C9orf72 and amyotrophic lateral sclerosis: For the most frequently mutated Mendelian ALS genes, antisense oligonucleotide-based therapies are being tested (ION363 for FUS-ALS),2 or early access programs are already available (Tofersen for SOD1-ALS).3 Despite a setback for the antisense oligonucleotide therapy against the C9orf72 hexanucleotide repeat expansion (HRE), new clinical trials for variant-specific antisense oligonucleotide therapies for C9orf72-ALS/frontotemporal dementia (FTD) are already recruiting patients (WVE-004 for C9orf72-ALS/FTD).