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Keywords:

  • Aspirin-intolerant asthma;
  • SLC6A12;
  • polymorphism;
  • haplotype

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Aspirin-intolerant asthma (AIA) occurs from asthma exacerbation after exposure to aspirin. However, the underlying mechanisms of AIA occurrence are still unclear. The critical role of the solute carrier family 6 (neurotransmitter transporter, betaine/GABA) member 12 (SLC6A12) gene in GABAergic transmission, which is associated with mucus production in asthma, makes it a candidate gene for AIA association study. Eight single nucleotide polymorphisms (SNPs) in SLC6A12 were genotyped in 163 aspirin-intolerant asthma (AIA) and 429 aspirin-tolerant asthma (ATA) patients of Korean ethnicity. Associations between polymorphisms of SLC6A12 and AIA were analysed using multivariate logistic analysis. Results showed that two polymorphisms and a haplotype in SLC6A12, rs499368 (P= 0.005; Pcorr= 0.03), rs557881 (non-synonymous C10R, P= 0.007; Pcorr= 0.04), and SLC6A12_BL1_ht1 (P= 0.009; Pcorr= 0.05) respectively, were significantly associated with AIA after multiple testing corrections. In addition, SNPs of SLC6A12 were significantly associated with the fall rate of FEV1 by aspirin provocation suggesting that SLC6A12 could affect reversibility of lung function abnormalities in AIA patients. Although these results are preliminary and future replications are needed to confirm these findings, this study showed evidence of association between variants in SLC6A12 and AIA occurrence among asthmatics in a Korean population.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Asthma, as provoked by inflammation of the lungs, is a disease that is triggered by interactions between genetic and environmental factors such as allergens. Often referred to as aspirin-intolerant asthma, the asthma that is exacerbated by aspirin is a distinct clinical diagnosis characterised by chronic hyperplastic rhinosinusitis, nasal polyps and asthma attacks after ingestion of aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) (Bel, 2004). Although a number of studies have provided estimates of 1–2% up to 20% of AIA prevalence (McDonald et al., 1972; Spector et al., 1979; Hedman et al., 1999), the pathophysiologic mechanisms underlying the development of this specific asthma phenotype have not yet been fully understood (Namazy & Simon, 2002).

The solute carrier family 6 (neurotransmitter transporter, betaine/GABA) member 12 (SLC6A12) gene, also referred to as sodium and chloride-dependent betaine/GABA transporter-1 (BGT-1), is widely expressed in the proximal tubules of the kidney and cells of the central nervous system (Rasola et al., 1995; Matskevitch et al., 1999). In the renal medulla, elevated transcription of SLC6A12 causes the cells to accumulate compatible osmolytes to high concentrations (Yamauchi et al., 1992) resulting in a balanced extracellular hypertonicity (Rasola et al., 1995), thus, reducing hypertonicity stress. The basolateral distribution of SLC6A12 is suggestive of either a post-synaptic site of action or alternatively, that this transporter serves to clear GABA from the cerebrospinal fluid/extracellular fluid in non-synaptic regions (Borden, 1996). The lack of agreement between in vivo and in vitro experiments regarding the expression and function of SLC6A12 explains why its precise physiological role in the nervous system has been difficult to determine.

An excitatory GABAergic system was described recently in the airway epithelium. It has been revealed that the γ-aminobutyric acid (GABA) signaling pathway in the airway epithelium plays a critical role in asthma development through its ability to enhance mucus production (Xiang et al., 2007). Previous studies have indicated that during the development of allergen-induced airway responses, activation of PI3K/Akt leads to an increase in IL-13 that in turn, activates the airway epithelial cell (AEC) GABAergic system which acts in autocrine and paracrine fashions to enhance mucus hypersecretion of AECs resulting to airway obstruction (Corry & Kheradmand, 2007; Lu & Inman, 2009). In another study, it has been found that aspirin is involved in the detoxification of GABA-lytic picrotoxin (PT), an antagonist for the GABAA receptor chloride channels (Golovko et al., 1995). The inhibition of picrotoxin by aspirin restores GABA activity. With the critical role played by SLC6A12 in GABAergic transmission in the brain, we considered it as a candidate gene in the study of AIA.

In an attempt to examine the genetic role in AIA occurrence, we focused our analysis on the association between SLC6A12 and the occurrence of aspirin-intolerance among asthmatics.

