Print version ISSN 0021-7557
J. Pediatr. (Rio J.) vol.84 no.3 Porto Alegre May/June 2008
Isabel C. J. de FariaI; Elisangela J. de FariaI; Adyléia A. D. C. ToroII; José Dirceu RibeiroIII; Carmen Silvia BertuzzoIV
Bióloga, Departamento de Genética, Faculdade de Ciências
Médicas, Universidade Estadual de Campinas (UNICAMP), Campinas, SP, Brazil
IIMestre. Médica assistente, Departamento de Pediatria, Faculdade de Ciências Médicas, UNICAMP, Campinas, SP, Brazil. Centro de Investigação em Pediatria, UNICAMP, Campinas, SP, Brazil
IIIProfessor livre docente, Departamento de Pediatria, Faculdade de Ciências Médicas, UNICAMP, Campinas, SP, Brazil. Pesquisador, Centro de Investigação em Pediatria, UNICAMP, Campinas, SP, Brazil
Doutora. Bióloga. Professora livre docente, Departamento de Genética, Faculdade de Ciências Médicas, UNICAMP, Campinas, SP, Brazil
To verify the association of transforming growth factor-b1(TGF-b1)
(C-509T and T869C), CD14 (C-159T), IL-4 (C-590T), IL-4R (ILe50Val) and ADAM33
(S_2) gene polymorphisms with asthma severity in a sample of patients with mild,
moderate and severe persistent atopic asthma.
METHODS: A clinical, laboratory, prospective study was performed in patients with persistent atopic asthma, compared to a control group at Hospital Universitário da Universidade Estadual de Campinas between 2006 and 2007. Analysis of the TGF-b1 T869C gene polymorphism was performed using the technique polymerase chain reaction (PCR) + amplification refractory mutation system (ARMS). TGF-b1 C-509T, CD14 C-159T, IL-4 C-590T, IL-4Ra ILe50Val, and ADAM33 S2 gene polymorphisms were detected by PCR and restriction enzyme.
RESULTS: This study included 88 patients with persistent atopic asthma (27 mild, 23 moderate and 38 severe) and 202 healthy blood donors. As to T869C polymorphism (TGF-b1), there was an association between the CC genotype and patients with severe asthma. There was no association in polymorphisms C-509T (TGF-b1), C-590T (IL-4) and S_2 (ADAM33). When distribution of C-159T polymorphism genotype frequency (CD14) in severe asthma was compared with the control group, there was a significant result with the TT genotype. There was significant association of the Val/Val genotype (IL-4R) with mild asthma.
CONCLUSION: Our results indicate that T869C (TGF-b1), C-159T (CD14) and Val/Val (IL-4R) polymorphisms might be involved in modulation of asthma severity.
Keywords: Asthma genes, polymorphisms, SNP, ADAM33, CD14, TGF-b1.
Asthma is the most common chronic disease in childhood and adolescence. It is caused by genetic and environmental factors, and many genes have been identified in its pathogenesis.1
Some studies, also including twins,2 have shown that a number of genes and their polymorphisms influence immune and pulmonary development and response to environmental factors, contributing to asthma occurrence and/or severity. The transforming growth factor-b1 (TGF-b1) is located on chromosome 19q13.3,4
Studies on the association of TGF-b1 C-509T and T869C gene polymorphisms with risk of asthma are controversial; some found a positive association,5-8 whereas in others such association is negative,9,10 with high levels of TGF-b1, plasma immunoglobulin E (IgE) and higher risk of asthma.
TGF-b1 protein is a multifunctional cytokine that is increased in the bronchial lavage fluid of asthmatics when compared with that of nonasthmatic individuals.11,12 It is important in growth, transformation, tissue repair, fibrosis and modulation of immune inflammatory responses.13 Its function in asthma is not completely known yet.
