Genetic, clinical, and pathological study of patients with severe hypertension-associated renal microangiopathy

BACKGROUND

Severe hypertension may be a prominent manifestation of complement-mediated thrombotic microangiopathy. Furthermore, patients with severe hypertension-associated thrombotic microangiopathy may present with concurrent hematologic abnormalities that mimic complement-mediated thrombotic microangiopathy. Whether or not severe hypertension-associated thrombotic microangiopathy is associated with genetic susceptibility in complement- and/or coagulation-pathway genes remains unclear, and there is thus a need to identify clinicopathological clues to distinguish between these entities.

METHODS

Forty-five patients with concomitant severe hypertension and thrombotic microangiopathy on kidney biopsy were identified retrospectively. Whole-exome sequencing was performed to identify rare variants in 29 complement- and coagulation-cascade genes. Clinicopathological features were compared between patients with severe hypertension-associated thrombotic microangiopathy and complement-mediated thrombotic microangiopathy with severe hypertension.

RESULTS

Three patients with pathogenic variants diagnostic of complement-mediated thrombotic microangiopathy and two with anti-factor H antibody positivity were diagnosed with complement-mediated thrombotic microangiopathy with severe hypertension. Among the 40 patients with severe hypertension-associated thrombotic microangiopathy, 53 rare variants of uncertain significance were found in the analyzed genes in 34 (34/40, 85%) patients, of whom 12 patients harbored two or more variants. Compared with complement-mediated thrombotic microangiopathy patients with severe hypertension, patients with severe hypertension-associated thrombotic microangiopathy were more likely to have left ventricular wall thickening (p < 0.001), less-severe acute glomerular thrombotic microangiopathy lesions including mesangiolysis and subendothelial space widening (both p < 0.001), and less arteriolar thrombosis formation (p < 0.001).

CONCLUSIONS

Rare genetic variants involving complement and coagulation pathways can be found in patients with severe hypertension-associated thrombotic microangiopathy; their role needs further investigation. Cardiac remodeling and acute glomerular TMA lesions may help to differentiate between severe hypertension-associated thrombotic microangiopathy and complement-mediated thrombotic microangiopathy with severe hypertension.

Immunological risk and complement genetic evaluations in early onset de novo thrombotic microangiopathy after living donor kidney transplantation: A Japanese multicenter registry

BACKGROUND

Thrombotic microangiopathy (TMA) after kidney transplantation (KTx), particularly early onset de novo (dn) TMA, requires immediate interventions to prevent irreversible organ damage. This multicenter study was performed to investigate the allogeneic clinical factors and complement genetic background of dnTMA after KTx.

METHODS

Perioperative dnTMA after KTx within 1 week after KTx were diagnosed based on pathological or/and hematological criteria at each center, and their immunological backgrounds were researched. Twelve aHUS-related gene variants were examined in dnTMA cases.

RESULTS

Seventeen recipients (15 donors) were enrolled, and all dnTMA cases were onset within 72-h of KTx, and 16 of 17 cases were ABO incompatible. The implementation rate of pre-transplant plasmaphereses therapies were low, including cases with high titers of anti-A/anti-B antibodies. Examination of aHUS-related gene variants revealed some deletions and variants with minor allele frequency (MAF) in Japan or East Asian genome databases in genes encoding alternative pathways and complement regulatory factors. These variants was positive in 8 cases, 6 of which were positive in both recipient and donor, but only in one graft loss case.

CONCLUSIONS

Although some immunological risks were found for dnTMA after KTx, only a few cases developed into TMA. The characteristic variations revealed in the present study may be novel candidates related to dnTMA in Japanese or Asian patients, but not pathogenic variants of aHUS. Future studies on genetic and antigenic factors are needed to identify factors contributing to dnTMA after KTx.

Clinical features and outcomes of patients with diacylglycerol kinase epsilon nephropathy: a nationwide experience

BACKGROUND

Thrombotic microangiopathy (TMA) is usually caused due to dysregulation of the alternative complement pathway. Rarely, thrombotic microangiopathy is caused by non-complement mediated mutations in diacylglycerol kinase epsilon (DGKE); information about therapy and outcome of these patients is limited.

METHODS

Medical records of patients, younger than 18 years, diagnosed with TMA and variants in DGKE were reviewed to include 12 patients from seven centers. Genetic studies included targeted exome sequencing and multiplex-ligation dependent probe amplification of CFH-CFHR5.

