From a molecular perspective, genetic and epigenetic mechanisms also play a significant role; specific genetic mutations (such as mutations in the APP, PSEN1, PSEN2 genes in familial Alzheimer’s [42] or the HTT gene in Huntington’s disease [43]) and epigenetic factors such as changes in DNA methylation can influence the expression of disease-related genes [44]. The gene discussed is PSEN2; the disease is juvenile Huntington disease.