Diversity of Extended HLA-DRB1 Haplotypes in the Finnish Population
et al. (2013) Diversity of Extended HLA-DRB1 Haplotypes in the Finnish
Population. PLoS ONE 8(11): e79690. doi:10.1371/journal.pone.0079690
Diversity of Extended HLA-DRB1 Haplotypes in the Finnish Population
Annika Wennerstro m 0
Efthymia Vlachopoulou 0
L. Elisa Lahtela 0
Riitta Paakkanen 0
Katja T. Eronen 0
Mikko Seppa nen 0
Marja-Liisa Lokki 0
Gualtiero I. Colombo, Centro Cardiologico Monzino IRCCS, Italy
0 1 Transplantation Laboratory, Haartman Institute , Helsinki , Finland , 2 Division of Infectious Diseases, Department of Medicine, Helsinki University Central Hospital , Helsinki , Finland
The Major Histocompatibility Complex (MHC, 6p21) codes for traditional HLA and other host response related genes. The polymorphic HLA-DRB1 gene in MHC Class II has been associated with several complex diseases. In this study we focus on MHC haplotype structures in the Finnish population. We explore the variability of extended HLA-DRB1 haplotypes in relation to the other traditional HLA genes and a selected group of MHC class III genes. A total of 150 healthy Finnish individuals were included in the study. Subjects were genotyped for HLA alleles (HLA-A, -B, -DRB1, -DQB1, and -DPB1). The polymorphism of TNF, LTA, C4, BTNL2 and HLA-DRA genes was studied with 74 SNPs (single nucleotide polymorphism). The C4A and C4B gene copy numbers and a 2-bp silencing insertion at exon 29 in C4A gene were analysed with quantitative genomic realtime-PCR. The allele frequencies for each locus were calculated and haplotypes were constructed using both the traditional HLA alleles and SNP blocks. The most frequent Finnish A,B,DR -haplotype, uncommon in elsewhere in Europe, was A*03,B*35,DRB1*01:01. The second most common haplotype was a common European ancestral haplotype AH 8.1 (A*01,B*08,DRB1*03:01). Extended haplotypes containing HLA-B, TNF block, C4 and HLA-DPB1 strongly increased the number of HLA-DRB1 haplotypes showing variability in the extended HLA-DRB1 haplotype structures. On the contrary, BTNL2 block and HLA-DQB1 were more conserved showing linkage with the HLA-DRB1 alleles. We show that the use of HLADRB1 haplotypes rather than single HLA-DRB1 alleles is advantageous when studying the polymorphisms and LD patters of the MHC region. For disease association studies the HLA-DRB1 haplotypes with various MHC markers allows us to cluster haplotypes with functionally important gene variants such as C4 deficiency and cytokines TNF and LTA, and provides hypotheses for further assessment. Our study corroborates the importance of studying population-specific MHC haplotypes.
-
Introduction
The Major Histocompatibility Complex located on
chromosome 6p21 has a complex allelic structure with extended linkage
disequilibrium (LD) and polymorphism. The traditional human
leukocyte antigen (HLA) genes encode the cell-surface
antigenpresenting proteins, the HLA molecules, and fall into two major
MHC classes; Class I (HLA-A, -C, and -B) and Class II
(HLADRB1, -DQB1, and DPB1). Many non-HLA genes related to
immune responses e.g. tumor necrosis factor (TNF), lymphotoxin-alpha
(LTA), complement C4 genes (C4A and C4B) and butyrophilin-like protein
2 (BTNL2), are located in the MHC class III region that resides
between the MHC Class I and II regions [13]. The location of
recombination hotspots and the length of LD blocks (genomic
fragments inherited together) are population specific [1,4,5].
Interestingly, it has been shown that the Finnish population has
distinctive population substructure compared with other
Europeans [68].
The HLA genes play a critical role in hematopoietic stem cell
transplantation, and HLA mismatching has been associated with
graft failure and graft-versus-host disease [9,10]. In addition to the
traditional HLA genes, it has been suggested that the HLA-SNP
haplotypes influence on the outcome of the transplantation [11].
The association between MHC and diseases has been known for
decades. The polymorphic HLA-DRB1 has been associated with
several complex and infectious diseases, such as acute coronary
syndrome [12], HSV2 related meningitis [13], type I diabetes,
celiac disease and multiple sclerosis (reviewed in [14]). Recently,
genome wide association analyses (GWA) have increased the
number of MHC gene associations with several drug-induced
hypersensitivity reactions, autoimmune, infectious and
inflammatory disorders [1520] (GWAS Integrator, http://genome.ucsc.
edu). However, the predisposing HLA-alleles are common in the
healthy population. Other genetic and environmental triggers are
required for disease susceptibility [15,21]. Thus, the complexity of
MHC makes the variant(s) responsible for the causal effect difficult
to pinpoint. As the traditional HLA typing is considered rather
expensive and laborious and the analysis of MHC regions is
complex, many studies do not probe MHC associations more
closely. Thus the functionality of the variants remains uncertain
although identification of a specific risk HLA allele could hel (...truncated)