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INTRODUCTION: Patients with familial early‐onset dementia (EOD) pose a unique opportunity for gene identification studies. METHODS: We present the phenotype and whole‐exome sequencing (WES) study of an autosomal dominant EOD family. Candidate genes were examined in a set of dementia cases and controls (n = 3712). Western blotting was conducted of the wild‐type and mutant protein of the final candidate. RESULTS: Age at disease onset was 60 years (range 56 to 63). The phenotype comprised mixed amnestic and behavioral features, and parkinsonism. Cerebrospinal fluid and plasma biomarkers, and a positron emission tomography amyloid study suggested Alzheimer's disease. WES and the segregation pattern pointed to a nonsense mutation in the TRIM25 gene (p.C168*), coding for an E3 ubiquitin ligase, which was absent in the cohorts studied. Protein studies supported a loss‐of‐function mechanism. DISCUSSION: This study supports a new physiopathological mechanism for brain amyloidosis. Furthermore, it extends the role of E3 ubiquitin ligases dysfunction in the development of neurodegenerative diseases. Highlights: A TRIM25 nonsense mutation (p.C168*) is associated with autosomal dominant early‐onset dementia and parkinsonism with biomarkers suggestive of Alzheimer's disease.TRIM25 protein studies support that the mutation exerts its effect through loss of function.TRIM25, an E3 ubiquitin ligase, is known for its role in the innate immune response but this is the first report of association with neurodegeneration.The role of TRIM25 dysfunction in development of amyloidosis and neurodegeneration merits a new line of research. [ABSTRACT FROM AUTHOR]

Introduction: Patients with familial early-onset dementia (EOD) pose a unique opportunity for gene identification studies., Methods: We present the phenotype and whole-exome sequencing (WES) study of an autosomal dominant EOD family. Candidate genes were examined in a set of dementia cases and controls (n = 3712). Western blotting was conducted of the wild-type and mutant protein of the final candidate., Results: Age at disease onset was 60 years (range 56 to 63). The phenotype comprised mixed amnestic and behavioral features, and parkinsonism. Cerebrospinal fluid and plasma biomarkers, and a positron emission tomography amyloid study suggested Alzheimer's disease. WES and the segregation pattern pointed to a nonsense mutation in the TRIM25 gene (p.C168*), coding for an E3 ubiquitin ligase, which was absent in the cohorts studied. Protein studies supported a loss-of-function mechanism., Discussion: This study supports a new physiopathological mechanism for brain amyloidosis. Furthermore, it extends the role of E3 ubiquitin ligases dysfunction in the development of neurodegenerative diseases., Highlights: A TRIM25 nonsense mutation (p.C168*) is associated with autosomal dominant early-onset dementia and parkinsonism with biomarkers suggestive of Alzheimer's disease. TRIM25 protein studies support that the mutation exerts its effect through loss of function. TRIM25, an E3 ubiquitin ligase, is known for its role in the innate immune response but this is the first report of association with neurodegeneration. The role of TRIM25 dysfunction in development of amyloidosis and neurodegeneration merits a new line of research., (© 2022 The Authors. Alzheimer's & Dementia published by Wiley Periodicals LLC on behalf of Alzheimer's Association.)