GLP‐1 together with glucose‐dependent insulinotropic peptide (GIP) are responsible for the incretin effect, ie, augmented insulinotropy in response to an ingested glucose load as opposed to an isoglycaemic intravenous glucose challenge.5 The incretin effect is reduced in type 2 diabetes.6 GLP‐1 is derived from the post‐translational processing of proglucagon in L‐cells and some brainstem neurones by prohormone convertase 1 (PC1). Here, PCSK1 is linked to type 2 diabetes mellitus.