Methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism and diabetic nephropathy susceptibility in patients with type 2 diabetes mellitus

Figures & data

Figure 1. (A) Schematic overview of the involvement of 5,10-methylenetetrahydrofolate reductase (MTHFR) in folate and homocystein metabolism, nucleotide synthesis and (re)methylation events. (B) Flow chart for study recruitment into the meta-analysis of the MTHFR C677T gene polymorphism and diabetic nephropathy relationship.

Table 1. General characteristics of the included studies in this meta-analysis.

					Case				Control
Author, Year	Ethnicity	Country	Genotyping methods	Source of control	TT	TC	CC	Total	TT	TC	CC	Total	HWE
Neugebauer, 1998	Asian	Japan	PCR-RFLP	Healthy	12	31	24	67	17	43	86	146	0.004
Odawara, 1999	Asian	Japan	PCR-RFLP	Hospital	26	65	52	143	25	68	38	131	0.579
Fujita, 1999	Asian	Japan	PCR-RFLP	Hospital	17	57	31	105	9	39	20	68	0.142
Blüthner, 1999	Caucasian	Germany, Poland	PCR-RFLP	Healthy	23	50	74	147	15	68	67	150	0.709
Shpichinetsky, 2000	Caucasian	Israel	PCR-RFLP	Hospital	10	22	23	55	6	16	21	43	0.317
Yang, 2001	Asian	China	PCR-RFLP	Healthy	23	27	17	67	8	28	26	62	0.914
Sun, 2001	Asian	China	PCR-RFLP	Healthy	8	20	11	39	31	16	10	57	0.008
Wang, 2001	Asian	China	PCR-RFLP	Healthy	28	34	20	82	12	36	37	85	0.503
Guo, 2002	Asian	China	PCR-RFLP	Healthy	22	19	12	53	5	11	12	28	0.392
Moczulski, 2003	Caucasian	Poland	PCR-RFLP	Hospital			45	121			75	159
Xu, 2003	Asian	China	PCR-RFLP	Healthy	21	33	15	69	7	25	20	52	0.853
Mao, 2004	Asian	China	PCR-RFLP	Healthy	6	20	14	40	3	18	26	47	0.961
Chen, 2004	Asian	China	PCR-RFLP	Healthy	14	21	6	41	5	9	21	35	0.038
Sun, 2004	Asian	China	PCR-RFLP	Healthy	26	53	45	124	22	34	74	130	0
Ksiazek, 2004	Caucasian	Poland	PCR-RFLP	Healthy	29	65	77	171	16	83	71	170	0.237
Yoshioka, 2004	Asian	Japan	PCR-RFLP	Hospital	6	13	21	40	29	107	71	207	0.261
Cao, 2005	Asian	China	PCR-RFLP	Hospital	14	20	6	40	26	18	3	47	0.961
Yue, 2006	Asian	China	PCR-RFLP	Healthy	34	55	23	112	2	11	17	30	0.903
Mtiraoui, 2007	Caucasian	Tunisia	PCR-RFLP	Healthy	62	135	163	360	36	94	270	400	0
Böger, 2007	Caucasian	Germany	PCR-RFLP	Hospital	32	219	188	439	15	69	64	148	0.566
Eroglu, 2007	Caucasian	Turkey	PCR-RFLP	Healthy	1	20	26	47	7	58	63	128	0.172
Maeda, 2008	Asian	Japan	PCR-RFLP	Hospital	5	6	14	25	10	51	26	87	0.046
Wen, 2008	Asian	China	PCR-RFLP	Healthy	23	50	22	95	5	25	27	57	0.816
Lin, 2009	Asian	China	PCR-RFLP	Hospital	47	36	56	139	24	22	93	139	0
Ukinc, 2009	Caucasian	Turkey	PCR-RFLP	Hospital	0	16	6	22	0	8	22	30	0.399
Nemr, 2010	Caucasian	Lebanon, Bahrain	PCR-RFLP	Hospital	78	162	236	476	41	186	410	637	0.002
Qian, 2010	Asian	China	PCR-RFLP	Hospital	22	35	15	72	22	63	42	127	0.845
Rahimi, 2010	Caucasian	Iran	PCR-RFLP	Hospital	17	63	60	140	2	26	45	73	0.438
Movva, 2011	Asian	India	PCR-RFLP	Healthy	0	30	106	136	0	9	91	100	0.637
Dai, 2012	Asian	China	PCR-RFLP	Healthy	12	26	22	60	2	27	31	60	0.177
El-Baz, 2012	African	Egypt	PCR-RFLP	Hospital	24	46	32	102	3	19	78	100	0.189
Sun, 2013a	Asian	China	PCR-RFLP	Healthy	30	123	75	228	6	42	30	78	0.094
Sun, 2013b	Asian	China	PCR-RFLP	Healthy	14	53	35	102	8	53	43	104	0.128

