Huntington's disease is caused by a polyQ expansion in huntingtin (HTT) protein, a nucleo-cytoplasmic protein, which has been shown to participate in axonal transport and in calcium signaling regulation. The androgen receptor (AR), the CAG-polyQ repeat expansion of which causes SBMA, is a nuclear receptor, best known for its roles in male reproductive system. Ataxin-1, the protein related to SCA1, is involved in RNA processing and transcriptional repression. Atrophin-1, the causal protein in DRPLA, is a transcriptional co-repressor. Ataxin-3 is a ubiquitin editing enzyme and mediates the ubiquitinated proteins degradation. Ataxin-7 is a member of the STAGA acetyl-transferase co-activator complex and participates in transcription regulation.