Conversely to more common neurodegenerative disorders, such as Alzheimer’s (AD) and Parkinson’s (PD) diseases, the cause of HD for all the patients is known: an aberrant expansion of the polymorphic trinucleotide sequence CAG (in the range of 37–121 repeats) at the N-terminus of the huntingtin (Htt) protein. Here, HTT is linked to Alzheimer disease.