Table 1. Basic characteristics of included studies.

author	year	case	control	case			control			HWE	source of control participants	genotype method	country	ethnicity	Quality score
				GG	AG	AA	GG	AG	AA
Riha [32]	2005	103	190	52	44	7	130	52	8	0.344	PB	TaqMan	UK	Caucasian	8
Li [30]	2006	24	48	11	10	3	35	12	1	0.981	HB	TaqMan	China	Asian	8
Liu [31]	2006	76	42	45	23	8	35	6	1	0.268	HB	PCR-RFLP	China	Asian	8
Popko [28]	2008	102	77	73	29	0	59	18	0	0.246	PB	PCR-RFLP	Poland	Caucasian	9
Bhushan [26]	2009	104	103	74	22	8	90	10	3	0.001	HB	PCR-RFLP	Indians	Asian	8
Karkucak [27]	2012	69	42	51	18	0	33	9	0	0.437	HB	PCR-RFLP	Turkish	Caucasian	8
Almpanidou [25]	2012	220	319	118	83	19	221	84	14	0.107	PB	PCR-RFLP	Greek	Caucasian	9
Guan [29]	2013	531	162	430	95	6	143	18	1	0.604	HB	PCR-RFLP	China	Asian	8
Li [17]	2013	155	100	137	18	0	88	12	0	0.523	PB	DNA sequencing	China	Asian	8
Wang [22]	2014	78	78	54	16	8	66	10	2	0.057	HB	PCR-RFLP	China	Asian	8
Petrek [15]	2015	116	351	85	30	1	248	98	5	0.175	PB	Mass Array technology	Czech	Caucasian	5
Zhu [16]	2015	200	200	124	46	30	166	31	3	0.278	HB	DNA sequencing	China	Asian	8
Zhang [14]	2019	750	800	576	153	21	656	132	12	0.077	HB	TaqMan	China	Asian	8
Abulikemu [23]	2021	67	67	42	20	5	60	6	1	0.098	HB	KASP	China	Asian	7

Abbreviation

HWE, Hardy-Weinberg equilibrium

PB,population-based

HB,hospital-based

PCR-RFLP:polymerase chain reaction-restriction fragment length polymorphism

KASP,kompetitive allele specific PCR.