Papillon-Lefevre syndrome (PLS) is a rare condition that causes psoriasiform hyperkeratosis of the palms and soles (palmar-plantar hyperkeratosis) in association with intense gingivitis with alveolar bone lysis and early loss of baby teeth. It is caused by mutations in the CTSC gene, which encodes a cysteine lysosomal protease belonging to the papain family, called dipeptidyl peptidase I.