HLA-C and Arthritis: However, the patients with allele 384 of the C1_4_4 microsatellite, telomeric to HLA-C, were significantly older at the onset of psoriasis (35.3 ± 12.6 versus 25.1 ± 13.7 years, P = 0.01) and of arthritis (42 ± 11.5 versus 33 ± 11.7 years, P = 0.01).