Immunosuppressive Therapy of Antibody-Mediated aHUS and TTP.

The recent classification of pediatric thrombotic microangiopathies (TMA) takes into consideration mechanisms of disease for guidance to targeted therapies. We present our experience with seven patients with antibody mediated atypical hemolytic uremic syndrome (aHUS) and thrombotic thrombocytopenic purpura (TTP). Five children had aHUS with antibodies against complement factor H (CFH-ab) and two with TTP with antibodies against metalloproteinase ADAMTS13. In the aHUS cases diagnosed and treated before the eculizumab era, CFH-ab was detected using the ELISA assay. Mutational analysis of selected complement genes was performed. TTP was diagnosed if, in addition to microangiopathic hemolytic anemia and thrombocytopenia, ischemic organ involvement and severe deficiency in ADAMTS13 activity were present. Treatment protocol consisted of plasma exchanges (PE) and steroid pulses, followed by the combination of cyclophosphamide and rituximab to achieve long-term immunosuppression. Four patients with CFH-ab and the TTP patients with ADAMTS13 antibodies came into sustained remission. After a median follow-up of 11.7 (range 7.7-12.9) years without maintenance therapy, no disease recurrence was observed; nevertheless, six patients, two had hypertension and two had proteinuria as a late consequence. One patient, with late diagnosis of CFH-ab and additional genetic risk factors who was treated only with PE and plasma substitution, reached end-stage renal disease and was later successfully transplanted using eculizumab prophylaxis. In the cases of antibody-mediated TMAs, PE and early immunosuppressive treatment may result in sustained remission with preserved kidney function. Further data are needed to establish optimal treatment of anti-FH antibody-associated HUS.

Ocular treatment of cystinosis with eye drop containing cysteamine / Ciszteamintartalmú szemcsepp alkalmazása cystinosisban

Cystinosis is a rare lysosomal storage disease affecting amino acid metabolism, characterized by the accumulation and crystallization of cystine in various tissues, primarily in the eye and kidney. The major ophthalmic symptom is photophobia, which is related to the corneal deposition of cystine crystals. The light sensitivity significantly impairs the quality of life of the affected patients, thus, effective ophthalmic treatment to reduce the crystal density is very importance. In the current case report, we present the characteristic ocular clinical appearance and treatment options of cystinosis by reviewing the literature. A simple aqueous solution of cysteamine, which aids in the dissolution of crystals, has been widely used in topical treatment in the past, however, its therapeutic efficacy is debatable. Recently, a new viscous formulation of cysteamine has been proposed for ophthalmic treatment. For the treatment of corneal cystine crystals in our patient, the new viscous format of cysteamine has been applied, and therapeutic effects were recorded for a year. Applying the viscous cysteamine formulation, a marked and gradual decrease in photophobia was observed in our patient in the first year of the treatment. Anterior-segment optical coherence tomography and in vivo confocal microscopy represented a continuous decrease in the density of corneal crystals even from the first month of the treatment period. The aim of our case report is to present the ophthalmic symptoms of cystinosis and the results of the first clinical application of viscous formulation of cysteamin eye drops in Hungary in a cystinosis patient.

FHR-5 Serum Levels and CFHR5 Genetic Variations in Patients With Immune Complex-Mediated Membranoproliferative Glomerulonephritis and C3-Glomerulopathy.

Background: Factor H-related protein 5 (FHR-5) is a member of the complement Factor H protein family. Due to the homology to Factor H, the main complement regulator of the alternative pathway, it may also be implicated in the pathomechanism of kidney diseases where Factor H and alternative pathway dysregulation play a role. Here, we report the first observational study on CFHR5 variations along with serum FHR-5 levels in immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) and C3 glomerulopathy (C3G) patients together with the clinical, genetic, complement, and follow-up data. Methods: A total of 120 patients with a histologically proven diagnosis of IC-MPGN/C3G were enrolled in the study. FHR-5 serum levels were measured in ELISA, the CFHR5 gene was analyzed by Sanger sequencing, and selected variants were studied as recombinant proteins in ELISA and surface plasmon resonance (SPR). Results: Eight exonic CFHR5 variations in 14 patients (12.6%) were observed. Serum FHR-5 levels were lower in patients compared to controls. Low serum FHR-5 concentration at presentation associated with better renal survival during the follow-up period; furthermore, it showed clear association with signs of complement overactivation and clinically meaningful clusters. Conclusions: Our observations raise the possibility that the FHR-5 protein plays a fine-tuning role in the pathogenesis of IC-MPGN/C3G.

