Multiple clinical features of Huntington's disease correlate with mutant HTT gene CAG repeat lengths and neurodegeneration.

Huntington's disease (HD) is a fatal neurodegenerative disease caused by mutant HTT gene expansions of CAG triplet repeat numbers that are inherited in an autosomal dominant manner. HD patients display multiple clinical features that are correlated with HTT CAG repeat numbers that include age of disease onset, motor dysfunction, cognitive deficits, compromised daily living capacity, and brain neurodegeneration. It is important to understand the significant relationships of the multiple HD clinical deficits correlated with the number of mutant HTT CAG expansions that are the genetic basis for HD disabilities. Therefore, this review highlights the significant correlations of the HD clinical features of age of onset, motor and cognitive disabilities, decline in living capabilities, weight loss, risk of death, and brain neurodegeneration with respect to their associations with CAG repeat lengths of the HTT gene. Quantitative HTT gene expression patterns analyzed in normal adult human brain regions demonstrated its distribution in areas known to undergo neurodegeneration in HD, as well as in other brain regions. Future investigation of the relationships of the spectrum of clinical HD features with mutant HTT molecular mechanisms will be important to gain understanding of how mutant CAG expansions of the HTT gene result in the devastating disabilities of HD patients.