C9 and amyotrophic lateral sclerosis: Given that C9ORF72 (C9) repeat expansions are the most common genetic cause of ALS and frontotemporal dementia [12], we decided to investigate the characteristics and function of brain microvascular endothelial cells (BMEC-like cells) using 5 different C9-ALS patient-derived pluripotent stem cell lines (hi-PSCs).