fig1

Figure 1. The figure summarizes the mechanisms possibly underlying the variable age at onset and clinical expression of idiopathic adult-onset focal dystonia. The genetic abnormality (Tracks 1 and 2) causes neurophysiologic changes lowering the threshold for disease susceptibility that tends to worsen over time. Age- and site-specific environmental factors capable of acting on dystonia-related mechanisms may thus trigger specific focal dystonias with variable age at onset (Track 1). It is also speculated that further deterioration of dystonia-related mechanisms by aging would worsen motor symptoms over time in blepharospasm and possibly make patients with adult-onset idiopathic dystonia more susceptible to spread of dystonia (Track 1). Subjects who carry the genetic mutation but are not exposed to any environmental factor affecting the neurophysiological mechanisms of dystonia do not manifest the clinical disease (Track 2). Environmental factors do not trigger dystonia in subjects who do not carry the genetic abnormality (Track 3) and have normal dystonia-related mechanisms. In healthy subjects, changes in dystonia-related mechanisms by aging do not approach the threshold for disease susceptibility.