C3 Mutation Research Articles

C3 glomerulopathy in cystic fibrosis: a case report

BackgroundC3 glomerulonephritis is a rare glomerulopathy characterized at renal biopsy by C3 deposition, alone or with scanty immunoglobulins, as well as by an electron-dense material in mesangium, subendothelial and subepithelial space. An abnormal systemic activation of the alternative pathway of the complement cascade is responsible for the development of the disease if triggered by several possible environmental conditions. We report the first case in literature of a patient affected by cystic fibrosis and C3GN.Case presentationOur case involves a young woman with cystic fibrosis, who had persistent microscopic hematuria, proteinuria and hypocomplementemia C3 for over three months. Renal biopsy confirmed the diagnosis of C3 glomerulopathy. Complement system dysregulation was tested and resulted in a strong terminal pathway activation proved by high levels of sC5b-9 complex, amounting to 1588 ng/ml (normal value < 400 ng/ml). Next generation sequencing (NGS) showed polymorphism in CFH (p.V62I in SCR1) and THBD (p.A473V), already known as pathogenic for C3GN, as well as a mutation in C3 (p.R102G) associated only with age-related macular degeneration (AMD) so far. Treatment was based on ACE inhibitors and kidney function is currently stable (GFR 50 ml/min, serum creatinine 1.7).ConclusionsThe co-existence of C3 glomerulopathy in a patient with CF, which is characterized by chronic infection/inflammation, makes this case an interesting model of chronic altered systemic activation of the alternative pathway of the complement cascade.

Ultra-rare C3 mutation leading to a dominant familial C3 glomerulopathy phenotype

Ultra-rare C3 mutation leading to a dominant familial C3 glomerulopathy phenotype

J-shaped association of circulating apolipoprotein C3 with cardiovascular mortality

Aim: Loss-of-function mutations in the apolipoprotein C3 (APOC3) gene, which encodes an inhibitor of lipoprotein lipase, are associated with lower circulating APOC3 and reduced cardiovascular risk. Oligomer antisense inhibition of APOC3 production results in pronounced reduction of circulating APOC3 but its effect on cardiovascular risk remains unknown. The present study was performed to elucidate the relationships of circulating APOC3 with all-cause and cardiovascular mortality.

Thrombotic microangiopathy mimicking membranoproliferative glomerulonephritis.

A 4-year-old boy presented with proteinuria and developed progressive renal failure over 6 years. In the patient's family, five individuals were affected with atypical haemolytic uraemic syndrome (aHUS) but not the patient. Renal biopsies (n = 3) showed glomerular basement membrane thickening with double contours, endothelial swelling and deposits of C3 and C1q. Electron microscopy revealed mesangial and subendothelial electron-dense deposits. Complement mutations in membrane cofactor protein (Y155D) and C3 (R713W and G1094R) were detected in all affected family members. The patient also had transient autoantibodies to factor H. The findings suggest that aHUS and glomerulopathy resembling membranoproliferative glomerulonephritis may have a common molecular background.

Echocardiographic characterization of hypertrophic cardiomyopathy in Chinese patients with myosin-binding protein C3 mutations

Hypertrophic cardiomyopathy (HCM) is a common autosomal dominant cardiac disease, affecting 1 in 500 people. Myosin-binding protein C3 (MyBPC3) gene mutations are the most common genetic cause of HCM. However, the prevalence of the MyBPC3 gene mutation in Chinese patients with HCM, and their echocardiographic characteristics, remain unknown. In the present study, 48 Chinese patients with HCM were sequenced to identify the MyBPC3 gene and were characterized by their clinical features using 2-dimensional echocardiography and real-time 3-dimensional echocardiography. Nine MyBPC3 mutations were identified in seven unrelated patients out of 48 cases, which accounts for a 15% prevalence of MyBPC3 mutations in Chinese patients with HCM. Family members of the seven patients were further tested and divided into the following two groups based on HCM phenotype and MyBPC3 mutations: Positive genotype with left ventricular (LV) hypertrophy (LVH) (G+/LVH+, n=18); and positive genotype without LVH (G+/LVH-, n=23). These groups were compared with matched normal control subjects (n=30). G+/LVH+ patients showed significantly lower septal and lateral Tissue Doppler imaging (TDI)-derived systolic, early and late diastolic mitral annular velocities compared with the controls. In addition, diastolic dyssynchrony index (DDI) was markedly higher in the G+/LVH+ subjects. However, only septal Ea was significantly lower in G+/LVH- subjects in comparison with controls, with no significant difference in lateral Sa, Ea and Aa, and DDI. In conclusion, the patients in the present study demonstrated a 15% prevalence of MyBPC3 gene mutations in the Chinese HCM population. MyBPC3 gene mutations may cause regional LV hypertrophic remodeling first and further proceed to global hypertrophic remodeling and myocardial diastolic dysfunction.

