Table 1.

The main characteristics of the studies included in the meta-analysis

Author	Year	Country	Ancestor	Source of control group	Mean age of control group	Gender index (case)	Gender index (control)	Case/Control
Rs1006737
Fatima [11]	2017	Pakistani	Caucasian	Population based	44	0.33	0.71	508/300
Lubeiro [20]	2018	Spain	Caucasian	Population based	29.52	0.72	0.98	50/101
Mallas [21]	2016	Mixed	Mixed	Population based	35.79	0.26	0.85	63/124
Porcelli [22]	2015	Korean	Asian	Hospital based	45.36	0.73	1.22	176/326
Ivorra [8]	2014	Spain	Caucasian	Mixed	43.61	0.79	0.75	3063/2847
He [15]	2013	China	Asian	Population based	30.6	0.53	0.86	1235/1235
Guan [23]	2013	China	Asian	Population based	34.2	0.87	0.83	1430/1570
Galaktionova [24]	2013	Russia	Caucasian	Population based	36	2.24	0.90	188/192
Zheng [13]	2013	China	Asian	Population based	32.4	1.05	1.04	5893/6319
Hori [18]	2012	Japan	Asian	Population based	46	0.82	1.93	552/1132
Zhang [25]	2011	China	Asian	Population based	22.3	0.49	0.60	318/401
Nyegaard [26]	2010	Denmark	Caucasian	Population based	–	–	–	976/1489
Bigos [27]	2010		Caucasian	Population based	33.09	0.230	1.16	282/440
Green [28]	2009	UK	Caucasian	Population based	–	0.47	1.04	479/2936
Rs2007044
Bustillo [29]	2017	United States	Caucasian	Population based	36	0.26	0.37	53/129
Zhang [30]	2018	China	Asian	Hospital based	27.14	0.15	0.28	53/129
Rs4765905
Sudesh [31]	2018	India	Indian	Population based	38.73	1.01	0.483	1005/1069

Notes: Gender index = female/male; Guan’s study included the main characteristics of both rs1006737 and rs4765905; Zheng’s study included the main characteristics of both rs1006737 and rs2007044