S-cysteinylation and S-sulfonation are the most common modifications in the blood and cerebrospinal fluid, which affect TTR stability and alter the propensity of TTR to form amyloid fibrils.

Reference
Pubmed: Duan G, Li Y, Ye M, Liu H, Wang N, Luo S. The Regulatory Mechanism of Transthyretin Irreversible Aggregation through Liquid-to-Solid Phase Transition. International journal of molecular sciences vol. 24,4 3729. 13 Feb. 2023, doi:10.3390/ijms24043729