PENK and Alzheimer disease: We also compared peptide levels in both diseases with those of controls and patients with amyotrophic lateral sclerosis (ALS) and Alzheimer’s disease (AD), which are neurodegenerative diseases characterized by lack (i.e. in the early stage) or low degree (i.e. in the middle-late stage) of striatal dysfunction/atrophy [11–13], to address the specificity of CSF PENK and PDYN-derived peptides as striatal atrophy/dysfunction markers.