Longitudinal cerebral perfusion in presymptomatic genetic frontotemporal dementia: GENFI results

Genetic frontotemporal dementia is most commonly attributable to mutations in the C9orf72, GRN, or MAPT genes. The disease has near-complete penetrance, making presymptomatic carriers an ideal population for ascertaining the earliest changes in disease progression and the identification of suitable biomarkers for designing therapeutic trials when minimal neuronal loss has occurred. Cerebral perfusion, as measured by arterial spin labelling (ASL) MRI, has shown promise in being one such biomarker. However, longitudinal profiles of change in perfusion over time in presymptomatic carriers across all three genetic subgroups are lacking.
Using data from the multicenter GENetic Frontotemporal dementia Initiative, we investigated longitudinal profiles of cerebral perfusion using ASL-MRI in C9orf72 (n = 42), GRN (n = 70), and MAPT (n = 31) presymptomatic mutation carriers and non-carrier controls (n = 158). ASL and T1w scans were processed with the ExploreASL pipeline to produce partial volume corrected perfusion images, which were parcellated to extract mean perfusion values from whole brain grey matter and regions defined by the second version of the automated anatomical atlas (AAL2). Linear mixed effects models were used to assess longitudinal perfusion change.
Mutation carrier groups and non-carriers were statistically indistinguishable by baseline demographic and clinical measures. Decline in whole brain grey matter perfusion over time was more pronounced in all three carrier subgroups relative to controls, with changes most pronounced in GRN, followed by C9orf72 and MAPT variants. Additionally, GRN and MAPT groups featured global grey matter hypoperfusion relative to non-carrier controls as early as one year after baseline measurement, with C9orf72 featuring significant hypoperfusion after two years. Region of interest analysis demonstrated that each genetic subgroup had its own regional profile in terms of longitudinal perfusion decline. Perfusion decline in C9orf72 was localized around the frontal lobe and subcortical structures with a slight right-hemispheric bias. GRN featured a more widespread perfusion decline, with notable asymmetry featuring a stronger left hemisphere involvement. Significant decline in perfusion in MAPT was limited to the thalamus, which was a region that was significant in all three mutation carrier groups. Cerebral blood flow relative to baseline measurements had declined to a greater extent in converter individuals versus presymptomatic carriers who were past their expected year of disease onset within specific frontal regions of the brain.
These results provide additional evidence that cerebral perfusion is a potential biomarker for assessment of genetic FTD and its genetic subgroups at the prodromal stage of the disease.