The cathepsin C gene (CTSC) encodes a cysteine lysosomal protease belonging to the papain family, called dipeptidyl peptidase I. The enzymatic function of this protease is the removal of amino terminal dipeptides of the protein substrate. Mutations in the CTSC gene have been implicated in Papillon Lefevre syndrome (PLS), an autosomal recessive disorder characterised by palmoplantar hyperkeratosis and early onset periodontitis.