Dystonia

Dystonic movements are typically patterned and repetitive, may be tremulous or jerky, and are frequently associated with overflow movements. Onset spans infancy through late adulthood, and the disorder is classified by age at onset, body distribution (focal, segmental, multifocal, hemidystonia, or generalised), and temporal pattern. Clinically, two principal categories are recognised: isolated dystonia, in which dystonia is the only presentation and which accounts for approximately 70% of all dystonia cases, and combined dystonia, in which dystonia is accompanied by other movement
disorders (such as myoclonus, tremor, or parkinsonism), additional neurologic features (such as
corticospinal signs or epilepsy), or systemic features (such as liver or kidney disease). Whereas gradual-onset focal or segmental dystonia is typical in adult-onset disease, fewer than half of childhood-onset presentations are isolated; dystonia in a child therefore warrants thorough assessment for combined forms.

The estimated prevalence is approximately 16.4 per 100,000 globally. Approximately 25% of affected individuals have a positive family history, and pathogenic variants in the 12 confirmed monogenic isolated-dystonia genes collectively account for less than 10% of isolated dystonia.

More than 50 genes are currently associated with dystonia. The genetic forms can be grouped into isolated and combined dystonia. The most common genetic cause is DYT-TOR1A (TOR1A, childhood-onset generalised dystonia). Isolated forms further include DYT-THAP1 (THAP1, adolescent-onset segmental or generalised dystonia), while combined forms include DYT/PARK-GCH1 (GCH1, levodopa-responsive, diurnally fluctuating dystonia) and myoclonus-dystonia (SGCE, dystonia combined with myoclonus).

The genetic conditions associated with dystonia follow heterogeneous inheritance patterns. Monogenic isolated dystonias are inherited in autosomal dominant or autosomal recessive patterns; the underlying inheritance mode is determined at the level of the identified gene.

• Where dystonia is suspected to have a genetic cause, molecular genetic testing can identify the underlying condition and confirm a clinical suspicion.
• The identified entity guides further clinical management and is a prerequisite for targeted medical care; therapeutic options are evaluated individually by the treating physicians.
• Identification of the underlying pathogenic germline variant enables predictive testing of at-risk family members and provides information relevant to family planning.

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