In 2010, Pramanik R. et al. have performed a study on the presence of proteins, MUC5B and MUC7 in different areas of the oral cavity in patients with salivary hyposecretion, some of whom had pSS, concluding that "the surfaces of the oral mucosa in patients with xerostomia can retain MUC5B and other salivary proteins, although the functional integrity of these proteins is uncertain." Also these authors therefore hypothesize a qualitative defect in the mucin (16). Here, MUC7 is linked to xerostomia.