Detailed genetic studies of tissue-specific and cell-specific knockouts showed that diabetes is specifically caused by the loss of Perk expression in β cells [22], exocrine pancreas dysfunction by the loss of Perk expression in acinar cells [23], and skeletal dysplasia and osteopenia by the loss of Perk expression in osteoblasts [24]. The gene discussed is EIF2AK3; the disease is diabetes mellitus.