Clinical bottom line
Rare inherited complement-mediated thrombotic microangiopathies (cTMAs) represent a distinct subset of thrombotic microangiopathies characterized by dysregulation of the alternative complement pathway, leading to microvascular thrombosis predominantly affecting the kidneys but also causing systemic manifestations. Early recognition and differentiation from other thrombotic microangiopathies are critical, as targeted complement inhibition can improve outcomes. Current evidence supports the use of complement C5 inhibitors as a key therapeutic modality, although response variability and relapse risk remain challenges. Genetic testing and functional complement assays aid diagnosis and risk stratification but require integration with clinical and histopathological data. Management remains complex and should be individualized, with ongoing research needed to optimize treatment duration and address extra-renal involvement.
What the evidence shows
Complement-mediated thrombotic microangiopathies are driven by genetic and acquired abnormalities in complement regulatory proteins, resulting in uncontrolled activation of the alternative complement pathway and endothelial injury (Cataland et al., 2014). This pathophysiology distinguishes cTMAs from other thrombotic microangiopathies such as thrombotic thrombocytopenic purpura or Shiga toxin–associated hemolytic uremic syndrome (Aigner et al., 2019).
Genetic variants in complement genes (e.g., CFH, CFI, MCP/CD46) are identified in a substantial proportion of patients and correlate with disease susceptibility and prognosis (Aigner et al., 2019). Functional assays assessing complement activity and dysregulation provide additional diagnostic support (Slagle et al., 2024). These tools are important given the phenotypic overlap and diagnostic challenges in clinical practice.
Therapeutically, complement C5 inhibitors such as eculizumab have transformed the management of cTMAs by blocking terminal complement activation, reducing endothelial damage and microvascular thrombosis (Brocklebank et al., 2017). Clinical experience and case series demonstrate improved renal outcomes and hematologic remission with these agents, although some patients exhibit incomplete response or relapse after therapy cessation (Musalem et al., 2025). The optimal duration of treatment remains uncertain.
Extra-renal manifestations including neurological, gastrointestinal, and cardiovascular involvement occur and may complicate the clinical course (Hofer et al., 2014). These systemic features underscore the need for multidisciplinary management and vigilance beyond kidney function monitoring.
Recent narrative reviews emphasize practical management strategies including early diagnosis, genetic counseling, individualized treatment plans, and monitoring for relapse or complications (Musalem et al., 2025). Case reports highlight the complexity of cTMA in the context of autoimmune diseases such as lupus nephritis, where complement dysregulation may predominate and influence therapeutic choices (Manchikalapati et al., 2025).
Caveats and uncertainty
Despite advances, several uncertainties persist. The penetrance and pathogenicity of many complement gene variants remain incompletely defined, complicating interpretation of genetic results (Aigner et al., 2019). Functional complement assays lack standardization and may not be widely available, limiting diagnostic certainty (Slagle et al., 2024).
While complement inhibition is effective in many cases, it is not universally curative. Relapse risk after discontinuation and potential infectious complications from prolonged complement blockade require careful risk-benefit assessment (Brocklebank et al., 2017). Long-term safety data are still emerging.
The heterogeneity of clinical presentations and overlap with secondary TMAs pose diagnostic challenges. Distinguishing inherited complement-mediated forms from secondary causes is essential but can be difficult, especially in patients with concomitant autoimmune or infectious triggers (Manchikalapati et al., 2025).
Extra-renal manifestations are under-recognized and their optimal management is not well defined (Hofer et al., 2014). More evidence is needed to guide comprehensive care beyond renal outcomes.
How this may change practice
Clinicians managing patients with thrombotic microangiopathies should maintain a high index of suspicion for inherited complement-mediated forms, especially in atypical or recurrent cases. Integration of genetic testing and complement functional assays into diagnostic algorithms can facilitate earlier and more accurate diagnosis.
Complement C5 inhibitors should be considered frontline therapy in confirmed or highly suspected cTMA, with individualized treatment duration guided by clinical response and risk factors for relapse. Multidisciplinary care including nephrology, hematology, immunology, and genetics is recommended to address systemic involvement and optimize outcomes.
Ongoing education on the spectrum of extra-renal manifestations and vigilance for complications of complement blockade will improve holistic patient management. Research into biomarkers predicting response and relapse, as well as novel complement-targeting agents, may further refine therapeutic strategies.