Adult-onset eculizumab-resistant hemolytic uremic syndrome associated with cobalamin C deficiency

Late-onset methylmalonic acidemia and homocysteinemia (cblC disease): systematic review

INTRODUCTION

Combined methylmalonic acidemia and homocystinuria, cblC type is an inborn error of intracellular cobalamin metabolism and the most common one. The age of onset ranges from prenatal to adult. The disease is characterised by an elevation of methylmalonic acid (MMA) and homocysteine and a decreased production of methionine. The aim is to review existing scientific literature of all late onset cblC patients in terms of clinical symptoms, diagnosis, and outcome.

METHODS

A bibliographic database search was undertaken in PubMed (MEDLINE) complemented by a reference list search. We combined search terms regarding cblC disease and late onset. Two review authors performed the study selection, data extraction and quality assessment.

RESULTS

Of the sixty-five articles included in this systematic review, we collected a total of 199 patients. The most frequent clinical symptoms were neuropathy/myelopathy, encephalopathy, psychiatric symptoms, thrombotic microangiopathy, seizures, kidney disease, mild to severe pulmonary hypertension with heart failure and thrombotic phenomena. There were different forms of supplementation used in the different studies collected and, within these studies, some patients received several treatments sequentially and/or concomitantly. The general outcome was: 64 patients recovered, 78 patients improved, 4 patients did not improve, or the disease progressed, and 12 patients died.

CONCLUSIONS

Most scientific literature regarding the late onset cblC disease comes from case reports and case series. In most cases treatment initiation led to an improvement and even recovery of some patients. The lack of complete recovery underlines the necessity for increased vigilance in unclear clinical symptoms for cblC disease.

Versatile Enzymology and Heterogeneous Phenotypes in Cobalamin Complementation Type C Disease

Nutritional deficiency and genetic errors that impair the transport, absorption, and utilization of vitamin B₁₂ (B₁₂) lead to hematological and neurological manifestations. The cblC disease (cobalamin complementation type C) is an autosomal recessive disorder caused by mutations and epi-mutations in the MMACHC gene and the most common inborn error of B₁₂ metabolism. Pathogenic mutations in MMACHC disrupt enzymatic processing of B₁₂, an indispensable step before micronutrient utilization by the two B₁₂-dependent enzymes methionine synthase (MS) and methylmalonyl-CoA mutase (MUT). As a result, patients with cblC disease exhibit plasma elevation of homocysteine (Hcy, substrate of MS) and methylmalonic acid (MMA, degradation product of methylmalonyl-CoA, substrate of MUT). The cblC disorder manifests early in childhood or in late adulthood with heterogeneous multi-organ involvement. This review covers current knowledge on the cblC disease, structure–function relationships of the MMACHC protein, the genotypic and phenotypic spectra in humans, experimental disease models, and promising therapies.

Clinical, phenotypic and genetic landscape of case reports with genetically proven inherited disorders of vitamin B12 metabolism: A meta-analysis

Inherited disorders of B₁₂ metabolism produce a broad spectrum of manifestations, with limited knowledge of the influence of age and the function of related genes. We report a meta-analysis on 824 patients with a genetically proven diagnosis of an inherited disorder of vitamin B₁₂ metabolism. Gene clusters and age categories are associated with patients' manifestations. The "cytoplasmic transport" cluster is associated with neurological and ophthalmological manifestations, the "mitochondrion" cluster with hypotonia, acute metabolic decompensation, and death, and the "B₁₂ availability" and "remethylation" clusters with anemia and cytopenia. Hypotonia, EEG abnormalities, nystagmus, and strabismus are predominant in the younger patients, while neurological manifestations, such as walking difficulties, peripheral neuropathy, pyramidal syndrome, cerebral atrophy, psychiatric disorders, and thromboembolic manifestations, are predominant in the older patients. These results should prompt systematic checking of markers of vitamin B₁₂ status, including homocysteine and methylmalonic acid, when usual causes of these manifestations are discarded in adult patients.

Adult-onset CblC deficiency: a challenging diagnosis involving different adult clinical specialists

Background

Methylmalonic aciduria and homocystinuria, CblC type (OMIM #277400) is the most common disorder of cobalamin intracellular metabolism, an autosomal recessive disease, whose biochemical hallmarks are hyperhomocysteinemia, methylmalonic aciduria and low plasma methionine. Despite being a well-recognized disease for pediatricians, there is scarce awareness of its adult presentation. A thorough analysis and discussion of cobalamin C defect presentation in adult patients has never been extensively performed. This article reviews the published data and adds a new case of the latest onset of symptoms ever described for the disease.

Results

We present the emblematic case of a 45-year-old male, describing the diagnostic odyssey he ventured through to get to the appropriate treatment and molecular diagnosis. Furthermore, available clinical, biochemical and molecular data from 22 reports on cases and case series were collected, resulting in 45 adult-onset CblC cases, including our own. We describe the onset of the disease in adulthood, encompassing neurological, psychiatric, renal, ophthalmic and thromboembolic symptoms. In all cases treatment with intramuscular hydroxycobalamin was effective in reversing symptoms. From a molecular point of view adult patients are usually compound heterozygous carriers of a truncating and a non-truncating variant in the MMACHC gene.

Conclusion

Adult onset CblC disease is a rare disorder whose diagnosis can be delayed due to poor awareness regarding its presenting insidious symptoms and biochemical hallmarks. To avoid misdiagnosis, we suggest that adult onset CblC deficiency is acknowledged as a separate entity from pediatric late onset cases, and that the disease is considered in the differential diagnosis in adult patients with atypical hemolytic uremic syndromes and/or slow unexplained decline in renal function and/or idiopathic neuropathies, spinal cord degenerations, ataxias and/or recurrent thrombosis and/or visual field defects, maculopathy and optic disc atrophy. Plasma homocysteine measurement should be the first line for differential diagnosis when the disease is suspected. To further aid diagnosis, it is important that genes belonging to the intracellular cobalamin pathway are included within gene panels routinely tested for atypical hemolytic uremic syndrome and chronic kidney disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02179-y.

