Atypical haemolytic uraemic syndrome associated with a CD46 mutation triggered by Shigella flexneri

The association between therapeutic plasma exchange and the risk of mortality among patients critically ill with COVID-19: a meta-analysis

Background: Cytokine storm has been widely known to contribute to the development of the critical condition in patients with coronavirus disease 2019 (COVID-19), and studies had been conducted to assess the potential aspect of cytokine storm elimination by performing therapeutic plasma exchange (TPE). However, contradictory findings were observed. The objective of this study was to assess the association between TPE and the reduction of mortality of critically ill COVID-19 patients. Methods: A meta-analysis was conducted by collecting data from PubMed, Scopus, and Web of Science. Data on the mortality rate of critically ill COVID-19 patients treated with TPE plus standard of care and that of patients treated with standard of care alone were analyzed using a Z test. Results: We included a total of four papers assessing the association between TPE and the risk of mortality among critically ill COVID-19 patients. Our findings suggested that critically ill COVID-19 patients treated with TPE had lower risk of mortality compared to those without TPE treatment. Conclusion: Our study has identified the potential benefits of TPE in reducing the risk of mortality among critically ill COVID-19 patients.

CD46 knock-out using CRISPR/Cas9 editing of hTERT immortalized human cells modulates complement activation

The kidney is especially sensitive to diseases associated with overactivation of the complement system. While most of these diseases affect kidney glomeruli and the microvasculature, there is also evidence for tubulointerstitial deposition of complement factors. Complement inactivating factors on cell membranes comprise CD55, CD59 and CD46, which is also termed membrane cofactor protein (MCP). CD46 has been described as localized to glomeruli, but especially also to proximal tubular epithelial cells (RPTECs). However, human cell culture models to assess CD46 function on RPTECs are still missing. Therefore, we here performed gene editing of RPTEC/TERT1 cells generating a monoclonal CD46^-/- cell line that did not show changes of the primary cell like characteristics. In addition, factor I and CD46-mediated cleavage of C4b into soluble C4c and membrane deposited C4d was clearly reduced in the knock-out cell line as compared to the maternal cells. Thus, human CD46^-/- proximal tubular epithelial cells will be of interest to dissect the roles of the epithelium and the kidney in various complement activation mediated tubulointerstitial pathologies or in studying CD46 mediated uropathogenic internalization of bacteria. In addition, this gives proof-of-principle, that telomerized cells can be used in the generation of knock-out, knock-in or any kind of reporter cell lines without losing the primary cell characteristics of the maternal cells.

Gastrointestinal pathogens in anti-FH antibody positive and negative Hemolytic Uremic Syndrome

BACKGROUND

Prodromal symptoms are frequently reported in the atypical form of Hemolytic uremic syndrome (aHUS) suggesting implication of infectious triggers. Some pathogens may also play a role in the mechanisms of production of autoantibody directed against Factor H (FH), a complement regulator, leading to aHUS.

METHODS

The presence of 15 gastrointestinal (GI) pathogens was investigated by using xTAG-based multiplex PCR techniques on stools collected at the acute phase in a cohort of Indian HUS children classified according to the presence or absence of anti-FH autoantibodies.

RESULTS

Prevalence of pathogens in patients with anti-FH antibody (62.5%) was twice that in those without (31.5%). Different pathogens were detected, the most frequent being Clostridium difficile, Giardia intestinalis, Salmonella, Shigella, Rotavirus, Norovirus and Entamoeba histolytica. No stool was positive for Shigatoxin.

CONCLUSION

This study reveals a higher prevalence of GI pathogens in anti-FH positive than in negative patients. No single pathogen was implicated exclusively in one form of HUS. These pathogens may play a role in the disease initiation by inducing complement activation or an autoimmune response.

Mutations in membrane cofactor protein (CD46) gene in Indian children with hemolytic uremic syndrome

Background

Mutations in the CD46 gene account for an important proportion of patients with atypical hemolytic uremic syndrome (aHUS) who characteristically show multiple relapses, no response to plasma exchange and low recurrence risk in allograft. We screened for mutations in CD46 in patients with and without circulating anti-factor H (FH) antibodies-associated aHUS.

Methods

We estimated CD46 surface expression by flow cytometry and sequenced the CD46 gene in 23 and 56 patients with and without circulating anti-FH antibodies, respectively. Human Splicing Finder and PolyPhen2 were used for in silico prediction of pathogenicity.

Results

Two novel and three known (c.286 +2T > G, c.104G > A and c.565T > G) mutations in CD46 were found in nine (11.4%) patients; one patient had a variant of unknown significance and two patients presented during the first year of life. Novel intronic (c.1127 + 46C > G) and exonic (c.911C > T) mutations are proposed to activate cryptic splicing sites or alter protein conformation. Markedly reduced CD46 surface expression was found in homozygous states in five patients.

