While calpain has been proposed to participate in various disorders related to abnormal protein folding, including Alzheimer’s disease (Nixon, 2003), Parkinson’s disease (Samantaray et al., 2008), and Huntington’s disease (Lee and Kim, 2006), the specific roles of calpain-1 in these disorders have rarely been addressed. Here, CAPN1 is linked to Huntington disease.