Hanne E. Akselsen

HLA-Encoded Genetic Predisposition in IDDM: DR4 Subtypes May Be Associated With Different Degrees of Protection

Recent studies have shown that the risk conferred by the high-risk DQAl*03-DQBl*0302 (DQ8) haplotype is modified by the DRB1*O4 allele that is also carried by this haplotype. However, many of these studies suffer from lack of sufficient numbers of DQ-matched control subjects, which are necessary because there is a strong linkage disequilibrium between genes in the HLA complex. In the present study, using a large material of IDDM patients and DQ-matched control subjects, we have addressed the contribution of DR4 subtypes to IDDM susceptibility. Our data, together with recent data from others, clearly demonstrate that some DR4-DQ8 haplotypes are associated with disease susceptibility, while others are associated with protection, depending on the DRB1*O4 allele carried by the same haplotype. In particular, our data demonstrate that DRBl*0401 confers a higher risk than DRBl*0404. Based on combined available data on the genetic susceptibility encoded by various DR4-DQ8 haplotypes and the amino acid composition of the involved DRβ*04 chains as well as the ligand motifs for these DR4 subtypes, we have developed a unifying hypothesis explaining the different risks associated with different DR4-DQ8 haplotypes. We suggest that disease susceptibility is mainly conferred by DQ8 while DR4 subtypes confer different degrees of protection. Some DR4 subtypes (i.e., DRB1*0405, 0402, and 0401) confer little or no protection, while others (i.e., DRB 1*0404, 0403, and 0406) cause an increasing degree of protection, possibly by binding a common protective peptide. Features of a protective peptide that fit such a model are briefly discussed.

Insulin gene region-encoded susceptibility to IDDM maps upstream of the insulin gene.

The gene region on chromosome 11p15.5 known to be involved in insulin-dependent diabetes mellitus (IDDM) susceptibility was recently mapped to a 4.1-kilobase region including the insulin gene. The region contains 10 candidate polymorphisms that are in strong linkage disequilibrium. By genotyping 7 of these 10 polymorphisms and the tyrosine hydroxylase microsatellite in Finnish Caucasoid IDDM patients and control subjects, we demonstrate that many of the polymorphisms found to be associated with IDDM in other Caucasoid populations do not show any association in this Finnish population. Of the polymorphisms typed, only those at –23 Hph I and the variable number of tandem repeats (VNTR) sites confer significant relative risk. Furthermore, we have demonstrated that the –23 Hph I polymorphism cannot explain the association. Comparison of the genotypic patterns observed here and previously suggests that the VNTR is the most likely candidate for IDDM2. The VNTR is located adjacent to defined regulatory DNA sequences affecting insulin gene expression, which suggests a possible effect on expression of insulin or one of the neighboring genes, tyrosine hydroxylase or insulin-like growth factor 2.

Evidence of at least two type 1 diabetes susceptibility genes in the HLA complex distinct from HLA-DQB1, -DQA1 and –DRB1

Susceptibility to, and protection against development of type 1 diabetes (T1D) are primarily associated with the highly polymorphic exon 2 sequences of the HLA class II genes: DQB1, DQA1 and DRB1. However, several studies have also suggested that additional genes in the HLA complex influence T1D risk, albeit to a lesser degree than the class II genes. We have previously shown that allele 3 of microsatellite marker D6S2223, 4.9 Mb telomeric of DQ in the extended class I region, is associated with a reduction in risk conferred by the DQ2-DR3 haplotype. Here we replicate this finding in two populations from Sweden and France. We also show that markers in the HLA class II, III and centromeric class I regions contribute to the DQ2-DR3 associated risk of T1D, independently of linkage disequilibrium (LD) with both the DQ/DR genes and the D6S2223 associated gene. The associated marker alleles are carried on the DQ2-DR3-B18 haplotype in a region of strong LD. By haplotype mapping, we have located the most likely location for this second DQ2-DR3 haplotype-modifying locus to the 2.35 Mb region between HLA-DOB and marker D6S2702, located 970 kb telomeric of HLA-B.