Conclusion

Patients with mutations in CD46 present at all ages, including the first year of life. Mutations in intron 2, (c.286 +2T > G) may be a potential hot spot in Indian children. Flow cytometry for CD46 expression is a satisfactory screening tool enabling early diagnosis.

Hemolytic Uremic Syndrome in Pregnancy and Postpartum

BACKGROUND

Pregnancy is associated with various forms of thrombotic microangiopathy, including hemolytic uremic syndrome. A previous small French study suggested that pregnancy-associated hemolytic uremic syndrome was to be included in the spectrum of atypical hemolytic uremic syndrome linked to complement alternative pathway dysregulation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We sought to retrospectively analyze the presentation, outcome, and frequency of complement alternative pathway gene variants in a larger international (France, United Kingdom, Italy) cohort of patients with pregnancy-associated hemolytic uremic syndrome.

RESULTS

Eighty-seven patients with pregnancy-associated hemolytic uremic syndrome were included. Hemolytic uremic syndrome occurred mainly during the first pregnancy (58%) and in the postpartum period (76%). At diagnosis, 56 (71%) patients required dialysis. Fifty-six (78%) patients underwent plasma exchanges, 21 (41%) received plasma infusions, and four (5%) received eculizumab. During follow-up (mean duration of 7.2 years), 41 (53%) patients reached ESRD, 15 (19%) had CKD, and 18 (28%) patients experienced hemolytic uremic syndrome relapse. Twenty-four patients (27%) received a kidney transplant and a recurrence of hemolytic uremic syndrome occurred in 13 (54%) patients. Variants in complement genes were detected in 49 (56%) patients, mainly in the CFH (30%) and CFI genes (9%).

CONCLUSIONS

Pregnancy-associated hemolytic uremic syndrome and atypical hemolytic uremic syndrome nonrelated to pregnancy have the same severity at onset and during follow-up and the same frequency of complement gene variants.

Factor H autoantibody is associated with atypical hemolytic uremic syndrome in children in the United Kingdom and Ireland

Factor H autoantibodies can impair complement regulation, resulting in atypical hemolytic uremic syndrome, predominantly in childhood. There are no trials investigating treatment, and clinical practice is only informed by retrospective cohort analysis. Here we examined 175 children presenting with atypical hemolytic uremic syndrome in the United Kingdom and Ireland for factor H autoantibodies that included 17 children with titers above the international standard. Of the 17, seven had a concomitant rare genetic variant in a gene encoding a complement pathway component or regulator. Two children received supportive treatment; both developed established renal failure. Plasma exchange was associated with a poor rate of renal recovery in seven of 11 treated. Six patients treated with eculizumab recovered renal function. Contrary to global practice, immunosuppressive therapy to prevent relapse in plasma exchange-treated patients was not adopted due to concerns over treatment-associated complications. Without immunosuppression, the relapse rate was high (five of seven). However, reintroduction of treatment resulted in recovery of renal function. All patients treated with eculizumab achieved sustained remission. Five patients received renal transplants without specific factor H autoantibody-targeted treatment with recurrence in one who also had a functionally significant CFI mutation. Thus, our current practice is to initiate eculizumab therapy for treatment of factor H autoantibody-mediated atypical hemolytic uremic syndrome rather than plasma exchange with or without immunosuppression. Based on this retrospective analysis we see no suggestion of inferior treatment, albeit the strength of our conclusions is limited by the small sample size.

Two cases of atypical hemolytic uremic syndrome (aHUS) and eosinophilic granulomatosis with polyangiitis (EGPA): a possible relationship

Atypical hemolytic uremic syndrome (aHUS) is a rare disease characterized by hemolysis, thrombocytopenia, and renal failure. It is related to genetic mutations of the alternative complement pathway and is difficult to differentiate from other prothrombotic microangiopathies. Eosinophilic granulomatosis with polyangiitis (EGPA) (Churg-Strauss syndrome, CSS) is a systemic ANCA-associated vasculitis and a hypereosinophilic disorder where eosinophils seem to induce cell apoptosis and necrosis and therefore, vasculitis. Here, we report the case of two CSS patients with a genetic complement disorder consistent with aHUS diagnosis. Both patients showed histologic features that supported the diagnosis of CSS, and a genetic complement study confirmed the suspected aHUS diagnosis. In the case where eculizumab was administered, the global response was excellent. There is very limited understanding of the genetics and epidemiology of both, atypical HUS and EGPA, but considering our two patients we suggest that an etiopathogenic link exists among patients diagnosed with both entities.

