We will include all types of observational studies with human subjects that investigated the concentrations of intended biomarkers (amyloid beta (Aβ-42), tau and phosphorylated tau (p-Tau), neurofilaments, S100β, cystatin C, progranulin (PGRN), glial fibrillary acidic protein (GFAP), monocyte chemoattractant protein-1 (MCP-1), brain-derived neurotrophic factor (BDNF), TAR DNA-binding protein-43 (TDP43), YKL-40, and CHIT1 in CSF or peripheral blood of ALS patients for initial assessment. This evidence concerns the gene BDNF and amyotrophic lateral sclerosis.