Genetic susceptibility to multiple sclerosis (MS) is associated with genes of the major histocompatibility complex, particularly with the HLA DRB1*1501-DQA1*0102-DQB1*0602 haplotype in Caucasians. To investigate the association of DRB1, DQA1 and DQB1 alleles and haplotypes with MS in Biscay, Basque Country, northern Spain, we examined 197 patients and 200 regionally matched controls. High resolution HLA class II typing was performed by polymerase chain reaction followed by sequence-specific oligonucleotide probe hybridization. Several alleles were overrepresented in MS patients compared with those of controls: DRB1*0402, DRB1*1303, DRB1*1501, DQA1*0102, DQB1*0301, and DQB1*0602. DQB1*0602 was the only potentially predisposing allele for MS that withstood Bonferroni correction and maintained the association in a logistic regression model. On the other hand, several alleles showed lower frequencies in the MS group: DRB1*0101, DQA1*0101, DQB1*0303, and DQB1*0501, but only DRB1*0101 and DQB1*0303 maintained a negative association with the disease in the regression analysis. Three haplotypes were identified as potentially predisposing for MS in our population: DRB1*1501-DQA1*0102-DQB1*0602, DRB1*0402-DQA1*0301-DQB1*0302, and HLA-DRB1*013-DQA1*05-DQB1*0301. Additionally, three haplotypes associated with a lower risk for MS were identified, exhibiting DRB1*0101-DQA1*0101-DQB1*0501 the strongest negative association with MS [12% in controls vs. 3.8% in MS, Pc = 0.00047, OR = 0.290 (95% CI = 0.160–0.528)], and suggesting, therefore, a putative protective role for this haplotype in the population under study.
Although we recognize that these data need to be confirmed in further studies and in other areas of the country using a similar method, we believe this study is the first to find such high figure of prevalence, being very similar to the figures reported in recent years in other southern European countries.
Multiple sclerosis (MS) can be considered a disease that appears in genetically predisposed persons who, by chance, are also affected by some unknown environmental factor, probably infectious, that sets in motion an abnormal immune response leading to an autoimmune disease. Infectious agents are involved in the appearance of autoreactive T cells against myelin via various mechanisms, such as molecular mimetism or acting as superantigens. Numerous possible microorganisms have been suggested, including bacteria like Chlamydophila pneumoniae and many viruses, e.g., canine distemper virus, measles, varicella zoster, human herpes virus 6 (HHV-6) and Epstein-Barr virus (EBV). The association with EBV is the best studied over recent years. The frequency (incidence and prevalence) of MS seems to be increasing, which is better explained by the effect of some environmental factor. In this study we analyze some of the infectious agents that have been associated with the disease and discuss the hygiene hypothesis, which is one of the possible explanations for the epidemiological changes reported over recent decades.
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