PRL and amenorrhea: While hyperprolactinemia, marked by chronically elevated PRL levels, is more widely recognized and has been extensively investigated due to its association with clear clinical manifestations (i.e. galactorrhea and oligo/amenorrhea in women, erectile dysfunction in men, loss of libido and infertility in both sexes), hypoprolactinemia, which is characterized by abnormally low or undetectable PRL levels, remains often overlooked and poorly understood like an endocrine Cinderella [37, 40].