Medical Definition of Huntington chorea
1.
An inherited adult-onset disease of the central nervous system.
It is characterised by dementia and bizarre involuntary movements. The disease is progressive and there is currently no known cure.
The identification of the gene (huntingtin) on chromosome 4p now allows for direct mutation analysis. The gene contains a trinucleotide repeat (CAG) that is found to be expanded in length in affected patients. The normal allele size ranges from 11 to 34 triplet repeat units, while 42 repeats or greater is considered diagnostic of Huntington disease.
As in other trinucleotide repeat disorders, the phenomenom of anticipation has been observed, in this case expressed as earlier age of onset in offspring, particularly with paternal transmission. A further complication is the presence of two neighboring trinucleotide repeats (both CCG) which can expand independently without causing the disease.
Early PCR primer sets encompassed these adjacent repeats, potentially yielding false positive test results, newer primers hone in more closely on the CAG repeat sequence.
Careful attention must be paid to the psychosocial support structure of prospective test subjects in Huntington disease genetic counseling. Established protocols require systematic neuropsychiatric assessment and informed consent prior to DNA testing.
Inheritance: autosomal dominant.
(29 Dec 1997)
Lexicographical Neighbors of Huntington Chorea
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