Hyun-Seok Jin

Recapitulation of two genomewide association studies on blood pressure and essential hypertension in the Korean population.

Essential hypertension causes high rates of morbidity and mortality, primarily due to its complications, and its development is regulated by genetic risk and environmental factors. However, until recent genomewide association studies (GWASs) were reported, the genetic factors were unknown. Two GWASs on systolic blood pressure (SBP), diastolic blood pressure (DBP) and hypertension in Caucasians—Global Blood Pressure Genetics (Global BPgen) and Cohorts for Heart and Aging Research in Genome Epidemiology (CHARGE)—reported 51 single-nucleotide polymorphisms (SNPs) in 12 loci at P<4 × 10−7. Because the prevalence, age of onset and severity of complications of hypertension vary between ethnic groups, we wanted to investigate these results in other ethnic groups. We examined the association of 27 of the 51 SNPs in 8512 unrelated individuals from Korean Association REsource (KARE), a GWAS that was based on epidemiological cohorts in Korea. Four loci—ATP2B1 (ATPase, Ca++ transporting, plasma membrane 1), CSK (c-src tyrosine kinase), CYP17A1 (cytochrome P450 17A1) and PLEKHA7 (pleckstrin homology domain-containing family A member 7)—were associated with blood pressure and hypertension in the Korean population.

Risk factors for device-associated infection related to organisational characteristics of intensive care units: findings from the Korean Nosocomial Infections Surveillance System.

Device-associated infections (DAIs) have been the major causes of morbidity and mortality of patients in intensive care units (ICUs). This study evaluated the risk factors for DAIs in ICUs. Ninety-six medical or surgical ICUs of 56 hospitals participated in the Korean Nosocomial Infections Surveillance System between July 2007 and June 2008. The occurrence of catheter-associated urinary tract infection (CAUTI), central line-associated bloodstream infection (CABSI), and ventilator-associated pneumonia (VAP) were monitored and DAI rates were calculated. Data associated with ICU characteristics were collected and Poisson regression was used for statistical analysis. Rates of CAUTI, CABSI, and VAP were 3.87 per 1000 urinary catheter days, 2.23 per 1000 central line days, and 1.89 per 1000 mechanical ventilator days, respectively. Rates of CAUTI were higher in ICUs in Seoul (P=0.032) and ICUs of major teaching hospitals (P=0.010). The ICUs of university-affiliated hospitals showed lower CAUTI rates (P=0.013). CABSI rates were higher in Seoul (P=0.001) and in medical ICUs (P=0.026). VAP rates were lower in ICUs of hospitals with more than 900 beds compared with hospitals with 400-699 beds (P=0.026). VAP rates were higher in surgical ICUs (P<0.0001) and increased 1.13-fold with each 100-unit increase in beds per infection control professional (P=0.003). The organisational and institutional characteristics of ICUs may influence DAI rates and there is a need for improvement in the incidence of VAP, CAUTI or CABSI.

Identification of KMT2D and KDM6A mutations by exome sequencing in Korean patients with Kabuki syndrome

Kabuki syndrome (KS) (OMIM#147920) is a multiple congenital anomaly/mental retardation syndrome. Recently, pathogenic variants in KMT2D and KDM6A were identified as the causes of KS in 55.8–80.0% of patients. To elucidate further the molecular characteristics of Korean patients with KS, we screened a cohort of patients with clinically defined KS for mutations in KMT2D and KDM6A. Whole-exome sequencing and direct sequencing for validation were performed in 12 patients with a clinical suspicion of KS. KMT2D and KDM6A mutations were identified in 11 (91.7%) patients. No recurrent mutation was observed, and 10 out of the 11 mutations found were novel. KMT2D mutations were detected in 10 patients, including four small deletions or insertions and four nonsense and two missense mutations. One girl had a novel splice-site mutation in KDM6A. Each patient had a unique individual mutation. This is the first report of mutational analysis via exome sequencing in Korean patients with KS. Because the mutation-detection rate was high in this study, rigorous mutation analysis of KMT2D and KDM6A may be an important tool for the early diagnosis and genetic counseling of Korean patients with KS.

