Essential tremor (ET): ET is a common neurologic movement disorder that becomes worse over time. It is characterized by a rhythmic back and forth movement of a body part of parts that a person cannot control. A tremor can either be postural or kinetic, or both. Postural means that when people try to hold one position, such as sitting or standing, they will have a tremor. A kinetic tremor is when a person tries to do a specific action, such as reaching a hand out towards an object, they will experience the tremor. ET can affect the hands or head commonly, less commonly, the voice, tongue or roof of mouth. The cause of ET is not known, and it can either occur randomly or be passed down from one generation to the next as an autosomal dominant trait.