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 etiolo gy and pathogenesis are unknown. Phenomenologically, ET overlaps and is ass ociated with other disorders of movement, such as parkinsonism and dystonia . There is large variation in the stated prevalence of ET as well as limite d availability of epidemiologic studies. Prevalence variations reflect diff erences 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 re ported percentage of patients with positive family history reflects ascerta inment and classification differences. Linkage of ET to two different chrom osome locations has been reported.