AbstractHyperinsulinemia is the earliest symptom of insulin resistance (IR), but a causal relationship between the two remains to be established. Here we show that a protein kinase D2 (PRKD2) nonsense mutation (K410X) in two rhesus monkeys with extreme hyperinsulinemia along with IR and metabolic defects by using extreme phenotype sampling and deep sequencing analyses. This mutation reduces PRKD2 at both the mRNA and the protein levels. Taking advantage of a PRKD2-KO mouse model, we demonstrate that PRKD2 deletion triggers hyperinsulinemia which precedes to IR and metabolic disorders in the PRKD2 ablation mice. PRKD2 deficiency promotes β-cell insulin secretion by increasing the expression and activity of L-type Ca²⁺ channels and subsequently augmenting high glucose- and membrane depolarization-induced Ca²⁺ influx. Altogether, these results indicate that down-regulation of PRKD2 is involved in the pathogenesis of hyperinsulinemia which, in turn, results in IR and metabolic disorders.