Exploring the CLEC16A gene reveals a MS-associated variant with correlation to the relative expression of CLEC16A isoforms in thymus.

Genomewide association studies have implicated the CLEC16A gene in several autoimmune diseases, including multiple sclerosis (MS) and type 1 diabetes. However, the most associated single-nucleotide polymorphism (SNP) varies, and causal variants are still to be defined. In MS, two SNPs in partial linkage disequilibrium with each other, rs6498169 and rs12708716, have been validated at genomewide significance level. To explore the CLEC16A association in MS in more detail, we genotyped 57 SNPs in 807 Norwegian MS patients and 1027 Norwegian controls. Six highly associated SNPs emerged and were then replicated in two large independent sample sets (Norwegian and British), together including 1153 MS trios, 2308 MS patients and 4044 healthy controls. In combined analyses, SNP rs12708716 gave the strongest association signal in MS (P=5.3 x 10⁻8, odds ratio 1.18, 95% confidence interval=1.11-1.25), and was found to be superior to the other SNP associations in conditional logistic regression analyses. Expression analysis revealed that rs12708716 genotype was significantly associated with the relative expression levels of two different CLEC16A transcripts in thymus (P=0.004), but not in blood, possibly implying a thymus- or cell-specific splice regulation.

Norwegian Sami differs significantly from other Norwegians according to their HLA profile.

This study reports extensive genomic data for both human leukocyte antigen (HLA) class I and II loci in Norwegian Sami, a native population living in the northwest of Europe. The Sami have a distinct culture and their own languages, which belong to the Uralic linguistic family. Norwegian Sami (n = 200) were typed at the DNA level for the HLA-A, -C, -B, -DRB1 and -DQB1 loci, and compared with a non-Sami Norwegian population (n = 576). The two populations exhibited some common genetic features but also differed significantly at all HLA loci. The most significantly deviating allele frequencies were an increase of HLA-A*03, -B*27, -DRB1*08 and -DQB1*04 and a decrease of HLA-A*01, C*01, -DRB1*04 and -DQB1*02 among Sami compared with non-Sami Norwegians. The Sami showed no deviation from Hardy-Weinberg equilibrium. The hypothesis of selective neutrality was rejected at all loci except for the A- and C- loci for the Sami. HLA haplotype frequencies also differed between the two populations. The most common extended HLA haplotypes were A*02-B*27-C*01-DR*08-DQB1*04 in the Sami and A*01-B*08-C*07-DR*03-DQB1*02 in the other Norwegians. Genetic distance analyses indicated that the Norwegian Sami were highly differentiated from other Europeans and were most closely related to Finns whose language also belongs to the Uralic linguistic family. In conclusion, the Norwegian Sami and the non-Sami Norwegians were significantly different at all HLA loci. Our results can be explained by the fact that the two populations have different origins and that the Sami population has remained smaller and more isolated than its neighbors.

Genetic variants of CC chemokine genes in experimental autoimmune encephalomyelitis, multiple sclerosis and rheumatoid arthritis.

Multiple sclerosis (MS) is a complex disorder of the central nervous system, causing inflammation, demyelination and axonal damage. A limited number of genetic risk factors for MS have been identified, but the etiology of the disease remains largely unknown. For the identification of genes regulating neuroinflammation we used a rat model of MS, myelin oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), and carried out a linkage analysis in an advanced intercross line (AIL). We thereby redefine the Eae18b locus to a 0.88 Mb region, including a cluster of chemokine genes. Further, we show differential expression of Ccl2, Ccl11 and Ccl11 during EAE in rat strains with opposite susceptibility to EAE, regulated by genotype in Eae18b. The human homologous genes were tested for association to MS in 3841 cases and 4046 controls from four Nordic countries. A haplotype in CCL2 and rs3136682 in CCL1 show a protective association to MS, whereas a haplotype in CCL13 is disease predisposing. In the HLA-DRB1* 15 positive subgroup, we also identified an association to a risk haplotype in CCL2, suggesting an influence from the human leukocyte antigen (HLA) locus. We further identified association to rheumatoid arthritis in CCL2, CCL8 and CCL13, indicating common regulatory mechanisms for complex diseases.

The impact of HLA-A and -DRB1 on age at onset, disease course and severity in Scandinavian multiple sclerosis patients.

