Biomarkers in cerebrospinal fluid for amyotrophic lateral sclerosis phenotypes

OBJECTIVE: Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease involving both upper and lower motor neurons. The motor phenotypes of ALS are highly clinically heterogeneous, and the underlying mechanisms are poorly understood. METHODS: A comparative proteomic analysis was performed in the cerebrospinal fluid (CSF) of bulbar‐onset (BO) and spinal‐onset (SO) ALS patients and controls (n = 14). Five biomarker candidates were selected from a differentially regulated protein pool, and further validation was performed in a larger independent cohort (n = 92) using enzyme‐linked immunosorbent assay (ELISA). RESULTS: A total of 1732 CSF proteins were identified, and 78 differentially expressed proteins were found among BO‐ALS patients, SO‐ALS patients, and controls. Five promising biomarker candidates were selected for further validation, and lipopolysaccharide‐binding protein (LBP) and HLA class II histocompatibility antigen, DR alpha chain (HLA‐DRA) were validated. CSF LBP levels were increased in ALS patients compared with controls and higher in BO‐ALS versus SO‐ALS. The increased CSF LBP levels were correlated with the revised ALS Functional Scale (ALSFRS‐R) score. CSF HLA‐DRA levels were specifically elevated in BO‐ALS patients, and there was no significant difference between SO‐ALS patients and controls. Increased HLA‐DRA expression was correlated with decreased survival. INTERPRETATION: Our data shows that elevated CSF LBP is a good biomarker for ALS and correlates with clinical severity, and increased HLA‐DRA is a specific biomarker for BO‐ALS and may predict short survival. It also suggests that the microglial pathway and HLA‐II‐related adaptive immunity may be differentially involved in ALS phenotypes and may be new therapeutic targets for ALS.