Thrombotic microangiopathy in children

The syndrome of thrombotic microangiopathy (TMA) is a clinical-pathological entity characterized by microangiopathic hemolytic anemia, thrombocytopenia, and end organ involvement. It comprises a spectrum of underlying etiologies that may differ in children and adults. In children, apart from ruling out shigatoxin-associated hemolytic uremic syndrome (HUS) and other infection-associated TMA like Streptococcus pneumoniae-HUS, rare inherited causes including complement-associated HUS, cobalamin defects, and mutations in diacylglycerol kinase epsilon gene must be investigated. TMA should also be considered in the setting of solid organ or hematopoietic stem cell transplantation. In this review, acquired and inherited causes of TMA are described with a focus on particularities of the main causes of TMA in children. A pragmatic approach that may help the clinician tailor evaluation and management is provided. The described approach will allow for early initiation of treatment while waiting for the definitive diagnosis of the underlying TMA.

Thrombotic Microangiopathy After Kidney Transplantation: An Underdiagnosed and Potentially Reversible Entity

Thrombotic microangiopathy is a rare but serious complication that affects kidney transplant recipients. It appears in 0.8–14% of transplanted patients and negatively affects graft and patient survival. It can appear in a systemic form, with hemolytic microangiopathic anemia, thrombocytopenia, and renal failure, or in a localized form, with progressive renal failure, proteinuria, or arterial hypertension. Post-transplant thrombotic microangiopathy is classified as recurrent atypical hemolytic uremic syndrome or de novo thrombotic microangiopathy. De novo thrombotic microangiopathy accounts for the majority of cases. Distinguishing between the 2 conditions can be difficult, given there is an overlap between them. Complement overactivation is the cornerstone of all post-transplant thrombotic microangiopathies, and has been demonstrated in the context of organ procurement, ischemia-reperfusion phenomena, immunosuppressive drugs, antibody-mediated rejection, viral infections, and post-transplant relapse of antiphospholipid antibody syndrome. Although treatment of the causative agents is usually the first line of treatment, this approach might not be sufficient. Plasma exchange typically resolves hematologic abnormalities but does not improve renal function. Complement blockade with eculizumab has been shown to be an effective therapy in post-transplant thrombotic microangiopathy, but it is necessary to define which patients can benefit from this therapy and when and how eculizumab should be used.

Hemolytic Uremic Syndrome Due to Methylmalonic Acidemia and Homocystinuria in an Infant: A Case Report and Literature Review

Methylmalonic acidemia and homocystinuria cobalamin C (cblC) type is the most common inborn error of the intracellular cobalamin metabolism, associated with multisystem involvement and high mortality rates, especially in the early-onset form of the disease. Hemolytic uremic syndrome (HUS) is a rare manifestation and needs to be distinguished from other causes of renal thrombotic microangiopathy. We describe a case of a 3-month-old infant, with failure to thrive, hypotonia and pallor, who developed HUS in the setting of cblC deficit, along with dilated cardiomyopathy, and presented delayed response to optic stimulation in visual evoked potentials, as well as enlarged bilateral subarachnoid spaces and delayed myelination in brain magnetic resonance imaging. Renal damage was reversed, while neurodevelopmental profile and eye contact improved after supplementation with parenteral hydroxycobalamin, oral folic acid, betaine and levocarnitine. Homozygous mutation of c.271dupA in the MMACHC gene was ultimately detected. In this report, we highlight the diagnostic challenges as well as the significance of early recognition and multidisciplinary management of this unusual condition. A brief review of published case reports of early-onset cblC deficit and related HUS is depicted, pointing out the initial clinical presentation, signs of renal damage and outcome, MMACHC gene type of mutations and accompanying extra-renal manifestations.

Hyperhomocysteinemia: a trigger for complement-mediated TMA?

A 34-year-old man of North African descent was referred to the emergency department because of malignant hypertension (220/113 mmHg), acute visual disturbances and acute kidney failure (serum creatinine 14.0 mg/dL). Blood analysis was compatible with thrombotic microangiopathy (TMA). Kidney biopsy confirmed this diagnosis with histological changes including intimal edema, arteriolar thrombi, and severe tubulointerstitial damage. Fundoscopy showed hypertensive retinopathy stage IV. Subsequent biochemical screening revealed normal complement testing and a marked elevation in homocysteine concentration (161 µmol/L; normal value 7-15 µmol/L). Other secondary causes of TMA were excluded. Further genetic testing for cobalamin C (cblC) deficiency showed no pathogenic mutations in the MMACHC gene. However, a homozygous c.665C>T polymorphism (NM_005957.4) in the methylenetetrahydrofolate reductase (MTHFR) gene was found explaining the severe hyperhomocysteinemia due to reduced activity of MTHFR. Additional genetic testing for alternative complement pathway proteins showed mutations in the genes encoding factor H and factor B, both categorized as possibly pathogenic using mutation prediction software. This is the first described case of TMA in a patient with severe hyperhomocysteinemia caused by a genetic defect other than cblC. We postulate that endothelial damage due to hyperhomocysteinemia and hypertension could have triggered the TMA episode in this patient with two possible predisposing pathogenic mutations in the alternative complement pathway. Furthermore, our case demonstrates the need for complete full diagnostic testing in patients with TMA.

Proteinuria as a presenting sign of combined methylmalonic acidemia and homocysteinemia: case report

Background

Disorders of the metabolism and absorption of vitamin B12 can lead to decrease in activity of methionine synthetase and methylmalonate coenzyme A mutase (MMUT), which results in increased levels of methylmalonic acid and homocysteine in blood and urine. Often, combined methylmalonic acidemia (MMA) and homocysteinemia is misdiagnosed due to a lack of specific symptoms. The clinical manifestations are diverse, but proteinuria as the initial presentation is rare.

Case presentation

Two cases of MMA with homocysteinemia in children are reported. Proteinuria were a primary presenting symptom, followed by anemia and neurologic symptoms (frequent convulsions and unstable walking, respectively). Screening of amino acids and acyl carnitine in serum showed that the propionyl carnitine:acetylcarnitine ratio increased. Profiling of urinary organic acids by gas chromatography–mass spectrometry revealed high levels of methylmalonic acid. Homocysteine content in blood was increased. Comprehensive genetic analyses of peripheral blood-derived DNA demonstrated heterozygous variants of methylmalonic aciduria type C and homocystinuria (MMACHC) and amnionless (AMN) genes in our two patients, respectively. After active treatment, the clinical manifestations in Case 1 were relieved and urinary protein ceased to be observed; Case 2 had persistent proteinuria and was lost to follow-up.

