Alejandra Rosales

Clinical practice. Today's understanding of the haemolytic uraemic syndrome.

The haemolytic uraemic syndrome (HUS) includes the triad of haemolytic anaemia, thrombocytopenia, and acute renal failure. The classical form [D(+) HUS] is caused by infectious agents, and it is a common cause of acute renal failure in children. The enterohaemorrhagic Escherichia coli-producing Shiga toxin (Stx) is the most common infectious agent causing HUS. Other infectious agents are Shigella and Streptococcus pneumoniae. Infections by S. pneumoniae can be particularly severe and has a higher acute mortality and a higher long-term morbidity compared to HUS by Stx. Atypical HUS [D(−)Stx(−)HUS] are often used by paediatricians to indicate a presentation of HUS without preceding diarrhoea. Almost all patients with D(−)Stx(−)HUS have a defect in the alternative pathway, for example, mutations in the genes for complement factor H, factor I, and membrane co-factor protein. Mutations in the factor H gene are described more often. The majority of children with D(+) HUS develop some degree of renal insufficiency, and approximately two thirds of children with HUS will require dialysis therapy, while about one third will have milder renal involvement without the need for dialysis therapy. General management of acute renal failure includes appropriate fluid and electrolyte management, antihypertensive therapy, and the initiation of renal replacement therapy when appropriate. Specific management issues in HUS include management of the haematological complications of HUS, monitoring for extra-renal involvement, avoiding antidiarrhoeal drugs, and possibly avoiding of antibiotic therapy. In addition to the obligatory supportive treatment and tight control of hypertension, there is anecdotal evidence that plasma therapy may induce remission and, in some cases, maintain it. Fresh frozen plasma contains factor H at physiological concentrations. A new therapy for D(−)Stx(−)HUS is a humanised monoclonal antibody (Eculizumab) that blocks complement activity by cleavage of the complement protein C5. It prevents the generation of the inflammatory peptide C5a and the cytotoxic membrane–attack complex C5b-9. We have first positive results, but it is still not approved for HUS.

Complement Factor H–Related Protein 1 Deficiency and Factor H Antibodies in Pediatric Patients with Atypical Hemolytic Uremic Syndrome

BACKGROUND AND OBJECTIVES This study evaluated the relevance of complement factor H (CFH)-related protein (CFHR) 1 deficiency in pediatric patients with atypical hemolytic uremic syndrome (aHUS) by evaluating both the frequency of deletions in CFHR1 and the presence of complement factor H (CFH) antibodies. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS A total of 116 patients (mainly from central Europe) and 118 healthy blood donors were included from 2001 to 2012. The presence of CFHR1 gene deletions was determined in 90 pediatric patients with aHUS and 118 controls by an easy, fast, and cheap PCR assay; 100 patients with aHUS and 42 controls were tested for CFH antibodies by ELISA. Questionnaires were administered to evaluate the clinical and laboratory data. RESULTS Homozygous deletion in CFHR1 was detected in 32% of the patients with aHUS tested, compared with 2.5% of controls (P<0.001). CFH antibodies were present in 25% of the patients and none of the controls. CFH antibodies were detected in 82% of patients with homozygous CFHR1 gene deletion and in 6% of patients without. CFH antibody-positive patients with aHUS showed a significantly lower platelet nadir at disease onset and significantly less frequent involvement of the central nervous system than did antibody-negative patients. Antibody-positive patients also received plasma therapy more often. CONCLUSION Homozygous deletion in CFHR1 is strongly associated with occurrence of CFH antibodies in pediatric patients with aHUS. However, despite this apparent genetic disease predisposition, it cannot be considered an exclusive cause for aHUS. Initial presentation of Shiga toxin-negative HUS with severe thrombocytopenia and no central nervous system complications in pediatric patients is especially suspicious for CFH antibody aHUS.

Treatment of enterohemorrhagic Escherichia coli-induced hemolytic uremic syndrome (eHUS).

Treatment of enterohemorrhagic Escherichia coli-induced hemolytic uremic syndrome (eHUS) still mostly relies on supportive intensive care regimens. Antibiotic treatment, as administered to eHUS patients during the 2011 O104:H4 outbreak, may reduce the shedding period, but this may apply only to this particular strain. In any case, there is no evidence for a beneficial use in the diarrheal phase and earlier warnings that antibiotic therapy at this stage may actually increase the likelihood of HUS remain unrefuted. Plasma exchange, a frequently chosen therapy in acute atypical HUS, was not beneficial for the outbreak patients and a prospective study of 274 pediatric eHUS patients even indicates a poorer long-term outcome. As eHUS is a disease where complement plays a pathophysiological role and individual beneficial treatments had been published, eculizumab was broadly administered during the outbreak, in particular to severely ill patients. The equally good outcome of treated versus untreated patients obviously does not allow a clear-cut statement, but rather points toward an advantageous use, at least for the severe cases. Although the role of complement should not be overestimated, the use of a complement blocker--not necessarily being a therapeutic option for uncomplicated eHUS--in severe disease may actually make the difference between favorable or detrimental outcome.

