Do primary adult-onset focal dystonias share aetiological factors?

To consider whether the various clinical types of primary late-onset dystonia have a common aetiological background, or are each distinct and separate entities, sharing only the clinical appearance of dystonia, we reviewed epidemiological, clinical, neurophysiological and imaging data reported in patients with different forms of primary late-onset dystonia. The epidemiological and clinical features that distinguished the various clinical types and suggest aetiological differences were prevalence, age of onset, sex preference, sensory tricks, and tendency to spread. Likewise, aetiological differences were also supported by the observation that environmental risk factors possibly triggering focal dystonias in predisposed subjects can differ from one form to the other. The fact that different forms of focal dystonia may coexist in the same individual as the result of spread nevertheless suggests that the various focal dystonias are related. Detailed examination of available familial and genetic data indicates that the different forms of primary late-onset dystonia share aetiological factors, most probably genetic. Neurophysiological and imaging studies have demonstrated a number of abnormalities in focal dystonias and some of these are shared by the different clinical types. The shared abnormality of sensorimotor integration (and cortical excitability) beyond the symptomatic body part identified in various clinical types and in unaffected relatives might reflect the genetic abnormality indicating the substrate on which the dystonia develops.