Material and Methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Study Subjects

To serve as primary subjects for this study, 592 asthmatics were recruited from among the patients enrolled at the Asthma Genome Research Center, a part of Soonchunhyang, Chunnam, Chungbuk, Seoul National and Chung-Ang University hospitals in Korea from 2003–2008. These subjects showed clinical symptoms that met the criteria for asthma, such as cough, wheeze, or shortness of breath, in accordance with the Global Initiative for Asthma (GINA) Global Strategy for Asthma Management and Prevention study. Evaluation of the subjects included airway reversibility measured by an inhalant bronchodilator-induced improvement of more than 15% of forced expiratory volume in 1s FEV1 and/or hyper-reactivity of less than 10mg/mL of metacholine (Crapo et al., 2000). In order to categorise the subjects as having aspirin-intolerant asthma (n = 163), an aspirin provocation test was performed on subjects with a history of aspirin hypersensitivity, or those detected with urticaria, nasal polyps and sinusitis on water's view. ATA controls (n = 429) consisted of asthmatics exhibiting 15% or more reduction of FEV1 without extrabronchial nasal or skin symptoms whereas subjects with hypertension and diabetes or those taking angiotensin converting enzyme (ACE) inhibitors were excluded from this study. Finally, a written consent was secured from the subjects prior to conducting the study and ethical approval was obtained from the Institutional Review Board of each hospital. Table 1 summarises clinical characteristics of the study subjects.

Table 1.  Clinical profiles of the study subjects.
Clinical profileAsthmatics (all subject)AIAATA
  1. Each clinical profile of AIA was compared to the respective ATA controls. *P < 0.05; **P < 0.0001 compared to ATA control.

  2. Age indicates a first medical examination. AIA, aspirin-intolerant asthma; ATA, aspirin-tolerant asthma.

Number of subjects (n)592163429
Age [year, mean (range)]46.15 (15.40–77.88)43.13 (17.22–72.73)*47.30 (15.40–77.88)
Sex (n, male/female)206/38659/104147/282
Total smoker (Current Smoker; Ex-Smoker) (%)27.70 (12.50; 15.20)21.47 (12.88; 8.59)*30.07 (12.35; 17.72)
Height (cm)160.78 ± 8.63161.72 ± 8.69160.42 ± 8.39
Weight (kg)62.81 ± 10.8461.25 ± 10.38*63.40 ± 10.97
Body mass index (kg/m2)24.24 ± 3.3923.39 ± 3.25*24.58 ± 3.39
% fall of FEV1 by aspirin provocation9.27 ± 13.2424.63 ± 16.11**3.54 ± 4.85
Blood eosinophil (%)6.01 ± 5.735.96 ± 5.216.03 ± 5.92
FEV1 (% predicted)90.54 ±16.9790.35 ± 14.04*91.66 ± 16.87
PC20 methacholine (mg/ml)6.43 ± 8.675.02 ± 7.83*6.91 ± 8.90
Total IgE (IU/ml)357.65 ± 604.09348.60 ± 596.44361.00 ± 607.56
Positive rate of skin test (%)56.4252.7657.81

SNP Selection and Genotyping

We chose several candidate genes from the literature, and SNPs in those genes were selected from dbSNP in the National Center for Biotechnology Information (build 36) and International HapMap Project (http://hapmap.ncbi.nlm.nih.gov/) based on the frequencies in the Asian population and LD status among the SNPs. To genotype the data, we adapted BeadXpress® (Illumina, San Diego, CA, USA) (Oliphant et al., 2002) which allows genotyping of 96–384 SNPs simultaneously. For examination of AIA risk association, we genotyped 96 polymorphisms including eight SNPs of SLC6A12. Genotyping in all study subjects, including 163 AIA and 429 ATA patients, was performed with assessment of data quality by duplicate DNAs (n = 10). The genotype quality score for retaining data was set to 0.25. SNPs that did not satisfy the following criteria were excluded from the study: (i) a minimum call rate of 90%; (ii) no duplicate error; (iii) Hardy-Weinberg equilibrium greater than P > 0.001. A total of eight SNPs in the SLC6A12 gene were successfully genotyped in 163 AIA and 429 ATA Korean subjects with an average call rate of 99.9%.

