Questioning the causality of HTT CAG-repeat expansions in FTD/ALS You can't judge a frontal dementia by its cover Response to Dewan et al., short HTT CAG-repeat expansions cause Huntington's disease with frontotemporal dementia-like phenotype. Dear Madam, Sir, We read the article written by Dewan and collaborators entitled "Pathogenic Huntingtin Repeat Expansions in Patients with Frontotemporal Dementia and Amyotrophic Lateral Sclerosis" published in Neuron (Dewan et al., 2020) with great interest. In this work, the authors report whole-genome analyses in 4 different large cohorts of i) 2,442 patients diagnosed with frontotemporal dementia (FTD) and/or amyotrophic lateral sclerosis (ALS), ii) 2,599 patients diagnosed with Lewy body dementia (LBD), iii) 3,158 neurologically healthy individuals and iv) 3,674 individuals diagnosed with FTD/ALS from an additional independent "replication" cohort. They identified a total of 8 individuals carrying pathogenic HTT CAG-expansion repeats, 3 in the initial FTD/ALS cohort and 5 more in the independent "replication" cohort, but none in either the LBD cohort or among healthy controls. They showed that this overall 0.13% carrier rate (8/6,116) is 4.4 times higher than