PSEN2 and histiocytic sarcoma: Furthermore, mice models such as Psen1–/Psen2–, Psen1–, and Ncstn+/– mice show follicular keratinization, cyst formation, epidermal hyperplasia, follicular atrophy, and/or absent sebaceous glands, which recapitulate the histological features of HS in humans (33, 34).