Hypermethylation of IG-DMR at the DLK1/MEG3 locus is the reason for the loss of MEG3 that occurs only in gonadotroph adenomas, and no gene in the DLK1/MEG3 locus was significantly downregulated in somatotroph adenomas compared to other PitNETs [16, 30]. The gene discussed is DLK1; the disease is growth hormone secreting pituitary adenoma 1.