B*27 in molecular diagnostics: impact of new alleles and polymorphism outside exons 2 and 3.

HLA-B*27 is known to be associated with ankylosing spondylitis and several methods have been applied to determine its presence or absence. In this report two molecular methods were used for detection of B*27. The polymerase chain reaction sequence-specific primer (PCR-SSP) method was performed to detect the presence or absence of B*27, whereas the sequence-based typing method (SBT) was used to identify the B*27 subtype. The PCR-SSP method used to detect B*27 was updated to enable the detection of all B*27 alleles. The typing results obtained by this method were compared with the serological typings of 262 individuals. Fifty of them were found to be B*27 positive by PCR-SSP and 46 also showed positive serological reactions with B27-specific sera. The four discrepancies were the result of the presence of B*2712 in three individuals and B*2715 in one individual; both alleles showed no serological reactions with B27-specific antisera. With SBT the sequences of exons 1 through 4 were determined to unequivocally assign the B*27 alleles. Eleven different subtypes were detected in 78 individuals, including three new B*27 alleles: B*27054, B*2715 and B*2717. The allele B*27054 showed an allelic drop out when exon 3 was amplified. Three differences with B*27052 were demonstrated; one in exon 1, one in intron 1 and one in intron 2, the latter being responsible for the allelic drop out. The B*2715 allele was serologically not detectable with several B27-specific sera, but showed Bw4-positive reactions. The sequence of B*2715 showed two mismatches with B*2704. The sequence of B*2717 showed one mismatch with B*27052 at position 248 (A-->T), which was considered to be a conserved position in all B alleles.