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Association between MBL2 polymorphism and T1D: Does ethnicity play a role in the susceptibility of this multifactorial disease?
Human Immunology (2008) 69, 577–579
Association between MBL2 polymorphism and T1D: Does ethnicity play a role in the susceptibility of this multifactorial disease? Lucas A. C. Brandãoa, Rafael L. Guimarãesa, Jacqueline Araujob, Luiz C. Arraesa, Ludovica Segatc,*, Sergio Crovellac,d a b c d
Laboratory of Immunopathology Keizo Asami, Federal University of Pernambuco, Recife, Brazil Pediatric Endocrinology Unit of Clinical Hospital, Federal University of Pernambuco, Brazil Genetic Service IRCCS Burlo Garofolo, Trieste, Italy Department of Genetics, Federal University of Pernambuco, Recife, Brazil
Received 16 May 2008; accepted 17 July 2008
KEYWORDS MBL2; Polymorphisms; Type 1 diabetes; Ethnicity; Control group
The association of functional MBL2 gene polymorphisms with type 1 diabetes (T1D) is still debated. We demonstrated in a previous work [1] that MBL2 polymorphisms can be considered potential risk factors for the onset of T1D in a northeastern Brazilian population. We screened MBL2 exon 1 functional polymorphisms in 214 children and adolescents with T1D and 214 healthy controls matched for age and sex. The carriers of the MBL2 0 allele demonstrated an increased risk of developing T1D [odds ratio ⫽ 1.72; 95% confidence interval ⫽ 1.24 to 2.39]. No correlation between MBL2 polymorphisms and the age of T1D onset existed. Recently, Aittoniemi et al. analyzed MBL2 functional polymorphisms in a larger group of Finnish T1D patients (470) and controls (501) and reported no correlation between MBL2 polymorphisms and the risk of developing T1D * Corresponding author. Fax: ⫹39.040.3785540. E-mail address: [email protected] (L. Segat).
[2]. Thus, we decided to check and revise our results in an attempt to explain the different findings reported in our study and that of Aittoniemi et al. Brazilian and Finnish populations undoubtedly differ in their genetic composition. Whereas Finnish are well known for their homogeneous features, the northeastern Brazilian population analyzed in our previous study comprises a combined admixture of African (44%), Caucasian (34%), and Native American (22%) genomes [3]. The genetic pool can strongly affect the outcome of an association study; thus, homogeneous populations are preferred. We agree with Aittoniemi et al. regarding their argument for a homogenous group and we recognize that in the northeastern Brazilian population the genetic pool contributions of African, Caucasian, and Native American ethnicities may have resulted in a different distribution of MBL2 polymorphisms compared with the Finnish population; however, without further investigation Brazilian genetic heterogene-
0198-8859/$ -see front matter © 2008 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.humimm.2008.07.007
578
L.A.C. Brandão et al.
ABBREVIATIONS T1D
type 1 diabetes
ity alone cannot lead us to exclude a possible role of MBL2 functional polymorphisms in the development of T1D, at least in the population studied. We must also consider that T1D is a multifactorial condition and susceptibility to the disease depends not only upon the genetic background, but also on an interplay with environmental factors [4]. With the aim of confirming the distribution of MBL2 polymorphisms previously reported for the North Eastern Brazilian population, as well as verifying the Caucasian and African frequencies (both ethnicities known to contribute to the Brazilian genetic pool), we screened 413 Caucasians (from Northern Italy), 225 Africans (from Zambia), and 529 northeastern Brazilians (from Pernambuco), all healthy individuals, for MBL2 polymorphisms using a melting temperature assay approach [5]. The distribution of the MBL2 0 allele did not significantly differ among the Finnish, Caucasian, and northeastern Brazilian control populations. Moreover, MBL2 polymorphism allelic and genotype frequencies of the 529 northeastern Brazilian controls were perfectly matched with those reported in our previous study [1] and the frequencies determined for Caucasians were equivalent to the frequencies reported for the Finnish population [2]. Only the African population demonstrated significantly different MBL2 frequencies compared with the Finnish, northeastern Brazilian, and Caucasian populations (see Table 1 for details). Because the frequencies of MBL2 polymorphism are similar in both Finnish and northeastern Brazilian control populations, we can hypothesize that the different results achieved by us and Aittoniemi et al. concerning the role of MBL2 in T1D susceptibility cannot be explained by ethnicity and genetic heterogeneity alone. Although allele and genotype frequencies are comparable in both Brazilian and Finnish control populations, we cannot completely exclude the possibility that a selection bias may have occurred in the selection of T1D patients. A comparison
