Based on the clinical manifestations, PA could be classified into the following subtypes: prolactinomas (PRL, also known as prolactin-secreting PAs), clinically nonfunctioning pituitary adenomas (NFPAs), growth hormone (GH)–secreting adenomas, adrenocorticotropin hormone (ACTH)–secreting adenomas (also known as Cushing's disease), and thyroid-stimulating hormone (TSH)–secreting adenomas. This evidence concerns the gene GH1 and adenoma.