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%. SummaryBackgroundDifferentiation 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.ObjectivesWe describe the clinical phenotype and nature of complement mutations in a cohort of aHUS patients referred as acute TMAs.Patients/methodsFourteen 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%.ResultsOf 14 aHUS patients, 11 (79%) had platelet counts < 30 × 109/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.ConclusionsWe 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.

The influence of clinical and genetic factors on left ventricular wall thickness in Ragdoll cats

ObjectivesTo investigate the effect of various genetic and environmental modifiers on left ventricular (LV) wall thickness in a cohort of cats genotyped for the myosin binding protein C3 mutation (MYBPC3). AnimalsSixty-four Ragdoll cats. MethodsAll cats were screened for HCM with echocardiography and genotyping for the HCM-associated MYBPC3:R820W mutation. Cats were also genotyped for previously identified variant polymorphisms of the angiotensin-converting enzyme (ACE) and cardiac beta-adrenergic receptor (ADRB1) genes. Plasma N-terminal pro-B-type natriuretic peptide and cardiac troponin I were also measured. Associations were evaluated between genotype (MYBPC3 negative/positive, and ACE and ADRB1 negative/heterozygous/homozygous), patient factors (body weight, age and sex) and echocardiographic measurements of LV wall thickness. ResultsMale cats had greater maximum wall thickness (LVmax; 5.8 mm, IQR 5.1–6.4 mm) than females (4.7 mm, IQR 4.4–5.3 mm, p = 0.002). Body weight positively correlated with LVmax (ρ = 0.604, p < 0.001). The MYBPC3:R820W-positive cats had a greater LVmax (5.44 mm, IQR 4.83–6.28 mm) than the negative cats (4.76 mm, IQR 4.36–5.32 mm, p = 0.001). Also, the ACE polymorphism genotype was associated with LVmax: the homozygous cats (5.37 mm, IQR 5.14–6.4 mm) had greater LVmax than the heterozygous cats (4.73 mm, IQR 4.41–5.55 mm, p = 0.014). Only the MYBPC3 genotype and body weight were independently associated with wall thickness in multivariable analysis. ConclusionsThis study provides evidence that the MYBPC3:R820W mutation is independently associated with LV wall thickness in Ragdoll cats. Body weight is also independently associated with maximum LV wall thickness, but is not currently accounted for in HCM screening. In addition, other genetic modifiers may be associated with variation in LV wall thickness in Ragdolls.

The molecular and structural bases for the association of complement C3 mutations with atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) associates with complement dysregulation caused by mutations and polymorphisms in complement activators and regulators. However, the reasons why some mutations in complement proteins predispose to aHUS are poorly understood. Here, we have investigated the functional consequences of three aHUS-associated mutations in C3, R592W, R161W and I1157T. First, we provide evidence that penetrance and disease severity for these mutations is modulated by inheritance of documented “risk” haplotypes as has been observed with mutations in other complement genes. Next, we show that all three mutations markedly reduce the efficiency of factor I-mediated C3b cleavage when catalyzed by membrane cofactor protein (MCP), but not when catalyzed by factor H. Biacore analysis showed that each mutant C3b bound sMCP (recombinant soluble MCP; CD46) at reduced affinity, providing a molecular basis for its reduced cofactor activity. Lastly, we show by electron microscopy structural analysis a displacement of the TED domain from the MG ring in C3b in two of the C3 mutants that explains these defects in regulation. As a whole our data suggest that aHUS-associated mutations in C3 selectively affect regulation of complement on surfaces and provide a structural framework to predict the functional consequences of the C3 genetic variants found in patients.