RESULTS

Patients presented at a median age of 11 (7.5, 12.3) months; all were younger than 2 years. All patients had an infectious prodrome; enteroinvasive, enteropathogenic, and enterotoxigenic Escherichia coli were detected in two patients with diarrhea. Chief features included those of microangiopathic hemolysis (n = 11), microscopic hematuria (n = 10), nephrotic range proteinuria (n = 10), hypoalbuminemia (n = 6), elevated total cholesterol (n = 6), and hypocomplementemia (n = 4). Histopathology showed thrombotic microangiopathy (n = 4), overlapping with membranoproliferative pattern of injury (n = 1). At median 3.3 years of follow-up, significant hypertension and/or proteinuria (40%), relapses (66.7%), and death or progression to CKD (60%) were common. Genetic sequencing showed 13 homozygous and compound heterozygous variants (7 pathogenic, 3 likely pathogenic) located throughout DGKE; 11 variants were novel.

CONCLUSIONS

This case series highlights the need to suspect DGKE nephropathy in young patients with TMA, especially those with severe proteinuria. Medium-term outcomes are unsatisfactory with risk of relapses, progressive kidney failure, and death. A higher resolution version of the Graphical abstract is available as Supplementary information.

Concurrent Cobalamin C and Plasminogen Deficiencies in a Patient with Chronic Thrombotic Microangiopathy

BACKGROUND

Although most patients with atypical hemolytic uremic syndrome (aHUS) have variants in genes participating in alternative complement pathways, rare variants in non-complement pathway-related genes, including DGKE, INF2, MMACHC, PLG, and THBD, have also been described.

CASE PRESENTATION

We report an 18-year-old male patient with renal biopsy-proven chronic thrombotic microangiopathy that raised suspicion of aHUS. Whole-exome sequencing revealed a novel pathogenic homozygous MMACHC c.484G>T (p.Gly162Trp) variant. Subsequently, clinical and laboratory findings confirmed cobalamin C (Cbl C) deficiency. Also, homozygous missense c.1112C>T PLG (p.Thr371Ile) variant was detected (it had been reported as a variant of unknown significance). However, the low serum plasminogen (PLG) activity proved the pathogenicity of c.1112C>T. Hence, the patient was diagnosed with concurrent Cbl C and PLG deficiencies. Segregation analysis revealed that the mother and father had the same heterozygous PLG and MMACHC variants. PLG variants have generally been described in aHUS patients concomitant with complement gene variants in the literature; therefore, the association between aHUS and PLG variants is controversial. The possible contribution of PLG deficiency to thrombotic microangiopathy was also discussed in this case.

CONCLUSION

Non-complement-mediated aHUS is an exceptional disorder. A limited number of genes are involved in this entity. To our knowledge, this is the first aHUS patient diagnosed with both Cbl C and PLG deficiencies in the literature.

MASP2 inhibition by narsoplimab suppresses endotheliopathies characteristic of transplant-associated thrombotic microangiopathy: in vitro and ex vivo evidence

Transplant-associated thrombotic microangiopathy (TA-TMA) is an endotheliopathy complicating up to 30% of allogeneic hematopoietic stem cell transplants (alloHSCT). Positive feedback loops among complement, pro-inflammatory, pro-apoptotic, and coagulation cascade likely assume dominant roles at different disease stages. We hypothesized that mannose-binding lectin-associated serine protease 2 (MASP2), principal activator of the lectin complement system, is involved in the microvascular endothelial cell (MVEC) injury characteristic of TA-TMA through pathways that are susceptible to suppression by anti-MASP2 monoclonal antibody narsoplimab. Pre-treatment plasmas from 8 of 9 TA-TMA patients achieving a complete TMA response in a narsoplimab clinical trial activated caspase 8, the initial step in apoptotic injury, in human MVEC. This was reduced to control levels following narsoplimab treatment in 7 of the 8 subjects. Plasmas from 8 individuals in an observational TA-TMA study, but not 8 alloHSCT subjects without TMA, similarly activated caspase 8, which was blocked in vitro by narsoplimab. mRNA sequencing of MVEC exposed to TA-TMA or control plasmas with and without narsoplimab suggested potential mechanisms of action. The top 40 narsoplimab-affected transcripts included upregulation of SerpinB2, which blocks apoptosis by inactivating procaspase 3; CHAC1, which inhibits apoptosis in association with mitigation of oxidative stress responses; and pro-angiogenesis proteins TM4SF18, ASPM, and ESM1. Narsoplimab also suppressed transcripts encoding pro-apoptotic and pro-inflammatory proteins ZNF521, IL1R1, Fibulin-5, aggrecan, SLC14A1, and LOX1, and TMEM204, which disrupts vascular integrity. Our data suggest benefits to narsoplimab use in high-risk TA-TMA and provide a potential mechanistic basis for the clinical efficacy of narsoplimab in this disorder.

