USP8 and neoplasm: Overexpression of the USP8 P681Q variant that we had found in our patient in murine corticotroph tumor cells caused an increase in POMC mRNA expression which was comparable to the USP8 hotspot S718P mutation (USP8 P618Q vs. USP8 S718P fold change: 1.26 ± 0.014 vs. 1.31 ± 0.11, Fig. 3A).