Extra-renal manifestations of complement-mediated thrombotic microangiopathies

Thrombotic microangiopathies (TMA) are rare but severe disorders, characterized by endothelial cell activation and thrombus formation leading to hemolytic anemia, thrombocytopenia, and organ failure. Complement over activation in combination with defects in its regulation is described in an increasing number of TMA and if primary for the disease denominated as atypical hemolytic-uremic syndrome. Although TMA predominantly affects the renal microvasculature, extra-renal manifestations are observed in 20% of patients including involvement of the central nerve system, cardiovascular system, lungs, skin, skeletal muscle, and gastrointestinal tract. Prompt diagnosis and treatment initiation are therefore crucial for the prognosis of disease acute phase and the long-term outcome. This review summarizes the available evidence on extra-renal TMA manifestations and discusses the role of acute and chronic complement activation by highlighting its complex interaction with inflammation, coagulation, and endothelial homeostasis.

Enterohemorrhagic Escherichia coli O26:H11-Associated Hemolytic Uremic Syndrome: Bacteriology and Clinical Presentation.

Infection by enterohemorrhagic ESCHERICHIA COLI (EHEC) is the most frequent cause of hemolytic uremic syndrome (HUS) in childhood. During a 6-year period, all patients with the clinical diagnosis of HUS were registered in a prospective multicenter study in Austria and Germany. EHEC O26:H11 was the second most frequent detected serotype, accounting for 15.4% of all EHEC isolates. The presence of EHEC O26:H11 was significantly associated with young age at the disease onset ( P < 0.001). Patients infected with this serotype were not different in their clinical presentation than those infected with other serotypes. This study underlines the importance of EHEC serotypes other than O157 in the etiology of HUS and emphasizes the importance of implementation of appropriate diagnostic methods to identify the whole spectrum of EHEC associated with HUS.

Shiga Toxin 2 Reduces Complement Inhibitor CD59 Expression on Human Renal Tubular Epithelial and Glomerular Endothelial Cells

ABSTRACT Infections with enterohemorrhagic Escherichia coli (EHEC) are a primary cause of hemolytic-uremic syndrome (HUS). Recently, Shiga toxin 2 (Stx2), the major virulence factor of EHEC, was reported to interact with complement, implying that the latter is involved in the pathogenesis of EHEC-induced HUS. The aim of the present study was to investigate the effect of Stx2 on the expression of membrane-bound complement regulators CD46, CD55, and CD59 on proximal tubular epithelial (HK-2) and glomerular endothelial (GEnC) cells derived from human kidney cells that are involved in HUS. Incubation with Stx2 did not influence the amount of CD46 or CD55 on the surface of HK-2 and GEnC cells, as determined by fluorescence-activated cell sorter analysis. In contrast, CD59 was significantly reduced by half on GEnC cells, but the reduction on HK-2 cells was less pronounced. With increasing amounts of Stx2, reduction of CD59 also reached significance in HK-2 cells. Enzyme-linked immunosorbent assay analyses showed that CD59 was not present in the supernatant of Stx2-treated cells, implying that CD59 reduction was not caused by cleavage from the cell surface. In fact, reverse transcription-quantitative PCR analyses showed downregulation of CD59 mRNA as the likely reason for CD59 cell surface reduction. In addition, a significant increase in terminal complement complex deposition on HK-2 cells was observed after treatment with Stx2, as a possible consequence of CD59 downregulation. In summary, Stx2 downregulates CD59 mRNA and protein levels on tubular epithelial and glomerular endothelial cells, and this downregulation likely contributes to complement activation and kidney destruction in EHEC-associated HUS.

Thrombotic microangiopathy: Atypical HUS: current diagnostic and therapeutic approaches

The management of patients with hemolytic uremic syndrome is challenging, and strategies for accurate diagnosis and effective treatment are needed. Intensive research over the past several years has revealed dysregulation of the complement system to be the main underlying cause of the syndrome, making this system the target of promising novel diagnostic and treatment strategies.