An increased risk of cervical intra-epithelial neoplasia grade II-III among human papillomavirus positive patients with the HLA-DQA1*0102-DQB1*0602 haplotype: A population-based case–control study of Norwegian women

Several recent studies have reported different associations between HLA specificities and human papillomavirus (HPV)‐associated disease of the cervix. We report the distribution of DQA1 and DQB1 genes and HPV infection in a population‐based case–control study including 92 patients with histologically verified cervical intraepithelial neoplasia grade II‐III (CIN II‐III) (thus including moderate and severe dysplasia and carcinoma in situ) and 225 control subjects. We found an overrepresentation of the DQA1*0102‐DQB1*0602 haplotype among HPV‐positive cases compared with controls. The association was even stronger when comparing HPV‐16–positive cases with HPV‐16–positive controls. In addition, among HPV‐16–positive individuals, we observed a decreased frequency of DQA1*0102‐DQB1*0604 in cases compared with controls. We were not able to detect any association between CIN II‐III and DQB1*03. Compared with previous findings in cervical cancer, our data indicate that carrying the DQA1*0102‐DQB1*0602 haplotype gives an increased risk of developing CIN when infected with HPV‐16, without influencing progression to cancer. Int. J. Cancer 76:19–24, 1998.© 1998 Wiley‐Liss, Inc.

A TLR2 polymorphism is associated with type 1 diabetes and allergic asthma

Type 1 diabetes (T1D) and allergic asthma are immune-mediated diseases. Pattern recognition receptors are proteins expressed by cells in the immune system to identify microbial pathogens and endogenous ligands. Toll-like receptors (TLRs) and CD14 are members of this family and could represent a molecular link between microbial infections and immune-mediated diseases. Diverging hypotheses regarding whether there exists a common or inverse genetic etiology behind these immune-mediated diseases have been presented. We aimed to test whether there exist common or inverse associations between polymorphisms in the pattern recognition receptors TLR2, TLR4 and CD14 and T1D and allergic asthma. Eighteen single nucleotide polymorphisms (SNPs) were genotyped in TLR2 (2), TLR4 (12) and CD14 (4) in 700 T1D children, 357 nuclear families with T1D children and 796 children from the ‘Environment and Childhood Asthma’ study. Allele and haplotype frequencies were analyzed in relation to diseases and in addition transmission disequilibrium test analyses were performed in the family material. Both T1D and allergic asthma were significantly associated with the TLR2 rs3804100 T allele and further associated with the haplotype including this SNP, possibly representing a susceptibility locus common for the two diseases. Neither TLR4 nor CD14 were associated with T1D or allergic asthma.

Multiple Loci in the HLA Complex Are Associated with Addison's Disease

CONTEXT A strong association between autoimmune Addisons disease (AAD) and major histocompatibility complex class II-encoded HLA-DRB1-DQA1-DQB1 haplotypes is well known. Recent evidence from other autoimmune diseases has suggested that class I-encoded HLA-A and HLA-B gene variants confer HLA-DRB1-DQA1-DQB1-independent effects on disease. OBJECTIVE We aimed to explore AAD predisposing effects of HLA-A and -B and further investigate the role of MICA and HLA-DRB1-DQA1-DQB1 in a much larger material than has previously been studied. DESIGN HLA-A, -B, -DRB1, and -DQB1 and a microsatellite in MICA were genotyped in 414 AAD patients and 684 controls of Norwegian origin. RESULTS The strongest association was observed for the DRB1 locus, in which the DRB1*03:01 and DRB1*04:04 conferred increased risk of AAD, particularly in a heterozygous combination [odds ratio 22.13; 95% confidence interval (11.39-43.98); P = 6 × 10(-20)]. After conditioning on DRB1, association with AAD was still present for HLA-B and MICA, suggesting the presence of additional risk factors. CONCLUSIONS The major histocompatibility complex harbors multiple risk loci for AAD, in which DRB1 appears to represent the main risk factor.

