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 polymorphism in a random population and in patients with seronegative spondyloarthritis from Sardinia compared to continental Italy.


METHODS
We analyzed the distribution of MICA triplet repeat polymorphism in 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 Sardinia, and compared the distribution of MICA-A alleles in HLA-B27 negative versus 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 populations (around 20%); this allele is strongly associated with both HLA-B*2709 and B*2705. No significant difference between HLA-B27+ patients with AS and healthy controls was found: the MICA-A4 allele was present in more than 90% of subjects. MICA-A4 was found in 16 out of 20 HLA-B27 negative Sardinian patients with AS, with a frequency (80%) more similar to that of the HLA-B27+ group of patients than that of controls.


CONCLUSIONS
The high frequency of MICA-A4 allele in HLA-B27 negative patients with AS from Sardinia, suggests the presence within the HLA region of a susceptibility factor other and certainly weaker than B27. This factor is likely to be more easily found by analyzing genetically homogeneous populations like the Sardinian, characterized by a small number of very frequent haplotypes.
Ricci-Vitiani
L
L
Department of Cell Biology and Development, University La Sapienza, Rome, Italy.
Vacca
A
A
Potolicchio
I
I
Scarpa
R
R
Bitti
P
P
Sebastiani
G
G
Passiu
G
G
Mathieu
A
A
Sorrentino
R
R
D015796:HLA-B27 Antigen / Q000235:genetics*; D015395:Histocompatibility Antigens Class I / Q000235:genetics*; D006801:Humans; D007558:Italy; D018895:Microsatellite Repeats / Q000235:genetics; D011110:Polymorphism, Genetic / Q000235:genetics*; D013167:Spondylitis, Ankylosing / Q000235:genetics*; D018911:Trinucleotide Repeats / Q000235:genetics*
D015796:HLA-B27 Antigen; D015395:Histocompatibility Antigens Class I; C099187:MHC class I-related chain A