Table 1.

Descriptive characteristics of studies included in the current meta-analysis

Ethnicity	Country	Published in	References	Diagnosis of IDD	Group	Age (year, mean ± SD)	Size	FokI alleles		FokI genotypes			HWE
T	C	TT	TC	CC	Pvalue
Caucasian	Finland	2011	[17]	Pfirrmann classification	Case	NA	81	75	87	12	51	18	0.017
Control	NA	101	82	120	17	48	36	0.883
Caucasian	Denmark	2010	[18]	No classification guideline offered	Case	13.1 ± 0.4	66	46	86	9	28	29	0.593
Control	13.1 ± 0.4	154	120	188	23	74	57	0.898
Asian	China	2007	[20]	Schneiderman classification	Case	42.7	81	75	87	12	51	18	0.017
Control	38.2	101	82	120	17	48	36	0.883
Caucasian	Italy	2012	[16]	No classification guideline offered	Case	NA	234	153	135	24	105	105	0.764
Control	NA	70	54	86	9	36	25	0.476
Hispanic	Brazil	2014	[13]	Pfirrmann classification	Case	40.0 ± 5.4 (M); 40.2 ± 5.9 (F)	121	84	158	17	50	54	0.624
Control	33.8 ± 8.2 (M); 33.8 ± 8.1 (F)	131	66	196	10	46	75	0.737
Hispanic	Mexican	2014	[15]	No classification guideline offered	Case	39.22 ± 6.88	100	95	105	15	65	20	0.002
Control	39.13 ± 6.80	100	54	86	17	51	32	0.664
Caucasian	Italy	2014	[14]	No classification guideline offered	Case	40.08 ± 9.56	267	180	354	30	120	117	0.926
Control	44.19 ± 9.11	220	163	277	32	99	89	0.601
Caucasian	Turkey	2010	[19]	Schneiderman classification	Case	NA	99	65	133	13	39	47	0.288
Control	NA	51	21	81	4	13	34	0.282

Note: IDD was diagnosed with magnetic resonance imaging. The exact P value was calculated by χ2 test. IDD, intervertebral disk degeneration; M, male; F, female; NA, not available; HWE, Hardy–Weinberg equilibrium.