Table 1. Main characters of studies included in this meta-analysis.

First author	Year	Country	Ethnicity	Control source	Sample size cases/controls	Cases				Controls			Genotype methods
						LL	LS	SS		LL	LS	SS
Janssen et al.	2009	Netherlands	Caucasian	HB	89/92	27	43	19		27	41	24	PCR-RFLP
Ozbek et al.	2009	Turkey	Caucasian	PB	69/69	11	21	37		12	37	20	PCR-RFLP
Safarinejad et al.	2009	Iran	Caucasian	PB	82/82	24	29	29		35	30	17	PCR-RFLP
Luo et al.	2011	China	Asian	HB	119/90	24	34	61		25	31	34	PCR-RFLP
Zuccarello et al.	2012	Italy	Caucasian	PB	89/100	22	49	18		33	51	16	PCR-RFLP
Huang et al.	2016	China	Asian	PB	114/101	18	61	35		22	48	31	PCR-RFLP
Salem et al.	2017	Egypt	African	HB	60/20	16	25	19		10	8	2	PCR-RFLP
Kham et al.	2018	Pakistan	Asian	PB	271/152	108	97	66		30	72	50	PCR-RFLP

HB, hospital based; PB, population based; PCR, polymerase chain reaction; RFLP, restriction fragment length polymorphism.