COVID-19: a trigger for severe thrombotic microangiopathy in a patient with complement gene variant

The evidence regarding thrombotic microangiopathy (TMA) related to Coronavirus Infectious Disease 2019 (COVID-19) in patients with complement gene mutations as a cause of acute kidney injury (AKI) are limited. We presented a case of a 23-year-old male patient admitted with an asymptomatic form of COVID-19, but with uncontrolled hypertension and AKI. Kidney biopsy showed severe lesions of TMA. In evolution patient had persistent microangiopathic hemolytic anemia, decreased level of haptoglobin and increased LDH level. Decreased complement C3 level and the presence of schistocytes were found for the first time after biopsy. Kidney function progressively decreased and the patient remained hemodialysis dependent. Complement work-up showed a heterozygous variant with unknown significance in complement factor I (CFI) c.-13G>A, affecting the 5' UTR region of the gene. In addition, the patient was found to be heterozygous for the complement factor H (CFH) H3 haplotype (involving the rare alleles of c.-331C>T, Q672Q and E936D polymorphisms) reported as a risk factor of atypical hemolytic uremic syndrome. This case of AKI associated with severe TMA and secondary hemolytic uremic syndrome highlights the importance of genetic risk modifiers in the alternative pathway dysregulation of the complement in the setting of COVID-19, even in asymptomatic forms.

Functional Analysis of Variants in Complement Factor I Identified in Age-Related Macular Degeneration and Atypical Hemolytic Uremic Syndrome

Complement factor I (FI) is a central inhibitor of the complement system, and impaired FI function increases complement activation, contributing to diseases such as age-related macular degeneration (AMD) and atypical hemolytic uremic syndrome (aHUS). Genetic variation in complement factor I (CFI) has been identified in both AMD and aHUS, with more than half of these variants leading to reduced FI secretion levels. For many of the variants with normal FI secretion, however, functional implications are not yet known. Here we studied 11 rare missense variants, with FI secretion levels comparable to wildtype, but a predicted damaging effects based on the Combined Annotation Dependent Depletion (CADD) score. Three variants (p.Pro50Ala, p.Arg339Gln, and p.Ser570Thr) were analyzed in plasma and serum samples of carriers affected by AMD. All 11 variants (nine for the first time in this study) were recombinantly expressed and the ability to degrade C3b was studied with the C3b degradation assay. The amount of degradation was determined by measuring the degradation product iC3b with ELISA. Eight of 11 (73%) mutant proteins (p.Pro50Ala, p.Arg339Gln, p.Ile340Thr, p.Gly342Glu, p.Gly349Arg, p.Arg474Gln, p.Gly487Cys, and p.Gly512Ser) showed significantly impaired C3b degradation, and were therefore classified as likely pathogenic. Our data indicate that genetic variants in CFI with a CADD score >20 are likely to affect FI function, and that monitoring iC3b in a degradation assay is a useful tool to establish the pathogenicity of CFI variants in functional studies.

Pregnancy associated atypical hemolytic uremic syndrome triggered by massive uterine bleeding after outpatient dilatation and evacuation

Background: Atypical Hemolytic Uremic Syndrome (aHUS) is a renal threatening multi-system disorder with significant hematologic findings of microangiopathic hemolytic anemia (MAHA) and thrombocytopenia. Early recognition and institution of late complement inhibitors can interrupt a cycle of progressive hemolysis and renal injury. Methods: We present an informative case of aHUS triggered by pregnancy termination. Diagnostic, laboratory, and treatment measures are reviewed. Results: Clinical evidence demonstrates immediate improvement in hemolysis, platelet consumption, and acute kidney injury following initiation of eculizumab. Conclusion: Pregnancy is a recognized trigger of aHUS and its proper management requires early recognition and institution of late complement blockade. Genetic testing can be sent for genetic counseling purposes, but initiation of treatment should neither await these results nor be discontinued when high-risk polymorphisms are absent.

Pediatric Atypical Hemolytic Uremic Syndrome Advances

Atypical hemolytic uremic syndrome (aHUS) is a rare disorder characterized by dysregulation of the alternate pathway. The diagnosis of aHUS is one of exclusion, which complicates its early detection and corresponding intervention to mitigate its high rate of mortality and associated morbidity. Heterozygous mutations in complement regulatory proteins linked to aHUS are not always phenotypically active, and may require a particular trigger for the disease to manifest. This list of triggers continues to expand as more data is aggregated, particularly centered around COVID-19 and pediatric vaccinations. Novel genetic mutations continue to be identified though advancements in technology as well as greater access to cohorts of interest, as in diacylglycerol kinase epsilon (DGKE). DGKE mutations associated with aHUS are the first non-complement regulatory proteins associated with the disease, drastically changing the established framework. Additional markers that are less understood, but continue to be acknowledged, include the unique autoantibodies to complement factor H and complement factor I which are pathogenic drivers in aHUS. Interventional therapeutics have undergone the most advancements, as pharmacokinetic and pharmacodynamic properties are modified as needed in addition to their as biosimilar counterparts. As data continues to be gathered in this field, future advancements will optimally decrease the mortality and morbidity of this disease in children.

Thrombotic microangiopathy and smoldering multiple myeloma after kidney transplant in a patient with MCP mutation

The most frequent cause of atypical hemolytic uremic syndrome (aHUS) is defective regulation of complement activation because of genetic anomalies. We present the case of 53-year-old man with a kidney transplant and stabilized kidney function (creatinine 2.5 mg/dL; proteinuria 0.4 g/24 h) with mycophenolate/tacrolimus/prednisone who was diagnosed of Thrombotic Microangiopathy (TMA). This diagnosis was associated with creatinine and proteinuria rise (3 mg/dL; 2.4 g/24 h) and a new monoclonal IgA/lambda component. Renal biopsy showed membranoproliferative glomerulonephritis; a pathogenic variant in the Membrane cofactor protein (MCP) gene with a polymorphism ggaac, typically associated to secondary aHUS, was identified. We suspected that immunoglobulin could be acting as a trigger for TMA in a genetically susceptible patient, so “clone-directed” therapy with bortezomib and dexamethasone was initiated.