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Early-onset generalized limb-onset dystonia
Early onset torsion dystonia (EOTD) is a rare movement disorder characterized by involuntary, repetitive, sustained muscle contractions or postures involving one or more sites of the body.
- Dystonia musculorum deformans
- Early-onset generalized torsion dystonia
- Early-onset primary dystonia
- Early-onset torsion dystonia
- Idiopathic dystonia
- Idiopathic torsion dystonia
- Oppenheim dystonia
- Prevalence: 1-9 / 1 000 000
- Inheritance: Autosomal dominant
- Age of onset: Adolescent, Childhood, Adult
- ICD-10: G24.1
- OMIM: 128100 602554
- UMLS: C0013423 C1851945 C3888090
- MeSH: -
- GARD: 2027
- MedDRA: -
A US study estimated the prevalence at approximately 1 in 30,000. The estimated prevalence in the general population of Europe seems to be lower, ranging from 1 in 330,000 to 1 in 200,000, although precise figures are currently not available. The estimated prevalence in the Ashkenazi Jewish population is approximately five to ten times higher, due to a founder mutation.
Symptoms of EOTD typically develop first in an arm or leg in middle to late childhood. In approximately 30% of patients, the disease progresses to other body regions (generalized dystonia) within about five years. Distribution and severity of symptoms vary widely between affected individuals.
The majority of cases from various ethnic groups are caused by an autosomal dominantly inherited deletion of 3 bp (GAG) in the DYT1 gene on chromosome 9q34. This gene encodes a protein named torsinA, which is presumed to act as a chaperone protein associated with the endoplasmic reticulum and the nuclear envelope. It may interact with the dopamine transporter and participate in intracellular trafficking, although its precise function within the cell remains to be determined.
Molecular testing and genetic counseling are recommended for individuals with an age of onset below 26 years, and may also be considered in those with onset after 26 years who have a relative with typical early onset dystonia.
Management and treatment
Treatment options include botulinum toxin injections for focal symptoms, pharmacological therapy such as anticholinergics (most commonly trihexiphenydil) for generalized dystonia and surgical approaches such as deep brain stimulation of the internal globus pallidus or intrathecal baclofen application in severe cases.
All patients have normal cognitive function, and despite a high rate of generalization of the dystonia, 75% of patients are able to maintain ambulation and independence, and therefore a comparatively good quality of life, with modern treatment modalities.