Conclusions

Analyses of the organic acids in blood and urine suggested MMA combined with homocysteinemia. In such diseases, reports of renal damage are uncommon and proteinuria as the initial presentation is rare. Molecular analysis indicated two different genetic causes. Although the pathologic mechanisms were related to vitamin B12, the severity and prognosis of renal lesions were different. Therefore, gene detection provides new insights into inherited metabolic diseases.

Atypical Hemolytic Uremic Syndrome: New Challenges in the Complement Blockage Era

Atypical hemolytic uremic syndrome (aHUS) is a rare cause of thrombotic microangiopathy (TMA), characterized by microangiopathic hemolytic anemia, consumptive thrombocytopenia, and multisystem end organ involvement, most commonly affecting the kidney. Diagnosis is clinical, after exclusion of other TMA causes. Primary aHUS arises from genetic abnormalities, resulting in uncontrolled complement activity, while a variety of clinical scenarios cause secondary aHUS, including infection, pregnancy, malignancy, autoimmune disease, and medications. They can also induce a temporary complement deregulation with an overlap between both scenarios, which can make differential diagnosis difficult. Primary aHUS can be sporadic or familial and is associated with a high rate of progression to ESRD. Many aHUS patients relapse in the native or transplanted kidneys, leading to kidney failure. The introduction of eculizumab has changed the prognosis of aHUS, by inducing hematologic remission, improving or stabilizing kidney functions, and preventing graft failure. The early institution of appropriate therapy can prevent multiorgan damage, so is essential to recognize and differentiate the TMA syndromes. Eculizumab is considered now the first-line treatment, and it is recommended lifelong therapy. However, the high cost of therapy has led to make efforts to develop precise complement functional and genetic studies that help physicians to determine the appropriate duration of eculizumab therapy. Nowadays, more studies are needed to select candidates to adjustment of therapy.

A case report of recurrent acute pancreatitis associated with life threatening atypical hemolytic uremic syndrome

INTRODUCTION

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy defined by the sudden onset of hemolytic anemia, thrombocytopenia, and acute kidney injury (AKI). HUS is categorized as either typical, caused by Shiga toxin-producing Escherichia coli infection, or atypical HUS (aHUS), usually complement mediated or secondary to systemic disease. We describe a rare case of aHUS in an adult male patient with recurrent acute pancreatitis.

PATIENT CLINICAL FINDINGS

A 32-year-old Caucasian male presented to our institution for his third episode of alcohol-induced pancreatitis. He presented with abdominal pain, elevated lipase and pancreatic inflammation on computed tomography consistent with acute pancreatitis. While admitted, he developed sudden onset severe thrombocytopenia, AKI and hemolytic anemia.

DIAGNOSIS, THERAPEUTIC INTERVENTIONS, OUTCOMES

Peripheral blood smear, haptoglobin and hemoglobin level confirmed microangiopathic hemolytic anemia. Worsening anemia, thrombocytopenia and AKI were consistent with the diagnosis of aHUS. The patient's pancreatitis resolved with supportive measures, but resolution of significant thrombocytopenia and AKI was not achieved until administration of eculizumab, a complement inhibiting therapy. Eculizumab therapy provided dramatic improvement in this patient, with platelet count increasing from a low of 11,000 to >100,000 within 48 hours of therapy. Creatinine and hemoglobin levels returned to baseline within 3 weeks.

CONCLUSION

Recurrent pancreatitis is suggested as the etiology of atypical HUS in this patient and this condition should be recognized and treated in a timely manner for optimal clinical outcomes.

Cobalamin c deficiency associated with antifactor h antibody-associated hemolytic uremic syndrome in a young adult

Background

Thrombotic microangiopathy (TMA) syndromes are characterized by the association of hemolytic anemia, thrombocytopenia and organ injury due to arteriolar and capillary thrombosis.

Case presentation

We report the first case of adult onset cobalamin C (Cbl C) disease associated with anti-factor H antibody-associated hemolytic uremic syndrome (HUS).

A 19-year-old woman was admitted to the nephrology department owing to acute kidney failure, proteinuria, and hemolytic anemia with schizocytes.

TMA was diagnosed and plasma exchanges were started in emergency.

Exhaustive analyses showed 1) circulating anti factor H antibody and 2) hyperhomocysteinemia, hypomethioninemia and high levels of methylmalonic aciduria pointing towards Clb C disease. Cbl C disease has been confirmed by methylmalonic aciduria and homocystinuria type C protein gene sequencing revealing two heterozygous pathogenic variants.

The kidney biopsy showed 1) intraglomerular and intravascular thrombi 2) noticeable thickening of the capillary wall with a duplication aspect of the glomerular basement membrane and a glomerular capillary wall IgM associated with Cbl C disease related TMA.

We initiated treatment including hydroxycobalamin, folinic acid, betaine and levocarnitine and Eculizumab. Rituximab infusions were performed allowing a high decrease in anti-factor H antibody rate.

Six month after the disease onset, Eculizumab was weaning and vitaminotherapy continued. Outcome was favorable with a dramatic improvement in kidney function.

Conclusion

TMA with renal involvement can have a complex combination of risk factors including anti-FH autoantibody in the presence of cblC deficiency.