Pathway-driven rare germline variants associated with transplant-associated thrombotic microangiopathy (TA-TMA)

The significance of rare germline mutations in transplant-associated thrombotic microangiopathy (TA-TMA) is not well studied. We performed a genetic association study in 100 adult TA-TMA patients vs. 98 post-transplant controls after matching by race, sex, and year. We focused on 5 pathways in complement, von Willebrand factor (VWF) function and related proteins, VWF clearance, ADAMTS13 function and related proteins, and endothelial activation (3641variants in 52 genes). In the primary analysis focused on 189 functional rare variants, no differential variant enrichment was observed in any of the pathways; specifically, 29 % TA-TMA and 33 % controls had at least 1 rare complement mutation. In the secondary analysis focused on 37 rare variants predicted to be pathogenic or likely pathogenic by ClinVar, Complement Database, or REVEL in-silico prediction tool, rare variants in the VWF clearance pathway were found to be significantly associated with TA-TMA (p = 0.008). On the gene level, LRP1 was the only one with significantly increased variants in TA-TMA in both analyses (p = 0.025 and 0.015). In conclusion, we did not find a significant association between rare variants in the complement pathway and TA-TMA; however, we discovered a new signal in the VWF clearance pathway driven by the gene LRP1 among likely pathogenic variants.

Mutations in the alternative complement pathway in multiple myeloma patients with carfilzomib-induced thrombotic microangiopathy

Thrombotic microangiopathy (TMA) has been reported to occur in multiple myeloma (MM) patients in association with treatment with carfilzomib, an irreversible proteasome inhibitor (PI). The hallmark of TMA is vascular endothelial damage leading to microangiopathic hemolytic anemia, platelet consumption, fibrin deposition and small-vessel thrombosis with resultant tissue ischemia. The molecular mechanisms underlying carfilzomib-associated TMA are not known. Germline mutations in the complement alternative pathway have been recently shown to portend increased risk for the development of atypical hemolytic uremic syndrome (aHUS) and TMA in the setting of allogeneic stem cell transplant in pediatric patients. We hypothesized that germline mutations in the complement alternative pathway may similarly predispose MM patients to carfilzomib-associated TMA. We identified 10 MM patients with a clinical diagnosis of TMA in the context of carfilzomib treatment and assessed for the presence of germline mutations in the complement alternative pathway. Ten, matched MM patients exposed to carfilzomib but without clinical TMA were used as negative controls. We identified a frequency of deletions in the complement Factor H genes 3 and 1 (delCFHR3-CFHR1) and genes 1 and 4 (delCFHR1-CFHR4) in MM patients with carfilzomib-associated TMA that was higher as compared to the general population and matched controls. Our data suggest that complement alternative pathway dysregulation may confer susceptibility to vascular endothelial injury in MM patients and predispose to development of carfilzomib-associated TMA. Larger, retrospective studies are needed to evaluate whether screening for complement mutations may be indicated to properly counsel patients about TMA risk with carfilzomib use.