Age-dependent association of the polymorphisms in the mitochondria-shaping gene, OPA1, with blood pressure and hypertension in Korean population.

BACKGROUND Essential hypertension is associated with mitochondrial dysfunction. Because mitochondrial dynamics; mitochondrial morphological changes are closely linked with various mitochondrial functions, we aimed to examine whether the genetic variation of the mitochondria-shaping genes influenced the susceptibility to blood pressure (BP) and hypertension. METHODS The quantitative BP trait analysis and hypertension case-control analysis for the total 52 single-nucleotide polymorphisms (SNPs) in the five major mitochondria-shaping genes were performed in the Korean Association Resource (KARE) study cohort (8,512 subjects). RESULTS In the total subjects of the KARE study cohort, there were no statistically significant associations of the SNPs in the five mitochondria-shaping genes with BP or hypertension after adjusting for multiple tests. However, the age group analysis in the 40s, 50s, and 60s age subgroups revealed that 15 SNPs out of 26 SNPs genotyped in the OPA1 gene were significantly associated with BP and/or hypertension in the 60s age subgroup and their association P values satisfied the Bonferroni-corrected significance level (P < 0.00625). Noticeably, nine SNPs were consistently associated with all the three traits; systolic BP (SBP), diastolic BP (DBP), and hypertension. In silico lookup of the associated SNPs in the Southern German population did not reveal associations with BP traits. CONCLUSIONS Our results indicate that genetic variation of the mitochondrial fusion-regulating gene, OPA1, might be associated with BP and hypertension in an age-dependent and population-specific manner in the Korean study cohort, and suggest that altered mitochondrial dynamics, especially involved in the mitochondrial fusion event, may play an important role in the pathogenesis of hypertension.

The PARK2 gene is involved in the maintenance of pancreatic β-cell functions related to insulin production and secretion.

Several association studies have implicated the PARK2 gene that encodes parkin--the key molecule orchestrating the mitochondrial quality control system--as a candidate susceptibility gene for diabetes. A total of 7551 unrelated Korean KARE cohort subjects were analyzed to investigate the association between the PARK2 single nucleotide polymorphism (SNP) and quantitative glycemic traits. Two SNPs, rs10455889 and rs9365294, were significantly associated with fasting plasma glucose level (p=∼1.2×10(-4)) and insulin secretion indices (p=∼7.4×10(-5)) in male KARE subjects. Parkin was expressed predominantly in the rat pancreatic islets. Downregulation of the Park2 gene in rat INS-1 β-cells resulted in a significant decrease in the glucose-stimulated insulin secretion, intracellular insulin gene expression, and intracellular ATP level. The Park2-depleted β-cells also exhibited increased mitochondrial fragmentation and ROS production and decreased mitochondrial membrane potential. Both population-based statistical evaluation and experimental evidence demonstrated a fundamental role of the PARK2 gene in the maintenance of β-cell function.

Inhibition of Bcl-xL by ABT-737 enhances chemotherapy sensitivity in neurofibromatosis type 1-associated malignant peripheral nerve sheath tumor cells

Neurofibromatosis type 1 (NF1) is one of the most commonly inherited autosomal dominant disorders. The malignant peripheral nerve sheath tumor (MPNST) is a major cause of mortality in patients with NF1. In this study, we found that overexpression of Bcl-xL in the established NF1-associated MPNST cell line and primary tissue cultured MPNST cells derived from an NF1 patient was closely associated with anticancer drug resistance of the NF1-associated MPNST cells. We demonstrated that high expression of Bcl-xL in the MPNST cells was caused by a decreased transcriptional expression of the NF1 gene. Downregulation of the NF1 gene by RNA interference (RNAi) induced an increase in Bcl-xL expression and a decrease in its sensitivity to apoptosis in the benign neurofibroma cell line and primary normal cells. These results suggest that an alteration of Bcl-xL expression levels by somatic expression changes in the NF1 locus may contribute to the malignant development of benign tumor tissues or normal tissues to MPNSTs. We further demonstrated that either depletion of Bcl-xL expression by RNAi or inactivation of Bcl-xL by ABT-737, a mimetic of the BH3-only protein BAD, was very effective in sensitizing the MPNST cells to apoptotic cell death by combined treatment with the tested anticancer drug doxorubicin. Notably, a low concentration of ABT-737 and doxorubicin could effectively induce synergistic cytotoxicity in the MPNST cells. These results suggest that pharmacological inhibition of Bcl-xL by ABT-737 in combination with doxorubicin can be a potential therapeutic strategy for the treatment of NF1-associated MPNSTs.