Atypical HUS and Crohn's disease-interference of intestinal disease activity with complement-blocking treatment.

BACKGROUND: In atypical hemolytic-uremic syndrome (aHUS), various defects of the complement system have been reported to explain pathophysiology. Therapeutic options for complement inhibition are well-recognized; however, the links between various immune-derived diseases and aHUS are unclear, and their interference with treatment efficacy during long-term complement-blocking therapy is scarcely known. CASE-DIAGNOSIS/TREATMENT: We present a pediatric patient who developed aHUS with acute kidney injury in parallel with the onset of Crohn's disease (CD), and who required long-term complement-blocking therapy with eculizumab (ECU). Unexpectedly, during the 6-year ECU treatment, an important intra-patient variation of the degree of complement inhibition was observed. In spite of continuous and stable doses of complement-blocking therapy, periods of incomplete blockade were observed in strong association with relapses of CD. When conventional and later biological therapy with adalimumab was introduced, with CD going into remission, complement blockade became complete again. Despite periodically low ECU levels and insufficient complement inhibition, no clinical or hematological signs of aHUS recurrence were detected during CD relapses. CONCLUSION: In aHUS cases secondary to CD, close monitoring of both complement inhibition and serum ECU levels is needed as intestinal disease can interfere with complement-blocking treatment. Increased doses of ECU may be necessary to maintain therapeutic blood levels of ECU and full complement blockade, especially if the intestinal disease is not under control.

De novo inflammatory bowel disease in children after solid organ transplantation / Szolidszerv-transzplantáció után kialakuló de novo gyulladásos bélbetegség gyermekkorban.

Összefoglaló. A gyulladásos bélbetegség (inflammatory bowel disease, IBD) incidenciája folyamatosan no, etiológiája egyelore ismeretlen. Kezelésében gyakran alkalmazunk immunszuppresszív, illetve immunmoduláns szereket. Egyes esetekben azonban szolidszerv-transzplantációt követoen, folyamatos immunszuppresszív kezelés mellett is megfigyelheto de novo IBD kialakulása. Célunk az volt, hogy Klinikánk beteganyagából összesítsük azon eseteket, amelyekben szolid szerv (máj, vese, tüdo) transzplantációját követoen de novo IBD alakult ki. A transzplantációt megelozoen szklerotizáló cholangitis miatt gondozott betegeket kizártuk. A Klinikánkon gondozott, szolid szerv transzplantációján (179 máj, 197 vese, 29 tüdo) átesett betegek közül 4 (2 máj- és 2 vesetranszplantált) gyermeknél alakult ki de novo IBD. A transzplantációhoz vezeto alapbetegségek biliaris atresia, polycystás vese és Denys-Drash-szindróma voltak. A transzplantációt követo immunszuppresszív terápia mind a 4 esetben tartalmazott szisztémásszteroid- és takrolimuszkezelést, emellett 3 esetben mikofenolát-mofetil (MMF)-terápiát is. A kivizsgálást indikáló fobb tünetek a haematochesia, hasmenés, fáradékonyság és fogyás voltak. A családi anamnézis 1 esetben volt pozitív. A de novo IBD diagnózisának felállítását követoen mind a 4 betegnél az addigi immunszuppressziós terápia módosításra került. Összességében elmondható, hogy a szolidszerv-transzplantációt követo de novo IBD kialakulása ritka, etiológiája tisztázatlan. Az irodalom felveti az alkalmazott immunszuppresszív szerek (takrolimusz és MMF), illetve infekciók etiológiai szerepét, de az is felmerül, hogy a de novo IBD olyan önálló entitás, mely elkülönül a klasszikus IBD kategóriáitól. Klinikai szempontból fontos a tünetek hátterében álló betegség tisztázása, hiszen a prezentációs tüneteknek megfelelo, a differenciáldiagnosztika során felmerülo egyéb betegségek terápiája meroben eltér. A megfelelo terápia hozzájárulhat a transzplantált betegek morbiditásának és mortalitásának csökkentéséhez. Orv Hetil. 2021; 162(18): 720-726. Summary. The incidence of inflammatory bowel disease (IBD) is increasing, however, the aetiology is still unknown. The therapy consists of immunosuppressants and immunomodulators. In some cases, despite the continuous immunosuppressant therapy, de novo IBD develops. Our aim was to evaluate patients diagnosed with de novo IBD after solid organ (liver, kidney, or lung) transplantation. Patients treated with sclerosing cholangitis prior to liver transplantation were excluded. 4 patients (two kidney and two liver transplants) were diagnosed with de novo IBD. The underlying diseases leading to transplantation were biliary atresia, polycystic kidney, and Denys-Drash syndrome. All patients received systemic steroid and tacrolimus treatment, and 3 patients (2 kidney and 1 liver transplant) also received mycophenolate mofetil (MMF). The main symptoms indicative of de novo IBD were haematochezia, diarrhoea, fatigue, and weight loss. Family history for IBD was positive in 1 case. Following the diagnosis of IBD, immunosuppressive therapy was modified. Overall, the development of de novo IBD following solid organ transplantation is quite rare, and its aetiology is unknown. According to the literature, immunosuppressants (tacrolimus and MMF) and infections play a role in the pathomechanism, but it seems that de novo IBD is a separate entity from the classical IBD categories. From a clinical point of view, it is important to elucidate the underlying disease of the symptoms, as the treatment of other diseases that arise during differential diagnosis according to the presentation symptoms is very different. Appropriate therapy can help reduce morbidity and mortality in transplant patients. Orv Hetil. 2021; 162(18): 720-726.

