Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.
Jason D. Theis, Mayo Clinic, Rochester, MN

Main Body of the Abstract
BACKGROUND: 42 different proteins form amyloid deposits. Of these, Cystatin C and Cathepsin K have been hypothesized to be precursor proteins of distinct amyloid types (ACys and ACatK1). ACys is described as a systemic disease whereas ACatK as a localized tumor-associated phenomenon.
Objective: We sought to determine the prevalence of Cystatin C (CysC) and Cathepsin K (Cat K) in proteomic-typed amyloids of various types, including Congo red (CR)-positive cases in which a definite amyloid type was not identified (“inconclusive”).
Methods: We retrospectively queried the Mayo Clinic amyloid proteome database containing 36,864 specimens analyzed by mass spectrometry-based proteomics (LC-MS/MS). The query was configured to identify any cases with at least 20 MS/MS spectral matches of either CysC or Cat K in all the CR+ dissections taken for proteomics analysis from that case.
Results: In N=40 cases (0.1%), both Cys C and Cat K were present in the CR+ deposits. 21 cases were diagnosed as another amyloid type (N=19 AL and N=2 AIns), and the remaining 19 cases were considered inconclusive. The inconclusive cases involved diverse anatomic sites (N=9 genitourinary, N=3 soft tissue, N=3 breast and N=4 miscellaneous).
Summary: Cys C and Cat K are rarely identified in amyloid specimens, but when present are usually found in tandem. In half of cases, they are present in association with another amyloid type, usually AL, but in the other half they may in tandem represent the amyloid precursor protein, with a possible predilection for genitourinary sites.

**Author Listing - Lead/ Submitting Author (we will be communicating with this individual): Name, Institution, City and State where the work was done. Co-authors will be added in a separate section.**
Jason D. Theis, Mayo Clinic, Rochester, MN

**Main Body of the Abstract**
**BACKGROUND:** 42 different proteins form amyloid deposits. Of these, Cystatin C and Cathepsin K have been hypothesized to be precursor proteins of distinct amyloid types (ACys and ACatK1). ACys is described as a systemic disease whereas ACatK as a localized tumor-associated phenomenon.
**Objective:** We sought to determine the prevalence of Cystatin C (CysC) and Cathepsin K (Cat K) in proteomic-typed amyloids of various types, including Congo red (CR)-positive cases in which a definite amyloid type was not identified (“inconclusive”).
**Methods:** We retrospectively queried the Mayo Clinic amyloid proteome database containing 36,864 specimens analyzed by mass spectrometry-based proteomics (LC-MS/MS). The query was configured to identify any cases with at least 20 MS/MS spectral matches of either CysC or Cat K in all the CR+ dissections taken for proteomics analysis from that case.
**Results:** In N=40 cases (0.1%), both Cys C and Cat K were present in the CR+ deposits. 21 cases were diagnosed as another amyloid type (N=19 AL and N=2 AIns), and the remaining 19 cases were considered inconclusive. The inconclusive cases involved diverse anatomic sites (N=9 genitourinary, N=3 soft tissue, N=3 breast and N=4 miscellaneous).
**Summary:** Cys C and Cat K are rarely identified in amyloid specimens, but when present are usually found in tandem. In half of cases, they are present in association with another amyloid type, usually AL, but in the other half they may in tandem represent the amyloid precursor protein, with a possible predilection for genitourinary sites.

Cathepsin K and Cystatin C are Co-deposited in Amyloid PC25 (#500)

We invite you to attend the XIX International Symposium on Amyloidosis to be held in Rochester, MN.

This symposium is organized as a hybrid meeting (with the focus on in-person) held from Sunday, May 26 through Thursday, May 30, 2024.

Together with the ISA Board and members of Mayo Clinic, a very attractive scientific hybrid program is being planned. The program will cover a variety of types of systemic amyloidosis: ATTR (hereditary and wild-type), AL (light-chain), AA and less frequent forms. There will be key lectures, specific symposia including those company sponsored, oral presentations and poster sessions of accepted abstracts.

COURSE DESCRIPTION
This program will provide a comprehensive review of state-of-the-art education in systemic amyloidosis: basic science, pathophysiology, diagnosis, current and emerging treatments. Scientific presentations will include competitive oral and poster abstracts. The rapid evolution of scientific discovery and expanding treatment options has created tremendous interest in the field and this meeting will fill and important gap in educating scientists and clinicians.