Updated project metadata. Prader-Willi syndrome (PWS) is a multisystem disorder caused by loss of expression of a cluster of paternally-expressed, imprinted genes. Neonatal failure to thrive is followed by childhood-onset hyperphagia, obesity, neurobehavioral abnormalities, and hormonal deficits. Prior evidence from a mouse model with a deletion of the orthologous PWS-domain identified abnormal pancreatic islet development with deficient insulin secretion, hypoglucagonemia, and postnatal onset of progressive, lethal hypoglycemia. To investigate PWS-genes in β-cell secretory function, we used CRISPR/Cas9 genome-editing to generate isogenic, clonal INS-1 insulinoma lines with 3.16 Mb deletions of the silent, maternal (control) or active, paternal (PWS) alleles. A significant reduction in basal and glucose-stimulated insulin secretion signifies a cell autonomous insulin secretion deficit in PWS β-cells. Parallel proteome and transcriptome studies revealed reduced levels of secreted peptides and for eleven endoplasmic reticulum (ER) chaperones, including HSPA5 and HSP90B1. In contrast to dosage compensation previously seen for ER chaperones in Hspa5 or Hsp90b1 gene knockouts, compensation is precluded by the widespread deficiency of ER chaperones in PWS cells. Remarkably, but consistent with reduced ER chaperone levels, PWS β-cells are more sensitive to ER stress activation of all three regulatory pathways (XBP1, eIF2α-P, ATF6-N). Therefore, a coordinated, chronic deficit of ER chaperones in PWS β-cells is hypothesized to lead to a delay in ER transit and/or folding of insulin and other cargo along the secretory pathway. These findings provide insight into the pathophysiological basis of hormone deficits in PWS and indicate key roles for PWS-imprinted genes in β-cell secretory function.