Functional characterization of 105 factor H variants associated with aHUS: lessons for variant classification

Merinero, Héctor Martín; Zhang, Yuzhou; Arjona, Emilia; Angel, Guillermo del; Goodfellow, Renee X.; Gómez-Rubio, Elena; Ji, Rui-Ru; Michelena, Malkoa; Smith, Richard J.H.; Córdoba, Santiago Rodrı́guez de

doi:10.1182/blood.2021012037

Cited by 39 publications

(38 citation statements)

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“…The one overlapping variant, T956M, demonstrated similar results to our data. Also, the SNPs (E936D, N1050Y, I1059T, Q1143E) have been reported and results of our functional data are comparable (Supplementary Figure 4) (44). Additionally, we demonstrate that the SNP E936D may have a potentially protective role since it helped improve the C3b binding for rare variant, T956M.…”

Section: Discussionsupporting

confidence: 78%

“…Additionally, we demonstrate that the SNP E936D may have a potentially protective role since it helped improve the C3b binding for rare variant, T956M. We used FH fragments which have been shown by us (16) and others (45)(46)(47) to be highly predictive of the results obtained with full-length protein (36,44). Nevertheless, the availability of commercially available full-length recombinant FH and the serum-based assays is an advance that should be taken advantage of.…”

Section: Discussionmentioning

confidence: 99%

“…This was an elegant approach to obtaining purified full-length FH which was available for 7 of 12 variants. While our manuscript was being prepared for submission, a second comprehensive study reported a functional assessment for 105 CFH variants associated with aHUS ( 44 ). In this study, full length FH was prepared recombinantly by ThermoFisher Scientific (Regensburg, Germany).…”

Section: Discussionmentioning

confidence: 99%

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Clinicopathologic Implications of Complement Genetic Variants in Kidney Transplantation

et al. 2021

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Genetic testing has uncovered rare variants in complement proteins associated with thrombotic microangiopathy (TMA) and C3 glomerulopathy (C3G). Approximately 50% are classified as variants of uncertain significance (VUS). Clinical risk assessment of patients carrying a VUS remains challenging primarily due to a lack of functional information, especially in the context of multiple confounding factors in the setting of kidney transplantation. Our objective was to evaluate the clinicopathologic significance of genetic variants in TMA and C3G in a kidney transplant cohort. We used whole exome next-generation sequencing to analyze complement genes in 76 patients, comprising 60 patients with a TMA and 16 with C3G. Ten variants in complement factor H (CFH) were identified; of these, four were known to be pathogenic, one was likely benign and five were classified as a VUS (I372V, I453L, G918E, T956M, L1207I). Each VUS was subjected to a structural analysis and was recombinantly produced; if expressed, its function was then characterized relative to the wild-type (WT) protein. Our data indicate that I372V, I453L, and G918E were deleterious while T956M and L1207I demonstrated normal functional activity. Four common polymorphisms in CFH (E936D, N1050Y, I1059T, Q1143E) were also characterized. We also assessed a family with a pathogenic variant in membrane cofactor protein (MCP) in addition to CFH with a unique clinical presentation featuring valvular dysfunction. Our analyses helped to determine disease etiology and defined the recurrence risk after kidney transplant, thereby facilitating clinical decision making for our patients. This work further illustrates the limitations of the prediction models and highlights the importance of conducting functional analysis of genetic variants particularly in a complex clinicopathologic scenario such as kidney transplantation.

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Section: Discussionsupporting

confidence: 78%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Clinicopathologic Implications of Complement Genetic Variants in Kidney Transplantation

et al. 2021

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“…Patients with DNASE1L3 mutations are prone for LN, high titer of ANA, APL, ANCA and low complement similar to Case 6 [ 58 ]. CFHR4 encodes one of the 5 complement factor H-related proteins and is linked to aHUS, a life threatening TMA characterized by dysregulation of the alternative pathway of complement [ 59 ]. While aHUS rarely causes acute pancreatitis and the association between these two diseases remain unclear, several reports revealed an episode of acute pancreatitis preceding TMA in cases with or without TMA related mutations [ 60 – 62 ].…”