Statistical Analyses

To determine the association between the genotype distributions of AIA patients and ATA controls, logistic analysis was carried out controlling for age (continuous value), gender (male = 0, female = 1), smoking status (non-smoker = 0, ex-smoker = 1, smoker = 2), atopy (absence = 0, presence = 1) and body mass index (BMI) as covariates to eliminate or reduce any confounds that might influence the findings. Lewontin's D′ (|D′|) and the LD coefficient r2 were examined to measure linkage disequilibrium between all pairs of biallelic loci (Hedrick, 1987). Using the eight SNPs, haplotypes were inferred using PHASE algorithm ver. 2.0 (Stephens et al., 2001), and its association analysis was performed using SAS version 9.1 (SAS Inc., Cary, NC). In addition, the differences in the fall rate in FEV1 following aspirin challenge among the genotypes and haplotypes were examined using a linear regression model. The effective number of independent marker loci detected from the SLC6A12 polymorphisms was calculated for multiple testing corrections using the SNPSpD (http://genepi.qimr.edu.au/general/daleN/SNPSpD/) software, which is based on the spectral decomposition (SpD) of matrices of pair-wise linkage disequilibrium (LD) between SNPs (Nyholt, 2004).

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Characteristics of the Study Subjects

In this study, SNPs (rs3759373, rs499368, rs557881, rs216244, rs216242, rs2284330, rs2284329, and rs2075228) from the human SLC6A12 gene in 163 aspirin-intolerant asthma case subjects and 429 aspirin-tolerant asthma control subjects were successfully genotyped to discover potential involvement of the gene with the occurrence of AIA in a Korean population. Table 1 depicts the clinical characteristics of the study subjects. From the data gathered, it was observed that AIA patients (23.39 ± 3.25 kg/m2) had lower BMI compared with ATA controls (24.58 ± 3.39 kg/m2). Our findings also showed a mean age of 43.1 for AIA patients and 47.3 for the control group. In addition, results from the aspirin provocation test in AIA patients showed significant increase of aspirin-induced fall rate in FEV1 to that of ATA controls (P < 0.0001). The predicted FEV1%, smoking status and PC20 methacholine in AIA patients were significantly lower than those of ATA controls (P < 0.05).

Distribution of SLC6A12 Variants

Eight polymorphisms, including two SNPs in the coding region (rs557881 and rs2075228) and six SNPs in the non-coding region (rs3759373, rs499368, rs216244, rs216242, rs2284330, and rs2284329) were successfully genotyped for AIA association study (Table 2; Fig. 1A). The distribution of each locus was in Hardy-Weinberg Equilibrium (P > 0.05; Table 2). The minor allele frequency (MAF) of each polymorphism was 0.109 (rs3759373), 0.342 (rs499368), 0.347 (rs557881), 0.341 (rs216244), 0.368 (rs216242), 0.458 (rs2284330), 0.458 (rs2284329) and 0.403 (rs2075228) as shown in Table 2. Pair-wise comparisons of eight SNPs were used to construct two LD blocks and haplotypes (Fig. 1B and 1C).

Table 2.  Variants of SLC6A12 identified in this study (n = 592).
rs numberPositionAlleleAA changeHWE*HeterozygosityMAF
KoreanCaucasianChineseJapaneseAfrican
  1. *P-values of deviation from Hardy-Weinberg Equilibrium in a Korean population.

  2. The MAFs of Caucasian, Chinese, Japanese and African were obtained from International HapMap and dbSNP database.

  3. MAF, minor allele frequency; AA, amino acid; HWE, Hardy-Weinberg Equilibrium.

rs3759373Intron1C>T 0.5670.1940.1090.0000.1110.0450.000
rs499368Intron2A>T 0.1040.450.3420.4750.3300.2500.594
rs557881Exon4T>CC10R0.1410.4530.3470.4580.3220.2330.675
rs216244Intron7T>G 0.1630.4540.3410.5250.3220.3750.233
rs216242Intron7A>T 0.7220.3560.3680.5170.3670.3890.233
rs2284330Intron14A>G 0.5670.1940.4580.4920.4000.4670.350
rs2284329Intron14T>G 0.3390.4490.4580.4920.3890.4670.325
rs2075228Exon17C>T 0.5060.4650.4030.3500.3440.3520.559
image

Figure 1. Physical map, haplotypes, and LD of the SLC6A12 gene. (A) Schematic gene map and SNPs in the SLC6A12 gene on chromosome 12p13 (23 kb). Black blocks represent coding exons and white blocks represent 5′ and 3′UTR. The first base of translation site was denoted as nucleotide +1. (B) Haplotypes of SLC6A12. (C) LD coefficient (|D′|) among SLC6A12 SNPs in a Korean population. UTR, untranslated region.

