Hummingbird sign in a patient with DNMT1-related disorder

A 63-year-old woman presented with gait disturbance, progressive hearing loss, and sensory dominant polyneuropathy. Brain MRI mainly revealed midbrain tegmental atrophy (hummingbird sign). Genetic testing identified a heterozygous DNMT1 exon 21 mutation, previously linked to autosomal dominant cerebellar ataxia, deafness, and narcolepsy (ADCA-DN), although her clinical presentation resembled hereditary sensory and autonomic neuropathy type 1E (HSAN1E). A review of previously published cases with the same mutation revealed variability in sensory involvement, cerebellar signs, and sleep disorders, supporting the existence of a wide disease spectrum of DNMT1-related disorders. This case illustrates the phenotypic and radiological overlap within DNMT1-related disorders and supports the concept of a disease spectrum, rather than discrete syndromes, highlighting the diagnostic value of combining neuroimaging with genetic analysis.