The CD14 gene is located on chromosome 5q. The C-159T polymorphism has been associated with changes in CD14 and IgE levels in many populations of different ethnicities.14,15
CD14 is a multifunctional receptor expressed in the surface of monocytes, macrophages and neutrophils or serum soluble.16 It is the main receptor of lipopolysaccharides (LPS) or inhaled endotoxins, which are potent inducers of pulmonary inflammation and may activate the immune system and cause Th1 differentiation and/or Th2 suppression.17
It has been proposed that altered CD14 expressions, more increased in asthmatics after LPS inhalation,18 can change the balance of Th1-Th2 cells, influencing IgE levels and inflammation in allergic diseases such as asthma.14
Thus, changes in CD14 expression seem to be important, especially in allergic asthma, and such expression is regulated, at least partially, by the gene.
The interleukin 4 (IL-4) gene, located on chromosome 5q31, has also been associated with atopy. IL-4 is the main cytokine responsible for change in B lymphocyte from immunoglobulin M (IgM) to IgE.19
Nucleotide replacement (C-T) in position -590 of the IL-4 gene promoting region is present in approximately 27% of Caucasians. The IL4-590T allele was associated with increased expression of in vitro gene and with higher levels of in vivo IgE.20 The IL4-590T was associated with asthma, rhinitis and atopy in a study including children at risk for allergic diseases.19 That allele has also been associated with low values of forced expiratory volume in 1 second (FEV1) in a Caucasian population with asthma.21 These data suggest that the C-590T polymorphism could influence asthma severity.
The IL-4 receptor gene (IL-4R) is located on chromosome 16 p12.1-p11.2, a region associated with increase in IgE responses. It plays a major role in allergic inflammation through its function of signaling IL-4 and IL-13.22
Many single nucleotide polymorphisms (SNP), identified in the codifying region of that gene, were associated with asthma and atopy.23,24 The Ile50Val polymorphism has been extensively studied and associated with IgE levels and atopic asthma23; however, not all associations were replicated in other populations.25,26
The disintegrin and metalloprotease 33 gene (ADAM33) is located on chromosome 20p13, and 37 SNP were initially identified.27 Since the first report of association between ADAM33 polymorphisms and asthma in two Caucasian populations in the United Kingdom and the USA, a large number of studies has been published, showing different results. Various associations between different asthma phenotypes, as well as bronchial hyperresponsiveness (BHR) and different SNP in the gene, have been demonstrated.28-30
ADAM33 was the first gene identified by positional cloning to be published as a possible candidate for the development of asthma and BHR.27 The ADAM33 protein is expressed in smooth muscle cells of bronchia and pulmonary fibroblasts, playing a major role in airway remodeling.31
Asthma has been described as a heterogeneous group of syndromes, but few advances have occurred to distinguish the varied clinical phenotypes from the genetic-molecular perspective.
This study aimed at verifying the association of TGF-b1 (C-509T and T869C), CD14 (C-159T), IL-4 (C-590T), IL-4R (ILe50Val) and ADAM33 (S_2) gene polymorphisms with asthma severity.
A clinical, laboratory and prospective study was carried out at the departments of genetics and pediatrics (sector of pediatric pulmonology) at Faculdade de Ciências Médicas da Universidade Estadual de Campinas (UNICAMP) in 2006-2007.
This study was evaluated and approved by the ethics committee of that institution (protocol 172/2006), and all patients signed an informed consent term before starting the study.
Children and adolescents of both genders and with persistent atopic asthma (PAA) (mild, moderate and severe) were included.
The patients were diagnosed according to degree of asthma severity based on the criteria of the Global Initiative for Asthma32 (GINA), and all had spirometric evidence of response to use of beta-agonist drugs, positive reactivity in skin tests of immediate hypersensitivity to inhaling antigens and increase in IgE serum levels. The DNA was extracted from peripheral blood cells, according to the traditional method of phenol/chloroform.33
Methods, primer sequence and restriction enzymes, as well as size of fragments generated by TGF-b1, CD14, IL-4, IL-4R and ADAM33 gene polymorphisms,34-37 are described in Table 1.
