matched control subjects. As a result, no significant associations of susceptibility to VaD with 13 selected SNPs were observed even without employing a multiple test (P>0.05). This study suggests that genetics of VaD might be quite different from that of AD, and cautions should be taken especially when inferences about genetic factors are made with patients with mixed dementia.

Identification of functional nucleotide and haplotype variants in the promoter of the CEBPE gene.

The current study examined the promoter activity of an association signal in a 5′-upstream region of the gene encoding CCAAT/enhancer binding protein epsilon (CEBPE) identified from a recent genome-wide association study (GWAS) for complex acute lymphoblastic leukemia (ALL). This follow-up study first compared the activity of reporter constructs with three haplotypes estimated with the rs2239633 and its proximity nucleotide variants in strong linkage. The most frequent haplotype was CTTTTGT (H1), and the second most frequent haplotype consisted of entirely opposite alleles to H1 (TCGCACC, H2). Their luciferase activity revealed the strongest expression with H2 and the weakest with H1. Subsequent analysis revealed that different luciferase activity was found by the single-nucleotide substitution at rs2239632 and rs2239633 (P<0.05). Especially, the difference in luciferase activity between two alleles of rs2239632 corresponded to the difference between H1 and H2. We concluded that rs2239632 could regulate the expression of the CEBPE gene. We suggest a hypothesis that its risk allele (G) might increase the gene product and lead to leukemogenesis. As a result, a person with the allele or the corresponding haplotype might have increased susceptibility to ALL. Further research is warranted to investigate this hypothesis and the underlying mechanisms.

Promoter sequence variants of LIGHT are associated with female vascular dementia

LIGHT (homologous to L ymphotoxins, exhibits I nducible expression, and competes with herpes simplex virus G lycoprotein D for H erpes virus entry mediator, a receptor expressed by T lymphocytes) is implicated in the inflammation by disrupted T cell homeostasis, primarily at a transcriptional level. We investigated the association of LIGHT promoter with ischemic stroke and vascular dementia induced by such inflammation. We determined transcription factor binding sites altered by promoter SNPs using transcription factor prediction programs. Six common haplotypes composed of the selected SNPs (C-770T, G-607T, G-543A, and A-399G) were used for the assay of reporter activity. The most frequent haplotype construct, CGGA, induced the highest luciferase activity. The haplotype TTGA showed the lowest expression with 0.39-fold activity (P < 0.001) of CGGA. The substitution from C to T at the locus of C-770T (TGGA) decreased the reporter activity by 47% (P < 0.001). The SNPs and haplotypes were further investigated to see their association with ischemic stroke and vascular dementia in 455 controls and 478 patients. Significant association with vascular dementia was shown in the allele T of C-770T (odds ratio [OR] = 1.54; P < 0.05) and the haplotype TTGA (OR = 10.59; P < 0.05) in females. We concluded that the allele T of C-770T and the haplotype TTGA of the promoter SNPs in LIGHT gene might decrease the expression of LIGHT and subsequently increase the susceptibility to vascular dementia in females.