Aims: To investigate whether the presence of the CCR5Δ32 allele was associated with atopy or asthma.
Methods: A total of 118 children with asthma, 145 children with non-asthmatic, but allergic phenotype, and 303 children without allergic or asthmatic disorders were studied.
Results: There were no significant differences in the frequency of CCR5Δ32, or in the distributions of genotypes between the groups. The relative eosinophil blood count was slightly lower in patients with heterozygous genotype, than in patients with wild type genotype.
Conclusion: No association was found between the susceptibility of allergy or asthma and the functional deficient CCR5Δ32 allele.
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Asthma is a pulmonary disease characterised by increased bronchial responsiveness to a variety of stimuli. Chemotactic cytokines, or chemokines, are small signalling proteins which are deeply involved in the physiology and pathophysiology of acute and chronic inflammatory processes, by attracting and stimulating specific subsets of leukocytes. Several studies have shown that chemokines and their receptors are implicated in asthma.1
A common 32 base pair (bp) deletion mutation in the CC chemokine receptor 5 gene (CCR5Δ32), which causes truncation and loss of CCR5 receptors on lymphoid cell surfaces has been described.2 Two recent studies in the Lancet have reported controversial results about the prevalence and role of the CCR5Δ32 mutation in asthmatic individuals. Hall et al have reported an association of the CCR5Δ32 allele with reduced risk of asthma in Scottish children,3 while Mitchell et al found no significant association for atopy or asthma/wheeze in families from Western Australia and Southern England.4
Given the potential importance of CCR5 in allergic inflammation, we determined the prevalence of the CCR5Δ32 mutation in three groups of Hungarian children.
A total of 118 asthmatic children (aged 3–18 years, mean 10.1 (SD 3.5) years), 145 non-asthmatic, allergic children (aged 1–18 years, mean 5.4 (SD 3.8) years), and 303 children of comparable age without atopic or allergic disorders were enrolled in the study.
The asthmatic children attended the Allergic Outpatient Consultation of the Budai Children's Hospital. All the asthmatic children had specialist physician diagnosed asthma with the following characteristics: (1) recurrent breathlessness and expiratory dyspnoea requiring treatment; (2) physician diagnosed wheeze; and (3) reversibility of the wheezing and dyspnoea by bronchodilator treatment, measured as forced expiratory volume in one second (FEV1) by a spirometer (Piston).
The non-asthmatic allergic children attended the Allergic Outpatient Consultation of Heim Pál Pediatric Hospital. All the allergic children had specialist physician diagnosed allergy with the following criteria: (1) clinical signs of severe allergy (including allergic rhinitis, atopic dermatitis, food allergy, and urticaria); and (2) atopy (defined as described elsewhere5).
The control children were selected from patients in the Heim Pál Pediatric Hospital who met all of the following criteria: (1) no symptoms and history of allergic diseases; and (2) total serum IgE below the general population mean for their ages.
Informed parental consent was obtained for each patient and the study was approved by an institutional review committee.
White blood cell counts and eosinophil cell counts were measured by Coulter MAXM Analyser. Genotyping of CCR5 was carried out as described previously.6
CCR5Δ32 allele frequencies were calculated by allele counting. Hardy–Weinberg equilibrium was tested by using a χ2 goodness of fit test. The technique of χ2 decomposition was used to test for differences in CCR5Δ32 distributions between the different phenotypes. Analysis of variance was used to estimate the impact of the polymorphism on quantitative traits. The power calculation was performed by StatMate software (GraphPad Software Inc., San Diego, California).
Table 1 presents the distribution of CCR5Δ32 genotypes and the allelic frequencies in the three groups. The results were overall in Hardy–Weinberg equilibrium. The allelic frequency in the controls (11.2%) was in good agreement with that found in a previous study of Hungarian newborns (11.6%). There were no significant differences in the frequency of CCR5Δ32, or in the distribution of genotypes between the groups. In contrast to the results of Hall and colleagues,3 there were several homozygous carriers for the Δ32 allele among the asthmatic patients (3.4%).
Based on the observed prevalence of CCR5Δ32 in our population, this study had an 80% power to detect a relative risk of 0.37 in the prevalence of asthma between carriers and non-carriers with a significance of p = 0.05. Hall and colleagues3 reported an odds ratio of asthma in individuals with the CCR5Δ32 of 0.36. Therefore, our study with the same power and at the same level of significance should be able to detect significance differences in the proportion of patients with asthma between carriers and non-carriers if they exist in the population tested.
To determine the role of the CCR5Δ32 allele in asthma, some clinical and biological characteristics of the asthmatic patients were compared between the different genotypes. Among the 118 asthmatics there were 87 atopic (73.7%) and 31 non-atopic (26.3%) patients.. There were no significant differences in the prevalence of the CCR5Δ32 allele or in the genotype distributions between atopic and non-atopic asthmatic patients (allele frequencies were 10.3% and 14.5%, respectively). The mean age of the patients at first diagnosis of asthma, total IgE concentration, white blood cell count, and absolute eosinophil cell count did not differ between the genotypes (data not shown). The relative eosinophil blood count was slightly lower in patients with heterozygous genotype than in patients with wild type genotype (3.9% SD 1.6%) v 5% (SD 1.9%), p = 0.02). In contrast, the relative eosinophil count was highest in patients with Δ32/Δ32 genotype (6% (SD 2.8%)), but because of the low number of patients with this genotype (four), the difference was not significant.
In our investigation of 566 Hungarian children, we found no variation in the prevalence of CCR5Δ32 allele between the asthmatic, allergic, and control groups, suggesting that the CCR5Δ32 allele does not protect from asthmatic or allergic diseases, and does not even contribute to a reduced risk in allergic individuals from the development of asthma. Our findings are not in agreement with those of Hall and colleagues,3 who found reduced prevalence for CCR5Δ32 in 98 Scottish asthmatic children, comparing them with 317 non-asthmatic children. In contrast, the results of Mitchell et al are comparable with ours.4 Although comparison of these results is difficult because of the possible genetic and environmental differences in the populations, the CCR5Δ32 allele seemed to be protective against asthma in Scotland, but not in our study population.
This study was supported by the following grants: OTKA (National Scientific Research Fund): T-016111, T032349, 022287/1997; Hungarian Ministry of Welfare: ETT 134/2001 474/96; János Bolyai Research Grant.