Table 2.

Characteristics of the included studies of the association between the COMT Val158Met polymorphism and cognitive dysfunction in PD.

First author	Year	Country	Number of		Mean age	Male/female	PD-NC			PD-CI			HWE		NOS score
			PD-NC	PD-CI			V-V	V-M	M-M	V-V	V-M	M-M	PD-CN	PD-CI
Dai	2015	China	702	385	63.0	631/456	344	291	67	192	162	33	0.632	0.887	7
Li	2014	China	68	71	59.64(11.61)	78/61	35	28	5	40	24	7	0.852	0.246	7
Wang	2014	China	91	75a	66.39	——	52	32	7	34	36	5	0.510	0.264	7
Wang	2014	China	91	99b	66.39	——	52	32	7	57	39	3	0.510	0.226	6
Białecka	2012	Poland	29	13	——	——	20	5	4	9	4	0	0.006	0.512	7

PD-NC, PD with no cognitive impairment; PD-CI, cognitive impairment in PD; a, mild cognitive impairment in PD; b, dementia in PD.