Table 2

OR and attributable proportions due to interaction for different doses of smoking and SE alleles, regarding the risk to develop ACPA-positive RA

		No SE		Heterozygotic SE (SSE)		Homozygotic SE (DSE)
Smoking dose	No of cases/controls	OR (95 % CI)^*	No of cases/controls	OR (95 % CI)^*	No of cases/controls	OR (95 % CI)^*
Non-smoker	38/154	1.0 (Ref)^†	107/150	3.2 (2.0 to 4.9)	62/43	6.3 (3.7 to 10.9)
0–9 pack years	25/104	1.0 (0.6 to 1.8)	80/96	3.4 (2.1 to 5.6)	54/19	12.0 (6.2 to 23.0)
AP	–	–	–	0.09 (−0.32 to 0.49)	–	0.47 (0.12 to 0.83)
10–19 pack years	18/68	1.2 (0.6 to 2.2)	83/56	7.3 (4.3 to 12.4)	43/10	24.6 (10.9 to 55.8)
AP	–	–	–	0.53 (0.30 to 0.76)	–	0.73 (0.50 to 0.95)
20 pack years	30/87	1.9 (1.1 to 3.5)	112/71	8.7 (5.3 to 14.4)	83/13	37.6 (18.3 to 77.4)
AP	–	–	–	0.51 (0.31 to 0.72)	–	0.80 (0.67 to 0.94)
P value for trend		p=0.11		p<0.0001		p<0.0001

↵* OR and corresponding 95% CI adjusted for sex, age and residential area.
↵† Reference category.
ACPA, anticitrullinated protein/peptide antibody; AP, attributable proportion due to interaction; DSE, double shared epitope; RA, rheumatoid arthritis; SE, shared epitope; SSE, single shared epitope.