Notes: PCR–RFLP: polymerase chain reaction-restriction fragment length polymorphism; HWE: Hardy–Weinberg equilibrium.

Figure 2. Association between T allele and diabetic nephropathy risk in the overall population.

Figure 3. Association of TT genotype with diabetic nephropathy risk in the overall population.

Figure 4. Association of CC genotype with diabetic nephropathy risk in the overall population.

Table 2. Meta-analysis of the association of MTHFR C677T gene polymorphism with diabetic nephropathy risk.

Genetic contrasts	Group and subgroups	Studies number	Q test p value	Model selected	OR (95% CI)	p
T versus C	Overall	32	<0.00001	Random	1.57 (1.31, 1.88)	<0.00001
	Asian	22	<0.00001	Random	1.55 (1.23, 1.95)	0.0002
	Caucasian	9	<0.00001	Random	1.41 (1.07, 1.86)	0.02
	African	1	–	Fixed	5.98 (3.62, 9.88)	<0.00001
TT versus CT + CC	Overall	32	<0.00001	Random	1.84 (1.43, 2.37)	<0.00001
	Asian	22	<0.0001	Random	1.80 (1.31, 2.47)	0.0003
	Caucasian	9	0.01	Random	1.73 (1.15, 2.60)	0.008
	African	1	–	Fixed	9.95 (2.89, 34.27)	0.0003
CC versus CT + TT	Overall	33	<0.00001	Random	0.60 (0.48, 0.74)	<0.00001
	Asian	22	<0.00001	Random	0.60 (0.44, 0.80)	0.0006
	Caucasian	10	<0.00001	Random	0.70 (0.04, 0.96)	0.03
	African	1	–	Fixed	0.13 (0.07, 0.24)	<0.00001
Sensitivity analysis according to HWE
T versus C	Overall	23	<0.00001	Random	1.57 (1.25, 1.97)	<0.0001
	Asian	15	<0.00001	Random	3.65 (1.23, 2.07)	0.0005
	Caucasian	7	0.01	Random	1.20 (0.92, 1.57)	0.18
	African	1	–	Fixed	5.98 (3.62, 9.88)	<0.00001
TT versus CT + CC	Overall	23	0.0002	Random	1.95 (1.41, 2.70)	<0.0001
	Asian	15	0.005	Random	2.03 (1.38, 2.98)	0.0003
	Caucasian	7	0.08	Random	1.40 (0.82, 2.39)	0.22
	African	1	–	Fixed	9.95 (2.89, 34.27)	0.0003
CC versus CT + TT	Overall	23	<0.00001	Random	0.61 (0.45, 0.82)	0.001
	Asian	15	<0.0001	Random	0.60 (0.43, 0.84)	0.003
	Caucasian	7	0.005	Random	0.83 (0.57, 1.21)	0.34
	African	1	–	Fixed	0.13 (0.07, 0.24)	<0.00001
Sensitivity analysis according the control source from healthy
T versus C	Overall	20	<0.00001	Random	1.81 (1.43, 2.28)	<0.00001
	Asian	15	<0.00001	Random	1.88 (1.48, 2.38)	<0.00001
	Caucasian	4	<0.0001	Random	1.20 (0.75, 1.92)	0.45
TT versus CT + CC	Overall	20	0.0007	Random	2.18 (1.57, 3.02)	<0.00001
	Asian	15	0.001	Random	2.20 (1.44, 3.38)	0.0003
	Caucasian	4	0.46	Fixed	1.87 (1.36, 2.56)	<0.0001
CC versus CT + TT	Overall	20	<0.00001	Random	0.49 (0.37, 0.66)	<0.00001
	Asian	15	0.02	Random	0.45 (0.35, 0.59)	<0.00001
	Caucasian	4	<0.00001	Fixed	0.90 (0.46, 1.77)	0.76