Follow-Up of Blood Pressure, Arterial Stiffness, and GFR in Pediatric Kidney Transplant Recipients.

Pediatric renal transplant recipients (RTx) were studied for longitudinal changes in blood pressure (BP), arterial stiffness by pulse wave velocity (PWV), and graft function. Patients and Methods: 52 RTx patients (22 males) were included; office BP (OBP) and 24 h BP monitoring (ABPM) as well as PWV were assessed together with glycemic and lipid parameters and glomerular filtration rate (GFR) at 2.4[1.0-4.7] (T1) and 9.3[6.3-11.8] years (T2) after transplantation (median [range]). Results: Hypertension was present in 67 and 75% of patients at T1 and T2, respectively. Controlled hypertension was documented in 37 and 44% by OBP and 40 and 43% by ABPM. Nocturnal hypertension was present in 35 and 30% at T1 and T2; 24 and 32% of the patients had masked hypertension, while white coat hypertension was present in 16 and 21% at T1 and T2, respectively. Blood pressure by ABPM correlated significantly with GFR and PWV at T2, while PWV also correlated significantly with T2 cholesterol levels. Patients with uncontrolled hypertension by ABPM had a significant decrease in GFR, although not significant with OBP. Anemia and increased HOMAi were present in ~20% of patients at T1 and T2. Conclusion: Pediatric RTx patients harbor risk factors that may affect their cardiovascular health. While we were unable to predict the evolution of renal function based on PWV and ABPM at T1, these risk factors correlated closely with GFR at follow-up suggesting that control of hypertension may have an impact on the evolution of GFR.

Pseudouridylation defect due to DKC1 and NOP10 mutations causes nephrotic syndrome with cataracts, hearing impairment, and enterocolitis.

RNA modifications play a fundamental role in cellular function. Pseudouridylation, the most abundant RNA modification, is catalyzed by the H/ACA small ribonucleoprotein (snoRNP) complex that shares four core proteins, dyskerin (DKC1), NOP10, NHP2, and GAR1. Mutations in DKC1, NOP10, or NHP2 cause dyskeratosis congenita (DC), a disorder characterized by telomere attrition. Here, we report a phenotype comprising nephrotic syndrome, cataracts, sensorineural deafness, enterocolitis, and early lethality in two pedigrees: males with DKC1 p.Glu206Lys and two children with homozygous NOP10 p.Thr16Met. Females with heterozygous DKC1 p.Glu206Lys developed cataracts and sensorineural deafness, but nephrotic syndrome in only one case of skewed X-inactivation. We found telomere attrition in both pedigrees, but no mucocutaneous abnormalities suggestive of DC. Both mutations fall at the dyskerin-NOP10 binding interface in a region distinct from those implicated in DC, impair the dyskerin-NOP10 interaction, and disrupt the catalytic pseudouridylation site. Accordingly, we found reduced pseudouridine levels in the ribosomal RNA (rRNA) of the patients. Zebrafish dkc1 mutants recapitulate the human phenotype and show reduced 18S pseudouridylation, ribosomal dysregulation, and a cell-cycle defect in the absence of telomere attrition. We therefore propose that this human disorder is the consequence of defective snoRNP pseudouridylation and ribosomal dysfunction.

