Genetics of essential tremor: From phenotype to genes, insights from both human and mouse studies

Essential tremor (ET) is a prevalent neurological disorder of unknown etiology characterized by the presence of an action tremor that occurs during voluntary motion and affects primarily the upper limbs. The worldwide prevalence of the disease in the general population is 0.9%, increasing to 4.6% in individuals ≥65 years old. Standard pharmaceutical treatments are only moderately effective, reducing tremor amplitudes in ∼50% of patients, a phenomenon partly explained by the fact that the diagnosis of ET is based solely on clinical findings rather than biological markers. Furthermore, the pathophysiological origin of ET remains controversial, leading to heated debates as to whether it should be considered a neurodegenerative disorder or as a dynamic oscillatory disturbances of neurologic origin. Progress has been made in the understanding of its etiology as it is now accepted that genetic components must at least explain the familial cases of ET, and the evidence implicating the olivocerebellar and cerebello-thalamo-cortical pathways is strong. However, a strong disconnection between human genetics, pathophysiological, and mouse genetics studies exists in the field of ET, with little use of all the knowledge gathered from the different research disciplines. This review highlights our current knowledge on ET from both a human population and mouse genetics perspective hoping to reconcile evidence from both fields and leading to novel clues guiding future studies. We argue that better communication between researchers of different fields is warranted to define the biological origin of ET in the hope of leading to the development of better treatments.