Observed and expected recurrence risk ratios for different genetic models assuming no dominance variance component and a population prevalence of 0.13%
| Observed | Single locus | Polygenic multiplicative | Two locus multiplicative | HLA, residual polygones | Five locus multiplicative | |
| MZ twins | 630 | 163 | 6694 | 282 | 3202 | 780 |
| First degree relatives | 82 | 82 | 82 | 82 | 82 | 82 |
| Second degree relatives | 10 | 41 | 9 | 27 | 11 | 15 |
| Third degree relatives | 7 | 21 | 3 | 11 | 4 | 5 |