Mutation-specific neuropathologic signatures in MAPT-associated frontotemporal lobar degeneration.

Autosomal-dominant frontotemporal lobar degeneration with tau pathology (FTLD-tau) is caused by pathogenic variants in the MAPT gene. Although abnormal tau aggregation is a shared endpoint, MAPT mutations produce distinct cellular phenotypes and regional patterns of tau deposition, the mutation specificity and familial consistency of which remain poorly defined. We performed a systematic neuropathologic and transcriptomic analysis of brains from clinically characterized families carrying MAPT V337M, P301L, or L284L mutations. Multiple affected members per family were examined, with interfamily comparisons for P301L. Quantitative assessment of regional tau burden, cellular morphology, and co-pathologies revealed distinct, mutation-specific signatures. The V337M mutation was characterized by predominantly neuronal tau pathology with vesicular pretangles, scattered neurofibrillary tangles, and fine neurites, with minimal glial involvement. P301L exhibited prominent astrocytic tau pathology, including globular and proximal inclusions, accompanied by neuronal pretangles. L284L produced extensive oligodendroglial tau pathology with thick fibrillar coiled bodies in gray and white matter. Additional distinguishing features included hippocampal sclerosis and TDP-43 pathology in V337M; severe cortical neuronal loss and dentate fascia tau in P301L; and extensive white matter and brainstem tau, including ventral pontine neurons, in L284L. These morphologic profiles were conserved within families and, for P301L, across unrelated families. Transcriptomic analyses suggested mutation-linked expression changes concordant with cellular pathology. These findings define reproducible, mutation-specific neuropathologic and molecular signatures of MAPT-associated FTLD-tau, emphasizing the importance of genotype-driven stratification in studies of tauopathy pathogenesis.