Next, mass spectrometry was used to assess changes in the cellular proteome and all secreted peptides in PWS vs. control INS-1 cell lines, under insulin secretion conditions of 22 mM glucose, separating cellular proteins by methanol-acetic acid extraction into soluble (mostly small) and insoluble (mostly large) protein fractions with the latter analyzed by quantitative proteomics (Fig 3A). Here, INS is linked to Prader-Willi syndrome.