Mutations in complement C3 from aHUS patients

In this issue of Blood, Schramm et al demonstrate that the majority of mutations in complement C3 identified in atypical hemolytic uremic syndrome (aHUS) patients cause dysregulation in the alternative pathway of complement.

Mapping interactions between complement C3 and regulators using mutations in atypical hemolytic uremic syndrome

AbstractThe pathogenesis of atypical hemolytic uremic syndrome (aHUS) is strongly linked to dysregulation of the alternative pathway of the complement system. Mutations in complement genes have been identified in about two-thirds of cases, with 5% to 15% being in C3. In this study, 23 aHUS-associated genetic changes in C3 were characterized relative to their interaction with the control proteins factor H (FH), membrane cofactor protein (MCP; CD46), and complement receptor 1 (CR1; CD35). In surface plasmon resonance experiments, 17 mutant recombinant proteins demonstrated a defect in binding to FH and/or MCP, whereas 2 demonstrated reduced binding to CR1. In the majority of cases, decreased binding affinity translated to a decrease in proteolytic inactivation (known as cofactor activity) of C3b via FH and MCP. These results were used to map the putative binding regions of C3b involved in the interaction with MCP and CR1 and interrogated relative to known FH binding sites. Seventy-six percent of patients with C3 mutations had low C3 levels that correlated with disease severity. This study expands our knowledge of the functional consequences of aHUS-associated C3 mutations relative to the interaction of C3 with complement regulatory proteins mediating cofactor activity.

Rare loss-of-function mutation in complement component C3 provides insight into molecular and pathophysiological determinants of complement activity.

The plasma protein C3 is a central element in the activation and effector functions of the complement system. A hereditary dysfunction of C3 that prevents complement activation via the alternative pathway (AP) was described previously in a Swedish family, but its genetic cause and molecular consequences have remained elusive. In this study, we provide these missing links by pinpointing the dysfunction to a point mutation in the β-chain of C3 (c.1180T > C; p.Met(373)Thr). In the patient's plasma, AP activity was completely abolished and could only be reconstituted with the addition of normal C3. The M373T mutation was localized to the macroglobulin domain 4 of C3, which contains a binding site for the complement inhibitor compstatin and is considered critical for the interaction of C3 with the AP C3 convertase. Structural analyses suggested that the mutation disturbs the integrity of macroglobulin domain 4 and induces conformational changes that propagate into adjacent regions. Indeed, C3 M373T showed an altered binding pattern for compstatin and surface-bound C3b, and the presence of Thr(373) in either the C3 substrate or convertase-affiliated C3b impaired C3 activation and opsonization. In contrast to known gain-of-function mutations in C3, patients affected by this loss-of-function mutation did not develop familial disease, but rather showed diverse and mostly episodic symptoms. Our study therefore reveals the molecular mechanism of a relevant loss-of-function mutation in C3 and provides insight into the function of the C3 convertase, the differential involvement of C3 activity in clinical conditions, and some potential implications of therapeutic complement inhibition.

Novel C3 Mutation Causing Atypical Hemolytic Uremic Syndrome Successfully Treated with Eculizumab

