Table 1.

Main characteristics of studies included in the systematic review and meta-analysis (n = 21).

Author (Year)	Country	Ethnicity	Disease	Genotyping Methods	Sample Size (Case/Control)	CC		CT		TT		Newcastle-Ottawa Scale
						Case	Control	Case	Control	Case	Control
Peters (2008) [36]	USA	>93% Caucasian American	Advanced distal colorectal adenoma	SNPlex or TaqMan	745/758	231	266	368	359	146	133	High
Méplan (2010) [35]	Czech Republic	Czech origin adults >29 years	Colorectal cancer	KASPar	729/664	229	249	364	301	136	114	Moderate
Steinbrecher (2010) [37]	Germany	European men	Prostate cancer	MassARRAY system	245/490	77	156	114	229	54	105	High
Du (2012) [46]	China	Chinese Han population	Kashin-Beck disease	PCR-RFLP	216/194	68	67	124	102	24	25	High
Karunasinghe (2012) [20]	New Zealand	European men	Prostate cancer	TaqMan	260/439	84	144	129	210	47	85	High
Jaworska (2013) [19]	Poland	Polish adults	Laryngeal cancer	Real-time PCR	111/213	42	68	46	108	23	37	High
			Lung cancer		95/176	39	54	47	97	9	25
Méplan (2013) [16]	Denmark	Danish women	Breast cancer	TaqMan	939/960	319	335	438	430	182	195	High
Khadzhieva (2014) [42]	Russia	Russian women	Recurrent miscarriage	PCR-RFLP	313/189	130	74	131	95	52	20	Moderate
Jablonska (2015) [17]	Poland	Polish women	Breast cancer	TaqMan	136/183	44	65	66 #	90 #	26	28	High
Peng (2016) [39]	China	Chinese Han women	Pre-eclampsia (PE)	TaqMan	1008/1386	333	402	497	661	178	323	Moderate
			Mild PE		158/1386	64	402	70	661	24	323
			Severe PE		850/1386	269	402	427	661	154	323
			Early onset PE		523/1386	181	402	253	661	89	323
			Late onset PE		485/1386	152	402	244	661	89	323
Xiao (2017) [23]	China	Han Chinese	Thyroid diseases	MassARRAY system	1022/898	318	300	704 *	598 *			Moderate
			Graves’ disease		675/898	213	300	462 *	598 *
			Hashimoto’s thyroiditis		347/898	105	300	242 *	598 *
da Rocha (2018) [24]	Brazil	South Brazilian adults	Alzheimer’s disease	TaqMan	103/108	28	34	49	42	25	29	Moderate
Wigner (2018) [25]	Poland	Adults	Depression	TaqMan	281/229	87	83	141	138	53	8	Moderate
Chen (2020) [38]	China	Chinese Han women	Pre-eclampsia (PE)	TaqMan	631/720	216	204	296	359	119	157	Moderate
			Mild PE		141/720	47	204	66	359	28	157
			Severe PE		490/720	169	204	230	359	91	157
			Early onset PE		249/720	94	204	112	359	43	157
			Late onset PE		382/720	122	204	184	359	76	157
Corredor (2020) [40]	Spain	Spanish	Hypertension	TaqMan	403/37	85	15	128	14	190	8	Moderate
Huang (2020) [22]	China	Han Chinese women	Endometriosis	TaqMan	90/130	33	22	38	72	19	36	Moderate
Mashkina (2020) [43]	Russia	Russian women	Pregnancy loss	PCR-RFLP	110/124	33	46	63	62	14	16	Moderate
Gusti (2021) [45]	Saudi Arabia	Saudi adult population	Type 2 diabetes mellitus	TaqMan	109/163	27	42	62	87	20	34	High
Synowiec (2021) [41]	Poland	Caucasian	Ischemic stroke	TaqMan	107/107	30	41	55	64	22	2	Moderate
Ściskalska (2022) [44]	Poland	Adults	Acute pancreatitis	PCR-RFLP	39/51	9	16	19	18	11	17	High
Wigner (2022) [26]	Poland	Native Polish adults	Multiple sclerosis	Real-time PCR	142/140	39	57	72	65	31	18	High

^# values were calculated from CT+TT values reported in the study; * the values represents CT+TT.