Table 1. Main characteristics of selected studies.

First author	Year	Country	Ethnicity	Sample size		Matching criteria	Genotyping method	Quality control
				case	control
Sharma [9]	1994	UK	European	100	73	Age and sex	PCR	No
Ueda [24]	1995	UK	European	488	188	Age and sex	PCR	Yes
Catto [25]	1996	UK	European	406	215	Age and sex	PCR	Yes
Margaglione [27]	1996	Italy	European	101	109	Sex	PCR	No
Kario [26]	1996	Japan	Asian	138	104	Age and sex	PCR	Yes
Agerholm-Larsen [28]	1997	Denmark	European	452	9038	Age	PCR	Yes
Nakata [30]	1997	Japan	Asian	55	61	Age and sex	PCR	No
Doi [29]	1997	Japan	Asian	181	271	Age and sex	PCR	Yes
Seino [32]	1998	Japan	Asian	26	28	Age and sex	PCR	No
Pfohl [31]	1998	Germany	European	91	297	–	PCR	Yes
Shen [33]	1998	China	Asian	44	62	Age and sex	PCR	No
Xu [34]	1998	China	Asian	65	117	Age	PCR	No
Kostulas [35]	1999	Sweden	European	96	93	Age and sex	PCR	No
Notsu [10]	1999	Japan	Asian	175	213	Sex	PCR	Yes
Zee [11]	1999	USA	European	338	338	Age	PCR	Yes
Lin [36]	2000	China	Asian	306	300	Age and sex	PCR	Yes
Wei [37]	2000	China	Asian	87	257	Age	PCR	No
Zhang [39]	2001	China	Asian	165	106	Age and sex	PCR	No
Zhang [38]	2001	China	Asian	74	72	Sex	PCR	No
Ohkubo [40]	2002	Japan	Asian	69	294	Age and sex	PCR	No
Szolnoki [41]	2003	Hungary	European	867	743	Age and sex	PCR	No
UM [42]	2003	Korea	Asian	208	636	Age and sex	PCR	No
Yuan [43]	2003	China	Asian	122	1229	Age	PCR	No
Zhang [47]	2004	Japan	Asian	151	150	Age and sex	PCR	Yes
Karagiannis [44]	2004	Greece	European	100	100	Age and sex	PCR	Yes
Wang [46]	2004	China	Asian	46	43	–	PCR	No
Rubattu [45]	2004	Italy	European	215	236	Age	PCR	Yes
Brenner [48]	2005	France	European	459	459	Age and sex	PCR	Yes
Pera [51]	2006	Poland	European	368	556	Age and sex	PCR	No
Dikmen [49]	2006	Turkey	European	141	50	–	PCR	No
Gao [50]	2006	China	Asian	100	100	Age and sex	PCR	Yes
Tuncer [52]	2006	Turkey	European	108	79	Age and sex	PCR	No
Tseng [58]	2007	China	Asian	92	780	–	PCR	Yes
Gormley [54]	2007	UK	European	299	600	Age and sex	PCR	No
Li [56]	2007	China	Asian	454	334	Sex	PCR	No
Lalouschek [55]	2007	Austria	European	450	817	–	PCR	Yes
Polupanov [57]	2007	Kirghiz	Asian	69	64	Age	PCR	No
Gawel [53]	2007	Poland	European	66	45	Age	PCR	No
Hong [59]	2008	Korea	Asian	232	225	Age and sex	PCR	No
Munshi [61]	2008	India	Asian	162	150	Age and sex	PCR	No
Mollsten [60]	2008	Sweden	European	222	542	Age and sex	PCR	Yes
Tascilar [64]	2009	Turkey	European	157	85	–	PCR	No
Saidi [63]	2009	Tunisia	African	228	323	Age and sex	PCR	No
Celiker [62]	2009	Turkey	European	162	107	–	PCR	No
Li [66]	2010	China	Asian	76	311	Age and sex	PCR	Yes
Domingues-Montanari [65]	2010	Spain	European	519	540	–	PCR	No
Kalita [12]	2011	India	Asian	193	188	Age and sex	PCR	Yes
Chutinet [67]	2011	Thailand	Asian	141	167	Age	PCR	No
Markoula [69]	2011	Greece	European	176	178	Age and sex	PCR	Yes
Indrajaya [68]	2011	Indonesia	Asian	30	30	Age and sex	PCR	No