The human leucocyte antigen (HLA) class II haplotype DRB1*15-DQB1*06 (DR15-DQ6) is associated with susceptibility to multiple sclerosis (MS), and HLA class I associations in MS have also been reported. However, the influence of HLA class I and II alleles on clinical phenotypes in MS has not yet been completely studied. This study aimed at evaluating the impact of HLA-A and -DRB1 alleles on clinical variables in Scandinavian MS patients. The correlation between HLA-A or -DRB1 alleles and age at onset, disease course and Multiple Sclerosis Severity Score (MSSS) were studied in 1457 Norwegian and Swedish MS patients by regression analyses and Kruskal-Wallis rank sum test. Presence of HLA-DRB1*15 was correlated with younger age at onset of disease (corrected P = 0.009). No correlation was found between HLA-A and the variables studied. This study analysed the effect of HLA-A on clinical variables in a large Scandinavian sample set, but could not identify any significant contribution from HLA-A on the clinical phenotype in MS. However, associations between HLA-DRB1*15 and age at onset of MS were reproduced in this extended Scandinavian MS cohort.

Low frequency of the disease-associated DRB1*15-DQB1*06 haplotype may contribute to the low prevalence of multiple sclerosis in Sami.

This study confirms a low frequency of multiple sclerosis (MS) among Sami. Only 12 Sami with a diagnosis of MS were identified in the Norwegian Sami population, which represents a significantly lower prevalence of MS in Sami (30/10(5)) compared with other Norwegians (73-164/10(5)). The clinical characteristics as well as the results of human leukocyte antigen (HLA)-DRB1 and -DQB1 typing of the Sami MS patients are reported, showing that three (27%) of the Sami MS patients carried the MS-associated HLA-DRB1*15-DQB1*06 haplotype. Interestingly, the DRB1*15-DQB1*06 haplotype had a significantly reduced frequency among Sami controls (0.086) compared with non-Sami Norwegian controls (0.163) (P(corrected) = 0.015). The low frequency of the disease-associated DRB1*15-DQB1*06 haplotype in the Sami population may contribute to the low prevalence of MS in Sami, in addition to other yet unidentified genetic and environmental factors.

Genetic association between juvenile rheumatoid arthritis and polymorphism in the SH2D2A gene.

T-cell-specific adapter protein (TSAd) involved in the negative control of T-cell activation is encoded by the SH2D2A gene. Our recent studies indicate that homozygosity for short (ie GA(13) and GA(16)) alleles of the SH2D2A gene promoter is associated with development of multiple sclerosis. To study whether the same SH2D2A promoter polymorphism also contributes to the genetic susceptibility to develop juvenile rheumatoid arthritis (JRA), we examined 210 JRA patients and 558 healthy unrelated controls from Norway. The frequency of the short allele GA(13) was increased among the JRA patients compared to control (0.098 vs 0.05; P(n=8)=0.042). There was a significant increased frequency of HLA-DRB1(*)08-positive patients carrying two copies of 'short' alleles GA(13) and/or GA(16) compared to healthy controls (16% vs 6%; P(n=4)=0.016). Our data indicate that the 'short' alleles of the SH2D2A promoter could contribute to the genetic susceptibility to JRA.

Genes in the HLA class I region may contribute to the HLA class II-associated genetic susceptibility to multiple sclerosis.

In order to analyze whether loci in the human leukocyte antigen (HLA) class I region may contribute to the HLA class II-associated genetic susceptibility to multiple sclerosis (MS), we examined selected microsatellite markers in 177 Nordic sib-pair families, 222 British sib-pair families, 323 sporadic Norwegian MS patients and 386 Norwegian controls. All samples were, in addition, genotyped for the HLA-DR DQ haplotype, and the Norwegian case-control samples were also typed for HLA-A and -B loci. In the Norwegian sporadic MS patients association was seen with HLA-A, HLA-B, and with the D6S265 marker, located 100 kb centromeric to HLA-A. Associations with HLA-A and D6S265 loci were also suggested when restricting the analysis to HLA-DR15 haplotypes. In the sib-pair data a similar trend was seen with marker D6S265. Higher genotypic relative risk (GRR) was found for individuals who carry both HLA-DR15 and -A3 (GRR = 15), compared to those who carry only HLA-DR15 (GRR = 7), only HLA-A3 (GRR = 3) or none of these alleles (GRR = 1). The highest risk was conferred by a combination of HLA-DR15 and -A3 (odds ratio (OR) = 5.2). These results suggest that HLA-A or a gene in linkage disequilibrium with it may contribute to the HLA class II-associated genetic susceptibility to MS.