A number sign (#) is used with this entry because of evidence that dystonia-deafness syndrome-1 (DDS1) is caused by heterozygous mutation in the beta-actin gene (ACTB; 102630) on chromosome 7p22.

Heterozygous mutation in the ACTB gene also causes Baraitser-Winter syndrome-1 (BRWS1; 243310), which may show phenotypic overlap with DDS1.

Dystonia-deafness syndrome-1 (DDS1) is an autosomal dominant neurologic disorder characterized by congenital or childhood onset of sensorineural deafness with later onset of progressive dystonia that often involves the bulbar region, resulting in dysarthria and dysphagia. Some affected individuals have dysmorphic features, skeletal anomalies, and/or mild developmental delay with impaired intellectual development. The disorder is associated with striatal abnormalities. The severity is variable: death from intractable dystonia in the second or third decades has been reported in some patients (Gearing et al., 2002; Conboy et al., 2017).

Gearing et al. (2002) reported the cases of male twins with the onset at age 12 years of rapidly progressive, dopa-unresponsive generalized dystonia. They found extensive neurologic involvement of the cortex and basal ganglia of a novel type suggesting that these identical twins suffered from a degenerative disorder not previously characterized. The dystonic manifestations in adolescence were heralded by early bulbar signs that suggested a widespread disorder. The twins were born with cleft lip and palate requiring multiple repairs. They were small for age, and their limbs were small in relation to the rest of their bodies. Skeletal abnormalities included high foreheads, hypoplastic scapulas, and externally rotated hips. By age 10 years, they began developing kyphoscoliosis and severe antecolis. Achalasia presented at age 2 years, requiring surgical repair in 1 twin. One twin developed spontaneous cataracts, aggravated later by trauma; by age 10 years, he was blind in 1 eye and had limited vision in the other. Vision in the other twin was not affected. Sensorineural hearing loss in both twins resulted in functional deafness by age 4 years, significantly affecting their speech development. Cognition was mildly subnormal but stable until the last few years. Genetic, metabolic, and imaging studies ruled out known causes of dystonia. Death occurred at ages 21 and 22 years.

Conboy et al. (2017) reported a 15-year-old boy, born of consanguineous Hutterite parents, who was noted to have sensorineural hearing loss at 8 months of age. He showed global developmental delay with mildly impaired intellectual development. He presented at 13 years of age with dystonia affecting the right upper limb that began about 2 years earlier. The dystonia progressed to involve the bulbar region, resulting in velopharyngeal insufficiency and dysphagia. He did not have dysmorphic features. Brain imaging showed T2-weighted hyperintensities in the caudate nuclei and basal ganglia. At age 15, he developed medically refractory dystonia, resulting in death.

Skogseid et al. (2018) reported a 23-year-old woman with adolescent-onset severe generalized dystonia and mutation in the ACTB gene. She had had hypotonia and swallowing difficulties in the neonatal period, and profound hearing loss was diagnosed at 2.5 years of age. She had slightly delayed psychomotor development with developmental stagnation at 10 years of age. At 12 to 13 years of age she developed a clumsy gait, and dystonic arm tremor appeared at 14 years of age, followed by axial dystonia. She needed a wheelchair from 16 years of age, and from age 17 years was mainly confined to bed. At 18 years of age she had severe constipation, weight loss, and swallowing difficulties. At 19 years of age, she had constant dystonia with axial predominance that was improved with an implanted device for pallidal stimulation. She had dysmorphic facial features including hypertelorism, broad nasal root, and flat malar region in infancy, which with age changed to long, prominent nose with thick nares and high nasal root. She had mild ptosis bilaterally, dysplastic simple ears, and high palate.

Freitas et al. (2020) reported a 52-year-old Brazilian woman with generalized dystonia and mutation in the ACTB gene. Left lower limb dystonia had onset at age 25 years and progressed to whole body dystonia by 47 years of age. She had progressive abnormal posture of the spine since onset of the dystonia, and scoliosis, which became severe, was detected 4 years after dystonia onset. She had a history of developmental delay and progressive bilateral sensorineural hearing loss since childhood. She developed focal epilepsy at 5 years of age. There was no facial dysmorphism.

Zavala et al. (2022) reported a 34-year-old Argentinian woman with DDS1 and mutation in the ACTB gene. She presented with writer's cramp at 24 years of age, followed by blepharospasm 9 years later. Progression to severe multifocal dystonia was rapid, with prominent cervical dystonia and right upper limb dystonia. Hearing loss was present at birth. Craniofacial abnormalities included retrognathia, wide nasal base, hypertelorism, wide mouth, high-arched eyebrows, and bilateral ptosis. Brain MRI was normal. Both her parents, her 2 sisters, and her niece had sensorineural hearing loss; dysmorphism was present in her mother and sister; and her mother had facial dystonia.

Neuropathologic Findings

The brains of the twins reported by Gearing et al. (2002) were macroscopically unremarkable. The most striking findings on microscopic examination were (1) eosinophilic, rod-like cytoplasmic inclusions in neocortical and thalamic neurons that were actin depolymerizing factor/cofilin-immunoreactive but only rarely actin-positive; and (2) abundant eosinophilic spherical structures in the striatum that were strongly actin- and actin depolarizing factor/cofilin-positive. Gearing et al. (2002) stated that aggregation of actin had not previously been reported as the predominant feature in any neurodegenerative disease. They suggested that this neuropathologic change associated with dystonia may represent a new degenerative mechanism involving actin. Since actin is a ubiquitous constituent of the cytoskeletal system the presence of congenital anomalies and developmental abnormalities may be explained by systemic involvement.

Skogseid et al. (2018) reported substantial benefit from an implanted neurostimulation device that targeted the posteroventral pallidum bilaterally in a woman with DDS1 and life-threatening constant generalized dystonia. The device was implanted at age 19 years. Four years postoperatively, she could walk with support and perform fine motor tasks with both hands. She had no dystonia at rest but had intermittent activation-induced dystonia in the neck, tongue, right arm, and left leg. Skogseid et al. (2018) noted that of the 7 patients reported to that time with DDS1 and the R183W mutation in the ACTB gene (102630.0001), the 4 who survived all received pallidal stimulation.

The heterozygous mutation in the ACTB gene that was identified in a patient with DDS1 by Conboy et al. (2017) occurred de novo.

In the monozygotic twins reported by Gearing et al. (2002), Procaccio et al. (2006) identified a heterozygous missense mutation in the ACTB gene (R183W; 102630.0001).

In a 15-year-old boy, born of consanguineous Hutterite parents, with DDS1, Conboy et al. (2017) identified a de novo heterozygous R183W mutation in the ACTB gene. The mutation, which was found by whole-exome sequencing and confirmed by Sanger sequencing, was not present in several public databases, including the Exome Sequencing Project and ExAC. Functional studies of the variant and studies of patient cells were not performed.

In a 22-year-old woman with DDS1, Skogseid et al. (2018) identified heterozygosity for the R183W mutation in the ACTB gene. The mutation was identified by whole-exome sequencing and confirmed with Sanger sequencing. Functional studies of the variant and studies of patient cells were not performed.

In a 52-year-old Brazilian woman with DDS1, Freitas et al. (2020) identified heterozygosity for the R183W mutation in the ACTB gene. The mutation was identified by whole-exome sequencing. Functional studies of the variant and studies of patient cells were not performed.

In a 34-year-old Argentinian woman with DDS1, Zavala et al. (2022) identified heterozygosity for the R183W mutation in the ACTB gene. The mutation was identified by whole-exome sequencing and confirmed by Sanger sequencing. Functional studies of the variant and studies of patient cells were not performed.