Concurrent fibrinogen Aα-chain amyloidosis and AA amyloidosis in a Humboldt penguin (Spheniscus humboldti)

Amyloidosis is a disease characterized by the deposition of abnormally folded proteins as amyloid fibrils in tissues and occurs in various mammals and birds. In some cases, amyloids derived from two different precursor proteins may coexist in the same individual, a condition known as double amyloidosis. Amyloid A (AA) amyloidosis is known to occur frequently in birds; however, little is known about other types of amyloidosis. In the present study, we report a case of amyloidosis in a Humboldt penguin involving two distinct types of amyloids. Histopathological examination, transmission electron microscopy, mass spectrometry-based proteomic analysis, and immunohistochemistry revealed the concurrent occurrence of fibrinogen Aα-chain (FibA) amyloidosis and AA amyloidosis. FibA-derived and AA amyloid deposits exhibited distinct nodular and diffuse morphologies, respectively, suggesting that their deposition patterns may provide a morphological clue for distinguishing between the two types of amyloids. To our knowledge, this is the first case of FibA amyloidosis in a penguin and the first report of the concurrent occurrence of two distinct types of systemic amyloidosis in a bird.