A polymorphism of the humanin gene with an incidence of 1–5% in individuals with African ancestry was shown to associate with lower plasma humanin levels and greater cognitive decline [17,109] Surprisingly, this SNP is common among individuals of European descent, with an incidence approaching 50%, and so far has not been associated with dementia, which must reflect the multifactorial nature of the condition. This evidence concerns the gene MT-RNR2 and dementia.