MUC1 and peeling skin syndrome: In 2019 Culp D.J. et al. have shown that, in patients with pSS, MUC1 is present in the deeper cells layers of the hard palate’s keratinized epithelium, unlike the non-keratinized epithelium of the lips, where MUC1 is present in the apical layers and much less in the basal ones.