SIGMAR1 and Alzheimer disease: Thus, a postmortem study reported that Sig-1Rs were reduced in the hippocampus in Alzheimer's disease (AD)15 and Sig-1R levels were also decreased in specimens from patients with early Parkinson's disease.16 A recent study reported a mutation in Sig-1R in patients with juvenile amyotrophic lateral sclerosis (ALS),17 however little is so far known about the role of Sig-1R in HD.