RPS6KB1 and Hypoinsulinemia: In vivo knock-in mouse models that harbor a non-phosphorylatable mutant of rpS6 showed small size, hypoinsulinemia, decreased beta cell size and muscle weakness—phenotypes similar to those of S6K1 knockout mice [64,65]—which is counterintuitive since S6K2 seems to be the primary kinase mediating rpS6 phosphorylation [64].