Protein biomarkers for amyotrophic lateral sclerosis (ALS) in the CSF

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with no effective treatments and unclear pathogenic mechanisms. We have explored protein‐based biomarkers in the cerebrospinal fluid (CSF) of ALS patients, healthy controls, and neurologic disease mimics. CSF was collected using standardized protocols from a total of 250 subjects (80 sporadic ALS, 20 familial ALS, 90 healthy controls, 20 multiple sclerosis, 20 Alzheimer's disease, 10 upper motor neuron disease, and 10 lower motor neuron disease). For purposes of this study we generated 25 sample groups, each containing equal amounts of CSF pooled from 10 individuals within a specific subject type. Each sample group was controlled for age, gender, medication, and site of disease onset (for ALS patients). Liquid chromatography mass spectrometry (LC‐MS/MS) was performed on each sample group to identify proteins by mass peptide fingerprinting. We obtained semi‐quantitative data on 4,400 proteins, representing the most complete proteome analysis of the human CSF performed to date. Specific proteins were identified that exhibit alterations in ALS patients. Unsupervised cluster analysis distinguished and separated the sporadic ALS, familial ALS and various control subject groups. We noted proteins that were altered only in specific ALS age groups, suggesting different pathogenic mechanisms in different age populations. Sporadic and familial ALS sample groups were easily distinguished from pure upper or lower motor neuron disease subject groups. We also detected age‐associated changes in proteins within the healthy control population. These findings identified novel protein biomarkers for ALS and highlight biochemical pathways altered during ALS and potential therapeutic targets.