C9orf72 and frontotemporal dementia: However, the hexanucleotide repeat expansion (HRE, greater than 30 repeats) causes FTLD (frontotemporal lobar degeneration), FTD−ALS (frontotemporal dementia–amyotrophic lateral sclerosis), and ALS [1–2] likely due to toxicity of the transcribed repeat, toxicity of protein dipeptides translated from the transcribed repeat, or loss of function of C9ORF72 [1, 3–5].