Hyperprolactinemia can be explained by (a) pituitary stalk compression due to pituitary thyrotrophic hyperplasia, disruption of hypothalamic inhibition, and/or (b) thyrotropin-releasing hormone (TRH)-related hyperprolactinemia with a progressive reduction in hypothalamic gonadotropin-releasing hormone (GnRH) pulse frequency. This evidence concerns the gene TRH and hyperprolactinemia.