Kallikrein-4 (KLK4) is also known as Enamel matrix serine proteinase 1 (EMSP1), Kallikrein-like protein 1 (KLK-L1), Prostase, Serine protease 17 (PRSS17), PSTS, which belongs to the peptidase S1 family and Kallikrein subfamily. KLK4 contains one peptidase S1 domain. KLK4 is expressed in prostate and involved in enamel formation. Defects in Kallikrein-4 / KLK4 are the cause of amelogenesis imperfecta hypomaturation type 2A1 (AI2A1) which is an autosomal recessive defect of enamel formation. The disorder involves both primary and secondary dentitions.