DNMT1 and narcolepsy: So far mutations in DNMT1 have been reported to cause two distinct neurological syndromes: hereditary sensory and autonomic neuropathy type IE with dementia and deafness (HSAN1E) related to mutations in exon 20 and autosomal dominant cerebellar ataxia, deafness and narcolepsy (ADCA-DN) with hearing loss and narcolepsy related to mutations in exon 21 [1].