In our first published study [11], we reported that Down’s syndrome patients diagnosed with periodontal disease and implant failure showed alterations in the gene expression (downregulation) of MT1B, MT1F, MT1X, MT1H, MT1M, MT1L, MT1E, MT2A, and MT1G isoforms, confirming the hypothesis that the MT1G isoforms are not functional, and the alternative hypothesis that MTs are expressed differently when comparing Down’s syndrome patients with periodontal disease and dental implant failure to those without periodontal disease and with a positive progression of their implants after two years. This evidence concerns the gene MT1X and Down syndrome.