Section: Discussionmentioning

confidence: 99%

Characteristics and genetic analysis of patients suspected with early-onset systemic lupus erythematosus

et al. 2022

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Background Systemic lupus erythematosus (SLE) is rarely diagnosed before 5-years-old. Those with disease onset at a very young age are predicted by a higher genetic risk and a more severe phenotype. We performed whole-exome sequencing to survey the genetic etiologies and clinical manifestations in patients fulfilling 2012 SLICC SLE classification criteria before the age of 5. Case presentation Among the 184 childhood-onset SLE patients regularly followed in a tertiary medical center in Taiwan, 7 cases (3.8%) of which onset ≦ 5 years of age were identified for characteristic review and genetic analysis. Compared to those onset at elder age, cases onset before the age of 5 are more likely to suffer from proliferative glomerulonephritis, renal thrombotic microangiopathy, neuropsychiatric disorder and failure to thrive. Causative genetic etiologies were identified in 3. In addition to the abundance of autoantibodies, patient with homozygous TREX1 (c.292_293 ins A) mutation presented with chilblain-like skin lesions, peripheral spasticity, endocrinopathy and experienced multiple invasive infections. Patient with SLC7A7 (c.625 + 1 G > A) mutation suffered from profound glomerulonephritis with full-house glomerular deposits as well as hyperammonemia, metabolic acidosis and episodic conscious disturbance. Two other cases harbored variants in lupus associating genes C1s, C2, DNASE1 and DNASE1L3 and another with CFHR4. Despite fulfilling the classification criteria for lupus, many of the patients required treatments beyond conventional therapy. Conclusions Genetic etiologies and lupus mimickers were found among a substantial proportion of patients suspected with early-onset SLE. Detail clinical evaluation and genetic testing are important for tailored care and personalized treatment.

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“…To assess FI co-factor activity, we developed a novel FI functional assay using C3b-decorated sheep erythrocytes (C3b-ShE) prepared as previously described ( 32 ). To minimize the effect of endogenous FH, patient serum or plasma was diluted 1:32 in GVB-Mg 2+ buffer ( 16 ).…”

Section: Methodsmentioning

confidence: 99%

Complement Factor I Variants in Complement-Mediated Renal Diseases

et al. 2022

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C3 glomerulopathy (C3G) and atypical hemolytic uremic syndrome (aHUS) are two rare diseases caused by dysregulated activity of the alternative pathway of complement secondary to the presence of genetic and/or acquired factors. Complement factor I (FI) is a serine protease that downregulates complement activity in the fluid phase and/or on cell surfaces in conjunction with one of its cofactors, factor H (FH), complement receptor 1 (CR1/CD35), C4 binding protein (C4BP) or membrane cofactor protein (MCP/CD46). Because altered FI activity is causally related to the pathogenesis of C3G and aHUS, we sought to test functional activity of select CFI missense variants in these two patient cohorts. We identified 65 patients (16, C3G; 48, aHUS; 1 with both) with at least one rare variant in CFI (defined as a MAF < 0.1%). Eight C3G and eleven aHUS patients also carried rare variants in either another complement gene, ADAMTS13 or THBD. We performed comprehensive complement analyses including biomarker profiling, pathway activity and autoantibody testing, and developed a novel FI functional assay, which we completed on 40 patients. Seventy-eight percent of rare CFI variants (31/40) were associated with FI protein levels below the 25th percentile; in 22 cases, FI levels were below the lower limit of normal (type 1 variants). Of the remaining nine variants, which associated with normal FI levels, two variants reduced FI activity (type 2 variants). No patients carried currently known autoantibodies (including FH autoantibodies and nephritic factors). We noted that while rare variants in CFI predispose to complement-mediated diseases, phenotypes are strongly contingent on the associated genetic background. As a general rule, in isolation, a rare CFI variant most frequently leads to aHUS, with the co-inheritance of a CD46 loss-of-function variant driving the onset of aHUS to the younger age group. In comparison, co-inheritance of a gain-of-function variant in C3 alters the phenotype to C3G. Defects in CFH (variants or fusion genes) are seen with both C3G and aHUS. This variability underscores the complexity and multifactorial nature of these two complement-mediated renal diseases.

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Functional characterization of 105 factor H variants associated with aHUS: lessons for variant classification

Cited by 39 publications

References 50 publications

Clinicopathologic Implications of Complement Genetic Variants in Kidney Transplantation

Clinicopathologic Implications of Complement Genetic Variants in Kidney Transplantation

Characteristics and genetic analysis of patients suspected with early-onset systemic lupus erythematosus

Complement Factor I Variants in Complement-Mediated Renal Diseases

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