Analyses of the associations between asthmatic patients and the control group were performed by Pearson's chi-square test, and in some analyses, due to the value of cases, genotypes were aggregated and Fisher's exact test was used. Odds ratio (OR) was calculated by Fisher's exact test. Difference between groups was statistically significant when the test value was p < 0.05. Epi-Info, version 1.1.2 was the statistical software used.
A total of 88 asthmatic children and adolescents were assessed: 53% girls, 7-18 years, mean age of 10.3±2.79 years and ethnic group comprised of 92% Caucasians, 7% mulattos and 1% Negroids. The control group was composed of 202 individuals (mean age 34±11.3 years), blood donors, 79.2% Caucasians, 20.3% Negroids and 0.5% of Eastern ethnicity.
Among patients with PAA, there were 27 mild, 23 moderate and 38 severe (Table 2).
As to the T869C polymorphism (TGF-b1), the sample of asthmatic patients was in Hardy-Weinberg equilibrium (HWE) (Ï2(2) = 2.83; p = 0.24), which did not occur with the control sample (Ï2(2) = 10.58; p = 0.005). There was no difference in genotype distribution between asthmatics and the control group (Ï2(2) = 0.67; p = 0.71), as well as between groups of variable severity. However, comparison of each severity group with the control group showed significant difference in relation to severe asthma and the control group (Ï2(2) = 9.70; p = 0.007). Such difference was due to an accumulation of individuals with CC genotype in severe asthmatics in relation to the control group.
Therefore, the CC genotype could be a severity factor for asthma (Ï2 = 7.80; p = 0.005; OR = 2.99, 1.25-7.09).
For the TGF-b1 C-509T gene polymorphism, the sample of asthmatic patients was in HWE (Ï2(2) = 0; p = 1), as well as the control sample (Ï2(2) = 1.79; p = 0.41). The CT and TT genotypes were grouped when showing value < 5 for statistical analysis. There were no significant differences as to asthma presence and severity.
As to the C-159T polymorphism (CD14), the sample of asthmatic patients was in HWE (Ï2(2) = 0.21; p = 0.90), which did not occur with the control sample (Ï2(2) = 18.72; p = 0.00008). Genotype distribution according to severity group did not show statistical difference.
When genotype distribution of severe asthma was compared with the control group, there was a significant result with the accumulation of TT genotype in relation to severe asthma (Ï2(2) = 44.02; p = 0.000000). It was verified that the TT genotype represented a risk factor for severe asthma (Ï2 = 31.94; p = 0.000; OR = 11.19, 3.74-34.24).
As to the Ile50Val polymorphism (IL-4R), the sample of patients (Ï2(2) = 1.47; p = 0.47) and controls (Ï2(2) = 0.11; p = 0.94) was in HWE. When genotype distribution was performed according to asthma severity, in comparison between mild and severe asthma, there was significant statistical difference with increase of patients with the Val/Val genotype in mild asthmatics. The Val/Val genotype represented a protection factor for asthma severity (Ï2(2) = 8.85; p = 0.004; OR = 9.0, 1.54-90.89).
As to the C-590T polymorphism (IL-4), the sample of patients (Ï2(2) = 0.06; p = 0.96) and controls (Ï2(2) =1.27; p = 0.53) was in HWE, and there were no significant differences as to asthma presence and severity.
As to the S-2 polymorphism (ADAM33), the sample of asthmatic patients was in HWE (Ï2(2) = 0.11; p = 0.94), which did not occur with the control sample (Ï2(2) = 19.50; p = 0.000058). When genotype distribution was compared between severity groups, there were no changes.
This is the first Brazilian study verifying the association of TGF-b1 (C-509T and T869C), CD14 (C-159T), IL-4 (C-590T), IL-4R (ILe50Val) and ADAM33 (S_2) gene polymorphisms with asthma severity.