MCPggaac haplotype is associated with poor graft survival in kidney transplant recipients with de novo thrombotic microangiopathy

De novo thrombotic microangiopathy (TMA) is associated with poor kidney graft survival, and as we previously described, it is a recipient driven process with suspected genetic background. Direct Sanger sequencing was performed in 90 KTR with de novo TMA and 90 corresponding donors on selected regions in CFH, CD46, C3, and CFB genes that involve variations with a functional effect or confer a risk for aHUS. Additionally, 37 recipients of paired kidneys who did not develop TMA were analyzed for the MCPggaac haplotype. Three-years death-censored graft survival was assessed using Kaplan-Meier and Cox regression models. The distribution of haplotypes in all groups was in the Hardy-Weinberg equilibrium and there was no clustering of haplotypes in any group. In the TMA group, we found that MCPggaac haplotype carriers were at a significantly higher risk of graft loss compared to individuals with the wild-type genotype. Worse 3-year death-censored graft survival was associated with longer cold ischemia time (HR 1.20, 95% CI 1.06, 1.36) and recipients’ MCPggaac haplotype (HR 3.83, 95% CI 1.42, 10.4) in the multivariable Cox regression model. There was no association between donor haplotypes and kidney graft survival. Similarly, there was no effect of the MCPggaac haplotype on 3-year graft survival in recipients of paired kidneys without de novo TMA. Kidney transplant recipients carrying the MCPggaac haplotype with de novo TMA are at an increased risk of premature graft loss. These patients might benefit from therapeutic strategies based on complement inhibition.

Atypical hemolytic uremic syndrome induced by SARS-CoV2 infection in infants with EXOSC3 mutation

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is a rare disease characterized by systemic thrombotic microangiopathy mainly in the kidneys and mostly due to genetic disorders leading to uncontrolled activation of the complement system. Severe complications of SARS-CoV2 infection are linked to microvascular injury and complement activation is suspected to play a role in the pathogenesis of endothelial cell damage in severe COVID-19.

METHODS

We present the first two cases of aHUS triggered by SARS-CoV-2 infection in two unrelated infants with the same mutation in the RNA exosome gene EXOSC3. This mutation is known to cause pontocerebellar hypoplasia type 1b, an autosomal-recessive neurodegenerative disease. So far, no kidney involvement in affected persons was reported.

RESULTS

As eculizumab treatment was unsuccessful and complement-mediated disorders were ruled out, we suppose that the atypical HUS in our two patients is not due to complement-mediated thrombotic microangiopathy but rather due to a dysfunction of the RNA exosome.

CONCLUSIONS

The RNA exosome is crucial for the precise processing and degradation of nuclear and cytoplasmatic RNA. We suspect that the SARS-CoV-2 infection led to changes in RNA that could not be offset by the defective RNA exosome in our two patients. The accumulation/wrong processing of the viral RNA must have led to the endothelial cell damage resulting in aHUS. This would be a new - "RNA-induced" - mechanism of aHUS.

Thrombotic microangiopathy associated with arboviral infection: Report of 3 cases

Dengue fever and chikungunya are viral diseases that have spread rapidly throughout the world in recent decades. The occurrence of complications is well known, including prerenal acute kidney injury (AKI), which is usually thought to be caused by dehydration and fluid loss. Thrombotic microangiopathy (TMA) is an uncommon aggravation of dengue fever and chikungunya, with only a few cases described in the medical literature. The aim of this study is to present 3 cases of TMA associated with arboviral infection. Three patients with clinical history, laboratory test, and kidney biopsy results compatible with TMA were selected for the study, 2 of whom had a serological diagnosis of dengue fever and 1 of chikungunya. The 3 patients were followed up at the Federal University of Maranhão Hospital’s Nephrology Service in 2018. A targeted gene panel sequencing (TGPS) plus multiple to atypical hemolytic uremic syndrome (aHUS) multiplex ligation–dependent probe amplification (MLPA) was performed in 2 of the patients and revealed in the patient 1 a heterozygous pathogenic variant in the gene THBD, as well as heterozygous deletions in CFH, CFHR1, and CFHR3. In the patient 2, there were heterozygous pathogenic variant in the genes CFI and CFB, in addition to heterozygous deletions in the genes CFHR1 and CFHR3. Both received treatment with eculizumab and undergone recovery of renal function. The third patient had TMA not classified as either aHUS or thrombotic thrombocytopenic purpura (TTP); he abandoned the treatment and returned to the service after 2 years for a dialysis emergency. Patients with arboviral infectious disease and changes that suggest TMA should have appropriate support to establish early diagnosis and useful treatment.

