Isolated hypoprolactinemia: The rarest of the rare?

Isolated hypoprolactinemia (IHP) can be defined as the presence of consistently low serum levels of prolactin in the absence of other anterior pituitary hormone abnormalities. It is an extremely rare condition, and consequently incompletely understood and unrecognized. A recent study has reported the first cases of IHP caused by mutation in the PRL gene. There are also cases where the pathogenesis of IHP is likely secondary to an autoimmune response against the PRL-secreting cells. But most published cases are acquired and idiopathic. The best characterized function of PRL is to facilitate milk production in the puerperium. Analysis of the GTEX data repository, however, shows that PRL is the most abundantly expressed gene in the human pituitary, independently of gender and age, suggesting the presence of additional roles for PRL. Newer studies have indeed revealed a much larger spectrum of PRL functions and will likely uncover novel clinical phenotypes associated with severe PRL deficiency.