Asthma can be said to be a complex genetic disease in which there are multiple genetic effects interacting with the environment to modify susceptibility and severity of this disease.38
In some polymorphisms, the control sample was not in HWE. It is believed that this is due to the fact that, in the Law, an ideal population is recommended, and our control sample was comprised of blood donors, among whom only healthy individuals are selected. With regard to the polymorphisms under investigation, since they interfere with mechanisms related to inflammation by using blood donors, individuals who have unfavorable genotypes will be excluded. That results in use of a more homogeneous and antagonistic population in phenotypical terms in relation to the asthmatic population and, therefore, small changes could be better identified. Anyhow, more value was given to results found between severity groups.
Pulleyn et al.5 found an association between the TGF-b1 C-509T gene polymorphism and asthma severity, and there was significant difference in frequency of C-509T genotypes when the mild and severe group and controls were compared. There was a high level of homozygotes for the -509T allele in the severe group. Almost twice more severe asthmatics (1.8 times) had the TT genotype, when compared to asthmatics in the mild group, and such difference increased to 5.6 times when compared to controls. A significant difference was also present when only the mild and severe groups were compared. These results suggest that this allele is more associated with severity than with asthma or atopy onset, in contrast with studies in which polymorphisms have been compared between asthmatics and controls, as in IL-13.39
There is evidence that TGF-b1 C-509T and T869C gene polymorphisms are associated with gene transcriptional activity. The C-509T polymorphism, in homozygosis, was associated with low levels of circulating TGF-b1 concentration, when compared with other genotypes, in white women and in the Indian population.3 On the other hand, the CC genotype of T869C polymorphism was related to a high concentration of TGF-b1 in Japanese individuals,40 but not in white individuals.41 In another study, Li et al.8 verified that the C-509T and T869C polymorphisms increased risk of asthma and atopy in Mexican children.
It has been suggested that increase in TGF-b1 expression should be harmful to the airways of asthmatic individuals, stimulating their remodeling. About that paradigm, genetic variations associated with high levels of TGF-b1, such as the T allele of C-509T and the C allele of T869C, should be associated with high prevalence or increase in asthma severity.7
The TGF-b1 T869C polymorphism, in our sample, showed an association between CC genotype and patients with severe asthma. There was no significant difference between the total group of asthmatics and the healthy control group regarding CC genotype. However, Mak et al.,7 studying 250 Chinese patients with asthma, showed that individuals with CC genotype were more susceptible to asthma. As to the C-509T polymorphism, there was no association in our study.
The CD14 C-159T gene polymorphism has been associated with increased in vitro CD14 expression and in the serum of children,14 with altered IgE serum levels and positive allergic tests in different populations.14,15 Kedda et al.35 confirmed associations between C-159T and atopy, but did not find association between this polymorphism and asthma or asthma severity in an Australian population.
It is possible that the C-159T polymorphism has an influence related to age in the development of atopy. Such polymorphism has been associated with increased expression of CD14 in the serum of children, and there are no differences in CD14 levels in the serum of adult blood donors with different genotypes for CD14.35 In addition, a longitudinal study including white individuals from Australia aged between 8-25 years showed that those with the CC genotype were probably the same that had earlier atopy, suggesting that the influence of the -159C polymorphism in atopy could be age specific.42 There is evidence that atopy and asthma are close entities and relates to a positive association between IgE serum level, positive allergic tests, hyperresponsiveness and development of asthma.43 Therefore, it is expected that alleles associated with atopy have a higher prevalence in asthmatics than in the general population.15 There are no publications showing association between the C-159T polymorphism and asthma severity, although it has been suggested that this polymorphism changes severity of air flow obstruction in asthmatic individuals.35
In the present study, when genotype distribution of the C-159T polymorphism in severe asthma was compared with the control group, there was a significant result with the TT genotype in relation to severe asthma. It was verified that the TT genotype represented a risk factor for severe asthma.
