Clinicopathologic Implications of Complement Genetic Variants in Kidney Transplantation

Abstract

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.

Identification of complement factor H variants that predispose to pre‐eclampsia: A genetic and functional study

“…The functional consequences of rare and unique variants observed in CFH were characterised using 293T cells transfected under serum‐free conditions 23 . Functional studies and surface plasmon resonance (SPR) interaction analyses with the Biacore X100 and Biacore 2000 instruments (GE Healthcare) were performed as previously described 22,24 .…”

“…The functional consequences of rare and unique variants observed in CFH were characterised using 293T cells transfected under serum-free conditions. 23 Functional studies and surface plasmon resonance (SPR) interaction analyses with the Biacore X100 and Biacore 2000 instruments (GE Healthcare) were performed as previously described. 22,24 Variants in CCP19 and CCP20 were purified as described, with the exception that they were eluted from a HisTrap column (GE Healthcare) at 285 mM NaCl as compared with variants in CCP2 and 3, which were eluted at 95 mM.…”

C3 glomerulopathy: Understanding an ultra‐rare complement‐mediated renal disease

“…Recently, Ren et al evaluated the clinicopathologic significance of genetic variants in a TMA and C3G kidney transplant cohort. The group reported 10 variants in CFH , of which were four pathogenic, one was likely benign, and five were classified as variants of uncertain significance (Ren, Perkins, Love‐Gregory, Atkinson, & Java, 2021). The presence of pathogenic variants increased the risk for recurrent disease in the transplant due to continued complement dysregulation in the recipient.…”

“Eculizumab First” in the Management of Posttransplant Thrombotic Microangiopathy

“…The majority of patients only carried polymorphisms or risk haplotypes. 16 , 31 Interestingly, we found that the 64% of patients carried the MCP aHUS risk haplotype C.∗897 T>C (rs7144). This condition affects the promoter region of the MCP gene and results in decreased gene transcription, suggesting a decrease expression of MCP on the cell surfaces.…”