Table 2.

Distribution of PD-1 rs2227981 C > T polymorphism genotype and allele

Study	Year	Case			Control			Case		Control		HWE
		CC	CT	TT	CC	CT	TT	T	C	T	C
Yin et al. [18]	2014	198	106	20	181	105	44	146	502	193	467	No
Savabkar et al. [23]	2013	50	66	6	89	70	7	78	166	84	248	Yes
Mojtahedi et al. [22]	2012	59	109	32	75	89	36	173	227	161	239	Yes
Haghshenas et al. [20]	2011	194	191	50	137	145	46	291	579	237	419	Yes
Hua et al. [21]	2011	295	169	22	244	210	24	213	759	258	698	Yes
Ivansson et al. [24]	2010	471	603	226	257	375	178	1055	1545	731	889	Yes
Dehaghani et al. [19]	2009	42	37	13	118	56	121	63	121	298	292	No