Homozygous DNMT1 mutation caused lethality at embryonic stages [57] while conditional DNMT1 mutation in rodents led to cortical and hippocampal neurodegeneration, and reduced their volume and memory consolidation [58, 59, 60] DNMT1 mutation in human caused hereditary sensory neuropathy characterized by reduced cytosine DNA methylation level, hearing loss, neurodegeneration and dementia [61]. The gene discussed is DNMT1; the disease is hereditary sensory and autonomic neuropathy.