In the article entitled “Electrostatic modifications of the HLA-DR P9 peptide-binding pocket in PSC: Back to the future with HLA DRβ” (volume 53, pages 1798–1800) an error appears on page 1799, in the second column, paragraph 2, lines 10 to 14 with the error on line 11 (underlined). The full sentence in the text reads “Risk alleles which encode asparagine at DRβ-37 (on risk haplotypes 1 and 2, table 1) form P9 pockets with similar structural architecture and with a consistently positive electrostatic potential.” The risk haplotypes referred to here should be haplotypes 1 and 3 where both expressed DRB1 alleles encode asparagine.

In the editorial haplotype 2 is incorrectly identified as carrying a DRB1 gene encoding asparagine at DRβ-37. This haplotype carries a DRB1 allele which encodes serine at position DRβ37. However the reader should be in no doubt that this haplotype is associated with an increased risk of PSC as stated in the discussion and it is important to note that the second expressed DRB gene on this haplotype (DRB5) the paralogous DRB gene does encode asparagine at position DRβ-37. This may explain the weak association with haplotype 2 that appears in some populations and not others which is discussed in the editorial.