Table 1
AA A0 00 A 0
among T1D patients, as well as controls from different ethnic origins, would be of interest and may help in an evaluation of the eventual influence of ethnicity on susceptibility to T1D. Another aspect that may account for the different results achieved by our study and that of Aittoniemi et al. concerns the choice of the control population. Aittoniemi et al. enrolled a well-characterized healthy control group of newborns screened for HLA-DQB1- and DQA1-based genetic T1D susceptibility to exclude the presence of T1D and any possible bias. However, the use of HLA genotyping alone cannot completely exclude the susceptibility for a future development of T1D because the disease is multifactorial and only in part related to the presence of HLA risk haplotypes [6]. Autoimmune disorders such as T1D are the result of a progressive etiopathogenetic process and the newborn control group may not be a perfect model for the study of a progressive autoimmune disease that may develop at an older age, even in subjects who are negative for the presence of HLA risk alleles. Our control group, in addition to being matched for ethnic origin (like the Finnish group), was matched for similar age with respect to the T1D patients (median age 13 and 9 years for T1D patients and controls group, respectively). The median age at the onset of T1D was 7.3 years (SD ⫾ 3.4), lower than the median age of our control group. Our control group can be considered truly T1D negative because their chance of developing the illness in the future is very low. In conclusion, we do believe that our findings, even if they are not comparable with the findings obtained by Aittoniemi et al. in a different population, indicate a possible role for MBL2 functional polymorphisms in the development of T1D in northeast Brazilian children and adolescents. However, we must bear in mind that T1D is a multifactorial condition in which genetic factors and the environment play different but important roles in susceptibility to the disease [4]: the comparison between MBL2 frequencies in T1D Finnish and northeastern Brazilian patients should account for environmental differences, lifestyle, geographical distribution, climate, and selective pressure from distinct pathogens affecting the two populations. Furthermore, the incidence of T1D in Finnish and northeastern Brazilian pop-
MBL2 exon 1 functional polymorphisms in healthy individuals of different populations. Finnisha n ⫽ 501 (%)
Northeastern Brazilian (children)b n ⫽ 214 (%)
Northeastern Brazilian n ⫽ 529 (%)
African n ⫽ 225 (%)
Caucasian n ⫽ 413 (%)
334 145 22 813 189
142 59 13 343 85
354 145 30 853 205
128 73 24 329 121
249 144 20 642 184
(66.7) (28.9) (4.4) (81.1) (18.9)
(66.3) (27.6) (6.1) (80.1) (19.9)
African vs. Finnish African vs. Caucasian African vs. Northeastern Brazilian African vs. Northeastern Brazilian (children) a Aittoniemi et al. [2]. b Araujo et al. [1].
(66.9) (27.4) (5.7) (80.6) (19.4)
genotype p ⫽ 0.002; allele p ⫽ 0.0007 genotype p ⫽ 0.025; allele p ⫽ 0.074 genotype p ⫽ 0.01; allele p ⫽ 0.002 genotype p ⫽ 0.074; allele p ⫽ 0.016
(56.9) (32.4) (10.7) (73.11) (26.89)
(60.3) (34.9) (4.8) (77.7) (22.3)
579
Association between MBL2 polymorphism and T1D ulations is quite different; the prevalence of T1D in Finland is the highest in the world and is still increasing [7]. Because genetic susceptibility to T1D is mainly determined by the HLA locus, other genes such as MBL2, considered in our study, could have a minor effect on the onset of disease that could be more variable than the main susceptibility locus. Future analysis of an increased number of T1D patients in other populations could help to better clarify the role of MBL2 functional polymorphisms in the onset and development of T1D.
