Huntington disease (HD) is an autosomal dominant, monogenic neurodegenerative disorder.Huntington’s disease is caused by a trinucleotide repeat expansion of CAG in IT15 gene at locus 4p16.3.The purpose of this study was to identify the relationship between CAG repeat length and the progression of Huntington’s disease. It is commonly reported that CAG repeat length is related to the age of onset of the disease. MRI measurements of early onset patients revealed the most rapid rates of atrophy and cognitive decline compared with those who developed symptoms during middle age or more advanced age. Further analysis suggested that patients with long repeat lengths (≥47) had an earlier age of onset and that the younger group of patients displayed significantly increased decline in both cognitive and neurologic functioning over the 2-year interval period of follow up than those with shorter repeats. These findings suggest that the CAG repeat length may influence or trigger the onset of HD but other factors might contribute to the progression of illness and the pace of neuronal degeneration.