Introduction: Hemolytic Uremic Syndrome (HUS) is a rare thrombotic microangiopathic disease characterized by hemolytic anemia, thrombocytopenia, and acute renal failure occurring after infection with a Shiga-like toxin producing bacteria. Patients without evidence of infection with such kind of bacteria are described as having atypical HUS (aHUS). aHUS can be classified as sporadic or familial, and both conditions are associated with complement abnormalities, more specifically with dysregulation of the alternative complement pathway. Familial aHUS is caused, most of the times, by either gain of function mutations in activators of complement or loss of function mutations in complement regulators. Among others, the genes commonly mutated in a HUS are CFH, C3, CFB, MCP and etc. Here we describe a novel mutation in C3 present in a patient with familial aHUS, and the successful treatment of this patient with the complement inhibitor Eculizumab.Report: A 40-year-old female presented at the emergency room with headache and anasarca. Physical exam was consistent with hypertension, pale skin and mucous membranes. Blood tests revealed renal insufficiency, anemia and low platelet counts. She had no history of infections. The first diagnostic hypothesis was thrombotic thrombocytopenic purpura and she was started on plasmapheresis and hemodialysis. She was discharged 40 days later with clinical improvement. One week after discharge she was admitted at our hospital with recurrence of the clinical picture. Blood tests at admission showed hemoglobin = 7,8 g/dL, platelet counts = 70.000 / uL, LDH = 1024 U/L, Creatinine = 4, 19 mg/dl, ADAMTS13 activity = 79%, C3 = 29,5 mg/dL, C4 = 16.2 mg/dL and factor H = 212 µg/mL. The patient informed that her mother and five aunts, died around 40 to 50 years of age due to renal insufficiency. Plasmapheresis and hemodialysis were resumed and she was started on Rituximab 375 mg/m² weekly. After an initial clinical response, but soon anemia, low platelets and high LDH recurred. At that point we made a hypothesis of aHUS, ordered a C3 sequencing and started a therapeutic trial with Eculizumab. She received 900 mg of eculizumab during four weeks, and maintenance of 1200 mg every two weeks. She showed a continuous improvement after the first dose and was discharged after the third dose, without the need for hemodialysis, with a serum creatinine = 2.1 mg/dl, hemoglobin = 711 g/dL, platelet counts = 262.000 / uL and LDH = 1024 U/L. Now, 6 months after discharge she remains in remission of her disease, with normal blood counts and serum creatinine of is 1.6 mg/dL with Eculizumab maintenance at dose of 1200 mg twice a month. The C3 sequencing revealed the following heterozygous mutations in the 6thexon, c.640C>T (p.Pro214Ser). Since this variant has not been previously described in the medical literature, we performed an in silico analysis using Polyphen2 software and the result was probably pathogenic.Discussion: We have presented a patient with aHUS harboring a novel heterozygous mutation in C3. At least 47 C3 mutations have been described at the FH aHUS database (http://www.fh-hus.org/) spanning almost the entire sequence of the gene (from Lys65 to Val1658). The mutation described here is novel and functional studies to characterize its consequences are needed. But the very strong family history, coupled with the clinical evolution of the patient, the in silico protein analysis and the complete response to eculizumab strongly suggests that this variant is pathogenic and may be used in the future as a predictor of response to Eculizumab. DisclosuresNo relevant conflicts of interest to declare.

Chronic Glomerulonephritis Causing Atypical Hemolytic Uremic Syndrome

Atypical hemolytic uremic syndrome (aHUS) is characterized by hemolytic anemia, thrombocytopenia and kidney failure. Unlike typical HUS which is usually caused by infection with certain strains of E.Coli, a-HUS is caused by abnormalities in complement system, triggered by certain environmental factors or genetic mutations. aHUS can be genetic, acquired, or idiopathic. Mutations in at least 10 genes identified so far (C3, CD46, CFB, CFH, CFHR1, 3, 4 and 5, CFI and THBD) appear to increase the risk of developing aHUS. CFH mutation is the most common accounting for approximately 30 percent of all cases. Pathophysiology is proposed to be microangiopathic in nature, where platelet thrombi occlude microcirculation resulting in organ dysfunction. It is believed that aHUS causes renal dysfunction but we propose that either condition can precede the other. Lucio et al (2013) followed patients who had biopsy-proven diagnosis of glomerulonephritis and found that significant number of them developed aHUS over a period of time.A 26-year old male with no past medical history presented to E.D. with malaise for one week. He denied any fever or chills, recent or remote diarrheal illness or any upper respiratory symptoms. Initial diagnostics revealed hemoglobin 6.8, hematocrit 19.7, WBC 9.2, platelets 79 with peripheral blood smear showing schistocyte, BUN 109, creatinine 28.6, LDH 813, and haptoglobin<10 consistent with hemolytic anemia, thrombocytopenia and renal insufficiency prompting the presumptive diagnosis of TTP/HUS. He was treated with emergent plasmapheresis and hemodialysis. ADAMTS13, complement C3and C4 levels were normal. Renal ultrasound discovered atrophic kidneys consistent with severe chronic kidney disease and kidney biopsy revealed focal segmental collapsing glomerulosclerosis without any evidence of microthrombi. Testing for HIV and hepatitis A, B, C and D were also negative. Given the absence of any preceding diarrheal illness, patient’s age at presentation, and triad of thrombocytopenia, hemolytic anemia and renal insufficiency prompted the diagnosis of a-HUS. Genetic studies for CFH, C3, CFB and CFI mutations were sent, which are still pending. Patient condition remained critical with ongoing hemolysis needing regular plasma exchange therapy and hemodialysis for over period of one month, consistent with aHUS refractory or dependent to plasma therapy. Patient was subsequently referred to a specialized center for treatment with Eculizumab and possible renal transplant.The sequence of events and kidney biopsy findings for our patient suggest that he had an underlying chronic glomerulonephritis which was complicated by aHUS, which has been reported previously. We propose that some common genetic mutations may predispose patients to glomerulonephritis and development of aHUS. Till now it has been postulated that underlying pathophysiology in aHUS is chronic, uncontrolled activation of the complement system. In this case normal complement levels and underlying chronic glomerulonephritis suggests an alternate mechanism for development of aHUS. We emphasizes the importance of further testing and research into the mechanism of aHUS and possible genetic linkage of chronic glomerulonephritis to aHUS. DisclosuresNo relevant conflicts of interest to declare.

