Renal-Limited Thrombotic Microangiopathy in Infants: A Case Series.

Rationale & Objective: Thrombotic microangiopathy (TMA), an intractable disease, can present in a renal-limited mode. Data on infantile-onset renal-limited TMA (RL-TMA) is lacking. This study describes 5 cases of RL-TMA in infants. Study Design: Case series. Setting & Participants: Five patients with infantile-onset RL-TMA who were admitted and/or followed up at Nanfang Hospital, Southern Medical University, from January 2024 to June 2025. Analytical Approach: Clinical data of 5 patients were collected. Amino acid conservation was analyzed by Clustal Omega, the secondary structure of the mutants was predicted by PolyPhen-2 and PHYRE2, and tertiary structure was predicted by AlphaFold3 and ChimeraX. Results: All patients presented with acute nephritic syndrome with hematuria and proteinuria with onset in infancy, but without hemolytic anemia or thrombocytopenia. Corticosteroid treatment was attempted in 3 patients with no response. Renal pathology revealed microthrombi; segmental endothelial cells that swelled with widening of the subendothelial gap and/or mesangiolysis were observed. Limitations: Functional verification of genetic variants of Conclusions: RL-TMA can occur in infancy, which has not been reported previously. Activation of the AP may be the common cause of infantile-onset RL-TMA. Its diagnosis and therapy are challenging. Promising outcomes can be achieved with eculizumab therapy.