Table 1. The main features of enrolled studies.

Ref. no.	Year	Country	Ethnicity	Sample size		Source of controls	Genotyping method	Adjusted factors	Quality score	Citation
				Case	Control
1	2010	Korean	Asian	93	93	HB	MS	NM	5.5	[15]
2	2013	China	Asian	878	900	PB	Taqman	Age and residential area	7.5	[2]
3	2013	China	Asian	914	967	PB	Taqman	Age and residential area	7.5	[2]
4	2013	China	Asian	685	730	HB	Taqman	Age, sex, and smoking status	7	[16]
5	2013	America	Caucasian	277	278	PB	SNPlex technology	Age, sex, ethnicity, and county of residence	7.5	[14]
6	2015	Korean	Asian	408	400	HB	PCR-RFLP	Age, gender, hypertension, diabetes mellitus	7	[24]
7	2015	Polish	Caucasian	135	170	HB	Taqman	NM	7.5	[25]
8	2016	Polish	Caucasian	100	100	NM	Taqman	NM	6	[13]
9	2016	Korean	Asian	147	209	HB	PCR-RFLP	Age, gender, hypertension, diabetes mellitus, drinking status, and smoking	7	[26]
10	2017	China	Asian	628	502	HB	HRM	Age, sex, region, smoking status, and drinking status	7	[27]

Abbreviations: HRM, high-resolution melting; MS, sequenome MS-based genotyping assay; PCR-RFLP, polymerase chain reaction-restriction fragment length polymorphism; NM, not mentioned.