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Association of Polymorphisms with Risk of Aspirin Intolerance among Asthmatics

Using a co-dominant model, results from logistic association analysis of the eight SNPs in SLC6A12 between AIA and ATA subjects of Korean ethnicity with age, sex, smoking status, atopy and BMI adjusted as covariates showed two single nucleotide polymorphisms displaying association signals at P < 0.05 level of significance after multiple testing corrections (Table 3). In particular, rs499368 and rs557881 polymorphisms showed significant associations (P= 0.005, Pcorr= 0.03; P= 0.007, Pcorr= 0.04, respectively) with the risk of AIA. The minor allele frequencies of rs499368 (MAF = 0.399) and rs557881 (MAF = 0.321) for AIA were significantly higher than those of ATA, respectively. These findings suggest a stronger contribution of the two polymorphisms in AIA patients. In addition, SNP rs557881T>C was a non-synonymous variant that translates to the amino acid change from cysteine to arginine. Since the fall rate of FEV1 by aspirin provocation is an important diagnostic marker for AIA, further association between SNPs of SLC6A12 and the fall rate of FEV1 by aspirin provocation was analysed. The association between SNPs and the fall rate of FEV1 following aspirin challenge was determined using regression analysis. Two SNPs (rs499368 and rs557881) and the haplotype (SLC6A12_BL1_ht2) containing these two variants showed significant differences with fall rate of FEV1 by aspirin provocation in AIA patients compared to that of ATA controls (P < 0.05, Table 4). This implies that genotypes of the SLC6A12 gene could be a causative factor for the reversibility of lung function abnormalities among AIA patients.

Table 3.  Association analysis of the SLC6A12 polymorphisms and haplotypes with the risk of AIA.
SNP/HaplotypePositionAA changeMAFCo-dominant
AIA (n = 163)ATA (n = 429)OR (95% CI)P*Pcorr**
  1. *P-values for logistic analyses controlling age, smoking status, atopy and BMI as covariates with aspirin-intolerant asthma patients, assuming

  2. co-dominant model. **P-values after multiple testing correction.

  3. AIA, aspirin-intolerant asthma; ATA, aspirin-tolerant asthma; AA, amino acid; MAF, minor allele frequency; OR, odds ratio; CI, confidence interval.

rs3759373Intron1 0.1380.0961.51 (1.01–2.26)0.05.
rs499368Intron2 0.3990.3211.49 (1.13–1.98)0.0050.03
rs557881Exon4C10R0.4020.3271.47 (1.11–1.94)0.0070.04
rs216244Intron7 0.3300.3420.98 (0.74–1.30)0.88.
rs216242Intron7 0.3530.3720.93 (0.71–1.23)0.62.
rs2284330Intron14 0.4690.4491.13 (0.86–1.47)0.38.
rs2284329Intron14 0.4690.451.12 (0.86–1.47)0.39.
rs2075228Exon17 0.4170.3951.12 (0.86–1.47)0.41.
SLC6A12_BL1_ht1  0.4020.3291.45 (1.10–1.92)0.0090.05
SLC6A12_BL1_ht2  0.2610.2231.30 (0.96–1.77)0.09.
SLC6A12_BL1_ht3  0.1380.0961.51 (1.01–2.26)0.05.
SLC6A12_BL2_ht1  0.4720.4970.89 (0.68–1.16)0.40.
SLC6A12_BL2_ht2  0.2940.3180.92 (0.69–1.24)0.59.
SLC6A12_BL2_ht3  0.1750.1311.42 (0.99–2.03)0.06.
Table 4.  Association analysis between genotypes of the SLC6A12 gene and the fall of FEV1 by aspirin provocation.
SNP/HaplotypeFall of FEV1 (AIA, n = 163)Fall of FEV1 (ATA, n = 429)
C/CC/RR/RP*C/CC/RR/RP*
  1. *P-values of regression analysis represent the co-dominant model controlling sex, smoking status, and atopy as covariates.

  2. C/C, C/R and R/R indicate the homozygote of common allele, and the heterozygote and homozygote of rare allele, respectively.

