MICA gene triplet repeat polymorphism in patients with HLA-B27 positive and negative ankylosing spondylitis from sardinia

Objective. We investigated the distribution of MICA triplet repeat polymorp hism in a random population and in patients with seronegative spondyloarthr itis from Sardinia compared to continental Italy. Methods. We analyzed the distribution of MICA triplet repeat polymorphism i n HLA-B*2709 [not associated with ankylosing spondylitis (AS)] and B*2705 ( associated with AS) haplotypes, to verify whether the strong association of MICA-A4 with HLA-B27 reported in other populations is maintained in Sardin ia, and compared the distribution of MICA-A alleles in HLA-B27 negative ver sus HLA-B27+ patients with AS. Results. We found that the frequency of MICA-A4 triplet repeat allele in a random Sardinia population is higher (53.2%) than in other Caucasian popula tions (around 20%): this allele is strongly associated with both HLA-B*2709 and B*2705. No significant difference between HLA-B27+ patients with AS an d healthy controls was found: the MICA-A4 allele was present in more than 9 0% of subjects. MICA-A4 was found in 16 out of 20 HLA-B27 negative Sardinia n patients with AS, with a frequency (80%) more similar to that of the HLA- B27+ group of patients than that of controls. Conclusion. The high frequency of MICA-A4 allele in HLA-B27 negative patien ts with AS from Sardinia, suggests the presence within the HLA region of a susceptibility factor other and certainly weaker than B27. This factor is l ikely to he more easily found by analyzing genetically homogeneous populati ons like the Sardinian, characterized by a small number of very frequent ha plotypes.