Validation of distinct pathogenic patterns in a cohort of membranoproliferative glomerulonephritis patients by cluster analysis.

BACKGROUND: A novel data-driven cluster analysis identified distinct pathogenic patterns in C3-glomerulopathies and immune complex-mediated membranoproliferative glomerulonephritis. Our aim was to replicate these observations in an independent cohort and elucidate disease pathophysiology with detailed analysis of functional complement markers. METHODS: A total of 92 patients with clinical, histological, complement and genetic data were involved in the study, and hierarchical cluster analysis was done by Ward method, where four clusters were generated. RESULTS: High levels of sC5b-9 (soluble membrane attack complex), low serum C3 levels and young age at onset (13 years) were characteristic for Cluster 1 with a high prevalence of likely pathogenic variations (LPVs) and C3 nephritic factor, whereas for Cluster 2-which is not reliable because of the small number of cases-strong immunoglobulin G staining, low C3 levels and high prevalence of nephritic syndrome at disease onset were observed. Low plasma sC5b-9 levels, decreased C3 levels and high prevalence of LPV and sclerotic glomeruli were present in Cluster 3, and patients with late onset of the disease (median: 39.5 years) and near-normal C3 levels in Cluster 4. A significant difference was observed in the incidence of end-stage renal disease during follow-up between the different clusters. Patients in Clusters 3-4 had worse renal survival than patients in Clusters 1-2. CONCLUSIONS: Our results confirm the main findings of the original cluster analysis and indicate that the observed, distinct pathogenic patterns are replicated in our cohort. Further investigations are necessary to analyse the distinct biological and pathogenic processes in these patient groups.

C4 nephritic factor in patients with immune-complex-mediated membranoproliferative glomerulonephritis and C3-glomerulopathy.

BACKGROUND: Acquired or genetic abnormalities of the complement alternative pathway are the primary cause of C3glomerulopathy(C3G) but may occur in immune-complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) as well. Less is known about the presence and role of C4nephritic factor(C4NeF) which may stabilize the classical pathway C3-convertase. Our aim was to examine the presence of C4NeF and its connection with clinical features and with other pathogenic factors. RESULTS: One hunfe IC-MPGN/C3G patients were enrolled in the study. C4NeF activity was determined by hemolytic assay utilizing sensitized sheep erythrocytes. Seventeen patients were positive for C4NeF with lower prevalence of renal impairment and lower C4d level, and higher C3 nephritic factor (C3NeF) prevalence at time of diagnosis compared to C4NeF negative patients. Patients positive for both C3NeF and C4NeF had the lowest C3 levels and highest terminal pathway activation. End-stage renal disease did not develop in any of the C4NeF positive patients during follow-up period. Positivity to other complement autoantibodies (anti-C1q, anti-C3) was also linked to the presence of nephritic factors. Unsupervised, data-driven cluster analysis identified a group of patients with high prevalence of multiple complement autoantibodies, including C4NeF. CONCLUSIONS: In conclusion, C4NeF may be a possible cause of complement dysregulation in approximately 10-15% of IC-MPGN/C3G patients.

Elevated Systemic Pentraxin-3 Is Associated With Complement Consumption in the Acute Phase of Thrombotic Microangiopathies.

Pentraxin-3 (PTX3) and C-reactive protein (CRP) have been shown to regulate complement activation in vitro, but their role has not been investigated in complement consumption in vivo. Thrombotic microangiopathies (TMA) are often accompanied by complement overactivation and consumption, therefore we analyzed the relation of the systemic pentraxin levels to the complement profile, laboratory parameters and clinical outcome of TMA patients. We determined the PTX3 and CRP levels, complement factor and activation product concentrations in blood samples of 171 subjects with the diagnosis of typical hemolytic uremic syndrome (STEC-HUS) (N = 34), atypical HUS (aHUS) (N = 44), secondary TMA (N = 63), thrombotic thrombocytopenic purpura (TTP) (N = 30) and 69 age-matched healthy individuals. Clinical data, blood count and chemistry were collected from medical records. To determine the in vitro effect of PTX3 on alternative pathway (AP) activation, sheep red blood cell-based hemolytic assay and AP activity ELISA were used. We found that PTX3 levels were elevated in the acute phase of STEC-HUS, aHUS and secondary TMA, whereas PTX3 elevation was exceptional is TTP. Conversely, a significantly higher median CRP was present in all patient groups compared to controls. PTX3, but not CRP was associated with signs of complement consumption in vivo, and PTX3 significantly decreased the AP hemolytic activity in vitro. Our results provide a detailed description of acute phase-TMA patients' complement profile linked to changes in the systemic pentraxin levels that may support further molecular studies on the function of PTX3 in disease pathogenesis and add to the laboratory assessment of complement consumption in TMA.

