Familial tremor is described as a form of essential tremor. It is present in more than one individual in a family. It has a genetic component and is inherited in an autosomal dominant pattern. Variants in the LINGO1 (leucine-rich repeat and immunoglobulin domain-containing protein 1) gene have been found to be a predisposing factor for the disease, although the gene responsible for FT has yet to be identified .
The clinical features of FT and non-familial ET are almost identical, with the distinction of a negative family history of tremors in sporadic ET. It is further suggested that FT has an earlier age of onset than sporadic ET . Most cases of ET have an onset in middle age, and a minority occur in children and the elderly.
There is no single definition of ET, however, The Movement Disorder Society's Tremor Investigation Group states that in cases of ET, there should not be an underlying etiology . The presentation varies greatly between individuals .
The effects of the tremor are most prominent in the upper extremities and rarely affect the lower limbs. Patients may have difficulty carrying out motor tasks such as writing, holding objects and using tools or utensils. In addition, there may be involvement of muscle groups in the head, neck, and eyes. This gives rise to features such as head nodding and vocal tremor.
The amplitude and frequency of tremors vary but may be less prominent at rest. Some patients experience paroxysmal tremors. Although symmetry is a typical feature, a degree of asymmetry is not uncommon. Moreover, tremors are exacerbated by caffeine, heightened emotional states, hunger, certain drugs, and sleep deprivation. In contrast, tremors are alleviated by the ingestion of alcohol (this has been used in the diagnosis of ET) and sleep . The signs are progressive, usually over many years . ET that is diagnosed after the fifth decade of life, tends to progress more rapidly .
There is no specific diagnostic test for essential tremor and familial tremor, thus the diagnosis is often clinical. If there are atypical features, clinicians may carry out laboratory and imaging studies to exclude other causes of observed symptoms. These include measuring thyroid, renal and liver function, as well as electrolyte balance. Electromyography is not a routine procedure, although it may be useful.
Imaging techniques employed are computerized tomography (CT) scanning, which should be normal in cases of ET and FT, as well as magnetic resonance imaging (MRI), to rule out central nervous system lesions. Single photon emission CT (SPECT) can be used to accurately diagnose Parkinson's disease, as some cases of ET can be mistaken for the former . Ultrasound has also been used to help delineate causes of tremor. Further conditions to rule out are tremors due to alcohol withdrawal, caffeine, drugs, or anxiety.