CC chemokine receptor 5 (CCR5) deletion polymorphism does not protect Czech males against early myocardial infarction

Dear Sir, Polymorphisms in genes coding for CC chemokine receptors, CCR2 and CCR5, have been studied as genetic markers of coronary artery disease (CAD) [1–5]. Whilst the VI genotype of the CCR2 V64I polymorphism has been implicated in the manifestation of myocardial infarction (MI) in different populations [1–3], the data on possible involvement of the CCR5 deletion variant in ethiopathogenesis of coronary atherosclerosis are conflicting [4, 5]. A protective effect of CCR5Δ32 allele against early MI was reported in Spanish males [4]. However, a recent study from the LURIC (Ludwigshafen Risk and Cardiovascular Health) cohort of male and female German patients with CAD did not show any difference between CCR5Δ32 frequencies in cases and controls [5]. We have, therefore, decided to replicate [6] the original study [4] in our Czech cohort of male patients with early occurrence of MI. Into our association study we enrolled 80 cases – Czech males, who had their first MI before the age of 55 years; MI was diagnosed according to the international consensus [7]. The controls comprised 247 healthy Czech males (blood donors), in whom cardiovascular symptomatology was excluded by questionnaire emphasizing family history of cardiovascular disease. Informed consent was obtained from all study participants and ethical committee approved the study. Genotyping methodology [polymerase chain reaction-sequence specific primers (SSP)] was described previously [8]. Significance of differences in CCR5Δ32 allele and genotype frequencies between cases and controls was assessed by standard 2 × 2 chi-square analysis using SIGTEST, a computer-based statistical programme that uses a Woolf-Haldane correction in cases of small numbers [8]. Both control and patient populations were in Hardy–Weinberg equilibrium with regard to the genotypes’ distribution (P > 0.05). Frequency of the CCR5Δ32 allele in Czech males with early MI did not differ from the frequency in control subjects (Table 1, first row). There was one homozygous individual (CCR5Δ32/CCR5Δ32) present amongst the patients (1.3%) and also one such individual appeared within controls (0.4%). The original statement about protective role of CCR5Δ32 variant in MI was based on less frequent occurrence of the deletion allele in male patients with early MI (Table 1, second row) and also on absence of CCR5Δ32 homozygous individuals amongst Spanish patients [4]. Studies of several chemokine polymorphisms including CCR5, which were performed in German [5] and also Hungarian [9] patients with CAD, did not, however, find significant relationship between CCR5Δ32 and CAD (see Table 2 for gene frequencies in these two populations). Interestingly, the German study in the LURIC cohort did not confirm CCR5Δ32-associated protection against premature MI, although no frequency data or the age limit for early MI was reported [5]. Despite both aforementioned negative studies [5, 9] have been performed in big cohorts of CAD patients, their data cannot be fully compared with the findings of the original Spanish study, which was limited to males with/without MI [4]. Cases and controls in both German and Hungarian studies comprised both sexes, in a range from 24% to 48% females [5, 9]. Although there have been no reports of differential distribution of CCR5Δ32 allele between healthy males and females and also our own data does not favour gender distinction [CCR5Δ32 allele frequency; males (n = 247), 11.1%; females (n = 139), 10.1%; P = 0.7], intrinsic or external factors in complex disease may cause increased occurrence of particular allele and/or genotype in patients of either sex. With aim to replicate the original study of CCR5Δ32 protective effect [4] as closely as possible we have designed our association study in Czech population accordingly: using only male cohorts we concentrated on patients with MI, in whom the disease occurred early, i.e. before the age of 55 years. Despite this unified approach, our data does not confirm original findings [4]. It is unlikely that this discrepancy was caused by differences in diagnostic or laboratory methodology. The clinical assignment of patients was similar in both studies with the exception that proportion of our patients, who in addition to standard criteria underwent coronary angiography, was higher than in the original study [4]. Regarding genotyping, our CCR5Δ32 frequency data in control and also in patient population (Table 1, first row) nearly equalled those obtained elsewhere by different approaches (Table 2). Finally, one may argue that the number of patients in our cohort was lower than in the original study [4]. We, however, tried to ensure compliance with the guidelines of performing genetic association studies such as appropriate size of the control group or relevant statistics including Hardy–Weinberg equilibrium [6, 10]. Moreover, our study brought the same conclusion as the study in the big LURIC cohort, which assessed the role of several genetic variants in chemokines and their receptors in male and female patients [5]. In context of the current opinion on genetic association studies [6, 10] and in view of our inability to replicate the original findings in Spanish population [4] we, therefore, suggest that CCR5Δ32 allele does not constitute a factor of protection against early occurrence of MI in males, at least for the Czech population. No conflict of interest was declared. The authors thank Dr J Drabek for methodical advice. Financial support: IGA MZ CR NI7308-3, MSM6198959205.