C9orf72 and Huntington disease: More than 40 REDs have been identified to date, including Huntington’s disease (HD), myotonic dystrophy type 1 (DM1), C9orf72-associated amyotrophic lateral sclerosis/frontotemporal dementia (ALS/FTD), and the FMR1 disorders, also known as the fragile X (FX)-related disorders (FXDs).