LINGO1 and AL amyloidosis: In order to understand whether the mutation frequency profile for scFvWFL was specific for this scFv sequence, or simply reflected innate frustration of the Ig-fold itself, we performed the same directed evolution screen on two other IgG scaffolds: a second industrially-derived scaffold (a scFv variant of the anti-LINGO-1 mAb, Li3342) and a λV6-57 VL domain (JTO) isolated from a patient with multiple myeloma with tubular cast nephropathy43 (Supplementary Figs. 9a and b).