8. ANEXOS
HLA-A, -B, -DRB1 allele and haplotype frequencies in 1000 human samples
from mixed population of the Minas Gerais state, Brazil
1,2
Raquel A. Fabreti Oliveira,
1
Cleusa G. Fonseca,
2
Eliane M. G. Vale,
2
Roselia M. Carvalho,
2,30
Evaldo Nascimento
1Human Genetics, Department of General Biology, Federal University of Minas Gerais, Minas Gerais, Brazil.2Laboratory IMUNOLABTx – Transplant
Immunology. 3Transplantation Center, Hospital of Santa Casa, Belo Horizonte, Minas Gerais and Clinical Hospital, Federal University of Minas Gerais,
Minas Gerais, Brazil.
Introduction
The human leukocyte antigen (HLA) system is
composed of a cluster of genes on the short arm of
human chromosome 6. HLA plays a central role in
immune responsiveness to pathogens, and its
polymorphism is a causal factor for rejection graft or
grafts versus host disease in organ transplantation.
The HLA genes are highly polymorphic with over 649
alleles identified at the locus A, over 1029 for locus B
and over 556 alleles for the locus DRB1 (June 2008
ImMunoGeneTics/HLA database release)
1
. Information
on allele an haplotype frequencies of the HLA loci also
provides a better understanding of the origin of human
population and investigation of genetic predisposition
to immune-mediated disorders including emerging
infectious diseases
2-4
.
Purpose
The goal of this study was to analyze the HLA-A, -B,
-DRB1 alleles and haplotypes frequencies in 1000
unrelated individuals randomly selected from mixed
population of the Minas Gerais state, Brazil.
Materials and Methods
Genomic DNA of each volunteer was prepared by
the standard salting-out method using PMNC (Miller et
al., 1988). HLA typing for HLA-A, -B, and -DRB1 was
done by polymerase chain reaction-sequence-specific
oligonucleotide probe SSOP (One Lambda, USA). All
statistical analyses and haplotype estimations were
performed using the PyPop package 0.6.0 version.
Results
The genotype frequencies of all three HLA loci were in
Hardy-Weinberg equilibrium [Guo and Thomson p values
0.8547 (HLA-A), 0.4590 (HLA-B) and 0.3951 (HLA-
DRB1)]. The number of heterozygotes observed wasn't
significantly different from that results expected (Table
1). Negative F
nd
values for Ewens–Watterson
homozygosis were observed at all three loci, and the F
nd
values were significantly low for all loci (P=0.0031 for the
HLA-A, 0.0011 for B and 0.0000 for DRB1), suggesting
that an action of balancing selection in shaping allelic
diversity at all loci. A total of 20 HLA A alleles were
identified. Four alleles, contributed approximately to 50%
of the allele frequency A*02 (0.2355), A*03 (0.0975),
A*01 (0.0810) and A*24 (0.0805). A total of 44 HLA B
alleles were identified. The most frequent alleles were
B*44 (0.1175), B*35 (0.1150), B*15 (0.0795) and B*51
(0.0715). A total of 15 HLA DRB1 alleles were identified.
The most frequent alleles were DRB1*13 (0.1565),
DRB1*07 (0.1420), DRB1*04 (0.1145), DRB1*11 and
DRB1*15 with the same frequencies (0.1080) and
DRB1*03 (0.1050). The most common ABDRB1
haplotype predicted by EM algorithm was A*01-B*08-
DRB1*03 (0.0274), followed by A*29-B*44-DRB1*07
(0.0150) and A*02-B*44-DRB1*07 (0.0101). The Linkage
Disequilibrium measures of the strength of association
between pairs of HLA loci were calculated. The B:DRB1
(D’=0.4432) associations are stronger than the
associations between other loci, but all pair wise
associations are statistically significant A:B (P=0.0029)
and A:DRB1 (P=0.0027).
Table 1: Heterozigosity at the HLA –A, B and DRB1 loci.
0.9040.8960.893A
0.8000.8970.890DRB
1
0.6820.9460.934B
PExpected H-W
heterozygotes
Observed
heterozygotes
Locus
References
1. Robinson J, Waller M.J., Parham P. et al. 2003. IMGT/HLA and IMGT/MHC: sequence databases for the study of the major histocompatibility
complex. Nucleic Acids Res. 31:311-4.
2. Cavalli-Sforza, L.L and Bodmer W.F. 1971 The Genetics of Human Populations.W.H. Freeman, San Francisco.
3. Hartl D.L. and Clark A.G. 1989. Principles of Population Genetics. 2nd edition. Sinauer Associates, Sunderland.
4. B. Tu, S. J. Mack, A. Lazaro, A. Lancaster, G. Thomson, K. Cao, M. Chen, G. Ling, R. Hartzman, J. Ng & C. K. Hurley. 2007. HLA-A, -B, -C, -DRB1
allele and haplotype frequencies in an African American population. Tissue Antigens 69:73-85.
Conclusions
These results provide information that can be used for
future anthropological studies. It also can guides the
search for HLA-matched unrelated hematopoietic stem
cell donor in the bone morrow donor Brazilian bank.