Vitamin B12 deficiency and metabolism-mediated thrombotic microangiopathy (MM-TMA)

Thrombotic microangiopathies (TMA) are characterized by microangiopathic hemolytic anemia, thrombocytopenia and organ damage resulting from mechanical factors, accumulation of the ultra-large von Willebrand factor multimers or complement-mediated abnormalities. Severe acquired vitamin B12 (Cobalamin - Cbl) deficiency or congenital defective Cbl metabolism could lead to a picture that mimics TMA. The later has been termed metabolism-mediated TMA (MM- TMA). This confusing picture is mediated partly by the large red cell fragmentation coupled with reduced platelet production in the absence of vitamin B12 and partly by the accumulated byproducts and metabolites that induce endothelial injury and hence organ damage. Expensive and complicated treatment for TMA is often initiated on an empiric basis, pending the results of confirmatory tests. In contrast, vitamin B12 Pseudo-TMA and MM-TMA could be treated with proper vitamin B12 supplementation. It is therefore important to identify these disorders promptly. The recent availability of a validated scoring system such as the PLASMIC score uses simple clinical and laboratory parameters. As it incorporates the mean corpuscular volume in its laboratory parameters, this helps in the identification of pseudo and MM-TMA. Perhaps some minor modification of this scoring system by changing the parameters of hemolysis to include reticulocytosis and rather than and/or other hemolytic parameters could even help refine this identification.

Haemolytic uremic syndrome: diagnosis and management

The thrombotic microangiopathies (TMAs) are a group of diseases characterised by microangiopathic haemolysis, thrombocytopenia, and thrombus formation leading to tissue injury. Traditionally, TMAs have been classified as either thrombotic thrombocytopenic purpura (TTP) or haemolytic uremic syndrome (HUS) based on the clinical presentation, with neurological involvement predominating in the former and acute kidney injury in the latter. However, as our understanding of the pathogenesis of these conditions has increased, it has become clear that this is an over-simplification; there is significant overlap in the clinical presentation of TTP and HUS, there are different forms of HUS, and TMAs can occur in other, diverse clinical scenarios. This review will discuss recent developments in the diagnosis of HUS, focusing on the different forms of HUS and how to diagnose and manage these potentially life-threatening diseases.

[Kidney disease in cobalamin C deficiency]

Cobalamin C deficiency (cblC) is the most common inborn error of vitamin B₁₂ metabolism. This autosomal recessive disease is due to mutations in MMACHC gene, encoding a cyanocobalamin decyanase. It leads to hyperhomocysteinemia associated with hypomethioninemia and methylmalonic aciduria. Two distinct phenotypes have been described : early-onset forms occur before the age of one year and are characterized by a severe multisystem disease associating failure to thrive to neurological and ophthalmological manifestations. They are opposed to late-onset forms, less severe and heterogeneous. CblC deficiency-associated kidney lesions remain poorly defined. Thirty-eight cases have been described. Age at initial presentation varied from a few days to 28 years. Most of the patients presented renal thrombotic microangiopathy (TMA) associated with acute renal failure, and 21 patients presented typical lesions of renal thrombotic microangiopathy on kidney biopsy. Prognosis was poor, leading to death in the absence of treatment, and related to the severity of renal lesions in the early-onset forms. Late-onset disease had better prognosis and most of patients were weaned off dialysis after treatment initiation. We suggest that all the patients with renal TMA be screened for cobalamin metabolism disorder, regardless of age and even in the absence of neurological symptoms, to rapidly initiate the appropriate treatment.

Plasmic score applicability for the diagnosis of thrombotic microangiopathy associated with ADAMTS13-acquired deficiency in a developing country

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is a potentially fatal disease that requires early diagnosis and treatment that can be made possible by applying the PLASMIC score. This study aims to evaluate this score applicability for patients with suspected TTP in a developing country.

METHODS

This was a retrospective study performed at a tertiary hospital in the northeastern region of Brazil. Patients were analyzed in two groups: ADAMTS13 activity <10% and activity >10%. Patients were stratified according to the PLASMIC score, and the level of agreement between the PLASMIC score and the ADAMTS13 activity was evaluated.

RESULTS

Eight patients with thrombotic microangiopathy were included. Four patients had ADAMTS13 activity <10%, all with a PLASMIC score =6. The other four had ADAMTS13 activity >10%, all with a score <6. Based on a score =6 for presumptive diagnosis of TTP, we attained a 100% diagnostic accuracy in our sample. The PLASMIC score was also able to accurately predict response to plasma exchange and the risk of long-term unfavorable outcomes.

CONCLUSIONS

The reproducibility of the PLASMIC score was quite satisfactory in our sample. It accurately discriminates between patients who had ADAMTS13 deficiency and those with normal enzyme activity, precluding the need for specific laboratory evaluation, which is not always available. This score can be useful for an early diagnosis and indicates which patients will benefit from the treatment in developing countries.

Secondary thrombotic microangiopathy and eculizumab: A reasonable therapeutic option

Understanding the role of the complement system in the pathogenesis of atypical haemolytic uraemic syndrome and other thrombotic microangiopathies (TMA) has led to the use of anti-complement therapy with eculizumab in these diseases, in addition to its original use in patients with paroxysmal nocturnal haemoglobinuria andatypical haemolytic uraemic syndrome. Scientific evidence shows that both primary and secondary TMAs with underlying complement activation are closely related. For this reasons, control over the complement system is a therapeutic target. There are 2scenarios in which eculizumab is used in patients with TMA: primary or secondary TMA that is difficult to differentiate (including incomplete clinical presentations) and complement-mediated damage in various processes in which eculizumab proves to be efficacious. This review summarises the evidence on the role of the complement activation in the pathophysiology of secondary TMAs and the efficacy of anti-complement therapy in TMAs secondary to pregnancy, drugs, transplant, humoral rejection, systemic diseases and glomerulonephritis. Although experience is scarce, a good response to eculizumab has been reported in patients with severe secondary TMAs refractory to conventional treatment. Thus, the role of the anti-complement therapy as a new treatment option in these patients should be investigated.

Cobalamin C Deficiency Induces a Typical Histopathological Pattern of Renal Arteriolar and Glomerular Thrombotic Microangiopathy

Introduction

Cobalamin C (cblC) deficiency is the most common inborn error of vitamin B₁₂ metabolism. Renal failure attributed to thrombotic microangiopathy (TMA) has occasionally been described in the late-onset presentation of cblC deficiency, but kidney lesions associated with cblC deficiency remain poorly defined. This study aims to describe the characteristics of kidney disease in cblC deficiency, and to provide a comparative histological analysis with cblC-independent renal TMA.

Methods

We performed a multicenter retrospective study including 7 patients with cblC deficiency and 16 matched controls with cblC-independent TMA. The patients included were aged 6 to 26 years at the time of the first manifestations. All patients presented with acute renal failure, proteinuria, and hemolysis; 5 patients required dialysis.

