A cerebral amyloid angiopathy characterized by onset in the 4th to 6th decade of life, progressive mental deterioration, spasticity, muscular rigidity but no tremors, spontaneous movements or sensory changes that has material basis in an autosomal dominant mutation of ITM2B on chromosome 13q14.2. The disease is Monarch Disease Ontology entry MONDO_0008306 (ABri amyloidosis). Also known as: FBD, cerebral amyloid angiopathy, British type, cerebral amyloid angiopathy, ITM2B-related, type 1, familial British dementia, familial dementia, British type, presenile dementia with spastic ataxia.