Complement mutations in diacylglycerol kinase-ε-associated atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome is characterized by vascular endothelial damage caused by complement dysregulation. Consistently, complement inhibition therapies are highly effective in most patients with atypical hemolytic uremic syndrome. Recently, it was shown that a significant percentage of patients with early-onset atypical hemolytic uremic syndrome carry mutations in diacylglycerol kinase-ε, an intracellular protein with no obvious role in complement. These data support an alternative, complement-independent mechanism leading to thrombotic microangiopathy that has implications for treatment of early-onset atypical hemolytic uremic syndrome. To get additional insights into this new form of atypical hemolytic uremic syndrome, the diacylglycerol kinase-ε gene in a cohort with atypical hemolytic uremic syndrome was analyzed. Eighty-three patients with early-onset atypical hemolytic uremic syndrome (<2 years) enrolled in the Spanish atypical hemolytic uremic syndrome registry between 1999 and 2013 were screened for mutations in diacylglycerol kinase-ε. These patients were also fully characterized for mutations in the genes encoding factor H, membrane cofactor protein, factor I, C3, factor B, and thrombomodulin CFHRs copy number variations and rearrangements, and antifactor H antibodies. Four patients carried mutations in diacylglycerol kinase-ε, one p.H536Qfs*16 homozygote and three compound heterozygotes (p.W322*/p.P498R, two patients; p.Q248H/p.G484Gfs*10, one patient). Three patients also carried heterozygous mutations in thrombomodulin or C3. Extensive plasma infusions controlled atypical hemolytic uremic syndrome recurrences and prevented renal failure in the two patients with diacylglycerol kinase-ε and thrombomodulin mutations. A positive response to plasma infusions and complement inhibition treatment was also observed in the patient with concurrent diacylglycerol kinase-ε and C3 mutations. Data suggest that complement dysregulation influences the onset and disease severity in carriers of diacylglycerol kinase-ε mutations and that treatments on the basis of plasma infusions and complement inhibition are potentially useful in patients with combined diacylglycerol kinase-ε and complement mutations. A comprehensive understanding of the genetic component predisposing to atypical hemolytic uremic syndrome is, therefore, critical to guide an effective treatment.

Association of the myosin binding protein C3 mutation (MYBPC3 R820W) with cardiac death in a survey of 236 Ragdoll cats

