TBK1-Associated Primary Lateral Sclerosis Followed by Right Temporal Variant Frontotemporal Dementia

We report a 58-year-old woman with a novel splice-site variant in the TANK-binding kinase 1 (TBK1:c.993-2A>C p.Ala332TyrfsTer39) who sequentially developed primary lateral sclerosis (PLS) followed by right temporal variant frontotemporal dementia (rtvFTD). Neuroimaging demonstrated right anterior temporal atrophy before cognitive symptoms, and prosopagnosia represented the earliest manifestation of rtvFTD. Molecular analysis revealed reduced levels of correctly spliced TBK1 transcripts, consistent with haploinsufficiency. Given the shared involvement of TDP-43 pathology in both PLS and rtvFTD, this case indicates TBK1 dysfunction as a fundamental genetic factor underlying the coexistence of these phenotypes, underscoring the clinical value of early neuroimaging and genetic evaluation.