FBD is associated with a Stop to Arg mutation in the BRI2 gene, which generates the de novo created amyloid molecule ABri after processing by furin-like proteases. Antibodies raised versus the C-terminal residues of ABri, not-existing in normal individuals, (Ab 338) allowed further immunohistochemical characterization of the deposits and WB probing. Circulating ABri molecules consist of 34 amino acids, and harbor a Glu residue at the N-terminus. Furin-like cleavage of BRI2 in normal individuals results in the production of CTF23, a peptide comprising the 23 first residues of ABri.