GDNF and colorectal carcinoma: Methylation frequencies for these genes differed between CRC and normal tissue (P < 0.0001 for all genes) with high methylation in CRC; SORCS1 (91.2%), SLC35F3 (88.2%), SNAP91 (85.3%), GDNF (76.5%) and HAND2 (73.5%) (Additional file 2: Figure S1).