SNP rs2243828 in MPO associated with myeloperoxidase level and atrial fibrillation risk in Chinese Han population

Abstract Previous studies shown that myeloperoxidase (MPO) level is higher in patients with atrial fibrillation (AF); however, no genetic evidence between MPO and AF risk in human population was observed. Therefore, the present study was aimed to investigate the association between rs2243828, a variant in promoter region of MPO and the risk of AF in Chinese GeneID population. The results demonstrated that the minor G allele of rs2243828 showed a significant association with AF in two independent population (GeneID‐north population with 694 AF cases and 710 controls, adjusted P‐adj = 6.25 × 10−3 with an odds ratio was 0.77, GeneID‐central population with 1106 cases and 1501 controls, P‐adj = 9.88 × 10−5 with an odds ratio was 0.75). The results also showed G allele was significantly associated with lower plasma concentration of myeloperoxidase in general population. We also observed a significant difference of odds ratio between subgroups of hypertension and non‐hypertension. Therefore, our findings identified variant in MPO associated with risk of AF and it may give strong evidence to link the inflammation with the incidence of AF.

tigate the association between rs2243828, a variant in promoter region of MPO and the risk of AF in Chinese GeneID population. The results demonstrated that the minor G allele of rs2243828 showed a significant association with AF in two independent population (GeneID-north population with 694 AF cases and 710 controls, adjusted P -adj = 6.25 × 10 −3 with an odds ratio was 0.77, GeneID-central population with 1106 cases and 1501 controls, P -adj = 9.88 × 10 −5 with an odds ratio was 0.75).
The results also showed G allele was significantly associated with lower plasma concentration of myeloperoxidase in general population. We also observed a significant difference of odds ratio between subgroups of hypertension and non-hypertension. Therefore, our findings identified variant in MPO associated with risk of AF and it may give strong evidence to link the inflammation with the incidence of AF.

K E Y W O R D S
atrial fibrillation, genetic association, inflammation, myeloperoxidase

| INTRODUC TI ON
Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and characterized by rapid and irregular beating of the atria. 1 The mechanisms underlying AF are complex and not clear. Myeloperoxidase (MPO) is a crucial regulator of modulating MMP activity and strongly linked to the oxidative stress and inflammation process of remodelling in atria. 2 Studies showed that plasma MPO level was higher in AF patients than in common controls, and AF patients with high MPO levels showed an increased risk of recurrence after catheter ablation. [3][4][5][6] Considering the important roles of oxidative stress and inflammation in the initiation and maintenance of AF, 7 it remains unclear whether MPO acts as a passive marker or as a risk factor in AF.
In this study, we evaluated the association between rs2243828, a variant in promoter region of MPO gene and the risk of AF in two independent case-control populations totally contained 1800 AF cases and 2211 controls from a Chinese GeneID population.

| Study patients
All samples were from the GeneID database. 8 The study was approved by Medical Ethical Committee of HUST and conformed to the guidelines set forth by the Declaration of Helsinki. Written informed consent was obtained from all patients. All patients were Han origin according to the medical records.
AF diagnosis was following the ACC/AHA/ESC guidelines. 9 Patients with other types of cardiac arrhythmias, congenital heart disease, thyroid dysfunction, cardiomyopathies and valvulopathies were excluded. Lone AF was defined as an AF patient that had no CAD, congestive heart failure, hypertension and diabetes.
All patients in the GeneID-north population mainly enrolled in the hospitals of north of China (Dalian, Liaoning province) and in GeneIDcentral population mainly in the hospitals of central of China (Hubei province). All the cases and controls were geographically matched.
Control patients were individuals without any evidence of AF and other types of arrhythmias based on data from ECG or echocardiography.

| Genotyping
Genotyping for SNP rs2243828 was carried out using the TaqMan allelic discrimination assay as previously described. 10 The genotyping results of TaqMan assay were verified by direct Sanger DNA sequencing of 48 patients randomly selected.

| Plasma myeloperoxidase measurements by enzyme-linked immunosorbent assay
To determine whether rs2243828 associated with quantity of myeloperoxidase in plasma, plasma myeloperoxidase concentrations of 177 common health people we measured by ELISA (CUSBIO), and the difference of the mean values (ng/mL) between different genotype carriers were compared using Student's t test.

| Statistical analysis
Pearson's 2 × 2 contingency tables chi-square tests were used to analyse the allelic association, and multivariate logistic regression model was used to adjust the potential confounders. Statistical power analysis was carried out by PS, Power and Simple Size Calculation software. 11

| Study populations
The demographic and clinical characteristics of the two study population are shown in Table 1   After adjusting for potential confounders including age, hypertension, gender and diabetes mellitus, the association remained significant (OR = 0.77 with an adjusted P or P-adj = 6.25 × 10 −3 ) ( Figure 1A).
The significant association was also observed when the population were divided into subgroups in condition of gender, hypertension, type 2 diabetes, without CAD and lone or complex AF ( Figure 1A).
A Breslow-Day test was used to compare the homogeneity of ORs between different subgroups to analyse whether rs2243828 interacted with risk factors, we observed a significant higher effect in subgroups of hypertension than non-hypertension (observed OR = 0.55 in patients with hypertension and 0.81 in patients without hypertension, P = 3.11 × 10 −4 ).

| Plasma Myeloperoxidase concentration was lower in G carriers of rs2243828 than in A allele carriers
We measured plasma myeloperoxidase in 177 common health people by ELISA and found that the concentration was lower in 57 G allele carriers (55 AG and 2 GG, 9.42 ± 4.12 ng/mL) than in 120 pa-

DATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.