Results

The histological study revealed arteriolar and glomerular TMA in all patients. After comparison with the cblC-independent TMA control group, a vacuolated aspect of the glomerular basement membrane and the intensity of glomerular capillary wall IgM deposits were more present in cblC deficiency patients than in controls. Six patients were treated with hydroxycobalamin. All of them improved, with disappearance of hemolysis, and 3 of the 4 patients requiring renal replacement therapy were weaned off dialysis.

Conclusion

This study provides a precise description of kidney pathology in cblC deficiency. Due to major therapeutic implications, we suggest that patients with renal TMA be screened for cblC deficiency regardless of age, particularly when the kidney biopsy provides evidence of long-lasting TMA, including a vacuolated aspect of the glomerular basement membrane and glomerular capillary wall IgM deposition.

Atypical adult-onset methylmalonic acidemia and homocystinuria presenting as hemolytic uremic syndrome

Thrombotic microangiopathy (TMA) syndromes can be secondary to a multitude of different diseases. Most can be identified with a systematic approach and, when excluded, TMA is generally attributed to a dysregulation in the activity of the complement alternative pathways-atypical hemolytic uremic syndrome (aHUS). We present a challenging case of a 19-year-old woman who presented with thrombotic microangiopathy, which was found to be caused by methylmalonic acidemia and homocystinuria, a rare vitamin B12 metabolism deficiency. To our knowledge, this is the first time that an adult-onset methylmalonic acidemia and homocystinuria presents as TMA preceding CNS involvement.

Eculizumab in secondary atypical haemolytic uraemic syndrome

Background. Complement dysregulation occurs in thrombotic microangiopathies (TMAs) other than primary atypical haemolytic uraemic syndrome (aHUS). A few of these patients have been reported previously to be successfully treated with eculizumab.

Methods. We identified 29 patients with so-called secondary aHUS who had received eculizumab at 11 Spanish nephrology centres. Primary outcome was TMA resolution, defined by a normalization of platelet count (>150 × 10⁹/L) and haemoglobin, disappearance of all the markers of microangiopathic haemolytic anaemia (MAHA), and improvement of renal function, with a ≥25% reduction of serum creatinine from the onset of eculizumab administration.

Results. Twenty-nine patients with secondary aHUS (15 drug-induced, 8 associated with systemic diseases, 2 with postpartum, 2 with cancer-related, 1 associated with acute humoral rejection and 1 with intestinal lymphangiectasia) were included in this study. The reason to initiate eculizumab treatment was worsening of renal function and persistence of TMA despite treatment of the TMA cause and plasmapheresis. All patients showed severe MAHA and renal function impairment (14 requiring dialysis) prior to eculizumab treatment and 11 presented severe extrarenal manifestations. A rapid resolution of the TMA was observed in 20 patients (68%), 15 of them showing a ≥50% serum creatinine reduction at the last follow-up. Comprehensive genetic and molecular studies in 22 patients identified complement pathogenic variants in only 2 patients. With these two exceptions, eculizumab was discontinued, after a median of 8 weeks of treatment, without the occurrence of aHUS relapses.

Conclusion. Short treatment with eculizumab can result in a rapid improvement of patients with secondary aHUS in whom TMA has persisted and renal function worsened despite treatment of the TMA-inducing condition.

Complement C5-inhibiting therapy for the thrombotic microangiopathies: accumulating evidence, but not a panacea

Thrombotic microangiopathy (TMA), characterized by organ injury occurring consequent to severe endothelial damage, can manifest in a diverse range of diseases. In complement-mediated atypical haemolytic uraemic syndrome (aHUS) a primary defect in complement, such as a mutation or autoantibody leading to over activation of the alternative pathway, predisposes to the development of disease, usually following exposure to an environmental trigger. The elucidation of the pathogenesis of aHUS resulted in the successful introduction of the complement inhibitor eculizumab into clinical practice. In other TMAs, although complement activation may be seen, its role in the pathogenesis remains to be confirmed by an interventional trial. Although many case reports in TMAs other than complement-mediated aHUS hint at efficacy, publication bias, concurrent therapies and in some cases the self-limiting nature of disease make broader interpretation difficult. In this article, we will review the evidence for the role of complement inhibition in complement-mediated aHUS and other TMAs.

Haemolytic uraemic syndrome

Haemolytic uraemic syndrome is a form of thrombotic microangiopathy affecting predominantly the kidney and characterised by a triad of thrombocytopenia, mechanical haemolytic anaemia, and acute kidney injury. The term encompasses several disorders: shiga toxin-induced and pneumococcus-induced haemolytic uraemic syndrome, haemolytic uraemic syndrome associated with complement dysregulation or mutation of diacylglycerol kinase ɛ, haemolytic uraemic syndrome related to cobalamin C defect, and haemolytic uraemic syndrome secondary to a heterogeneous group of causes (infections, drugs, cancer, and systemic diseases). In the past two decades, experimental, genetic, and clinical studies have helped to decipher the pathophysiology of these various forms of haemolytic uraemic syndrome and undoubtedly improved diagnostic approaches. Moreover, a specific mechanism-based treatment has been made available for patients affected by atypical haemolytic uraemic syndrome due to complement dysregulation. Such treatment is, however, still absent for several other disease types, including shiga toxin-induced haemolytic uraemic syndrome.

Thrombotic microangiopathy caused by methionine synthase deficiency: diagnosis and treatment pitfalls

BACKGROUND

Inborn errors of cobalamin (Cbl) metabolism form a large group of rare diseases. One of these, Cbl deficiency type C (CblC), is a well-known cause of thrombotic microangiopathy (TMA), especially in infants. However, there has only been a single published case of TMA associated to Cbl deficiency type G (CblG), also known as methionine synthase deficiency (MSD).