[Solid organ transplantation in childhood]. / Szervtranszplantáció gyermekkorban.

Paediatric organ transplantation today is considered and accepted and widely available therapy in children with end-stage organ failure. It is important to know that in childhood, diseases leading to end-stage organ failure differ from those in adults. Beside this, in children there are different surgical and paediatric challenges before and after transplantation (size differences of the patient and donor organ, special and paediatric infections, different pharmacokinetics and pharmacodynamics of immunosuppressive drugs, noncompliance). However, paediatric organ transplantation in the last decades became a success story of the Hungarian health care owing to several working groups in Hungary and outside the country. Orv Hetil. 2018; 159(46): 1948-1956.

Analysis of Linear Antibody Epitopes on Factor H and CFHR1 Using Sera of Patients with Autoimmune Atypical Hemolytic Uremic Syndrome.

INTRODUCTION: In autoimmune atypical hemolytic uremic syndrome (aHUS), the complement regulator factor H (FH) is blocked by FH autoantibodies, while 90% of the patients carry a homozygous deletion of its homolog complement FH-related protein 1 (CFHR1). The functional consequence of FH-blockade is widely established; however, the molecular basis of autoantibody binding and the role of CFHR1 deficiency in disease pathogenesis are still unknown. We performed epitope mapping of FH to provide structural insight in the autoantibody recruitment on FH and potentially CFHR1. METHODS: Eight anti-FH positive aHUS patients were enrolled in this study. With overlapping synthetic FH and CFHR1 peptides, we located the amino acids (aa) involved in binding of acute and convalescence stage autoantibodies. We confirmed the location of the mapped epitopes using recombinant FH domains 19-20 that carried single-aa substitutions at the suspected antibody binding sites in three of our patients. Location of the linear epitopes and the introduced point mutations was visualized using crystal structures of the corresponding domains of FH and CFHR1. RESULTS: We identified three linear epitopes on FH (aa1157-1171; aa1177-1191; and aa1207-1226) and one on CFHR1 (aa276-290) that are recognized both in the acute and convalescence stages of aHUS. We observed a similar extent of autoantibody binding to the aHUS-specific epitope aa1177-1191 on FH and aa276-290 on CFHR1, despite seven of our patients being deficient for CFHR1. Epitope mapping with the domain constructs validated the location of the linear epitopes on FH with a distinct autoantibody binding motif within aa1183-1198 in line with published observations. SUMMARY: According to the results, the linear epitopes we identified are located close to each other on the crystal structure of FH domains 19-20. This tertiary configuration contains the amino acids reported to be involved in C3b and sialic acid binding on the regulator, which may explain the functional deficiency of FH in the presence of autoantibodies. The data we provide identify the exact structures involved in autoantibody recruitment on FH and confirm the presence of an autoantibody binding epitope on CFHR1.

Decreased Neutrophil Extracellular Trap Degradation in Shiga Toxin-Associated Haemolytic Uraemic Syndrome.

BACKGROUND: Neutrophil extracellular traps (NETs) can stimulate thrombosis, and their degradation is decreased in several autoimmune disorders. It was recently reported that some patients with haemolytic uraemic syndrome (HUS) also fail to degrade NETs and that neutrophils from Shiga toxin-associated HUS are primed to form NETs. METHOD: We used a well-characterized cohort of 74 thrombotic microangiopathy (TMA) patients, with a subset also providing follow-up samples, and 112 age-matched controls to investigate NET degradation and serum nuclease activity in TMA before, during and after treatment. RESULTS: We identified that in the cohort of TMA patients, 50% of patients with Shiga toxin-associated HUS displayed a decreased ability to degrade NETs. NET degradation correlated with serum nuclease activity, but not with autoantibodies against double-stranded DNA, which has been previously observed in some autoimmune disorders. Further, NET degradation negatively correlated with serum creatinine levels, suggesting that kidney function was negatively impacted by the low NET degradation ability. CONCLUSIONS: We revealed that decreased NET degradation is a common feature of Shiga toxin-associated HUS and that it is associated with decreased kidney function in these patients. It remains to be clarified whether improving NET degradation would be beneficial for the patient.