In the IL-4 C-590T gene polymorphism, its variant is related to increased gene transcription. Incidence of such polymorphism in a study including an American population was 40%, and the T allele was associated with increased IgE production, positive allergic tests and asthma.20 Such association was not found in Australian, British44 and Italian individuals.45 Studies including Japanese individuals confirmed the associations of that polymorphism with asthma25 and atopic dermatitis.20 That polymorphism was also related to atopy20 and decreased pulmonary function.44 Kamali-Sarvestani et al.,46 when analyzing the C-590T polymorphism in Iranian asthmatics, verified that such polymorphism was associated with asthma and could modulate its severity.
IL-4 performs its activities through ligation with its receptor (IL-4R). In the IL-4Ra Ile50Val gene polymorphism, the variant Ile50 was associated with atopic asthma and had no association with nonatopic asthma in Japanese individuals. Conversely, Noguchi et al.25 verified that the Ile50Val polymorphism does not play a role in genetic predisposition of atopy or asthma etiology in another Japanese population. Other studies did not find association between this polymorphism and asthma in other ethnic groups.26,47,48 Zhang et al.,49 when investigating an association between the Ile50Val polymorphism and asthma and high IgE levels in three Asian populations from China, Malaysia and India, verified that in China the prevalence of the Ile50/Ile50 genotype was significantly lower than in Malaysia, and that genotype is related to increased IgE only in Malaysia. That study showed that the association between that polymorphism and asthma differs in those ethnic groups. Howard et al.50 analyzed IL-4R gene polymorphisms in families in Germany and did not find evidence that the ILe50VaL is the main responsible for susceptibility to allergy, suggesting that other IL-4R polymorphisms are associated with asthma and atopy.
As to the IL-4 C-509T gene polymorphism, there was no association in our study. As to the IL-4R Ile50Val gene polymorphism, it was verified that the Val/Val genotype represented a protection factor for asthma severity.
Hirota et al.51 found a significant association with asthma susceptibility in a Japanese population for three SNP (S_2, T_1, T_2). These results are consistent with another study in a Caucasian population in the USA.52
Jongepier et al.28 investigated genetic and environmental factors that could have contributed for such accelerated decline in 200 patients with chronic asthma, who were annually studied for 25 years. Those authors showed that the polymorphism variant of S_2 allele was significantly associated with decline in FEV1 values and concluded that this ADAM33 variant was not only important in asthma development, but also in disease progression and increase in airway remodeling.
Simpson et al.53 have recently verified that ADAM33 polymorphisms could influence pulmonary function in childhood and concluded that, in early life, it is genetically modified and may increase risk of asthma. In this study, there was no association regarding ADAM33 and allergy.
In the present study, when genotype distribution of the S_2 polymorphism was compared between severity groups, there were no changes.
It is likely that different results can be found in other populations or race groups. Since ethnic and race differences are common in polymorphic systems, variant alleles or interacting gene groups induce expression of clinical phenotype in different populations.
Therefore, in our study, the TGF-b1 T869C, CD14 C-159T, and IL-4R Ile50Val gene polymorphisms can be modulators of asthma severity. Although our study has included several genes and their polymorphisms and has showed that distinct genotypes can have different clinical expressions, other studies including larger populations may clarify the actual role of genetic polymorphisms in varied degrees of asthma severity.
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correspondence: Manuscript received
Oct 17 2007, accepted for publication Feb 28 2008. No conflicts of
interest declared concerning the publication of this article.
Carmen Silvia Bertuzzo
Departamento de Genética Médica
Faculdade de Ciências Médicas, UNICAMP
Caixa Postal 6111, Bairro Cidade Universitária Zeferino Vaz
CEP 13083-970 - Campinas, SP - Brazil
Tel.: +55 (19) 3521.8907, +55 (19) 3521.8904
Fax: +55 (19) 3521.8909
Email: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org
Manuscript received Oct 17 2007, accepted for publication Feb 28 2008.
No conflicts of interest declared concerning the publication of this article.