PDYN and early-onset autosomal dominant Alzheimer disease: Reduced CSF PDYN was recently reported in manHD patients compared with controls using targeted LC-MS.42 This study found that levels of PDYN were not decreased in other neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis, suggesting that changes of CSF PDYN may be unique to HD.42 We found PDYN to be significantly reduced in preHD (P = 0.004), early/mid HD (P = 0.012) and late HD (P = 0.0003) compared with controls.