  3. Fall rate values are mean ± SD.

rs3759373120 (24.24 ± 16.29)39 (24.73 ± 16.60)4 (18.45 ± 13.88)0.746349 (3.49 ± 4.90)78 (3.97 ± 4.56)2 (−3.60 ± 0.57)0.805
rs49936851 (27.39 ± 18.57)91 (23.79 ± 15.49)21 (18.32 ± 11.55)0.020195 (3.44 ± 4.74)193 (3.85 ± 4.88)41 (2.58 ± 5.14)0.751
rs55788151 (27.39 ± 18.57)90 (23.31 ± 14.88)22 (20.53 ± 15.32)0.049191 (3.46 ± 4.69)194 (3.83 ± 4.96)43 (2.65 ± 5.06)0.742
rs21624469 (25.59 ± 14.94)80 (22.50 ± 17.66)13 (24.80 ± 10.96)0.468184 (3.38 ± 4.53)195 (3.60 ± 5.12)49 (3.93 ± 4.99)0.479
rs21624266 (26.46 ± 15.58)80 (22.46 ± 17.58)17 (23.73 ± 11.14)0.270168 (3.43 ± 4.50)203 (3.49 ± 5.13)58 (4.06 ± 4.86)0.464
rs228433042 (24.98 ± 15.75)88 (25.08 ± 17.71)33 (20.90 ± 12.31)0.328128 (3.49 ± 4.45)216 (3.34 ± 5.08)84 (4.16 ± 4.85)0.392
rs228432942 (24.98 ± 15.75)88 (25.08 ± 17.71)33 (20.90 ± 12.31)0.328128 (3.49 ± 4.45)215 (3.34 ± 5.09)85 (4.15 ± 4.83)0.398
rs207522853 (22.79 ± 17.63)85 (24.65 ± 16.10)25 (25.74 ± 13.90)0.403155 (3.43 ± 4.92)209 (3.66 ± 4.67)65 (3.44 ± 5.27)0.834
SLC6A12_BL1_ht151 (27.39 ± 18.57)90 (23.31 ± 14.88)22 (20.53 ± 15.32)0.049191 (3.43 ± 4.68)194 (3.85 ± 4.97)44 (2.66 ± 5.00)0.789
SLC6A12_BL1_ht285 (26.28 ± 17.94)70 (22.90 ± 14.31)8 (13.73 ± 5.87)0.026261 (3.54 ± 4.76)145 (3.75 ± 4.84)23 (2.30 ± 5.86)0.575
SLC6A12_BL1_ht3120 (24.24 ± 16.29)39 (24.73 ± 16.60)4 (18.45 ± 13.88)0.746349 (3.49 ± 4.90)78 (3.97 ± 4.56)2 (−3.60 ± 0.57)0.805
SLC6A12_BL2_ht144 (20.78 ± 11.46)85 (24.70 ± 18.28)34 (27.44 ± 15.72)0.076106 (4.02 ± 4.90)220 (3.32 ± 4.97)103 (3.52 ± 4.53)0.409
SLC6A12_BL2_ht278 (24.92 ± 15.33)75 (23.24 ± 17.70)10 (25.98 ± 12.26)0.800197 (3.37 ± 4.56)191 (3.62 ± 5.08)41 (4.02 ± 5.17)0.434
SLC6A12_BL2_ht3110 (25.18 ± 17.15)47 (21.91 ± 14.13)6 (24.50 ± 15.31)0.360323 (3.56 ± 4.90)100 (3.41 ± 4.68)6 (5.03 ± 5.30)0.856

In this study, we also performed a haplotype analysis on 6 major haplotypes within 2 haplotype blocks. A significant association between the SLC6A12_BL1_ht1 haplotype and AIA occurrence with frequencies of 0.402 and 0.329 for AIA and ATA respectively was observed (P= 0.009), indicating a possible involvement of this specific haplotype with the risk of AIA. However, the significance was decreased to nominal evidence after multiple testing corrections (Pcorr= 0.05).

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

It has been understood that asthma occurs as a result of inflammation of the lungs and is characterised by cough, wheezing and shortness of breath due to airway obstruction. Both genetic and environmental factors contribute to disease provocation, and exposure to triggers such as allergens and aspirin leads to asthma exacerbation. Previous studies have reported genetic factors responsible for the occurrence of asthma and exacerbation of the disease by exposure to aspirin. Specifically, a study in a Korean population, showed that the negative regulation of leukotriene C4 synthase (LTC4S) by thromboxane A2 receptor (TBXA2) being modulated by the TBXA2R+795T>C polymorphism, augmented bronchoconstrictive response to acetyl salicylic acid (ASA), which can contribute to AIA susceptibility (Kim et al., 2005).

