Abstract: SA-PO0231
Beyond the Usual Suspects: An Uncommon Genetic Etiology of Complement-Mediated Thrombotic Microangiopathy
Session Information
- Onconephrology: MGRS, HSCT, Electrolytes, RCC, and More
November 08, 2025 | Location: Exhibit Hall, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Onconephrology
- 1700 Onconephrology
Authors
- Alnemer, Faisal Khalid, King Abdulaziz Medical City in Riyadh, Riyadh, Riyadh Province, Saudi Arabia
- Alsadhan, Abdulmajeed Abdullah, King Abdulaziz Medical City in Riyadh, Riyadh, Riyadh Province, Saudi Arabia
- Tawhari, Mohammed Hadi, King Abdulaziz Medical City in Riyadh, Riyadh, Riyadh Province, Saudi Arabia
- Alzahrani, Nora Mohsin M, King Abdulaziz Medical City in Riyadh, Riyadh, Riyadh Province, Saudi Arabia
Introduction
Complement-mediated thrombotic microangiopathy (CM-TMA), or atypical hemolytic uremic syndrome (aHUS), is caused by dysregulated activation of the alternative complement pathway. This often requires both a genetic predisposition and an environmental trigger. While homozygous or compound heterozygous CFHR1/CFHR3 deletions are established risk factors, the role of heterozygous deletions remains less clear.
Case Description
A 45-year-old female with breast cancer received neoadjuvent chemotherapy (4 cycles of doxorubicin and cyclophophamide, then 12 weekly doses of paclitaxel), with the last dose 2 months prior to presentation, followed by lumpectomy. She presented with pancytopenia (Hb 73 gm/L, WBC 1.81, PLT 96) and kidney impairement (Cr 103 μmol/L, baseline 65), without microangiopathic hemolytic anemia: LDH 240 U/L, total bilirubin 9.1 μmol/L, reticulocytes 2.93%, haptoglobin 2.35 g/L, and <1% schistocytes. Her Cr peaked at 731 μmol/L with worsening thrombocytopenia (PLT 51). Kindey biopsy confirmed TMA. Patient was emperically treated with plasma exchange (PLEX) for suspected TTP, which was discontinued upon confirmation of normal ADAMTS-13 activity (0.67 IU/mL). Subsequently, Ravulizumab, a long-acting monoclonal complement inhibitor, was started for possible CM-TMA. Genetic testing revealed a digenic non-compound heterozygous deletion of the entire CFHR1 and CFHR3 genes. She received 3 doses of ravulizumab with improvement in Cr (to 380) and PLT (to 101).
Discussion
This case illustrates CM-TMA triggered by chemotherapy in a genetically susceptible host. While homozygous or compound heterozygous CFHR1/CFHR3 deletions are well-documented, this case suggests that even a large heterozygous deletion may be pathogenic in the right setting. The abscence of MAHA and normal ADAMTS-13 helped exclude TTP. The patient's response to ravulizumab supports complement-mediated pathology. Clinicians should consider CM-TMA in similar presentations, even without classical genetic findings.