Clinical and genetic spectrum of 18 unrelated Korean patients with Sotos syndrome: frequent 5q35 microdeletion and identification of four novel NSD1 mutations

Sotos syndrome is an overgrowth syndrome with characteristic facial dysmorphism, variable severity of learning disabilities and macrocephaly with overgrowth. Haploinsufficiency of the nuclear receptor SET domain-containing protein 1 (NSD1) gene located on 5q35 has been implicated as the cause of Sotos syndrome. This study was performed to investigate the mutation spectrum of NSD1 abnormalities and meaningful genotype−phenotype correlations in Korean patients with Sotos syndrome. Eighteen unrelated Korean patients with Sotos syndrome were enrolled for clinical and molecular analyses. Cytogenetic studies were performed to confirm 5q35 microdeletion, and NSD1 sequencing analysis was performed to identify intragenic mutations. NSD1 abnormalities were identified in 15 (83%) patients. Among them, eight patients (53%) had 5q35 microdeletions and the other seven patients (47%) had seven different NSD1 intragenic mutations including four novel mutations. The mutation spectrum of Korean patients with Sotos syndrome was similar to that of previous studies for Japanese patients. Height was significantly shorter and age of walking alone was significantly older in the microdeletion group compared with those in the intragenic mutation group. No significant differences were observed for other clinical characteristics between the microdeletion and intragenic mutation groups. Further studies with a larger number of patients will be necessary to draw conclusive genotype−phenotype correlations.

Genome-wide association study of serum albumin:globulin ratio in Korean populations

Low albumin:globulin (A/G) ratios are associated with vascular adverse events, nephrotic syndrome and autoimmune disease. Genome-wide association studies (GWASs) have been identifying genetic variants associated with total serum protein, serum albumin and globulins, but A/G ratio has never been considered the target phenotype. To identify the genetic basis of the A/G ratio, we performed a GWAS on A/G ratio in 4205 individuals from the Ansan cohort and confirmed the results in 4637 subjects from the Ansung cohort. The single-nucleotide polymorphism (SNP) genotypes of Affymetrix SNP array 5.0 were obtained from the Korean Association Resource Consortium, and we selected 290 659 common SNPs with a minor allele frequency >0.05. Genetic factors for A/G ratio were analyzed by linear regression analysis, controlling for age, sex, body mass index, smoking status and alcohol drinking status as covariates. From the GWAS of the Ansan cohort, we identified two significant genome-wide signals (P-values<5 × 10−8) and 36 moderate signals (P-value<1.0 × 10−4). These 38 signals were tested in the Ansung population. Eleven SNPs from six loci (GALNT2, IRF4, HLA-DBP1, SLC31A1, FADS1 and TNFRSF13B) were replicated, with P-values<0.05. The most compelling association was observed in the TNFRSF13B locus on chromosome 17p11.2 (SNP: rs4561508), with an overall combined P-value=7.80 × 10−24. The other significant signal was observed on chromosome 11q12.2—the FADS1 locus (SNP: rs174548)—with an overall combined P-value=3.54 × 10−8.

