C9orf72 and frontotemporal dementia: Finally, we note that the calculation of [18F]AV‐1451 BPND data uses the superior cerebellar gray matter as a reference region, as in our other recent papers.5, 7, 9 Although across most of the genetic and sporadic forms of FTD this region remains unaffected, in previous cases with C9orf72 expansion, cerebellar atrophy and dipeptide aggregation have been described.21 In mitigation of this potential shortcoming, whilst as expected there was cerebellar gray matter atrophy in the present C9orf72, there was no observable elevated cerebellar [18F]AV‐1451 signal in the uncorrected PET BPND map.