Mean (SD) age of disease onset (in years) in familial and non-familial RA groups
| Familial | Non-familial | p | |
| All | 42.0 (14.3) | 46.5 (10.9) | 0.0020 |
| Men | 47.5 (12.6) | 46.6 (10.9) | NS |
| Women | 39.9 (14.4) | 46.5 (10.9) | <0.001 |
| RF positive patients | 41.2 (13.2) | 46.7 (11.3) | <0.001 |
| RF negative patients | 46.8 (19.4) | 46.0 (9.5) | NS |
| DR4 positive | 41.5 (14.7) | 45.2 (11.3) | 0.044 |
| DR4 negative | 43.0 (13.3) | 48.1 (10.2) | 0.014 |