Reproducible association with type 1 diabetes in the extended class I region of the major histocompatibility complex

The high-risk human leukocyte antigen (HLA)-DRB1, DQA1 and DQB1 alleles cannot explain the entire type 1 diabetes (T1D) association observed within the extended major histocompatibility complex. We have earlier identified an association with D6S2223, located 2.3 Mb telomeric of HLA-A, on the DRB1*03-DQA1*0501-DQB1*0201 haplotype, and this study aimed to fine-map the associated region also on the DRB1*0401-DQA1*03-DQB1*0302 haplotype, characterized by less extensive linkage disequilibrium. To exclude associations secondary to DRB1-DQA1-DQB1 haplotypes, 205 families with at least one parent homozygous for these loci, were genotyped for 137 polymorphisms. We found novel associations on the DRB1*0401-DQA1*03-DQB1*0302 haplotypic background with eight single nucleotide polymorphisms (SNPs) located within or near the PRSS16 gene. In addition, association at the butyrophilin (BTN)-gene cluster, particularly the BTN3A2 gene, was observed by multilocus analyses. We replicated the associations with SNPs in the PRSS16 region and, albeit weaker, to the BTN3A2 region, in an independent material of 725 families obtained from the Type 1 Diabetes Genetics Consortium. It is important to note that these associations were independent of the HLA-DRB1-DQA1-DQB1 genes, as well as of associations observed at HLA-A, -B and -C. Taken together, our results identify PRSS16 and BTN3A2, two genes thought to play important roles in regulating the immune response, as potentially novel susceptibility genes for T1D.

Linkage disequilibrium and haplotype blocks in the MHC vary in an HLA haplotype specific manner assessed mainly by DRB1 * 03 and DRB1 * 04 haplotypes

First generation linkage disequilibrium (LD) and haplotype maps of the human major histocompatibility complex (MHC) have been generated in order to aid the unraveling of the numerous disease predisposing genes in this region by offering a first set of haplotype tagSNPs. Several parameters, like the population studied, the marker map used, the density of polymorphisms and the applied algorithm, are influencing the appearance of haplotype blocks and selection of tags. The MHC comprises a limited number of ancestral, conserved haplotypes. We address the impact of the underlying HLA haplotypes on the LD patterns, haplotype blocks and tag selection throughout the entire extended MHC (xMHC) by studying DR-DQ haplotypes, mainly those carrying DRB1*03 and DRB1*04 alleles. We observed significantly different degree and extent of LD calculated on different HLA backgrounds, as well as variation in the size and boundaries of the defined haplotype and tags selected. Our results demonstrate that the underlying ancestral HLA haplotypic architecture is yet another parameter to take into consideration when constructing LD maps of the xMHC. This may be essential for mapping of disease susceptibility genes since many diseases are associated with and map on particular HLA haplotypes.

HLA Dr‐Dq haplotypes and the TNFA‐308 polymorphism: associations with asthma and allergy

Background:  The HLA (human leukocyte antigen) class II genes DQB1 and DRB1 and the Tumor Necrosis Factor α gene (TNFA) within the HLA complex (chromosome 6p21) have been associated with asthma and allergy. Due to the strong linkage disequilibrium characterizing this complex and the multiple asthma/allergy expressions, we aimed to determine which of these genes were primarily involved in specific asthma/allergy traits.

No Independent Associations of LMP2 and LMP7 Polymorphisms With Susceptibility to Develop IDDM

Results from a recent study suggested that polymorphisms within the HLA class II genes LMP2 and LMP7 were associated with the susceptibility for developing IDDM, and that this association could not be explained by linkage disequilibrium to HLA-DR or -DQ genes. We typed 285 IDDM patients and 337 HLA-DRB1-DQA1-DQB1 genotypically matched control subjects from an ethnically homogeneous population for both the G/T polymorphism in intron 6 of the LMP7 gene and the Arg-His polymorphism in the LMP2 gene. In addition, we typed IDDM families in which at least one parent was homozygous for a DRB1-DQA1-DQB1 haplotype and performed a transmission/disequilibrium test of these LMP polymorphisms. Our data suggest that none of these LMP2 or LMP7 polymorphisms are independently associated with IDDM susceptibility, in contrast to what has been previously reported by others. Further, our results suggest that one partial explanation for the previously reported independent association between IDDM and these LMP polymorphisms may have been that patients and control subjects were not matched for DRB1*04 subtypes. Our results emphasize the need for a complete matching for DRB1, DQA1, and DQB1 alleles between patients and control subjects when attempting to detect independent effects of other polymorphisms in the HLA complex on IDDM susceptibility or protection.