CASE DIAGNOSIS/TREATMENT

A 21-month-old boy presented with pallor and oral ulcers during episodes of upper respiratory infection (URI). Further examination revealed signs of TMA, and the patient progressed to acute renal failure (ARF). Renal biopsy showed TMA. Evaluation for infection and autoantibodies were negative. The C3 and C4 complement fractions were normal. Analysis of the bone marrow aspirate suggested megaloblastic anemia and signs of hematopoiesis activation (secondary to peripheral hemolysis). Although the serum vitamin B12 level was normal, the patient was treated with cyanocobalamin, with no improvement. The ARF and hematologic parameters improved with conservative treatment. A severe relapse occurred during the follow-up, with normal ADAMTS13 activity. The presumed diagnosis was atypical hemolytic uremic syndrome, and the patient was started on eculizumab, but his response was poor, even when the dosage was increased. At this point it was also recognized that his developmental speech was delayed. Based on these findings, whole exome sequencing was performed, leading to the detection of two novel deleterious variants in the gene coding for methionine synthase, confirming the diagnosis of MSD. Subsequent treatment consisted of elevating the patient's serum homocysteine level and starting him on hydroxicobalamin, with normalization of all hematologic parameters although the microalbuminuria remained.

CONCLUSIONS

Methionine synthase deficiency is very rare and characterized by megaloblastic anemia and neurological symptoms. We report the second case of MSD associated to TMA previously diagnosed as aHUS in which the patient had a poor response to eculizumab.

None of the above: thrombotic microangiopathy beyond TTP and HUS

Acquired thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are appropriately at the top of a clinician's differential when a patient presents with a clinical picture consistent with an acute thrombotic microangiopathy (TMA). However, there are several additional diagnoses that should be considered in patients presenting with an acute TMA, especially in patients with nondeficient ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity (>10%). An increased awareness of drug-induced TMA is also essential because the key to their diagnosis more often is an appropriately detailed medical history to inquire about potential exposures. Widespread inflammation and endothelial damage are central in the pathogenesis of the TMA, with the treatment directed at the underlying disease if possible. TMA presentations in the critically ill, drug-induced TMA, cancer-associated TMA, and hematopoietic transplant-associated TMA (TA-TMA) and their specific treatment, where applicable, will be discussed in this manuscript. A complete assessment of all the potential etiologies for the TMA findings including acquired TTP will allow for a more accurate diagnosis and prevent prolonged or inappropriate treatment with plasma exchange therapy when it is less likely to be successful.

HUS and atypical HUS

Hemolytic uremic syndrome (HUS) is a thrombotic microangiopathy characterized by intravascular hemolysis, thrombocytopenia, and acute kidney failure. HUS is usually categorized as typical, caused by Shiga toxin-producing Escherichia coli (STEC) infection, as atypical HUS (aHUS), usually caused by uncontrolled complement activation, or as secondary HUS with a coexisting disease. In recent years, a general understanding of the pathogenetic mechanisms driving HUS has increased. Typical HUS (ie, STEC-HUS) follows a gastrointestinal infection with STEC, whereas aHUS is associated primarily with mutations or autoantibodies leading to dysregulated complement activation. Among the 30% to 50% of patients with HUS who have no detectable complement defect, some have either impaired diacylglycerol kinase ε (DGKε) activity, cobalamin C deficiency, or plasminogen deficiency. Some have secondary HUS with a coexisting disease or trigger such as autoimmunity, transplantation, cancer, infection, certain cytotoxic drugs, or pregnancy. The common pathogenetic features in STEC-HUS, aHUS, and secondary HUS are simultaneous damage to endothelial cells, intravascular hemolysis, and activation of platelets leading to a procoagulative state, formation of microthrombi, and tissue damage. In this review, the differences and similarities in the pathogenesis of STEC-HUS, aHUS, and secondary HUS are discussed. Common for the pathogenesis seems to be the vicious cycle of complement activation, endothelial cell damage, platelet activation, and thrombosis. This process can be stopped by therapeutic complement inhibition in most patients with aHUS, but usually not those with a DGKε mutation, and some patients with STEC-HUS or secondary HUS. Therefore, understanding the pathogenesis of the different forms of HUS may prove helpful in clinical practice.

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.

Renal thrombotic microangiopathy in patients with cblC defect: review of an under-recognized entity

Methylmalonic aciduria and homocystinuria, cobalamin C (cblC) type, is the most common genetic type of functional cobalamin (vitamin B₁₂) deficiency. This metabolic disease is characterized by marked heterogeneity of neurocognitive disease (microcephaly, seizures, developmental delay, ataxia, hypotonia) and variable extracentral nervous system involvement (failure to thrive, cardiovascular, renal, ocular) manifesting predominantly early in life, sometimes during gestation. To enhance awareness and understanding of renal disease associated with cblC defect, we studied biochemical, genetic, clinical, and histopathological data from 36 patients. Consistent clinical chemistry features of renal disease were intravascular hemolysis, hematuria, and proteinuria in all patients, with nephrotic-range proteinuria observed in three. Renal function ranged from normal to renal failure, with eight patients requiring (intermittent) dialysis. Two thirds were diagnosed with atypical (diarrhea-negative) hemolytic uremic syndrome (HUS). Renal histopathology analyses of biopsy samples from 16 patients revealed glomerular lesions typical of thrombotic microangiopathy (TMA). Treatment with hydroxycobalamin improved renal function in the majority, including three in whom dialysis could be withdrawn. Neurological sequelae were observed in 44 % and cardiopulmonary involvement in 39 % of patients, with half of the latter group demonstrating pulmonary hypertension. Mortality reached 100 % in untreated patients and 79 and 56 % in those with cardiopulmonary or neurological involvement, respectively. In all patients presenting with unclear intravascular hemolysis, hematuria, and proteinuria, cblC defect should be ruled out by determination of blood/plasma homocysteine levels and/or genetic testing, irrespective of actual renal function and neurological status, to ensure timely diagnosis and treatment.

