Dense deposit disease and the factor H H402 allele

Chronic kidney disease enhances alternative pathway activity: a new paradigm

Reduced kidney function is associated with increased risk of cardiovascular disease in addition to kidney disease progression. Kidney disease is considered an inflammatory state, based on elevated levels of C-reactive protein and inflammatory cytokines. A key mediator of cardiovascular and kidney disease progression in the setting of reduced kidney function is systemic and vascular inflammation. However, the exact pathways that link chronic kidney disease (CKD) with inflammation remain incompletely understood. For decades it has been known that factor D, the main activator of the alternative complement pathway, is increased in the plasma of patients with reduced kidney function. Recent biomarker evidence suggests alternative pathway activation in this setting. CKD, therefore, seems to alter the balance of alternative pathway proteins, promoting inflammation and potentially exacerbating complement-mediated diseases and CKD-associated complications. In this manuscript, we review the impact of reduced kidney function on biomarkers of the alternative complement pathway and the implications of alternative pathway activation on cardiovascular disease and kidney disease progression. Importantly, we highlight the need for ongoing research efforts that may lead to opportunities to target the alternative pathway of complement withx the goal of improving kidney and cardiovascular outcomes in persons with reduced kidney function.

A CHILD WITH DENSE DEPOSIT DISEASE AND DECREASED CLASSIC COMPLEMENT PATHWAY ACTIVITY

We report a rare case of nephritic syndrome underlying dense deposit disease (DDD) with alternative complement pathway dysfunction explained with both C3 nephritic factor (C3NeF) antibodies and DDD associated polymorphism of factor H. An 8-year-old boy presented with macroscopic hematuria, hypertension and periorbital edema followed by persistently low C3 during the 8-week follow-up. Positive C3 staining on immunofluorescence microscopy, supported by dense deposits within the glomerular basement membrane on electron microscopy, confirmed the diagnosis of DDD. Preliminary tests for complement activation showed decreased classic pathway and deficient alternative complement pathway, as well as slightly positive C3NeF, supporting the diagnosis of DDD. Genetic analysis revealed a polymorphism of the complement factor H gene with an increased risk of developing DDD. Supportive therapy led to satisfactory recovery of renal function and normalization of C3. Given the poor prognosis of the disease, proper approach to such specific glomerulopathy is important to avoid or at least slow down progression to end-stage renal disease.

C3 glomerulopathy and atypical hemolytic uremic syndrome: an updated review of the literature on alternative complement pathway disorders

The complement system plays a significant role within the pathological process of C3 glomerulopathy (C3GP) and atypical hemolytic uremic syndrome (aHUS). In daily practice, clinicians should differentiate the subgroups of C3GP because of they should apply different treatment modalities. In the past, C3GP was considered as a part of membranoproliferative glomerulonephritis (MPGN). MPGN is defined as glomerular capillary thickening secondary to the synthesis of the new glomerular basement membrane and mesangial cellular hyperplasia with mesangial matrix expansion. Atypical hemolytic uremic syndrome is an ultra-rare disease that can be outlined by the triad of Coombs negative microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Recent advances demonstrated that these diseases share common abnormalities of the control of the alternative complement system. Therefore, nowadays, most researchers advocate that there may be overlap in the pathogenesis of C3GP and aHUS. This review will provide recent novel mechanisms and treatment options in these diseases. For the purposes that we mentioned above and to help clinicians, we aimed to describe the etiology, pathophysiology, and treatment of C3GP and aHUS in this comprehensive review.

Causes of alternative pathway dysregulation in dense deposit disease

BACKGROUND AND OBJECTIVES

This study was designed to investigate the causes of alternative pathway dysregulation in a cohort of patients with dense deposit disease (DDD).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Thirty-two patients with biopsy-proven DDD underwent screening for C3 nephritic factors (C3Nefs), factor H autoantibodies (FHAAs), factor B autoantibodies (FBAAs), and genetic variants in CFH. C3Nefs were detected by: ELISA, C3 convertase surface assay (C3CSA), C3CSA with properdin (C3CSAP), two-dimensional immunoelectrophoresis (2DIEP), and immunofixation electrophoresis (IFE). FHAAs and FBAAs were detected by ELISA, and CFH variants were identified by Sanger sequencing.

