Familial British dementia (FBD): a cerebral amyloidosis with systemic amyloid deposition

Introduction:  FBD is an autosomal dominant disease with neuropathological similarities to Alzheimer's disease (AD) as it is characterized by amyloid angiopathy, parenchymal amyloid plaque deposition and neurofibrillary degeneration. FBD is associated with a stop codon mutation in the BRI2 gene encoding a type II transmembrane protein, BriPP. Mutation results in an extended precursor protein, ABriPP, from which a C-terminal 34 amino acid peptide (ABri) is generated by furin-like proteolytic cleavage and deposited as amyloid and preamyloid in the central nervous system. Despite the morphological parallels with AD the sequences of the amyloidogenic peptides, ABri in FBD and Aβ in AD, are completely different. We examined systemic tissues in FBD for ABri deposition. Materials and methods:  Immunohistochemistry using an ABri-specific antibody, Ab338, counterstained with Thioflavin S and Ab338 immuno-electron microscopy identified ABri deposits and determined whether these were amyloid or preamyloid in nature. Results:  Amyloid bearing blood vessels stained positively for ABri in myocardium, uterus, bladder, spleen, pancreas, lung and skeletal muscle. ABri was also identified in either amyloid or preamyloid conformation in the parenchyma of myocardium, adrenal, pancreas and skeletal muscle. Conclusion:  This study demonstrates that FBD is the first described cerebral amyloidosis with neurofibrillary pathology and dementia to be accompanied by systemic amyloid deposition.