| Genotype c.20 | Age at disease onset (years) | Duration of disease (months) | Year of onset | ||||||
| Mean | SD | Median | Mean | SD | Median | Mean | SD | Median | |
| TT | 29.9 | 12.2 | 28 | 16.6 | 5.8 | 16 | 1998.4 | 2.4 | 1999 |
| TC | 29.6 | 10.3 | 25 | 15.7 | 5.2 | 14.5 | 1999.0 | 2.4 | 1999 |
| CC | 33.5 | 9.8 | 29 | 19.5 | 8.4 | 19 | 1998.6 | 2.6 | 1998 |
SD, standard deviation.