Since the discovery of the C9orf72 repeat expansion, there have been numerous studies investigating tandem repeat DNA and structural variation in ALS (DeJesus-Hernandez et al., 2011; Renton et al., 2011; Blauw et al., 2012; Lattante et al., 2018; Tazelaar et al., 2019, 2020; Course et al., 2020; Al Khleifat et al., 2022). This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.