Epidemiology and genetics of essential tremor.

Essential tremor (ET) is probably the most common movement disorder and is a common cause of social, physical, and psychological handicaps. Its etiology and pathogenesis are unknown. Phenomenologically, ET overlaps and is associated with other disorders of movement, such as parkinsonism and dystonia. There is large variation in the stated prevalence of ET as well as limited availability of epidemiologic studies. Prevalence variations reflect differences in the definition of ET and the methodologies of investigation. The familial and sporadic forms of ET are generally assumed to be similar. The familial form appears to have a narrow phenotype. Wide variation in the reported percentage of patients with positive family history reflects ascertainment and classification differences. Linkage of ET to two different chromosome locations has been reported.