Table 4.

Interaction betweenUCHL1 S18Y polymorphism and smoking status affecting sporadic Parkinson’s disease in a Japanese population

	Ever smoked
	Yes		No
Genotype	No. cases/controls	Adjusted OR (95 % CI)*	No. cases/controls	Adjusted OR (95 % CI)*
CC + CA	42/113	1.00	117/166	2.73 (1.62 − 4.61)
AA	20/32	1.72 (0.87 − 3.38)	50/46	4.08 (2.18 − 7.63)
P for multiplicative interaction = 0.74
Measures of additive interaction†
Relative excess risk due to interaction (RERI) = 0.63 (95 % CI: -1.48 − 2.75)
Attributable proportion due to interaction (AP) = 0.16 (95 % CI: -0.31 − 0.62)
Synergy index (S) = 1.26 (95 % CI: 0.59 − 2.68)

*Adjusted for sex, age, region of residence, and caffeine intake.

^†Statistically significant when the 95 % CI of RERI > 0, the 95 % CI of AP > 0, or the 95 % CI of S > 1, indicating additive interaction.