Huntington disease is an autosomal dominant inherited neurodegenerative disease with a prevalence of 5-7:100,000 in the Central European population. The average age disease onset is 40 years; children and the elderly patients are rarely affected. The symptoms are mainly movement disorders that become choreatic over time, character changes that range from frequent depressive moods and mental deterioration in the beginning to dementia due to atrophy of the caudate nucleus and the putamen or cortex. The disease has an average duration of 15 years.
The disease is caused by a CAG triplet repeat expansion in exon 1 of the HTT gene. Normal subjects have alleles with 6-26 CAG repeats; Huntington disease always occurs from 40 repeats onward. There is a certain statistic correlation between repeat length and the age of onset. Due to the CAG repeat expansion, increased glutamine residues are incorporated into the huntingtin protein. This leads to an aggregation of the proteins and thus to a disturbance of the physiological processes in the nerve cells. The mechanism by which atrophy only occurs in certain areas of the brain is not yet fully understood. There is no causal treatment available; movement disorders and psychological changes can be treated symptomatically.
In patients who already show symptoms, the symptomatic genetic diagnosis serves to ensure the clinical suspected diagnosis or the differential diagnosis.
Predictive diagnostics involves the examination of healthy individuals considered at risk, usually first degree relatives of those affected. According to the German Genetic Diagnostics Act (GenDG), genetic counselling should be offered with every diagnostic genetic examination. According to the GenDG, predictive genetic diagnostics require genetic counselling before the examination and after the results are available (§10, paragraph 2 GenDG). According to the recommendations of professional associations, psychotherapeutic care should be available before, during and after the examination phase.
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