Abstract

Background: The B*2709 allele, first described among the Italian population, has been found not to be associated with AS in the Sardinian and in continental Italy populations. It has been reported to be present in few cases seronegative peripheral arthritis without axial involvement. If the B*2709 subtype is actually not associated with AS and has a neutral role in the development of the disease, like any other AS-unrelated allele of B locus, the presentation of sporadic B*2709þ AS patients is to be expected by chance, and should be regarded as a case of B27- negative AS, but has never been reported.
Methods: A 36-yr-old sardinian woman presented for chronic low back pain and stiffness since the age of 30. The onset was reported to be insidious, characterized by lumbar pain and early morning stiffness; the pain was also present bilaterally in the gluteal area and in the sacroiliac (SI) region, and was irradiated to the lower limbs down to the dorsal thigh, and alternate from side to side. Conventional radiography showed erosions in the iliac and sacrum side of the SI joint and mild sclerosis of the subcortical bone, bilaterally on the iliac sides. CT scan of the SI joints confirmed bilateral irregular articular profiles on both iliac and sacrum sides due to marginal erosions, and mild sclerosis of iuxtaarticular iliac bone. SI joint MRI confirmed the diagnosis. HLA typing was: A23, 23; B14, *2709; CW1, 8; DRB1* 13, 16; DQA1 0102, 0102; DQB1 05, 05. The HLA-B14 subtyping was B*1403.
Results: Recent reports suggest to take into consideration all the alleles of the HLA-B locus, since it is emerged that in B27-negative AS patients some B alleles are associated with the disease; this is the case of the B*1403 subtype in a West African population. These alleles may be related with AS, like B27 ‘susceptible’ subtypes, either for an intrinsic pathogenetic role or for the proximity to another gene directly responsible for the susceptibility to the disease. Thus, in the patient described, susceptibility to AS may be related to the presence of this AS-associated allele rather than to B*2709, which in this case would have a ‘neutral’ role. Furthermore, it is noteworthy that the patient has another allele, the HLA-DR16, which has been found to be present in the extended haplotype that in Sardinia is strongly associated with AS. The peculiar mixed phenotype of this patient, whose family is currently under investigation, makes her a good subject to study in the search for AS genetic susceptibility factors.
Conclusions: In conclusion, this is the first observation of the presence of the HLA-B*2709 subtype in a patient with AS. However, the peculiar HLA phenotype of this patient suggests caution in interpreting these results because of the presence of other alleles, B*1403 and DR16, involved in the susceptibility to AS.

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