[2]
[3]
[4]
[5]
Acknowledgment This work was supported by Research Grant RC03/04 from IRCCS Burlo Garofolo (Trieste, Italy).
[6]
References
[7]
[1] Araujo J, Brandão LA, Guimarães RL, Santos S, Falcão EA, Milanese M, et al. Mannose binding lectin gene polymorphisms
are associated with type 1 diabetes in Brazilian children and adolescents. Hum Immunol 2007;68:739-43. Aittoniemi J, Turpeinen H, Tiittanen M, Knip M, Simell O, Ilonen J, et al. Relation among mannose-binding lectin 2 genotype, beta-cell autoantibodies, and risk for type 1 diabetes in Finnish children. Hum Immunol 2008;69:108-11. Alves-Silva J, da Silva Santos M, Guimarães PE, Ferreira AC, Bandelt HJ, Pena SD, et al. The ancestry of Brazilian mtDNA lineages. Am J Hum Genet 2000;67:444-61. Knip M, Veijola R, Virtanen SM, Hyöty H, Vaarala O, Akerblom HK. Environmental triggers and determinants of type 1 diabetes. Diabetes 2005;54(Suppl 2):S125-36. Arraes LC, de Souza PR, Bruneska D, Castelo Filho A, Cavada Bde S, de Lima Filho JL, et al. A cost-effective melting temperature assay for the detection of single-nucleotide polymorphism in the MBL2 gene of HIV-1-infected children. Braz J Med Biol Res 2006; 39:719-23. Aly TA, Ide A, Jahromi MM, Barker JM, Fernando MS, Babu SR, et al. Extreme genetic risk for type 1A diabetes. Proc Natl Acad Sci USA 2006;103:14074-9. Patterson CC, Dahlquist G, Soltész G, Green A, EURODIAB ACE Study Group. Europe and diabetes. Is childhood-onset type I diabetes a wealth-related disease? An ecological analysis of European incidence rates. Diabetologia 2001;44(Suppl 3):B9-16.
Association between MBL2 polymorphism and T1D: Does ethnicity play a role in the susceptibility of this multifactorial disease? Lucas A. C. Brandãoa, Rafael L. Guimarãesa, Jacqueline Araujob, Luiz C. Arraesa, Ludovica Segatc,*, Sergio Crovellac,d a b c d
Laboratory of Immunopathology Keizo Asami, Federal University of Pernambuco, Recife, Brazil Pediatric Endocrinology Unit of Clinical Hospital, Federal University of Pernambuco, Brazil Genetic Service IRCCS Burlo Garofolo, Trieste, Italy Department of Genetics, Federal University of Pernambuco, Recife, Brazil
Received 16 May 2008; accepted 17 July 2008
KEYWORDS MBL2; Polymorphisms; Type 1 diabetes; Ethnicity; Control group
The association of functional MBL2 gene polymorphisms with type 1 diabetes (T1D) is still debated. We demonstrated in a previous work [1] that MBL2 polymorphisms can be considered potential risk factors for the onset of T1D in a northeastern Brazilian population. We screened MBL2 exon 1 functional polymorphisms in 214 children and adolescents with T1D and 214 healthy controls matched for age and sex. The carriers of the MBL2 0 allele demonstrated an increased risk of developing T1D [odds ratio ⫽ 1.72; 95% confidence interval ⫽ 1.24 to 2.39]. No correlation between MBL2 polymorphisms and the age of T1D onset existed. Recently, Aittoniemi et al. analyzed MBL2 functional polymorphisms in a larger group of Finnish T1D patients (470) and controls (501) and reported no correlation between MBL2 polymorphisms and the risk of developing T1D * Corresponding author. Fax: ⫹39.040.3785540. E-mail address: [email protected] (L. Segat).
