A peculiar sequence motif in the alpha-1-domain of the HLA-C molecule in psoriasis

Background: Most immunogenetic studies restrict the location of the suscept ibility gene for psoriasis to the HLA-C locus. Objective: The present study evaluates the amino acid sequences of the HLA-C binding groove associated with the disease in a restricted population of Italian descent: Pavia, Nort hern Italy. Method: Forty patients, affected by psoriasis, underwent genomi c analysis of exons 2 and 3 of the HLA-C gene by means of the PCR-SSP techn ique. Results: The HLA-C*0602 gene frequency was significantly higher in pa tients with respect to 122 sex-, age- and ethnically matched controls (25 v s. 8.6%, chi(2) = 14.65, p = 0.000129). This frequency rose to 39.5% in pat ients with a family history positive for psoriasis. In particular, 4 amino acid substitutions were shown to be crucial for the predisposition to the d isease, namely Ala 73 and Asn 77 (located in the C pocket of the antigen bi nding groove), Lys 80 in the F pocket and Asp 90 in the outer loop of the m olecule. This peculiar motif, entirely located in the al-domain of the HLA- C molecule, was characteristic of psoriatic patients being present in 77.5% of the cases against the 50.82% of controls (chi(2) = 8.77; p = 0.0031). H omozygosity for the amino acids considered at these residues was found in 1 5% of patients and in 0% of controls (chi(2) = 20.74, p = 0.0000053). Concl usion: The most important results emerging from this study indicate that Al a 73, Asn 77, Lys 80 and Asp 90 together form a motif restricted to few pat hogenic peptides to be studied in the near future. Copyright (C) 2000 S. Ka rger AG, Basel.