A single-center experience of post-transplant atypical hemolytic uremic syndrome.

Purpose: Atypical hemolytic uremic syndrome (aHUS) is a genetic-based thrombotic microangiopathy (TMA) that is mediated by the activation of the alternative complement pathway. Heterozygous deletion in CFHR3-CFHR1 occurs in 30% of the general population and has not been classically linked to aHUS. Post-transplant aHUS has been associated with a high rate of graft loss. Herein, we report our case series of patients who developed aHUS after solid-organ transplantation.

Materials and methods: Five consecutive cases of post-transplant aHUS were identified at our center. Genetic testing was performed in all but one.

Results: One patient had a presumed TMA diagnosis before transplant. One heart and 4 kidney (KTx) transplant recipients were diagnosed with aHUS based on the clinical picture of TMA, acute kidney injury, and normal ADAMTS13 activity. Genetic mutation testing revealed heterozygous deletion in CFHR3-CFHR1 in 2 patients and a heterozygous complement factor I (CFI) variant of uncertain clinical significance (VUCS) (Ile416Leu) in a third. Four patients were on tacrolimus, 1 had anti-HLA-A68 donor-specific antibody (DSA), and another had borderline acute cellular rejection at the time of aHUS diagnosis. Four responded to eculizumab, and 1 out of 2 patients came off renal replacement therapy. One KTx recipient died from severe bowel necrosis in the setting of early post-transplant aHUS.

Conclusion: Calcineurin inhibitors, rejection, DSA, infections, surgery, and ischemia-reperfusion injury are common triggers that could unmask aHUS in solid-organ transplant recipients. Heterozygous deletion in CFHR3-CFHR1 and CFI VUCS may be important susceptibility factors acting as the first hit for alternative complement pathway dysregulation.