HLA-B and psoriasis: The most significant association with PsA compared with PsC after correcting for age of psoriasis onset was to an amino acid at position 97 of HLA-B (p=1.54×10−9), where the presence of an asparagine (OR 2.46, 95% CI 1.78 to 3.42) or serine (OR 1.45, 95% CI 1.22 to 1.74) residue increased the risk of PsA (table 1).