Abstract
Background and Aims
Advances in the past 2 decades have shown atypical hemolytic uremic syndrome (aHUS) to be a disorder of the alternative pathway of complement. Most aHUS cases involve sequence variations in genes encoding complement proteins The term pregnancy associated aHUS (P-aHUS) refer to the thrombotic microangiopathy (TMA) that result from uncontrolled complement activation during pregnancy or the postpartum period. P-aHUS is a devastating systemic disease, with high maternal mortality and morbidity rates, in the pre-eculizumab era. The term ‘C3 glomerulopathy’ (C3GN) encompasses a heterogeneous spectrum of immune-mediated nephropathies that share a common pathological feature, glomerular deposition of C3. This entity may progress to advanced stages of chronic kidney disease and shares a common genetic risk factors with aHUS. Even more, some authors even suggest that C3GN and aHUS represent two forms of a disease spectrum with a common pathogenic principle. Here, we report this rare association and describe the family genetic variants that could cause it
Method
We describe the clinical and laboratoy data of a patient with the association of aHUS and C3 Glomerulopathy. A genetic study was performed and her available relatives were also screened for mutations/polymorphisms in aHUS-associated complement genes. After extracting gDNA from whole blood (Wizard Genomic DNA Purification Kit, Promega), PCR products of coding sequences and intronic flanking regions of complement genes were sequenced by ABI PRISM 310 Genetic Analyzer (Applied Biosystems). In silico analysis for pathogenicity was completed with Polyphen2-HDIV, PhyloP/Phastcons (MutationTaster), SIFT and PANTHER. All the participants provided informed written consent
Results
In 3/2012 a 27-year-old patient, with no family history, started his current illness one month after his first natural birth, with acute renal failure and microangiopathic hemolytic anemia, demonstrating a severe TMA in a renal biopsy. Laboratory results showed low C3 serum levels, but C4 were normal, haptoglobine was undetectably low, and all ADAMTS13 parameters were normal. Her urine tests showed also glomerular hematuria and proteinuria in the nephrotic range. She was treated with plasmapheresis and fresh frozen plasma with hematological improvement, but hemodialysis was required for more than 3 months. Despite partial recovery of renal function, six months later reappeared anemia and developed severe arterial hypertension, congestive heart failure and progressive renal insufficiency. Diagnosis of aHUS was made and start treatment with eculizumab with progressive recovery of renal function in the following months. Nevertheless the C3 serum levels persisted low and the proteinuria and hematuria did not change even after long term treatment with eculizumab. Retrospectively, her urynalisis before the pregnant showed proteinuria and hematuria, and a revision of a renal biopsy revealed the presence of dominant C3 deposits in the immunofluorescence, and electrondense deposits in the electronic microscopy, suggesting the diagnostic of C3GN. In a genetic study two novel single nucleotide variants were founded (CFH c.575G>A, p.C192Y (exon 5) (NM_000186), predicted to be pathogenic by 4 of 5 available pathogenicity prediction programs; and CFI c.1189G>T, p.V397L (exon 11) (NM_000204), predicted pathogenic by 0 of 6 available pathogenicity prediction programs). (Figure 1)
Conclusion
We present here the family genetic bases of a patient who developed a C3GN and a aHUS with a different response to treatment with eculizumab. In this case we identified two novel genetic variants in the CFH and CFI genes in a patient with aHUS, who inherited one variant from each parent. Although the CFI variant is predicted to be benign, the CFH variant is predicted to be damaging. It is located in exon 5, which encodes a portion of the factor H protein implicated in binding to C3b
Pathogenicity prediction of non-synonymous single nucleotide variants in dilated cardiomyopathy