It has also been known that overproduction of cys-leukotrienes (cysLTs) in bronchial epithelium and inhibition of prostaglandin synthesis by cyclooxygenase (COX) inhibition underlie the development of AIA (Sampson et al., 1997; Pierzchalska et al., 2000; Antczak et al., 2002). However, in contrast to that, a recent study showed that LTC4S and cysteinyl leukotriene receptor 1 (CYSLTR1) gene polymorphisms were not associated with AIA occurrence in a study involving Korean individuals (Choi et al., 2004). The disparity between previous reports might be due to extraneous factors overlooked in the study methodology. Despite recent advances in asthma research and aspirin hypersensitivity among asthmatics, there are still major gaps in our understanding of the underlying mechanisms of AIA.

Recently, the airway remodeling of asthma (Warner & Knight, 2008) and the correlation of the extraneuronal GABAergic system have been implicated in AIA. To elucidate any genetic influence of the GABAergic system in AIA occurrence, we investigated the genetic association of SLC6A12 with AIA in a Korean population. Our findings demonstrated not only significant associations between SLC6A12 variants and aspirin-intolerance among asthmatics, but also a relationship between the genotypes of the SLC6A12 gene with fall rate of aspirin in AIA patients. The minor allele frequencies of two polymorphisms (rs499368 and rs557881) and one haplotype (SLC6A12_BL1_ht1), which were exhibited in the logistic association analysis, were significantly higher in AIA than in ATA, suggesting that these variants might be involved mainly in the risk of aspirin-intolerance among asthmatics.

To strengthen the association between SLC6A12 polymorphisms and AIA, six SNPs (rs216250, rs216247, rs216243, rs2284328, rs542736, and rs1051104) in SLC6A12 region were also imputed from the International MapMap Project based on the haplotypes of Asian populations (Chinese and Japanese). Due to the absolute LD of the imputed SNPs with the genotyped ones in this study (|D′| = 1 and r2= 1), the significance of associations were identical to those shown in Table 3, showing that the LD plot of the imputed SLC6A12 was equivalent to that of the Asian population (Fig. 2).

image

Figure 2. Imputation of SLC6A12. (A) LD plot of the imputed SLC6A12. LD coefficient (|D′|) among SLC6A12 SNPs, which are composed of eight genotyped in this study and six imputed from the International HapMap Project. (B) Haplotypes of the imputed SLC6A12. The imputed SNPs of rs216250, rs216247, and rs216243 show an absolute LD with rs216244; rs2284328 with rs2284329; rs542736 and rs1051104 with rs2075228, respectively (|D′| = 1 and r2= 1). Asterisks indicate the imputed SNPs.

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Moreover, our findings also indicate a non-synonymous variant that translates to the amino acid (C10R) change from T (cysteine) to C (arginine) in rs557881 polymorphism. Cysteine is an amino acid with a non-polar side chain that contains uncharged functional groups at physiological pH and groups incapable of participating in hydrogen bonding, whereas arginine is an amino acid with a polar side chain that contains groups that are either charged at physiological pH or groups that are able to participate in hydrogen bonding. Modification of cysteine by introducing either a methyl or t-butyl group in the free sulfhydryl group and replacing the guanidine group with a urea linkage in the side chain of arginine could be a risk factor for asthma and thus, might merit the interest of functional studies in the future.

Considering the function of SLC6A12 as a GABA transporter in GABAergic transmission in the brain with respect to asthma occurrence and exacerbation, a new link between aspirin intolerance and genetic variations of the SLC6A12 gene, especially a non-synonymous C10R variant, was suggested by the key findings in this study. Although there have been extensive research studies conducted on asthma disease, few such efforts were directed towards the study of AIA until recently. Our discovery of associations between the variants of SLC6A12 and AIA is of considerable significance because it strengthens our additional understanding of the physiological role played by SLC6A12 in relation to AIA, which is beyond the functions of SLC6A12 in the nervous system, and addresses the disparity between the previous studies.

Although findings from this study are the first to demonstrate the clinical association of SLC6A12 with AIA in a Korean population, future replication in an independent study cohort is needed to confirm these findings.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

This work was supported by a grant from the Korea Health 21 R&D Project (A010249); a grant, number M1-0302-00-0073, from Korea Science and Engineering Foundation (KOSEF) funded by the Korea government (MEST) (No. 2009-0080157); an Intramural Research Grant of the Korea National Institute of Health (grant number 4800-4845-300-260-00); an Intramural Research Grant from Sogang University (grant number 200810021.01); and a Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0093822). The DNA samples were generously provided by Soonchunhyang University, Bucheon Hospital Biobank, a member of the National Biobank of Korea, supported by the Ministry of Health, Welfare and Family Affairs, Republic of Korea.

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  1. Top of page
  2. Summary
  3. Introduction
  4. Material and Methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References
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