Synergistic effects of ADAMTS13 deficiency and complement activation in pathogenesis of thrombotic microangiopathy

Severe deficiency of plasma ADAMTS13 activity is the primary cause of thrombotic thrombocytopenic purpura (TTP) whereas overwhelming activation of complement via an alternative pathway results in atypical hemolytic uremic syndrome (aHUS), the prototypes of thrombotic microangiopathy (TMA). However, clinical and pathogenic distinctions between TTP and aHUS are often quite challenging. Clinical reports have suggested that complement activation may play a role in the development of TTP, which is caused by severe deficiency of plasma ADAMTS13 activity. However, the experimental evidence to support this hypothesis is still lacking. Here, we show that mice with either Adamts13 -/- or a heterozygous mutation of complement factor H (cfh) at amino acid residue of 1206 (ie, cfh W/R ) alone remain asymptomatic despite the presence of occasional microvascular thrombi in various organ tissues. However, mice carrying both Adamts13 -/- and cfh W/R exhibit thrombocytopenia, low haptoglobin, increased fragmentation of erythrocytes in peripheral blood smear, increased plasma levels of lactate dehydrogenase activity, blood urea nitrogen, and creatinine, as well as an increased mortality rate, consistent with the development of TMA. Moreover, mice with a homozygous mutation of cfh (ie, cfh R/R ) with or without Adamts13 -/- developed severe TMA. The mortality rate in mice with Adamts13 -/- cfh R/R was significantly higher than that in mice with cfh R/R alone. Histological and immunohistochemical analyses demonstrated the presence of disseminated platelet-rich thrombi in terminal arterioles and capillaries of major organ tissues in these mice that were either euthanized or died. Together, our results support a synergistic effect of severe ADAMTS13 deficiency and complement activation in pathogenesis of TMA in mice.

Acquired Complement Regulatory Gene Mutations and Hematopoietic Stem Cell Transplant-Related Thrombotic Microangiopathy

Hematopoietic stem cell transplant-related thrombotic microangiopathy (HSCT-TMA) is a severe complication whose pathophysiology is unknown. We describe 6 patients in which the disease was associated with complement regulatory gene abnormalities received from their respective donors. It is suggested that mutated and transplanted monocyte-derived cells are responsible for production of abnormal proteins, complement dysregulation, and, ultimately, for the disease. This observation might have important drawbacks as far as HSCT-TMA pathophysiology and treatment are concerned.

Syndromes of Thrombotic Microangiopathy

Thrombotic thrombocytopenia purpura (TTP) and the hemolytic uremic syndrome (HUS) are rare thrombotic microangiopathies that can be rapidly fatal. Although the acquired versions of TTP and HUS are generally highest on this broad differential, multiple rarer entities can produce a clinical picture similar to TTP/HUS, including microangiopathic hemolysis, renal failure, and neurologic compromise. More recent analysis has discovered a host of genetic factors that can produce microangiopathic hemolytic syndromes. This article discusses the current understanding of thrombotic microangiopathy and outlines the pathophysiology and causative agents associated with each distinct syndrome as well as the most accepted treatments.

VEGF regulates local inhibitory complement proteins in the eye and kidney

Outer retinal and renal glomerular functions rely on specialized vasculature maintained by VEGF that is produced by neighboring epithelial cells, the retinal pigment epithelium (RPE) and podocytes, respectively. Dysregulation of RPE- and podocyte-derived VEGF is associated with neovascularization in wet age-related macular degeneration (ARMD), choriocapillaris degeneration, and glomerular thrombotic microangiopathy (TMA). Since complement activation and genetic variants in inhibitory complement factor H (CFH) are also features of both ARMD and TMA, we hypothesized that VEGF and CFH interact. Here, we demonstrated that VEGF inhibition decreases local CFH and other complement regulators in the eye and kidney through reduced VEGFR2/PKC-α/CREB signaling. Patient podocytes and RPE cells carrying disease-associated CFH genetic variants had more alternative complement pathway deposits than controls. These deposits were increased by VEGF antagonism, a common wet ARMD treatment, suggesting that VEGF inhibition could reduce cellular complement regulatory capacity. VEGF antagonism also increased markers of endothelial cell activation, which was partially reduced by genetic complement inhibition. Together, these results suggest that VEGF protects the retinal and glomerular microvasculature, not only through VEGFR2-mediated vasculotrophism, but also through modulation of local complement proteins that could protect against complement-mediated damage. Though further study is warranted, these findings could be relevant for patients receiving VEGF antagonists.