ObjectivesA mutation identified in the myosin binding protein C3 gene (MYBPC3 R820W) has been associated with hypertrophic cardiomyopathy (HCM) in Ragdoll cats. Ragdolls with HCM are reported to have a poor prognosis and homozygous cats seem particularly likely to develop severe HCM, although the outcome in Ragdolls tested for the MYBPC3 mutation has not been reported. We aimed to determine the influence of genotype on survival in Ragdoll cats using a questionnaire, and hypothesized that homozygous Ragdolls had shorter lifespans and were more likely to suffer cardiac death than heterozygous or wild-type (WT) cats. Animals251 client owned Ragdoll cats. MethodsA questionnaire for breeders/owners of MYBPC3 genotyped Ragdolls included items related to genotype, age, sex, current status (alive/dead), and date and circumstances of death. Death was categorized as cardiac or non-cardiac. Survival was analyzed using Kaplan–Meier curves and log rank tests. ResultsCompleted questionnaires were received for 236 cats (156 WT, 68 heterozygous, 12 homozygous). Median survival time for homozygous cats was 5.65 years (95%CI 0.4–10.9 years) compared to heterozygous (>16.7 years) or WT (>15.2 years). Homozygous cats were more likely to die from cardiac death (p = 0.004 vs. WT; p = 0.003 vs. heterozygous) and had significantly shorter time to cardiac death (vs. WT p < 0.001; vs. heterozygous p < 0.001). ConclusionsRagdoll cats homozygous for the MYBPC3 R820W mutation have a shorter survival time than WT or heterozygous cats. This suggests a mode of inheritance that follows an incomplete dominance pattern.

Postoperative atypical hemolytic uremic syndrome associated with complement c3 mutation.

Atypical hemolytic uremic syndrome (aHUS) can be distinguished from typical or Shiga-like toxin-induced HUS. The clinical outcome is unfavorable; up to 50% of affected patients progress to end-stage renal failure and 25% die during the acute phase. Multiple conditions have been associated with aHUS, including infections, drugs, autoimmune conditions, transplantation, pregnancy, and metabolic conditions. aHUS in the nontransplant postsurgical period, however, is rare. An 8-month-old boy underwent surgical repair of tetralogy of Fallot. Neurological disturbances, acute renal failure, thrombocytopenia, and microangiopathic hemolytic anemia developed 25 days later, and aHUS was diagnosed. Further evaluation revealed that his complement factor H (CFH) level was normal and that anti-FH antibodies were not detected in his plasma. Sequencing of his CFH, complement factor I, membrane cofactor protein, complement factor B, and thrombomodulin genes was normal. His ADAMTS-13 (a disintegrin-like and metalloprotease with thrombospondin-1 repeats 13) activity was also normal. However, he had a potentially causative mutation (R425C) in complement component C3. Restriction fragment length polymorphism analysis revealed that his father and aunt also had this mutation; however, they had no symptoms of aHUS. We herein report a case of aHUS that developed after cardiovascular surgery and was caused by a complement C3 mutation.

Human embryonic stem cells from a preimplantation genetic diagnosis-tested and affected embryo with mutation in myosin binding protein C3 phenocopies hypertropic cardiomyopathy

Human embryos carrying natural mutations causative of diseases are typically discarded following preimplantation genetic diagnosis (PGD). However, PGD-tested and affected embryos may be used for derivation of disease-specific human embryonic stem cells (hESC) that may represent powerful in vitro models to study disease development, progression, and screen potential therapeutics. Aims were to produce genetically normal and hypertrophic cardiomyopathy (HCM) disease-specific hESC lines, direct their differentiation to cardiomyocytes, and determine if the disease-specific hESC line phenocopied HCM.

Two novel mutations in apolipoprotein C3 underlie atheroprotective lipid profiles in families

Apolipoprotein C3 (APOC3) mutations carriers typically display high plasma high-density lipoprotein cholesterol (HDL-C) and low triglycerides (TGs). We set out to investigate the prevalence and clinical consequences of APOC3 mutations in individuals with hyperalphalipoproteinemia. Two novel mutations (c.-13-2A>G and c.55+1G>A) and one known mutation (c.127G>A;p.Ala43Thr) were found. Lipid profiles and apoCIII isoform distributions were measured. c.55+1G>A mutation carriers displayed higher HDL-C percentiles (35.6 ± 35.8 vs 99.0 ± 0, p = 0.002) and lower TGs (0.51 (0.37-0.61) vs 1.42 (1.12-1.81) mmol/l, p = 0.007) and apoCIII levels (4.24 ± 1.57 vs 7.33 ± 3.61 mg/dl, p = 0.18). c.-13-2A>G mutation carriers did not display significantly different HDL-C levels (84.0 ± 30.0 vs 63.7 ± 45.7, p = 0.50), a trend towards lower TGs [0.71 (0.54 to 0.78) vs 0.85 (0.85 to -) mmol/l, p = 0.06] and significantly lower apoCIII levels (3.09 ± 1.08 vs 11.45 ± 1.06 mg/dl, p = 0.003). p.Ala43Thr mutation carriers displayed a trend towards higher HDL-C percentiles (91.2 ± 31.8 vs 41.0 ± 29.7 mmol/l, p = 0.06) and significantly lower TGs [0.58 (0.36-0.63) vs 0.95 (0.71-1.20) mmol/l, p = 0.02] and apoCIII levels (4.92 ± 2.33 vs 6.60 ± 1.60, p = 0.25). Heterozygosity for APOC3 mutations results in high HDL-C and low TGs and apoCIII levels. This favourable lipid profile in patients with genetically low apoCIII levels holds promise for current studies investigating the potential of apoCIII inhibition as a novel therapeutic in cardiovascular disease prevention.

