Longitudinal Brain Atrophy Rates in Presymptomatic Carriers of Genetic Frontotemporal Dementia.

ABSTRACT

BACKGROUND AND OBJECTIVES: It is important to identify at what age brain atrophy rates in genetic frontotemporal dementia (FTD) start to accelerate and deviate from normal aging effects to find the optimal starting point for treatment. We investigated longitudinal brain atrophy rates in the presymptomatic stage of genetic FTD, using normative brain volumetry software. METHODS: Presymptomatic GRN, MAPT, and C9orf72 pathogenic variant carriers underwent longitudinal volumetric T1-weighted magnetic resonance imaging of the brain as part of a prospective cohort study. Images were automatically analyzed with Quantib® ND which consisted of volume measurements (CSF and sum of gray and white matter) of lobes, cerebellum, and hippocampus. All volumes were compared to reference centile curves based on a large population-derived sample of non-demented individuals (n=4951). Mixed-effects models were fitted to analyze atrophy rates of the different gene groups as a function of age. RESULTS: 34 GRN, eight MAPT, and 14 C9orf72 pathogenic variant carriers were included (mean age=52.1, standard deviation=7.2; 66% female). Mean follow-up duration of the study was 64±33 months (median=52; range 13-108). GRN pathogenic variant carriers showed faster decline than the reference centile curves for all brain areas, though relative volumes remained between 5th and 75th percentile between the ages of 45-70. In MAPT pathogenic variant carriers, frontal lobe volume was already at the 5th percentile at age 45, and showed further decline between the ages 50-60. Temporal lobe volume started in the 50th percentile at age 45, but showed fastest decline over time compared to other brain structures. Frontal, temporal, parietal and cerebellar volume already started below the 5th percentile compared to the reference centile curves at age 45 for C9orf72 pathogenic variant carriers, but there was minimal decline over time until the age of 60. DISCUSSION: We provide evidence for longitudinal brain atrophy in the presymptomatic stage of genetic FTD. The affected brain areas and the age after which atrophy rates start to accelerate and diverge from normal aging slopes differed between gene groups. These results highlight the value of normative volumetry software for disease-tracking and staging biomarkers in genetic FTD. These techniques could help in identifying the optimal time window for starting treatment and monitoring treatment response.