Actual and future strategies for transplantation in atypical HUS associated with mutations in factor H

The hemolytic uremic syndrome (HUS) is characterized by hemolytic anemia, thrombocytopenia, and acute renal failure. The majority of the cases ( 90%) are associated with an infection caused by shigatoxin-producing Escherichia coli (STEC). Ten percent of patients with HUS are referred to as ‘‘atypical’’ HUS (aHUS). This subgroup is defined by a high rate of disease recurrence and a significant risk for progression to chronic renal insufficiency. Most patients demonstrate an activation of the complement system, due to uncontrolled activation of the alternative pathway (1). Mutations and disease causing polymorphisms in complement proteins or complement regulatory proteins, like factor H (fH) (2), membrane cofactor protein (MCP, CD46) (2), factor I (fI) (3, 4), factor B (fB) (5), C3 (6) and thrombomodulin (7) have been described. Antibodies against factor H accompanied by a homozygous deletion of CFHR1/3 have been elucidated recently in a small group of patients (10%) (8). These alterations (mutations and antibodies) account for approximately 60– 70% of all causes of aHUS (8). However, the term aHUS is not well characterized. In addition, this group of patients is very heterogeneous. Diarrhea negative (D-HUS) is often used as a definition, although a small number of patients with mutations may present with diarrhea at a HUS onset (9). On the other hand, the term STEC-negative HUS (a subset that we favor) does not take other infections into account. In summary, HUS without evidence of any infection should be considered as atypical HUS. Factor H mutations are the most frequent mutations found in aHUS, with 40–45% familial and 10–20% sporadic cases (8). This major regulator of the alternative pathway activity consists of 23 exons comprising 20 short consensus repeats (SCR). Mutations in aHUS especially accumulate in the C-terminal region, in SCR 19 and 20 (exon XXII and XXIII). This results in reduced binding to C3b and glycosaminoglycans and therefore diminished inactivation of surface bound C3b (10) (Fig. 1). The clinical course of patients with aHUS associated with mutations of factor H is characterized by a high rate of HUS recurrence after renal transplantation (RT) and frequent graft loss (2, 8, 11). In a review of 27 pediatric and adult patients with a fH mutation who received 36 renal grafts, at least one graft failure was reported in 77.8% of patients, in 86.7% due to HUS recurrence. In 85.7% HUS flare occurred within the first year after renal transplantation (12).

Therapeutic plasma exchange in children: One center's experience

Therapeutic plasma exchange (TPE) has evolved to an accepted therapy for selected indications. However, it is technically challenging in children. Moreover, data on safety and efficacy are mainly derived from adult series. The aim of this study was to review the procedure in the context of clinical indications, effectiveness, and safety.

Effects of nutritional vitamin D supplementation on markers of bone and mineral metabolism in children with chronic kidney disease

Background We investigated the effects of nutritional vitamin D supplementation on markers of bone and mineral metabolism, i.e. serum levels of fibroblast growth factor 23 (FGF23), Klotho, bone alkaline phosphatase (BAP) and sclerostin, in two cohorts with chronic kidney disease (CKD). Methods In all, 80 vitamin D-deficient children were selected: 40 with mild to moderate CKD from the ERGO study, a randomized trial of ergocalciferol supplementation [estimated glomerular filtration rate (eGFR) 55 mL/min/1.73 m2], and 40 with advanced CKD from the observational Cardiovascular Comorbidity in Children with Chronic Kidney Disease (4C) study (eGFR 24 mL/min/1.73 m2). In each study, vitamin D supplementation was started in 20 children and 20 matched children not receiving vitamin D served as controls. Measures were taken at baseline and after a median period of 8 months. Age- and gender-related standard deviation scores (SDSs) were calculated. Results Before vitamin D supplementation, children in the ERGO study had normal FGF23 (median 0.31 SDS) and BAP (-0.10 SDS) but decreased Klotho and sclerostin (-0.77 and -1.04 SDS, respectively), whereas 4C patients had increased FGF23 (3.87 SDS), BAP (0.78 SDS) and sclerostin (0.76 SDS) but normal Klotho (-0.27 SDS) levels. Vitamin D supplementation further increased FGF23 in 4C but not in ERGO patients. Serum Klotho and sclerostin normalized with vitamin D supplementation in ERGO but remained unchanged in 4C patients. BAP levels were unchanged in all patients. In the total cohort, significant effects of vitamin D supplementation were noted for Klotho at eGFR 40-70 mL/min/1.73 m2. Conclusions Vitamin D supplementation normalized Klotho and sclerostin in children with mild to moderate CKD but further increased FGF23 in advanced CKD.