RESUMO
BACKGROUND: The Mediterranean island of Sardinia has a strikingly high incidence of the autoimmune disorders Type 1 Diabetes (T1D) and Multiple Sclerosis (MS). Furthermore, the two diseases tend to be co-inherited in the same individuals and in the same families. These observations suggest that some unknown autoimmunity variant with relevant effect size could be fairly common in this founder population and could be detected using linkage analysis. METHODS: To search for T1D and MS loci as well as any that predispose to both diseases, we performed a whole genome linkage scan, sequentially genotyping 593 microsatellite marker loci in 954 individuals distributed in 175 Sardinian families. In total, 413 patients were studied; 285 with T1D, 116 with MS and 12 with both disorders. Model-free linkage analysis was performed on the genotyped samples using the Kong and Cox logarithm of odds (LOD) score statistic. RESULTS: In T1D, aside from the HLA locus, we found four regions showing a lod-score > or =1; 1p31.1, 6q26, 10q21.2 and 22q11.22. In MS we found three regions showing a lod-score > or =1; 1q42.2, 18p11.21 and 20p12.3. In the combined T1D-MS scan for shared autoimmunity loci, four regions showed a LOD >1, including 6q26, 10q21.2, 20p12.3 and 22q11.22. When we typed more markers in these intervals we obtained suggestive evidence of linkage in the T1D scan at 10q21.2 (LOD = 2.1), in the MS scan at 1q42.2 (LOD = 2.5) and at 18p11.22 (LOD = 2.6). When all T1D and MS families were analysed jointly we obtained suggestive evidence in two regions: at 10q21.1 (LOD score = 2.3) and at 20p12.3 (LOD score = 2.5). CONCLUSION: This suggestive evidence of linkage with T1D, MS and both diseases indicates critical chromosome intervals to be followed up in downstream association studies.
Assuntos
Diabetes Mellitus Tipo 1/genética , Ligação Genética , Predisposição Genética para Doença , Repetições de Microssatélites/genética , Esclerose Múltipla/genética , Adolescente , Adulto , Criança , Mapeamento Cromossômico , Diabetes Mellitus Tipo 1/complicações , Feminino , Marcadores Genéticos/genética , Haplótipos , Humanos , Masculino , Ilhas do Mediterrâneo , Pessoa de Meia-Idade , Esclerose Múltipla/complicações , Locos de Características Quantitativas , Estatísticas não ParamétricasRESUMO
BACKGROUND: Multiple sclerosis (MS) is consistently associated with particular HLA-DRB1-DQB1 haplotypes. However, existing evidence suggests that variation at these loci does not entirely explain association of the HLA region with the disease. The MOG locus is a prime positional and functional candidate for such additional predisposing effects but the analysis is complicated by the strong, albeit labyrinthine pattern of linkage disequilibrium in the region. Here we have assessed the association of MOG variation with MS in the Sardinian population to see if it represents an independent contributor to MS predisposition. RESULTS: After re-sequencing the MOG gene in 21 healthy parents of MS patients we detected 134 variants, 33 of which were novel. A set of 40 informative SNPs was then selected and assessed for disease association together with 1 intragenic microsatellite in an initial data set of 239 MS families. This microsatellite and 11 SNPs were found to be positively associated with MS, using the transmission disequilibrium test, and were followed up in an additional 158 families (total families analysed = 397). While in these 397 families, 8 markers showed significant association with MS, through conditional tests we determined that these MOG variants were not associated with MS independently of the main DRB1-DQB1 disease associations. CONCLUSION: These results indicate that variation within the MOG gene is not an important independent determinant of MS-inherited risk in the Sardinian population.
Assuntos
Predisposição Genética para Doença , Esclerose Múltipla/genética , Glicoproteína Associada a Mielina/genética , Polimorfismo de Nucleotídeo Único/genética , População Branca/genética , Adolescente , Adulto , Criança , Feminino , Haplótipos , Humanos , Itália , Desequilíbrio de Ligação , Masculino , Pessoa de Meia-Idade , Proteínas da Mielina , Glicoproteína Mielina-OligodendrócitoRESUMO
A genome-wide association scan of approximately 6.6 million genotyped or imputed variants in 882 Sardinian individuals with multiple sclerosis (cases) and 872 controls suggested association of CBLB gene variants with disease, which was confirmed in 1,775 cases and 2,005 controls (rs9657904, overall P = 1.60 x 10(-10), OR = 1.40). CBLB encodes a negative regulator of adaptive immune responses, and mice lacking the ortholog are prone to experimental autoimmune encephalomyelitis, the animal model of multiple sclerosis.