Searching for psoriasis susceptibility genes in Italy: Genome scan and evidence for a new locus on chromosome 1

Psoriasis is a chronic inflammatory dermatitis, affecting approximate to 2% of the population. Major clinical features include red, scaly patches on s calp, elbows, and knees, with or without severe arthritis. Several putative susceptibility loci have been mapped by parametric and non-parametric link age analysis to chromosome regions 2p, 4q, 6p, 8q, 16q, 17q, and 20p; howev er, the most significant results and confirmation of linkage are only avail able for the 17q and 6p chromosome regions at present. In this study, 22 mu ltiplex Italian families were investigated for linkage to 6p and 17q suscep tibility regions, using a set of four microsatellites. These analyses faile d to detect significant linkage with any of the examined markers. A genome- wide scan was then performed on one of the largest pedigrees, searching for an additional susceptibility locus. This study disclosed a putative linkag e to chromosome 1cen-q21 markers. When these microsatellites were analyzed in the remaining families of the sample, a significant linkage was observed using both parametric and non-parametric methods. The highest two-point lo d score value was obtained with D1S305 marker (3.75 at theta = 0.05). Non-p arametric analysis at this locus also demonstrated a significant excess of allele sharing (p = 0.0001).