Importantly, in addition to PERK, the other three kinases catalyze eIF2α phosphorylation, without the concomitant activation of the IRE1 and ATF6 pathways: protein kinase R (PKR), in response to viral infection; general control nonderepressible 2 kinase (GCN2), in response to amino acid starvation; and heme-regulated inhibitor kinase (HRI), in response to heme deficiency. The gene discussed is EIF2AK2; the disease is hyperinsulinemic hypoglycemia, familial, 4.