Neurocognitive functions of pediatric kidney transplant recipients.

BACKGROUND: End-stage renal disease (ESRD) in children is associated with impaired neurocognitive function and development. However, data on factors associated with neurocognitive dysfunctions in children with kidney transplants are limited. METHODS: We conducted a cross-sectional analysis comparing cognitive functions (using the Woodcock-Johnson International Edition, WJIE) in 35 kidney transplant and 35 healthy control children. Data on laboratory measurements, comorbidities, and social characteristics were collected. RESULTS: Transplant children had significantly worse scores on the intelligence quotient (IQ) test compared with controls [Full Scale IQ score 85 (26) vs 107 (10), p <0.001]. Lower maternal education level was significantly associated with lower WJIE cognitive test scores; however, no association was found between laboratory values and WJIE scores. Among children with kidney transplants, those with medical comorbid conditions had significantly lower Verbal Ability and Full Scale IQ scores. Earlier age of dialysis onset and a longer total time on dialysis (>9 months) were associated with lower test scores. Age-standardized duration of hospitalization was inversely correlated with IQ (r = -0.46, p <0.01) and was an independent significant predictor (Beta = -0.38, p = 0.02) of IQ scores in transplanted children. CONCLUSIONS: Child kidney transplant recipients have neurocognitive function impairments that are associated with markers of socioeconomic status (SES) and factors related to disease severity.

Genetic analysis and functional characterization of novel mutations in a series of patients with atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome (aHUS) is a rare disorder caused by dysregulation of the complement alternative pathway, and associated with mutations in genes of complement components and regulators. In the recent years several studies have been published describing these mutations, however, no data is available from the Central and Eastern European region. In this study we present a detailed genetic analysis of our 30 patients, hospitalized with the diagnosis of aHUS in the past 7 years. We analyzed the genetic variants of genes CFH, CFI, CD46, THBD, CFB and C3; furthermore the possible effect of mutations that may alter the function or level of factor H protein was also investigated. We identified 27 (12 novel and 15 previously described) potentially disease-causing mutations in the candidate genes in 23 patients. Genetic analysis of family members revealed that in most cases the disease develops in individuals with multiple genetic risk factors, which may explain the low penetrance of the mutations. Here we showed that two novel mutations (p.W198R, p.P1161T) and a previously reported one (p.R1215Q) in CFH caused impaired regulation as indicated by increased lysis in hemolytic test, while four CFH mutations (p.V609D, p.S722X, p.T1216del and p.C448Y) were associated with decreased factor H protein level in serum as determined by allele-specific immunoassay. These results further point to the necessity of complete genetic workup of patients with aHUS and to the importance of functional characterization of novel variations.

The role of complement in Streptococcus pneumoniae-associated haemolytic uraemic syndrome.

BACKGROUND: Atypical forms of haemolytic uraemic syndrome (aHUS) include HUS caused by defects in the regulation of alternative complement pathway and HUS linked to neuraminidase-producing pathogens, such as Streptococcus pneumoniae. Increasing data support a pathogenic role of neuraminidase in the development of S. pneumoniae-associated haemolytic uraemic syndrome (SP-HUS), but the role of complement has never been clarified in detail. Therefore, we aimed to investigate whether the pathologic complement profile and genetic risk factors of aHUS are present in patients with SP-HUS. METHODS: Enrolling five patients with SP-HUS classical and alternative pathway activity, besides C3, C4, factors H, B, I and anti-factor H autoantibody levels were determined. The coding regions of CFH, CFI, CD46 (MCP), THBD, C3 and CFB genes were sequenced and the copy number of CFI, CD46, CFH and related genes were also analyzed. RESULTS: We found that in the acute phase samples of SP-HUS patients, complement components C4, C3 and activity of the classical and alternative pathways were decreased, indicating severe activation and complement consumption, but most of these alterations normalized later in remission. Three of the patients carried mutations and risk haplotypes in complement-mediated aHUS associated genes. The identified mutations include a previously published CFI variant (P50A) and two novel ones in CFH (R1149X) and THBD (T44I) genes. CONCLUSIONS: Our results suggest that severe complement dysregulation and consumption accompany the progress of invasive pneumococcal disease (IPD)-associated SP-HUS and genetic variations of complement genes may contribute to the development of this complication in a proportion of the affected patients.