[2]. Thus, we decided to check and revise our results in an attempt to explain the different findings reported in our study and that of Aittoniemi et al. Brazilian and Finnish populations undoubtedly differ in their genetic composition. Whereas Finnish are well known for their homogeneous features, the northeastern Brazilian population analyzed in our previous study comprises a combined admixture of African (44%), Caucasian (34%), and Native American (22%) genomes [3]. The genetic pool can strongly affect the outcome of an association study; thus, homogeneous populations are preferred. We agree with Aittoniemi et al. regarding their argument for a homogenous group and we recognize that in the northeastern Brazilian population the genetic pool contributions of African, Caucasian, and Native American ethnicities may have resulted in a different distribution of MBL2 polymorphisms compared with the Finnish population; however, without further investigation Brazilian genetic heterogene-
0198-8859/$ -see front matter © 2008 American Society for Histocompatibility and Immunogenetics. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.humimm.2008.07.007
578
L.A.C. Brandão et al.
ABBREVIATIONS T1D
type 1 diabetes
ity alone cannot lead us to exclude a possible role of MBL2 functional polymorphisms in the development of T1D, at least in the population studied. We must also consider that T1D is a multifactorial condition and susceptibility to the disease depends not only upon the genetic background, but also on an interplay with environmental factors [4]. With the aim of confirming the distribution of MBL2 polymorphisms previously reported for the North Eastern Brazilian population, as well as verifying the Caucasian and African frequencies (both ethnicities known to contribute to the Brazilian genetic pool), we screened 413 Caucasians (from Northern Italy), 225 Africans (from Zambia), and 529 northeastern Brazilians (from Pernambuco), all healthy individuals, for MBL2 polymorphisms using a melting temperature assay approach [5]. The distribution of the MBL2 0 allele did not significantly differ among the Finnish, Caucasian, and northeastern Brazilian control populations. Moreover, MBL2 polymorphism allelic and genotype frequencies of the 529 northeastern Brazilian controls were perfectly matched with those reported in our previous study [1] and the frequencies determined for Caucasians were equivalent to the frequencies reported for the Finnish population [2]. Only the African population demonstrated significantly different MBL2 frequencies compared with the Finnish, northeastern Brazilian, and Caucasian populations (see Table 1 for details). Because the frequencies of MBL2 polymorphism are similar in both Finnish and northeastern Brazilian control populations, we can hypothesize that the different results achieved by us and Aittoniemi et al. concerning the role of MBL2 in T1D susceptibility cannot be explained by ethnicity and genetic heterogeneity alone. Although allele and genotype frequencies are comparable in both Brazilian and Finnish control populations, we cannot completely exclude the possibility that a selection bias may have occurred in the selection of T1D patients. A comparison
Table 1
AA A0 00 A 0
among T1D patients, as well as controls from different ethnic origins, would be of interest and may help in an evaluation of the eventual influence of ethnicity on susceptibility to T1D. Another aspect that may account for the different results achieved by our study and that of Aittoniemi et al. concerns the choice of the control population. Aittoniemi et al. enrolled a well-characterized healthy control group of newborns screened for HLA-DQB1- and DQA1-based genetic T1D susceptibility to exclude the presence of T1D and any possible bias. However, the use of HLA genotyping alone cannot completely exclude the susceptibility for a future development of T1D because the disease is multifactorial and only in part related to the presence of HLA risk haplotypes [6]. Autoimmune disorders such as T1D are the result of a progressive etiopathogenetic process and the newborn control group may not be a perfect model for the study of a progressive autoimmune disease that may develop at an older age, even in subjects who are negative for the presence of HLA risk alleles. Our control group, in addition to being matched for ethnic origin (like the Finnish group), was matched for similar age with respect to the T1D patients (median age 13 and 9 years for T1D patients and controls group, respectively). The median age at the onset of T1D was 7.3 years (SD ⫾ 3.4), lower than the median age of our control group. Our control group can be considered truly T1D negative because their chance of developing the illness in the future is very low. In conclusion, we do believe that our findings, even if they are not comparable with the findings obtained by Aittoniemi et al. in a different population, indicate a possible role for MBL2 functional polymorphisms in the development of T1D in northeast Brazilian children and adolescents. However, we must bear in mind that T1D is a multifactorial condition in which genetic factors and the environment play different but important roles in susceptibility to the disease [4]: the comparison between MBL2 frequencies in T1D Finnish and northeastern Brazilian patients should account for environmental differences, lifestyle, geographical distribution, climate, and selective pressure from distinct pathogens affecting the two populations. Furthermore, the incidence of T1D in Finnish and northeastern Brazilian pop-
MBL2 exon 1 functional polymorphisms in healthy individuals of different populations. Finnisha n ⫽ 501 (%)
Northeastern Brazilian (children)b n ⫽ 214 (%)
Northeastern Brazilian n ⫽ 529 (%)
African n ⫽ 225 (%)
Caucasian n ⫽ 413 (%)
334 145 22 813 189
142 59 13 343 85
354 145 30 853 205
128 73 24 329 121
249 144 20 642 184
(66.7) (28.9) (4.4) (81.1) (18.9)
(66.3) (27.6) (6.1) (80.1) (19.9)
African vs. Finnish African vs. Caucasian African vs. Northeastern Brazilian African vs. Northeastern Brazilian (children) a Aittoniemi et al. [2]. b Araujo et al. [1].
