Ailesel behçet sendromu ailelerinde hla-b5 geninin genetik ve epigenetik analizleri

Behçet's Syndrome (BS) is a chronic multisystemic inflammatory disorder, primary symptoms of which are oral and genital ulceration and uveitis. The disease is also chracterized by inflammation in tissues and organs throughout the body such as vessels, lungs, kidneys, joints, gastrointestinal and central nervous system. BS usually occurs in second and third decades of the life with a severe disease course. It exists most commonly in Mediteranean and Middle East populations. In Turkey, frequency of the disease changes between 20 and 420 of 100.000. BS risk factors include genetic predisposition which is mainly based on familial aggregation and increased HLA-B51 carrier rate as well as infectious agents, environmental causes and yet undefined immunological mechanisms. Even though HLA-B51 allele has shown to be the most associated marker for BS, the presence of healthy individuals who carry HLA-B51 allele and similarly BS patients without HLA-B51 allele have led us question other mechanisms for BS causation. Epigenetic mechanisms have gained exceeding importance for their effects on DNA and chromatin structures without altering DNA sequence. DNA methylation is one of the mostly studied epigenetic mechanisms. HLA-B gene has shown to comprise a CpG island (CpGi) which span 1346 nucletides where CG ratio is 66.6 %, therefore methylation of cytosine residues may lead to a change in gene expression levels. We previously investigated global methylation and HLA-B locus specific methylation in a group of 4 MZ BS twins and 4 DZ BS twins; which suggested an involvement of an epigenetic regulation in HLA-B exon 1-2 region. BS twins had a higher methylation levels for HLA-B gene (p=0.0024). In this thesis we wanted to further our preliminary findings in familial BS cases and more directly examine the influence of HLA-B51 carrier rate and its methylation upon the presence of the clinical phenotype. Therefore, involvement of genetic and epigenetic roles of HLA-B51 region in BS would be better analysed and the sample size would be increased by including familial BS cases with their affected and unaffected relatives. 100 BS patients were contacted from Cerrahpaşa Medical Faculty, Rheumatology Polyclinic between 2013 and 2015 and asked if they have an affected relative. Within those 1800 index patients, 150 patients had a family member with BS. Among those, 15 families accepted to enroll in the study. So the study consists of 15 index patients; 17 affected relatives and 26 unaffected relatives. Peripheral blood samples were collected and genomic DNA was isolated from leukocytes. Patients and relatives were genotyped for HLA-B51 alleles using sequence specific PCR method. HLA-B51 positivity ratio was found to be 12/15 for index patients, 13/17 for affected relatives , 22/26 for unaffected relatives. Among BS and healthy family members, HLA-B51 frequency did not show a statistically significant diffrence. For healthy controls, who are not related with families, HLA-B51 positivity was 8/25. However, HLA-B51 positivity for BS patients was statistically higher when compared to healthy controls (p=0.0005). After determining HLA-B51 positivity, methylation profiles on HLA-B gene were analyzed and compared between groups using Real-time PCR based OneStep qMethyl Kit. For exon-1 and exon-2 region of HLA-B gene, BS patients had statistically higher methylation levels compared with healthy individuals in the family (p=0.0065). Methylation levels were not significantly different among HLA-B51(+) and HLA-B51(-) individuals for index patients, relatives with BS and healthy relatives. Observed results were also correlated with the data from our previous studies. These findings suggested us a room for epigenetic modifications which might be independent from HLA-B51 positivity.