ZDHHC13 and primary systemic amyloidosis: Furthermore, sequences of all amyloid-related genes in the candidate regions were normal except for the single mutation (R425X) in Zdhhc13. The coexistence of AL and AA systemic amyloidosis could be attributed to the fact that the presence of AL type amyloid fibrils acting as an amyloid-enhancing factor (AEF) and enhance the AA amyloid deposition [23]–[26].