A Case Report and Literature Review of Eculizumab Withdrawal in Atypical Hemolytic-Uremic Syndrome

BACKGROUND Recent advances in the treatment of atypical hemolytic-uremic syndrome (aHUS) have resulted to better long-term survival rates for patients with this life-threatening disease. However, many questions remain such as whether or not long-term treatment is necessary in some patients and what are the risks of prolonged therapy. CASE REPORT Here, we discuss the case of a 37-year-old woman with CFH and CD46 genetic abnormalities who developed aHUS with severe renal failure. She was successfully treated with three doses of rituximab and a three month treatment with eculizumab. After eculizumab withdrawal, symptoms of thrombotic micro-angiopathy (TMA) recurred, therefore eculizumab treatment was restarted. The patient exhibited normal renal function and no symptoms of aHUS at one-year follow-up with further eculizumab treatment. CONCLUSIONS This case highlights the clinical challenges of the diagnosis and management of patient with aHUS with complement-mediated TMA involvement. Attention was paid to the consequences of the treatment withdrawal. Exact information regarding genetic abnormalities and renal function associated with aHUS, as well as estimations of the relapse risk and monitoring of complement tests may provide insights into the efficacy of aHUS treatment, which will enable the prediction of therapeutic responses and testing of new treatment options. Improvements in our understanding of aHUS and its causes may facilitate the identification of patients in whom anti-complement therapies can be withdrawn without risk.

Atypical hemolytic uremic syndrome

Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy (TMA) that affects multiple organs and the kidneys in particular. aHUS can be sporadic or familial and is most commonly caused by dysregulation of the alternative complement pathway. The initial attack of aHUS can occur at any age, and is associated with a high rate of progression to end stage renal disease. Many aHUS patients relapse in the native or transplanted kidneys, and require close monitoring and long-term management. Availability of anticomplement therapy has revolutionized the management of aHUS, and can change the natural course of aHUS by inducing hematologic remission, improving or stabilizing kidney functions, and preventing graft failure. As a result, it is important to succeed in the challenging task of differentiating aHUS from other TMAs and initiate adequate treatment early during the course of disease. Considering the high cost of currently available anticomplement therapy, it is important also from a financial point of view to accurately diagnose aHUS early during the course of disease and determine the necessary length of therapy. This highlights the need for development of precise complement functional and genetic studies with rapid turnaround time.

Thrombotic Microangiopathy Care Pathway: A Consensus Statement for the Mayo Clinic Complement Alternative Pathway-Thrombotic Microangiopathy (CAP-TMA) Disease-Oriented Group

Thrombotic microangiopathies (TMAs) comprise a heterogeneous set of conditions linked by a common histopathologic finding of endothelial damage resulting in microvascular thromboses and potentially serious complications. The typical clinical presentation is microangiopathic hemolytic anemia accompanied by thrombocytopenia with varying degrees of organ ischemia. The differential diagnoses are generally broad, while the workup is frequently complex and can be confusing. This statement represents the joint recommendations from a multidisciplinary team of Mayo Clinic physicians specializing in the management of TMA. It comprises a series of evidence- and consensus-based clinical pathways developed to allow a uniform approach to the spectrum of care including when to suspect TMA, what differential diagnoses to consider, which diagnostic tests to order, and how to provide initial empiric therapy, as well as some guidance on subsequent management.

Stratification of responders towards eculizumab using a structural epitope mapping strategy

The complement component 5 (C5)-binding antibody eculizumab is used to treat patients with paroxysmal nocturnal hemoglobinuria (PNH) and atypical haemolytic uremic syndrome (aHUS). As recently reported there is a need for a precise classification of eculizumab responsive patients to allow for a safe and cost-effective treatment. To allow for such stratification, knowledge of the precise binding site of the drug on its target is crucial. Using a structural epitope mapping strategy based on bacterial surface display, flow cytometric sorting and validation via haemolytic activity testing, we identified six residues essential for binding of eculizumab to C5. This epitope co-localizes with the contact area recently identified by crystallography and includes positions in C5 mutated in non-responders. The identified epitope also includes residue W917, which is unique for human C5 and explains the observed lack of cross-reactivity for eculizumab with other primates. We could demonstrate that Ornithodorus moubata complement inhibitor (OmCI), in contrast to eculizumab, maintained anti-haemolytic function for mutations in any of the six epitope residues, thus representing a possible alternative treatment for patients non-responsive to eculizumab. The method for stratification of patients described here allows for precision medicine and should be applicable to several other diseases and therapeutics.

[Hemolytic kidney failure and transient ischemic attack in a 32-year-old female]

We report on the case of a 32-year-old female patient who initially presented with oliguric acute renal failure, hemolytic anemia with moderate thrombocytopenia and subsequently developed a transient ischemic attack in the cerebellum. The kidney biopsy revealed clinically suspected atypical hemolytic-uremic syndrome (aHUS), which was confirmed by intraglomerular thrombotic microangiopathy (TMA). Treatment with plasmapheresis and sustained administration of the C5 inhibitor eculizumab resulted in hematological remission but without improvement of kidney function. Further etiological investigations led to reduced plasma levels of inhibitory complement factor I on the basis of a heterozygous CFI mutation. In patients with aHUS molecular genetic investigations are indicated in order to determine the underlying cause, to regulate the therapeutic regimen and to allow prognostic statements with respect to a potential kidney transplantation.

The alternative pathway of complement and the thrombotic microangiopathies

Thrombotic microangiopathies (TMA) are disorders defined by microangiopathic hemolytic anemia, non-immune thrombocytopenia and have multi-organ involvement including the kidneys, brain, gastrointestinal, respiratory tract and skin. Emerging evidence points to the central role of complement dysregulation in leading to microvascular endothelial injury which is crucial for the development of TMAs. This key insight has led to the development of complement-targeted therapy. Eculizumab is an anti-C5 monoclonal antibody, which has revolutionized the treatment of atypical hemolytic uremic syndrome. Several other anti-complement therapeutic agents are currently in development, offering a potential armamentarium of therapies available to treat complement-mediated TMAs. The development of sensitive, reliable and easy to perform assays to monitor complement activity and therapeutic efficacy will be key to devising an individualized treatment regime with the potential of safely weaning or discontinuing treatment in the appropriate clinical setting.

Critical appraisal of eculizumab for atypical hemolytic uremic syndrome

The biology of atypical hemolytic uremic syndrome has been shown to involve inability to limit activation of the alternative complement pathway, with subsequent damage to systemic endothelial beds and the vasculature, resulting in the prototypic findings of a thrombotic microangiopathy. Central to this process is the formation of the terminal membrane attack complex C5b-9. Recently, application of a monoclonal antibody that specifically binds to C5, eculizumab, became available to treat patients with atypical hemolytic uremic syndrome, replacing plasma exchange or infusion as primary therapy. This review focuses on the evidence, based on published clinical trials, case series, and case reports, on the efficacy and safety of this approach.

