The 6 sequences, referred to as SAA1, SAA1 des Arg, SAA2-alpha, SAA2-alpha des Arg, SAA2-beta, and SAA2-beta des Arg, are resolved by electrofocusing into 6 isoforms. SAA1 is the product of one gene, while SAA2-alpha and SAA2-beta, which differ by only a single amino acid, represent allelic sequences of a second gene. Although the first reported AA protein corresponded to SAA2-beta, subsequent analyses showed that the vast majority of the protein isolated from amyloid deposits is derived from SAA1.

This gene product also represents the predominant SAA form isolated from or detected in the plasma of patients experiencing an acute phase response.