GNAS and growth hormone-producing pituitary gland neoplasm: GNAS1 activating mutations (gsp mutations) are found in approximately 40% of sporadic somatotropinomas [6], commonly found in codons 201 and 227, and are thought to be associated with smaller, densely granulated somatotropinomas that present higher GH secretion and higher somatostatin receptor subtype 2 (SST2) expression; however, this phenotype has not been clearly defined [7,8,9,10,11].