The absence of disease-specific polymorphisms within the HLA-B51 gene thatis the susceptible locus for Behcet's disease

Behcets disease is known to be associated with HLA-B51 in many different po pulations. Genetic evidence supports that the susceptible gene for Behcet's disease is the HLA-B51 allele at the HLA-B locus. This study was aimed to determine the HLA-B51 nucleotide sequence variation in three Behget's disea se patients and three healthy controls in order to elucidate if any disease specific mutations or polymorphisms may exist in the HLA-B51 gene of patie nts. Long-range polymerase chain reaction (PCR) was first carried out to gi ve a PCR-amplified product of 9.5 kb which was then used as a template for nested PCR to give a final amplified product of 4.2 kb. This final product containing the 1.3-kb promoter/enhancer region and the entire HLA-B gene ex cept for a 363-bp 3' terminal end segment encoding the 3' untranslated regi on was subcloned by the BP cloning technique and sequenced. The sequencing results showed that all the patients possessed the HLA-B*51011 allele, and there were no differences in the exonic nucleotide sequences between the th ree Behget's disease patients and the three healthy controls. The HLA-B*510 11 intronic and promoter/enhancer nucleotide sequences from the three patie nts had 22 single nucleotide polymorphisms (SNPs), a single insertion of 6 bp and a single deletion of 2 bp. On the other hand, the three healthy cont rols had 24 SNPs in their intronic and promoter/enhancer regions. However, none of these polymorphisms in the patients were specific for the disease. Therefore, these results clearly demonstrate that the HLA-B exonic sequence that encodes the HLA-B51 allele is the real pathogenic factor in Behcets d isease.