Table 1.

Characteristics of included studies.

First author	Year	Country	Ethnicity	Genotype method	NOS score	Hearing loss type	Case	Control	GST T1				GST M1
									Case		Control		Case		Control
									WT	null	WT	null	WT	null	WT	null
Manche	2016	India	Indian	Multiplex-PCR	8	ARHL	220	270	119	101	202	68	121	99	201	69
Zhu	2011	China	Chinese	Multiplex-PCR	8	ARHL	110	114	61	49	58	56	39	71	33	81
Bared	2010	USA	Mixed	Multiplex-PCR	8	ARHL	55	79	21	31	52	27	16	36	41	38
Ates	2005	Turkey	Turkish	Real-time PCR	8	ARHL	68	69	54	14	53	16	36	32	40	29
Shen	2012	China	Chinese	PCR-RFLP	8	NIHL	444	445	215	229	210	235	198	246	253	192
Abreu-Silva	2011	Brazil	Brazilian	PCR-RFLP	8	NIHL	151	104	40	111	22	82	115	36	77	27
Liu	2006	China	Chinese	PCR	8	NIHL	123	123	58	60	48	66	38	85	54	69
Yang	2005	China	Chinese	Multiplex-PCR	8	NIHL	93	101	31	62	47	57	37	56	35	66
Carlsson	2005	Sweden	Swedish	PCR-RFLP	8	NIHL	103	112	90	13	104	8	50	53	59	53
Choeyprasert	2013	Thailand	German	Multiplex-PCR	8	DIHL	55	13	38	17	4	9	24	31	5	8
Jurajda	2012	Czech	Czechs	PCR	7	DIHL	12	26	10	2	20	6	4	8	10	16
Palodetto	2010	Brazil	Brazilian	Multiplex-PCR	5	DIHL	10	20	8	2	13	7	6	4	11	9
Barahmani	2009	USA	Mixed	Multiplex-PCR	7	DIHL	19	15	13	6	10	5	11	8	9	6
Oldenburg	2007	Norway	Norwegians	Multiplex-PCR	7	DIHL	89	84	75	14	70	14	49	40	45	39
Peters	2000	Germany	Thai	PCR	8	DIHL	19	20	12	8	16	3	11	9	8	11
Um	2011	Korea	Korean	Multiplex-PCR	6	SSHL	98	343	51	47	173	170	40	58	138	205
Cadoni	2006	Italy	Italian	Multiplex-PCR	8	SSHL	80	80	60	20	62	18	41	39	36	44

NOS: Newcastle-Ottawa Scale. GST: glutathione s-transferase. ARHL: age-related hearing loss. NIHL: noise-induced hearing loss. DIHL: drug-induced hearing loss. SSHL: sudden sensorineural hearing loss. WT: wild type. PCR-RFLP: polymerase chain reaction-restriction fragment length polymorphis.