HLA-Balleles andcomplotypes inMexican patients withseronegative spondyloarthropathies

Objectives-To analysemajor histocompatibility complex(MHC)haplotypes inMexicanmestizopatients withseronegative spondyloarthropathies (SSpA) andnormalcontrols, todiscover ifthere areotherantigens, besides B27,inthe HLA region thatmightshowassociation withthedisease. Methods-Thestudyincluded 100Mexicanmestizo patients withSSpAand200of theirfirst degreerelatives. Thesegroups were comparedwith 85 ethnically matchedcontrols. Theclass Iandclass III MHC antigens wereobtained bystandard methods.Thesignificance ofdifferences betweenpatients andcontrols wastested by x2analysis; linkage disequilibrium amongthedifferent alleles ineachhaplotypewas estimated bycomputing delta values. Results-Wefounda significantly increased frequency oftheHLA-B27antigen(pcorr. =1x 10-5, oddsratio (OR)=334, 95%confidence interval (CI) =9-3-142.0). Inthegroupof45SSpApatients negative for the B27 antigen,independent increased frequencies ofHLA-B49antigen (Pcorr. =0-03, OR =6-5, 95%CI=1-5-32-8)) and theFC31 complotype (pco,. =0*04, OR=3-7,95% CI=12-11-1) werefound. Significant delta values wereobtained for the[B27;SC30] haplotype (p=0.0005) but notforhaplotypes markedbytheFC31 complotype. HLA-Bantigens onthehomologouschromosomein B27 positive patients weremainly HLA-B51(18%)and HLA-B60(16%);however, theobserved genotypes B27/B51 andB27/B60 werenot significantly different thanexpected from theallele frequencies alone. Conclusions-These