(66.9) (27.4) (5.7) (80.6) (19.4)
genotype p ⫽ 0.002; allele p ⫽ 0.0007 genotype p ⫽ 0.025; allele p ⫽ 0.074 genotype p ⫽ 0.01; allele p ⫽ 0.002 genotype p ⫽ 0.074; allele p ⫽ 0.016
(56.9) (32.4) (10.7) (73.11) (26.89)
(60.3) (34.9) (4.8) (77.7) (22.3)
579
Association between MBL2 polymorphism and T1D ulations is quite different; the prevalence of T1D in Finland is the highest in the world and is still increasing [7]. Because genetic susceptibility to T1D is mainly determined by the HLA locus, other genes such as MBL2, considered in our study, could have a minor effect on the onset of disease that could be more variable than the main susceptibility locus. Future analysis of an increased number of T1D patients in other populations could help to better clarify the role of MBL2 functional polymorphisms in the onset and development of T1D.
[2]
[3]
[4]
[5]
Acknowledgment This work was supported by Research Grant RC03/04 from IRCCS Burlo Garofolo (Trieste, Italy).
[6]
References
[7]
[1] Araujo J, Brandão LA, Guimarães RL, Santos S, Falcão EA, Milanese M, et al. Mannose binding lectin gene polymorphisms
are associated with type 1 diabetes in Brazilian children and adolescents. Hum Immunol 2007;68:739-43. Aittoniemi J, Turpeinen H, Tiittanen M, Knip M, Simell O, Ilonen J, et al. Relation among mannose-binding lectin 2 genotype, beta-cell autoantibodies, and risk for type 1 diabetes in Finnish children. Hum Immunol 2008;69:108-11. Alves-Silva J, da Silva Santos M, Guimarães PE, Ferreira AC, Bandelt HJ, Pena SD, et al. The ancestry of Brazilian mtDNA lineages. Am J Hum Genet 2000;67:444-61. Knip M, Veijola R, Virtanen SM, Hyöty H, Vaarala O, Akerblom HK. Environmental triggers and determinants of type 1 diabetes. Diabetes 2005;54(Suppl 2):S125-36. Arraes LC, de Souza PR, Bruneska D, Castelo Filho A, Cavada Bde S, de Lima Filho JL, et al. A cost-effective melting temperature assay for the detection of single-nucleotide polymorphism in the MBL2 gene of HIV-1-infected children. Braz J Med Biol Res 2006; 39:719-23. Aly TA, Ide A, Jahromi MM, Barker JM, Fernando MS, Babu SR, et al. Extreme genetic risk for type 1A diabetes. Proc Natl Acad Sci USA 2006;103:14074-9. Patterson CC, Dahlquist G, Soltész G, Green A, EURODIAB ACE Study Group. Europe and diabetes. Is childhood-onset type I diabetes a wealth-related disease? An ecological analysis of European incidence rates. Diabetologia 2001;44(Suppl 3):B9-16.