C9orf72 and Mental deterioration: Gene-specific cognitive decline during the presymptomatic period has been demonstrated by both cross-sectional and longitudinal studies.6,10,15, -, 26 For example, previous reports have shown decline in memory,17,19,20,26 language,17,20,23 and social cognition17,19,20 in MAPT pathogenic variant carriers, decline in attention15,16,19,20 and executive function15,16,18,20 in GRN pathogenic variant carriers, and a decline in social cognition in C9orf72 pathogenic variant carriers.22,24,25 However, other studies on genetic FTD failed to find these results.13,21,26,27