Synthetic substrates, Ala‐Ala‐Pro‐ and Gly‐Ala‐Pro‐p‐nitroanilide, are used for the assay of PTP‐A, and it has been proposed that PTP‐A is involved in the degradation of type I collagen in connection with periodontitis inflammation (Ito et al., 2006). This evidence concerns the gene PTPA and periodontitis.