[Atypical hemolytic uremic syndrome (aHUS): new insights into pathogenesis leading to novel therapeutic approaches]

The atypical hemolytic-uremic syndrome (aHUS) belongs to the thrombotic mictroangiopathies (TMA). This group of diseases has traditionally been divided on clinical grounds by affected organs into thrombotic-thrombocytopenic purpura (TTP) and hemolytic-uremic syndrome (HUS), the latter being termed atypical if not preceeded by diarrhea. Tremendous scientific advances of the last two decases have shown that these clinically overlaping syndromes are caused by distinct molecular mechanisms. The definition of clinical syndromes has therefore been replaced by a TMA-classification on a molecular-mechanistic basis. aHUS is caused by an uncontrolled activation of the alternative complement pathway mostly due to genetic defects. These insights and particularly the development of a specific terminal complement inhibitor have revolutionized the treatment of aHUS and considerably improved its prognosis.

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.

Complement activation in diseases presenting with thrombotic microangiopathy

The complement system contains a great deal of biological "energy". This is demonstrated by the atypical hemolytic uremic syndrome (aHUS), which is a thrombotic microangiopathy (TMA) characterized by endothelial and blood cell damage and thrombotic vascular occlusions. Kidneys and often also other organs (brain, lungs and gastrointestinal tract) are affected. A principal pathophysiological feature in aHUS is a complement attack against endothelial cells and blood cells. This leads to platelet activation and aggregation, hemolysis, prothrombotic and inflammatory changes. The attacks can be triggered by infections, pregnancy, drugs or trauma. Complement-mediated aHUS is distinct from bacterial shiga-toxin (produced e.g. by E. coli O:157 or O:104 serotypes) induced "typical" HUS, thrombotic thrombocytopenic purpura (TTP) associated with ADAMTS13 (an adamalysin enzyme) dysfunction and from a recently described disease related to mutations in intracellular diacylglycerol kinase ε (DGKE). Mutations in proteins that regulate complement (factor H, factor I, MCP/CD46, thrombomodulin) or promote (C3, factor B) amplification of its alternative pathway or anti-factor H antibodies predispose to aHUS. The fundamental defect in aHUS is an excessive complement attack against cellular surfaces. This can be due to 1) an inability to regulate complement on self cell surfaces, 2) hyperactive C3 convertases or 3) complement activation and coagulation promoting changes on cell surfaces. The most common genetic cause is in factor H, where aHUS mutations disrupt its ability to recognize protective polyanions on surfaces where C3b has become attached. Most TMAs are thus characterized by misdirected complement activation affecting endothelial cell and platelet integrity.

[Clinicomorphological characteristics of renal disorders in patients with genetic thrombophilia]

AIM

To characterize the course and clinicomorphological features of chronic glomerulonephritis (CGN) in patients with genetic thrombophilia.

MATERIAL AND METHODS

A clinical picture and evidence on renal biopsy from 25 patients (12 females, mean age 32 +/- 12 years and 13 males, mean age 36 +/- 8.8 years) admitted to hospital with diagnosis of chronic glomerulonephritis were analysed. Mean duration of renal problem to the moment of biopsy was 37.6 +/- 39 months. Renal end point was stable rise of Scr > 1.4 mg/dl for 6 months. Polymerase chain reaction defined polymorphisms of the genes MTHFR C677T; PTG G20210A; FV Leiden G1691A; FGB G455A; ITGB3 T176C L33P; PAI-1 4G/5G 675.

RESULTS

Mutation in one gene was detected in 24% patients, a multigenic form of thrombophilia--in 76% patients. Morphologically, all the patients' renal tissue had the signs of thrombotic microangiopathy (TMA), 8 patients had a combination of acute and chronic TMA. TMA was the only histological sign of nephropathy in 3 (13%) patients, the rest patients showed TMA combination with different morphological variants of CGN. Sclerotic alterations were most severe in combined carriage of the alleles 4G PAI-1 and T MTHFR. A correlation was found between the renal end point and number of mutant alleles (r = 0.6, p < 0.05), the presence of allele 4G (r = 0.46, p = 0.05) and interstitial sclerosis (r = 0.5, p = 0.05).

CONCLUSION

Hereditary thrombophilia promotes induction of nephrosclerosis leading to activation of intraglomerular blood clotting which contributes to CGN progression. Patients with genetic thrombophilia may develop acute TMA as the only variant of renal damage.