Early studies utilizing ssNMR and IR spectroscopy by Landsbury and Griffin suggested that amylin 20-29 fibrils are composed of antiparallel β-sheet structures. These finding were later corroborated by Nielsen and coworkers who also employed ssNMR to investigate the structure of amylin 20-29 fibrils. The Landsbury-Griffin-Nielsen studies, however, have been contradicted by others, who suggest that amylin 20-29 fibrils can also form parallel β-sheet structures. Middleton and coworkers employed ssNMR and X-ray fiber diffraction to investigate amylin 20-29 fibrils. Their analysis of C cross-polarization MAS and RR ssNMR data revealed that amylin 20-29 can form both parallel and antiparallel β-sheet fibril polymorphs, despite electron micrographs of their fibril samples appearing morphologically homogeneous. Similarly, Song et al. published a recent cryo-EM study, which also suggests that amylin 20-29 fibrils can adopt parallel β-sheet structures.