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Spiral ganglion deficiency in adult-onset deafness-dystonia syndrome.

Deafness-dystonia syndromes are rare group of syndromes that present with deafness and dystonia as the dominant symptoms and are increasingly being recognized for their clinical and genetic heterogeneity (1). Most reported cases are due to X-linked deafness-dystonia-optic neuronopathy (DDON) or Mohr-Tranebjaerg syndrome (MTS); autosomal recessive Woodhouse-Sakati syndrome; succinate-coenzyme A (CoA) ligase, ADP-forming, b subunit (SUCLA2)-related mitochondrial DNA depletion syndrome; or organic acidurias (1). With respect to general phenotype, these individuals are characterized by pre- or post-lingual progressive auditory neuropathy (AN), dystonias that have a variable age of onset, association with optic atrophy in some cases (DDON in particular), and an association with psychosis, dementia and mental retardation in the more severe cases/syndromes (1,2). While previously most cases of deafness-dystonia syndrome have been associated with the onset of deafness in childhood, there is a small group of cases reporting onset of deafness at later ages into adulthood (1). Merchant and colleagues demonstrated the near-total loss of spiral ganglion neurons in patients with DDON despite an intact organ of Corti (3). Brookes and colleagues reported only marginal cochlear implant performance after 2 years in a child with DDON who underwent cochlear implantation (4). This patient exhibited continued poor scores in standardized speech, language, and audiometric tests and required higher than normal current for the most-comfortable-level implant setting (4). While the histopathology of this entity has been documented in patients with childhood-onset deafness, the histopathology of patients with deafness-dystonia syndrome who present with adult-onset deafness has not been previously reported.