PCSK1 and Prader-Willi syndrome: Interestingly, although both mRNA (Pcsk1) and protein levels of prohormone convertase PC1 were reduced in iPSC-derived neurons from PWS patients and in whole islets of inbred Snord116-deficient mice [23,60], neither PC1 protein nor Pcsk1 or Pcsk2 mRNA levels were changed in PWS INS-1 cell lines (S12E Fig).