Psoriatic arthritis (PsA) has been defined as an inflammatory arthritis associated with psoriasis that may affect as many as 30% of psoriasis patients. Epidemiological study reported strong familial clustering of PsA although the precise etiology of PsA is poorly understood. Recently, a genomewide linkage scan in PsA revealed a LOD score of 2.17 on chromosome 16q and provided strong evidence for a paternal imprinting effect. That region surrounds a psoriasis susceptibility locus including the CARD15 gene which has convincingly been shown to confer susceptibility to Crohn's disease. The existence of a common susceptibility gene for psoriasis/PsA and Crohn disease was recently demonstrated by evidence of association of CARD15 polymorphisms with PsA. To confirm these results in an independent population, we analyzed a data set of 193 Italian PsA patients and 150 controls for CARD15 polymorphisms (R702W, G908R and leu1007finsC) previously demonstrated associated with PsA. Here we report no evidence for association in the examined population for CARD15 polymorphisms, suggesting that the positive association previously reported in a genetically isolated population was the result of a linkage disequilibrium due to a founder effect.
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