An international consensus approach to the management of atypical hemolytic uremic syndrome in children

Atypical hemolytic uremic syndrome (aHUS) emerged during the last decade as a disease largely of complement dysregulation. This advance facilitated the development of novel, rational treatment options targeting terminal complement activation, e.g., using an anti-C5 antibody (eculizumab). We review treatment and patient management issues related to this therapeutic approach. We present consensus clinical practice recommendations generated by HUS International, an international expert group of clinicians and basic scientists with a focused interest in HUS. We aim to address the following questions of high relevance to daily clinical practice: Which complement investigations should be done and when? What is the importance of anti-factor H antibody detection? Who should be treated with eculizumab? Is plasma exchange therapy still needed? When should eculizumab therapy be initiated? How and when should complement blockade be monitored? Can the approved treatment schedule be modified? What approach should be taken to kidney and/or combined liver-kidney transplantation? How should we limit the risk of meningococcal infection under complement blockade therapy? A pressing question today regards the treatment duration. We discuss the need for prospective studies to establish evidence-based criteria for the continuation or cessation of anticomplement therapy in patients with and without identified complement mutations.

Atypical aHUS: State of the art

Tremendous advances in our understanding of the thrombotic microangiopathies (TMAs) have revealed distinct disease mechanisms within this heterogeneous group of diseases. As a direct result of this knowledge, both children and adults with complement-mediated TMA now enjoy higher expectations for long-term health. In this update on atypical hemolytic uremic syndrome, we review the clinical characteristics; the genetic and acquired drivers of disease; the broad spectrum of environmental triggers; and current diagnosis and treatment options. Many questions remain to be addressed if additional improvements in patient care and outcome are to be achieved in the coming decade.

Ocular disease in the cobalamin C defect: a review of the literature and a suggested framework for clinical surveillance

The association between combined methylmalonic acidemia and homocystinuria of cblC type (cobalamin C defect, cblC) and ocular disease is now well recognized, and is a significant component of morbidity and disability associated with the condition. In this review, through collation of historically reported cases of early- and late-onset cblC and previously unreported cases, we have attempted to characterize the epidemiology, clinical features, and pathomechanisms of individual ocular features of cblC. These data suggest that maculopathy and nystagmus with abnormal vision are extremely common and affect the majority of children with early-onset cblC, usually before school age; strabismus and optic atrophy are also seen at relatively high frequency. The timing of progression of macular disease may coincide with a critical period of postnatal foveal development. Maculopathy and retinal disease may be subclinical and show only partial correlation with the extent of visual deficits, and visual deterioration may be relentlessly progressive in spite of aggressive treatment of biochemical abnormalities. In later-onset forms of the disease, visual loss and ocular complications appear to be infrequent. Finally, we discuss investigational strategies in diagnosing and characterizing eye disease in individuals with cblC, explore possible therapeutic avenues that may attenuate progression and severity of eye disease, and propose a clinical surveillance guideline for monitoring progression of ocular disease in children and adults with cblC.

[Diagnostic and therapeutic guidelines of thrombotic microangiopathies of the Spanish Apheresis Group]

Thrombotic microangiopathies (TMA) are disorders defined by the presence of a microangiopathic hemolytic anemia (with the characteristic hallmark of schistocytes in the peripheral blood smear), thrombocytopenia and organ malfunction of variable intensity. Thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are the most important forms of TMA and, without the adequate treatment, they are associated with high morbimortality. In recent years, significant advances in the knowledge of the pathophysiology of TMA have occurred. Those advances have allowed us to move from a syndromic diagnosis with a similar treatment to all entities to the search of etiologic diagnosis which would lead to a specific treatment, finally leading to a better outcome of the patient. This document pretends to summarize the current status of knowledge of the pathophysiology of TMA and the therapeutic options available, and to offer a diagnostic and therapeutic practical tool to the professionals caring for the patients.

Three new cases of late-onset cblC defect and review of the literature illustrating when to consider inborn errors of metabolism beyond infancy

Background

The cblC defect is a rare inborn error of intracellular cobalamin metabolism. Biochemical hallmarks are elevated homocysteine and low methionine in plasma accompanied by methylmalonic aciduria. Due to the heterogeneous clinical picture, patients with the late-onset form of the disease (onset >12 months) come to the attention of diverse medical specialists, e.g. paediatricians, neurologists, nephrologists, psychiatrists or haematologists. The report reviews the published clinical data and adds three new cases to raise awareness for this severe but often treatable disease.

Methods

The Pubmed and the Cochrane databases were searched for clinical reports on cblC patients and three unreported cases are presented to illustrate the clinical spectrum.

Results

Reports on 58 cases (30 females, 22 males, 6 = no information) and the three new cases underlined the clinical heterogeneity of the disease. Time between first symptoms and diagnosis ranged from three months to more than 20 years. Haemolytic uraemic syndrome and pulmonary hypertension were main presenting symptoms in preschool children. In older children/adolescents, psychiatric symptoms, cognitive impairment, ataxia and myelopathy were frequently observed while thromboembolic events and glomerulopathies were almost exclusively seen in adults. Brain atrophy, white matter lesions and myelopathy were frequently encountered. The majority of patients showed marked biochemical and clinical response to treatment with parenteral hydroxocobalamin combined with oral betaine, folate, carnitine and rarely methionine. The course was less favourable in late treated or untreated patients.

Conclusions

The late-onset cblC defect is a rare disease and unfortunately, diagnosis is often delayed. Raising awareness for this disorder can significantly improve patients’ outcome and perspective by timely initiation of targeted treatment. Newborn screening (NBS) for the cblC defect might be of benefit especially for late-onset patients since treatment seems efficient when initiated before irreversible organ damage. In general, inborn errors of metabolisms should be considered in unexplained medical cases at any age, especially in patients with multisystemic disease. More specifically, total homocysteine in plasma and methylmalonic acid in urine/plasma should be measured in unexplained neurologic, psychiatric, renal, haematologic and thromboembolic disease.