NF1 deficiency causes Bcl-xL upregulation in Schwann cells derived from neurofibromatosis type 1-associated malignant peripheral nerve sheath tumors

Since the bi-allelic inactivation of both neurofibromin 1 (NF1) gene alleles (NF1(-/-)) in Schwann cells (SCs) is common in both benign plexiform neurofibromas (PNs) and malignant peripheral nerve sheath tumors (MPNSTs) in patients with neurofibromatosis type 1 (NF1), other genetic alterations in SCs may be required for tumor progression of PNs to MPNSTs. We found that the anti-apoptotic Bcl-xL protein is upregulated in MPNST tissues compared to PN tissues from patients with NF1 by immunohistological staining. In addition, we investigated whether Bcl-xL is upregulated in SCs derived from MPNSTs and found a significantly higher Bcl-xL expression level in sNF96.2 MPNST-derived SCs compared to normal human SCs (HSCs). We also discovered that the increased Bcl-xL expression caused an increase in drug resistance to doxorubicin in MPNST-derived SCs. Manipulation of NF1 gene expression levels by treatment with small interfering RNA (siRNA) and overexpression of the neurofibromin GAP-related domain (NF1-GRD) demonstrated that upregulated Bcl-xL expression in MPNST-derived SCs was caused by NF1 deficiency. Treatment with the Erk1/2 inhibitor, PD98059, resulted in a slight increase in Bcl-xL levels in neurofibromin-depleted normal HSCs, indicating that Bcl-xL upregulation in MPNST-derived SCs is mediated by activated Erk1/2, which is a Ras downstream protein regulated by neurofibromin. As the reduction of Bcl-xL expression restored sensitivity to doxorubicin-induced apoptosis in sNF96.2 cells, we examined the effect of the small molecule Bcl-xL inhibitor ABT-737 on sNF96.2 cells. A very low dose of ABT-737 combined with doxorubicin synergistically enhanced sensitivity to doxorubicin-induced apoptosis in sNF96.2 cells, suggesting that ABT-737 and doxorubicin may be a good combination to effectively treat NF1-associated MPNSTs with minimal side-effects. Collectively, our results suggest that upregulation of Bcl-xL in MPNST-derived SCs may be caused by the NF1 deficiency-mediated elevation in Ras/MAPK signaling and may provide a new potential chemotherapeutic target in patients with NF1 and MPNSTs.

Association of the I264T variant in the sulfide quinone reductase-like (SQRDL) gene with osteoporosis in Korean postmenopausal women.

To identify novel susceptibility variants for osteoporosis in Korean postmenopausal women, we performed a genome-wide association analysis of 1180 nonsynonymous single nucleotide polymorphisms (nsSNPs) in 405 individuals with osteoporosis and 722 normal controls of the Korean Association Resource cohort. A logistic regression analysis revealed 72 nsSNPs that showed a significant association with osteoporosis (p<0.05). The top 10 nsSNPs showing the lowest p-values (p = 5.2×10-4–8.5×10-3) were further studied to investigate their effects at the protein level. Based on the results of an in silico prediction of the protein’s functional effect based on amino acid alterations and a sequence conservation evaluation of the amino acid residues at the positions of the nsSNPs among orthologues, we selected one nsSNP in the SQRDL gene (rs1044032, SQRDL I264T) as a meaningful genetic variant associated with postmenopausal osteoporosis. To assess whether the SQRDL I264T variant played a functional role in the pathogenesis of osteoporosis, we examined the in vitro effect of the nsSNP on bone remodeling. Overexpression of the SQRDL I264T variant in the preosteoblast MC3T3-E1 cells significantly increased alkaline phosphatase activity, mineralization, and the mRNA expression of osteoblastogenesis markers, Runx2, Sp7, and Bglap genes, whereas the SQRDL wild type had no effect or a negative effect on osteoblast differentiation. Overexpression of the SQRDL I264T variant did not affect osteoclast differentiation of the primary-cultured monocytes. The known effects of hydrogen sulfide (H2S) on bone remodeling may explain the findings of the current study, which demonstrated the functional role of the H2S-catalyzing enzyme SQRDL I264T variant in osteoblast differentiation. In conclusion, the results of the statistical and experimental analyses indicate that the SQRDL I264T nsSNP may be a significant susceptibility variant for osteoporosis in Korean postmenopausal women that is involved in osteoblast differentiation.