Finally, clinicians must be aware of drug-induced hyperprolactinemia (particularly with antipsychotics [20] and antiemetics [21]) and the presence of macroprolactin, a biologically inactive immune complex between prolactin and IgG [22] which is causative in approximately 10% of cases of hyperprolactinemia [23]. The gene discussed is PRL; the disease is hyperprolactinemia.