RESULTS

Twenty-five patients (78%) were positive for C3Nefs. Three C3Nef-positive patients were also positive for FBAAs and one of these patients additionally carried two novel missense variants in CFH. Of the seven C3Nef-negative patients, one patient was positive for FHAAs and two patients carried CFH variants that may be causally related to their DDD phenotype. C3CASP was the most sensitive C3Nef-detection assay. C3CASP and IFE are complementary because C3CSAP measures the stabilizing properties of C3Nefs, whereas IFE measures their expected consequence-breakdown of C3b.

CONCLUSIONS

A test panel that includes C3CSAP, IFE, FHAAs, FBAAs, and genetic testing for CFH variants will identify a probable cause for alternative pathway dysregulation in approximately 90% of DDD patients. Dysregulation is most frequently due to C3Nefs, although some patients test positive for FHAAs, FBAAs, and CFH mutations. Defining the pathophysiology of DDD should facilitate the development of mechanism-directed therapies.

Allelic variants of complement genes associated with dense deposit disease

The alternative pathway of the complement cascade plays a role in the pathogenesis of dense deposit disease (DDD). Deficiency of complement factor H and mutations in CFH associate with the development of DDD, but it is unknown whether allelic variants in other complement genes also associate with this disease. We studied patients with DDD and identified previously unreported sequence alterations in several genes in addition to allelic variants and haplotypes common to patients with DDD. We found that the likelihood of developing DDD increases with the presence of two or more risk alleles in CFH and C3. To determine the functional consequence of this finding, we measured the activity of the alternative pathway in serum samples from phenotypically normal controls genotyped for variants in CFH and C3. Alternative pathway activity was higher in the presence of variants associated with DDD. Taken together, these data confirm that DDD is a complex genetic disease and may provide targets for the development of disease-specific therapies.

Kidney function, albuminuria and age-related macular degeneration in NHANES III

BACKGROUND

Age-related macular degeneration (AMD) and kidney disease may have shared risk factors, including cardiovascular disease risk factors; additionally AMD and dense deposit disease share a common causal link, with both associated with polymorphisms in the complement pathway. Accordingly, we explored a population-based cohort of US adults to examine if markers of kidney disease identify a higher risk population for prevalent AMD.

METHODS

A cross-sectional nested case-control study matching on age, sex and race was performed using data on adult participants in the Third National Health and Nutrition Examination Survey. Predictor variables included urine albumin-to-creatinine ratio and estimated glomerular filtration rate (eGFR). Study outcomes included late AMD, defined as neovascular disease or geographic atrophy (5:1 matching), and a composite of both early AMD, defined as soft drusen or pigment irregularities with or without any drusen, and late AMD (1:1 matching).

RESULTS

There were 51 participants with late AMD and 865 with any AMD. In conditional logistic regression adjusting for diabetes, hypertension and total cholesterol, lower eGFR was independently associated with late AMD [odds ratio (OR) = 3.05, 95% confidence interval (CI): 1.51-6.13], while albuminuria was not significant. For any AMD, neither albuminuria nor eGFR were significant in adjusted models. In sensitivity analyses excluding diabetics, albuminuria was associated with any AMD (OR = 1.56, 95% CI: 1.11-1.29 and 1.57, 95% CI: 0.61-3.69 for micro- and macroalbuminuria, respectively, P = 0.03).

CONCLUSIONS

Late AMD is more common among individuals with reduced kidney function. Whether this association reflects a common causal pathway or shared risk factors such as hypertension requires additional investigation.

Dense deposit disease associated with monoclonal gammopathy of undetermined significance

Dense deposit disease (DDD) is a rare glomerular disease that typically affects children, young adults, and much less commonly, older patients. The pathophysiologic process underlying DDD is uncontrolled activation of the alternative pathway (AP) of complement cascade, most frequently secondary to an autoantibody to C3 convertase called C3 nephritic factor, although mutations in factor H and autoantibodies to this protein can impair its function and also cause DDD. Since 1995, we have diagnosed DDD in 14 patients aged 49 years or older; 10 of these patients (71.4%) carry a concomitant diagnosis of monoclonal gammopathy of undetermined significance (MGUS). In 1 of these 10 patients, the index case described here, we evaluated the AP and showed low serum AP protein levels consistent with complement activity, heterozygosity for the H402 allele of factor H, and low levels of factor H autoantibodies, which can affect the ability of factor H to regulate AP activity. In aggregate, these findings suggest that in some adults with MGUS, DDD may develop as a result of autoantibodies to factor H (or other complement proteins) that on a permissive genetic background (the H402 allele of factor H) lead to dysregulation of the AP with subsequent glomerular damage. Thus, DDD in some older patients may be a distinct clinicopathologic entity that represents an uncommon complication of MGUS.