However, more study is required to obtain an optimal number of codon pairs or rare codons to be replaced in order to obtain an optimal level of gene expression, which is required to maintain the normal physiological functions of the ACE2, BMAL1, CD147, FURIN, and TMPRSS2 genes so that the pathological consequences of SARS-CoV-2 infection and periodontitis may be avoided. The gene discussed is ACE2; the disease is periodontitis.