Table 1. Characteristics of include studies about MTHFR C677T polymorphism.

Author, year	Country	Race	Case group				Control group				pHWE	NOS
			CC	CT	TT	Total	CC	CT	TT	Total
Jang, 2013	South Korea	Asian	74	82	47	203	140	203	60	403	0.62	8
Xu, 2019	China	Asian	42	28	31	101	70	26	24	120	0.10	8
Yin, 2012	China	Asian	171	157	112	440	182	190	68	440	0.30	7
Kailibinuer, 2012	China	Asian	22	31	35	88	30	45	11	86	0.65	7
Wang, 2004	China	Asian	13	28	17	58	19	32	7	58	0.51	7
Qiu, 2002	China	Asian	23	32	14	69	42	47	12	101	0.98	7
Hsu, 2001	China	Asian	60	40	7	107	55	44	8	107	0.98	8
Lu, 2002	China	Asian	18	42	30	90	31	66	46	143	0.73	8
Guo, 2002	China	Asian	4	26	33	63	16	35	29	80	0.66	7
Zheng, 2000	China	Asian	12	31	10	53	62	45	15	122	0.34	8
Lin, 2000	China	Asian	53	50	9	112	76	41	8	125	0.75	7
He, 2010	China	Asian	15	27	21	63	26	36	13	75	1.00	7
Li, 2015	China	Asian	71	107	68	246	97	155	40	292	0.21	8
Gao, 2008	China	Asian	16	34	14	64	14	39	11	64	0.21	7
Dong, 2013	China	Asian	16	37	15	68	15	41	12	68	0.23	8
Hsu TS, 2001	China	Asian	48	28	7	83	43	33	6	82	1.00	8
Karmadonova, 2014	Russia	Caucasian	76	79	19	174	226	201	34	461	0.50	7
Spiroski, 2008	Macedonia	Caucasian	20	33	10	63	34	35	11	80	0.92	7
Bezemer, 2007	Netherlands	Caucasian	2044	1891	440	4375	2245	2094	517	4856	0.68	8
Almawi, 2005	America	Caucasian	80	77	41	198	350	270	77	697	0.08	7
Miranda, 2002	Netherlands	Caucasian	67	90	14	171	233	186	42	461	0.86	6
Zalavras, 2002	Greece	Caucasian	70	82	24	176	117	153	30	300	0.14	7
Amparo, 2010	Spain	Caucasian	14	19	9	42	23	42	14	79	0.79	7
Tawfik, 2012	Egypt	Caucasian	20	4	25	49	22	1	1	24	0.01	7
Hanson, 2001	America	Caucasian	58	63	16	137	130	158	41	329	0.80	7
Ray, 2001	Canada	Caucasian	49	61	19	129	72	44	13	129	0.30	6
Gerald, 2000	Australia	Caucasian	67	73	15	155	122	141	35	298	0.84	6
Phillip, 2000	Canada	Caucasian	25	28	12	65	21	35	8	64	0.53	6
Ben, 2012	Tunisia	Caucasian	20	6	0	26	101	79	17	197	0.96	7
Kupeli, 2011	Turkey	Caucasian	49	24	7	80	78	26	0	104	0.35	8
Lupi-Herrera, 2018	Mexico	Caucasian	77	106	29	212	33	54	35	122	0.45	8

pHWE, P values for Hardy–Weinberg equilibrium test.