Postinfectious Hemolytic Uremic Syndrome

Post-infectious hemolytic uremic syndrome (HUS) is caused by specific pathogens in patients with no identifiable HUS-associated genetic mutation or autoantibody. The majority of episodes is due to infections by Shiga toxin (Stx) producing Escherichia coli (STEC). This chapter reviews the epidemiology and pathogenesis of STEC-HUS, including bacterial-derived factors and host responses. STEC disease is characterized by hematological (microangiopathic hemolytic anemia), renal (acute kidney injury) and extrarenal organ involvement. Clinicians should always strive for an etiological diagnosis through the microbiological or molecular identification of Stx-producing bacteria and Stx or, if negative, serological assays. Treatment of STEC-HUS is supportive; more investigations are needed to evaluate the efficacy of putative preventive and therapeutic measures, such as non-phage-inducing antibiotics, volume expansion and anti-complement agents. The outcome of STEC-HUS is generally favorable, but chronic kidney disease, permanent extrarenal, mainly cerebral complication and death (in less than 5 %) occur and long-term follow-up is recommended. The remainder of this chapter highlights rarer forms of (post-infectious) HUS due to S. dysenteriae, S. pneumoniae, influenza A and HIV and discusses potential interactions between these pathogens and the complement system.

The role of ADAMTS-13 activity and complement mutational analysis in differentiating acute thrombotic microangiopathies

ESSENTIALS: Molecular diagnostics has improved the differentiation of acute thrombotic microangiopathys (TMAs). Atypical hemolytic uremic syndrome may have features mimicking thrombotic thrombocytopenic purpura. We identified novel complement mutations and a high incidence of CD46, with favorable long term outcomes. Complement mutation analysis in TMA where the diagnosis is unclear and ADAMTS-13 activity is >10%.

BACKGROUND

Differentiation of acute thrombotic microangiopathy (TMA) at presentation has historically been dependent on clinical parameters. Confirmation of thrombotic thrombocytopenic purpura (TTP) is increasingly reliant on demonstrating deficient ADAMTS-13 activity. The identification of alternative complement pathway abnormalities in atypical hemolytic uremic syndrome (aHUS), along with the proven efficacy of terminal complement inhibitors in treatment, has increased the need for rapid differentiation of TTP from aHUS.

OBJECTIVES

We describe the clinical phenotype and nature of complement mutations in a cohort of aHUS patients referred as acute TMAs.

PATIENTS/METHODS

Fourteen consecutive aHUS patients were screened for mutations in C3, CD46, CFH, CFI, and CFB, as well as factor H (FH) antibodies. All aHUS patients had ADAMTS-13 activity > 10%.

RESULTS

Of 14 aHUS patients, 11 (79%) had platelet counts < 30 × 10(9) /L during the acute phase. Median presenting creatinine level was 295 μmol L(-1) , while five (36%) of 14 presented with a serum creatinine level < 200 μmol L(-1) . Alternative complement pathway mutations were detected in 9 (64%) of 14 patients, including CD46 mutations in five (36%) of 14 patients. Patients were identified with novel mutations in CFB and C3 that have not been previously reported.

CONCLUSIONS

We demonstrate that diagnostic differentiation based on platelet count and renal function is insufficient to predict an underlying complement mutation in some aHUS cases. Specifically, we demonstrate a high frequency of functionally significant CD46 mutations which may mimic TTP. ADAMTS-13 activity > 10% in a patient with a TMA should necessitate genetic screening for complement abnormalities.

Incomplete penetrance of CD46 mutation causing familial atypical hemolytic uremic syndrome

BACKGROUND

Hemolytic uremic syndrome (HUS) secondary to homozygous mutations in CD46 is uncommon. While heterozygous individuals may remain asymptomatic, homozygous mutations with severely depleted CD46 surface expression without disease manifestation is rare.

METHODS

We report on two siblings with features suggestive of hemolytic uremic syndrome. Estimation of CD46 expression by flow cytometry and gene sequencing were performed in members of this family.

RESULTS

Three siblings, two of whom were symptomatic, had markedly decreased (<10%) cell surface expression of CD46 and homozygous splice site mutation (IVS2 + 2 T > G) in the CD46 gene; the other 10-year-old sibling was asymptomatic. The illness was preceded by dengue shock syndrome in the index case. Both parents and two other siblings were heterozygous for this CD46 mutation.

CONCLUSIONS

Homozygous IVS2 + 2 T > G mutation in CD46 gene, similar to heterozygous mutation, may be clinically silent at least during childhood. The role of antecedent infections in triggering the disease requires further examination.