MTHFR and systemic lupus erythematosus: Individuals who are homozygous for the wild-type C allele have normal enzyme activity, whereas heterozygotes retain 65% of wild-type MTHFR enzymatic activity.35 The data in relation to periodontitis confirm our results previously found22 and in relation to SLE are consistent with Salimi, et al.44 (2017) that found no association too.