ATXN1 and early-onset autosomal dominant Alzheimer disease: We previously reported a link between HTT IAs and an α-synucleinopathy called multisystem atrophy and the presence of expanded HTT CAG repeats in three patients with Parkinson’s disease, thus supporting a possible role of Htt on Parkinson’s disease aetiology.22 However, the association of the ATXN1 and ATXN2 with risk for Parkinson’s disease could be difficult to explain, although an association of ATXN2 and the ATXN1 CAG repeats with Alzheimer’s disease, frontotemporal dementia and amyotrophic lateral sclerosis has been described.24,32