Atypical haemolytic uraemic syndrome with underlying glomerulopathies. A case series and a review of the literature

Primary or secondary glomerulonephritis has been anecdotally reported in association with atypical haemolytic uraemic syndrome (aHUS). We here report a series of six patients who developed aHUS and glomerulopathy, and review the literature on aHUS and glomerulonephritis. Out of all patients diagnosed at our unit with biopsy-proven glomerular diseases between March 2007 and October 2011, selected cases developing aHUS during the follow-up are presented. The following tests were performed in all six patients: serum C3 and C4 levels, ADAMTS13 activity, CFH levels and anti-CFH autoantibodies and genetic screening for CFH, MCP, CFI, C3 and CFHR1-3 mutations and risk haplotypes associated with aHUS. Two hundred and forty-eight patients received a biopsy-proven diagnosis of glomerulopathy and were followed for a median of 31 months (range 2-58). Of these, six developed aHUS, within a median of 15 months (range 1-36) of their initial diagnosis of glomerulopathy. One of these patients had focal segmental glomerulosclerosis (FSGS), two membranoproliferative glomerulonephritis (MPGN) type I, one C3 glomerulonephritis and two systemic small vessel vasculitis [one granulomatosis with polyangiitis (Wegener's), one Henoch-Schoenlein purpura]. Five patients (one of them heterozygous for a CFH mutation) carried, in homo- or heterozygosity, the risk haplotype CFH-H3 (CFH tgtgt), previously described to be associated with aHUS, while another one patient was homozygous for the MCPggaac risk haplotype predisposing to aHUS when present on both alleles. Different types of glomerulopathies can be complicated by aHUS. Several mechanisms can contribute to this association, such as nephrotic-range proteinuria, mutations or aHUS-risk haplotypes involving genes encoding alternative complement regulatory proteins in some patients and inflammatory triggers associated with systemic immune-mediated diseases.

Combined Complement Gene Mutations in Atypical Hemolytic Uremic Syndrome Influence Clinical Phenotype

Several abnormalities in complement genes reportedly contribute to atypical hemolytic uremic syndrome (aHUS), but incomplete penetrance suggests that additional factors are necessary for the disease to manifest. Here, we sought to describe genotype-phenotype correlations among patients with combined mutations, defined as mutations in more than one complement gene. We screened 795 patients with aHUS and identified single mutations in 41% and combined mutations in 3%. Only 8%-10% of patients with mutations in CFH, C3, or CFB had combined mutations, whereas approximately 25% of patients with mutations in MCP or CFI had combined mutations. The concomitant presence of CFH and MCP risk haplotypes significantly increased disease penetrance in combined mutated carriers, with 73% penetrance among carriers with two risk haplotypes compared with 36% penetrance among carriers with zero or one risk haplotype. Among patients with CFH or CFI mutations, the presence of mutations in other genes did not modify prognosis; in contrast, 50% of patients with combined MCP mutation developed end stage renal failure within 3 years from onset compared with 19% of patients with an isolated MCP mutation. Patients with combined mutations achieved remission with plasma treatment similar to patients with single mutations. Kidney transplant outcomes were worse, however, for patients with combined MCP mutation compared with an isolated MCP mutation. In summary, these data suggest that genotyping for the risk haplotypes in CFH and MCP may help predict the risk of developing aHUS in unaffected carriers of mutations. Furthermore, screening patients with aHUS for all known disease-associated genes may inform decisions about kidney transplantation.