Table 4 Concordance in dizygotic pairs by HLA‐DR genotype risk group in index and co‐twin.
| Risk genotype group in the co‐twin† | Total | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| G1 | G2 | G3–G4 | G5 | ||||||
| Con | Dis | Con | Dis | Con | Dis | Con | Dis | ||
| Risk genotype group in the index twin† | |||||||||
| G1 (DR3/3, DR3/7) | 1 | 5 | 0 | 1 | 1 | 6 | 0 | 3 | 17 |
| G2 (DR5/7) | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 7 | 9 |
| G3–G4 (DR3/X, DR4/4, DR4/7, DR7/7) | 1 | 3 | 0 | 2 | 2 | 10 | 0 | 4‡ | 22 |
| G5 (DR4/Y, DR5/X, DR7/Z) | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 2 |
| Total | 2 | 9 | 0 | 4 | 3 | 17 | 0 | 15 | 50 |
Con, number of concordant co‐twins; Dis, number of discordant co‐twins.
†HLA grouping is according to relative risks for coeliac disease estimated in the Italian population according to Margaritte‐Jeannin and colleagues.15 DR3 haplotype carries DQB1*0201 and DQA1*0501, DR7 carries DQB1*0202, DR5 carries DQA1*0501, and DR4 carries DQB1*0302.
‡One co‐twin is DR13/13.
X = not DR3 or 7; Y = not DR3, 4, or 7; Z = not DR3, 4, 5, or 7.