Sensitivity analysis according the control source from hospital
T versus C	Overall	13	<0.00001	Random	1.41 (1.02, 1.96)	0.04
	Asian	7	<0.00001	Random	1.02 (0.66, 1.58)	0.91
	Caucasian	5	0.0003	Random	1.62 (1.09, 2.43)	0.02
	African	1	–	Fixed	5.98 (3.62, 9.88)	<0.00001
TT versus CT + CC	Overall	13	<0.00001	Random	1.62 (1.05, 2.49)	0.03
	Asian	7	0.03	Random	1.31 (0.83, 2.06)	0.25
	Caucasian	5	0.002	Random	1.77 (0.73, 4.28)	0.20
	African	1	–	Fixed	9.95 (2.89, 34.27)	0.0003
CC versus CT + TT	Overall	14	<0.00001	Random	0.70 (0.47, 1.02)	0.06
	Asian	7	<0.00001	Random	1.13 (0.60, 2.14)	0.70
	Caucasian	6	0.02	Random	0.60 (0.43, 0.84)	0.003
	African	1	–	Fixed	0.13 (0.07, 0.24)	<0.00001
Sensitivity analysis according to sample size of case (≥100)
T versus C	Overall	11	<0.00001	Random	1.64 (1.23, 2.19)	0.0007
	Asian	5	0.0001	Random	1.62 (1.04, 2.52)	0.03
	Caucasian	5	<0.00001	Random	1.35 (0.96, 1.90)	0.08
	African	1	–	Fixed	5.98 (3.62, 9.88)	<0.00001
TT versus CT + CC	Overall	11	0.001	Random	1.82 (1.29, 2.57)	0.0007
	Asian	5	0.13	Fixed	1.54 (1.12, 2.12)	0.008
	Caucasian	5	0.009	Random	1.75 (1.12, 2.75)	0.01
	African	1	–	Fixed	9.95 (2.89, 34.27)	0.0003
CC versus CT + TT	Overall	12	<0.00001	Random	0.59 (0.42, 0.82)	0.002
	Asian	5	0.0005	Random	0.56 (0.32, 0.98)	0.04
	Caucasian	5	<0.00001	Random	0.75 (0.52, 1.09)	0.13
	African	1	–	Fixed	0.13 (0.07, 0.24)	<0.00001
Sensitivity analysis according to sample size of case (<100)
T versus C	Overall	21	<0.00001	Random	1.53 (1.20, 1.96)	0.0007
	Asian	17	<0.00001	Random	1.53 (1.15, 2.01)	0.003
	Caucasian	4	0.01	Random	1.55 (0.87, 2.77)	0.14
TT versus CT + CC	Overall	21	0.0001	Random	1.87 (1.28, 2.73)	0.001
	Asian	17	<0.00001	Random	1.91 (1.27, 2.87)	0.002
	Caucasian	14	0.13	Fixed	1.76 (0.85, 3.64)	0.13
CC versus CT + TT	Overall	21	<0.00001	Random	0.60 (0.43, 0.82)	0.002
	Asian	17	<0.00001	Random	0.61 (0.42, 0.88)	0.008
	Caucasian	4	0.01	Random	0.56 (0.26, 1.18)	0.13

Note: HWE: Hardy–Weinberg equilibrium.

Figure 5. Association between T allele and diabetic nephropathy risk in Asians.

Figure 6. Association between TT genotype and diabetic nephropathy risk in Asians.

Figure 7. Association between CC genotype and diabetic nephropathy risk in Asians.

Figure 8. Begg’s funnel plots with pseudo 95% confidence limits. Evaluation of publication bias for the association of MTHFR C677T gene polymorphism with diabetic nephropathy risk in the overall population (A), Asians (B) and Caucasians (C).