Hereditary essential tremor (ET) is an inherited movement disorder characterized by intentional involuntary tremor, mainly of the hands.
ET is the most frequent movement disorder with a prevalence of 2-4% and 80% of cases are thought to be hereditary ET (HET). HET is therefore not considered to be a rare disease.
The age of onset varies widely between childhood and adulthood, but two onset peaks are described around the 2nd and 6th decade. It is underdiagnosed and may be misdiagnosed as Parkinsonian, physiologic, dystonic or psychogenic tremor. The most consistent symptom is an involuntary, rhythmic tremor of the hands or arms, although the tremor can affect any body part. The tremor is mainly manifested during posture maintenance and action, but may occur during targeted movements and, rarely, at rest. Tremor is the major complaint of the patients, although a mild gait disturbance may also occur. Cognition, sensory system and life expectancy are not affected by this chronic disease. In around 70% of patients, the tremor temporarily improves after ingestion of small amounts of alcohol.
The causative genes for HET have not yet been detected, but three chromosomal loci have been linked to the disease (ETM 1-3) and a genome-wide association study has found particular alleles of the LINGO1 gene (15q24.3) to be a risk factor.
Diagnosis exclusively relies on clinical examination.
Treatment options include propranolol, primidone, gabapentin, topiramate, clonazepam and deep brain stimulation (DBS).
Treatment improves the symptoms but so far does not slow progression.
- Pr Günther DEUSCHL