Data on IL-6 c.-174 G>C genotype and allele frequencies in patients with coronary heart disease in dependence of cardiovascular outcome

In this data article we present data on the distribution of alleles and genotypes of the interleukin (IL)-6 c.-174 G>C polymorphism (rs 1800795) in patients with coronary heart disease (CHD) in dependence of the incidence of new cardiovascular events (combined endpoint: myocardial infarction, stroke/TIA, cardiac death, death according to stroke) within three years follow-up. Moreover, we investigated putative associations between individual expression of IL-6 genotypes and IL-6 serum level. This investigation is a subanalysis of the article entitled “The Interleukin 6 c.-174 CC genotype is a predictor for new cardiovascular events in patients with coronary heart disease within three years follow-up“ (ClinicalTrials.gov identifier: NCT01045070) (Reichert et al., 2016) [1].


a b s t r a c t
In this data article we present data on the distribution of alleles and genotypes of the interleukin (IL)-6 c.-174 G 4C polymorphism (rs 1800795) in patients with coronary heart disease (CHD) in dependence of the incidence of new cardiovascular events (combined endpoint: myocardial infarction, stroke/TIA, cardiac death, death according to stroke) within three years follow-up. Moreover, we investigated putative associations between individual expression of IL-6 genotypes and IL-6 serum level. This investigation is a subanalysis of the article entitled "The Interleukin 6 c.-174 CC genotype is a predictor for new cardiovascular events in patients with coronary heart disease within three years follow-up" (Clin-icalTrials.gov identifier: NCT01045070) ( Data may improve the development of individual therapeutic strategies in order to prevent new adverse events in patients with coronary heart disease.

Data
Patients who were carrier of the IL-6 c.-174 CC genotype suffered more frequently from a new cardiovascular event whereas carriers of the genotype CG experienced the combined endpoint less often. There was no significant association between the genotype GG and incidence of the combined endpoint (Table 1). Regarding the allele distribution we obtained a positive association between C allele and new adverse events ( Table 2). There were no significant differences regarding IL-6 serum levels between carriers of the genotypes GG, CG, and CC (Fig. 1).

Patient group at baseline
The investigation was carried out in accordance with the ethical guidelines of the "Declaration of Helsinki" and its amendment in "Tokyo and Venice" and were approved by the local ethics committee.
This subanalysis comprised 942 in-patients with CHD (age 66.8 711.01 years, males 74%) at study entry from October 2009 to February 2011. Inclusion criteria were age Z18 years and known CHD as defined by a stenosis of Z50% of a main coronary artery by coronary angiography or percutaneous coronary intervention (PCI) or coronary artery bypass surgery (CABG). At least four own teeth except for the third molars needed to be present. Exclusion criteria were pregnancy, antibiotic therapy during the last 3 months, subgingival scaling and root planing during the last 6 months or psychological reasons rendering study participation impractical. Patients with current alcohol or drug abuse might be not completely able to understand the aim of the study and the necessity of an additional dental examination. If a drug or alcohol abuse was known from patient's file or a patient reported during the interview about a current drug or alcohol abuse he/she was not included in the study.

Follow-up
A follow-up was performed after three years from November 2013 to January 2015. The incidence of the predefined combined endpoint (combined endpoint: myocardial infarction, stroke/transient ischemic attack, cardiac death, death caused by stroke) was calculated. This information was obtained from electronic patient files, physicians, relatives, and civil registration offices. For acquiring followup data we sent out a standardized questionnaire. If patients did not return the questionnaires, we conducted a telephone interview with the patient or his/her relatives or contacted the patient's physician. If follow-up information could not be obtained from these persons, we contacted civil registration offices and requested information about current address or date of death.
From 895 of 942 initial included patients follow-up data were available (drop-out rate 4.9%) after three years follow-up (153.4 748.8 weeks). The incidence of the combined endpoint was 16.1%.

Determination of IL-6 serum level and c.-174 IL-6 polymorphism
Blood samples for determination of IL-6 serum level and IL-6 genotyping were taken at begin of the study from all study participants during their hospital stay. Serum level for IL-6 was determined with electrochemiluminescent immunoassay (ECLIA) using a Cobas e 602 module (Roche Diagnostics) in the central laboratory of University Clinics Halle (Saale).
The determination of IL-6 c.-174 G 4C polymorphism was carried out with PCR-SSP (sequence specific oligonucleotides) using the CYTOKINE Genotyping array CTS-PCR-SSP kit (Collaborative Transplant Study, Department of Transplantation Immunology of the University Clinic of Heidelberg, Germany) in the laboratory of the Department of Operative Dentistry and Periodontology.

Statistical analyses
Statistical analyses were carried out using commercial available software (SPSS v.20.0 package, IBM, Chicago, IL). The IL-6 genotype and allele frequencies were calculated by direct counting and then dividing by the number of subjects to produce genotype frequency, or by the number of chromosomes to produce allele frequency. Differences between patients and controls were determined by chi-square test. The values for IL-6 serum level were checked for normal distribution using the Kolmogorov-Smirnov test and the Shapiro-Wilk test. As they were not normally distributed, comparisons in dependence of IL-6 genotypes were carried out with Kruskal-Wallis test. In general, p values r0.05 were accepted as statistically significant.