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.

Eculizumab Use in a Temporarily Dialysis-Dependent Patient With Shiga Toxin–Producing Escherichia Coli Hemolytic Uremic Syndrome With Neurological Complications

Shiga toxin–producing Escherichia coli hemolytic uremic syndrome (STEC-HUS) is the most common cause of acute renal failure in children, and it is associated with thrombocytopenia and hemolytic anemia. Although this disease primarily affects the kidney, it can also contribute to cellular damage in other organ systems, such as the CNS. Eculizumab is a monoclonal antibody that binds to complement proteins to prevent complement-mediated intravascular hemolysis in atypical HUS. In STEC-HUS, complement activation also occurs by Shiga toxin, and previous cases of eculizumab use in the setting of neurological involvement have been shown to be successful. We report the successful use of eculizumab in the setting of typical STEC-HUS–induced neurological symptoms including seizure, altered mental status, and left arm weakness. The patient also experienced concomitant renal failure requiring dose adjustment for hemodialysis. Following 2 doses of eculizumab, our patient was discharged to an inpatient rehabilitation facility with resolution of her renal injury, seizures, and altered mentation without adverse effects from eculizumab throughout the admission. Based on our case study, it appears that eculizumab may be given during or between hemodialysis without dose adjustment.

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.