Which condition leads to an increased risk of amenorrhea due to high prolactin levels?

Pituitary tumors, particularly prolactin-secreting adenomas (also known as prolactinomas), lead to increased levels of prolactin in the bloodstream. Elevated prolactin can disrupt the normal regulation of the menstrual cycle by inhibiting the secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus. GnRH is essential for stimulating the pituitary gland to produce follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both of which are critical for ovulation and the maintenance of menstruation. As a result, women with high prolactin levels due to pituitary tumors often experience amenorrhea or irregular menstrual cycles.

In contrast, conditions such as Turner syndrome and Fragile X syndrome are genetic disorders that can lead to premature ovarian insufficiency and secondary amenorrhea, but they do not primarily involve hyperprolactinemia as a causative factor. Hyperthyroidism could potentially affect menstruation, but it is generally associated with a decrease in prolactin levels rather than an increase. Therefore, the link between pituitary tumors and elevated prolactin is the key factor that makes this answer the best choice regarding the risk of amenorrhea.