Detection of FGA c.1634A>T (p.E545V) in Residual Paraffin-Embedded Kidney Biopsies in Fibrinogen Alpha Amyloidosis: Proof-of-Concept

Background: Fibrinogen Aα-chain amyloidosis (AFib) is the most common hereditary amyloidosis affecting the kidney; 90% of cases are due to pathogenic variant c.1634A>T (p. Glu545Val or p.E545V) in Fibrinogen Alpha Chain gene (FGA). The method of choice for diagnosis of AFib is liquid chromatography-tandem mass spectrometry (LC-MS/MS), which may allow detection of the variant in the amyloid deposits. However, LC-MS/MS has reduced sensitivity. Germline genetic testing (from peripheral blood) is the gold standard for variant detection but is not routinely pursued in AFib. In this proof-of-concept study, we performed genetic testing from residual paraffin-embedded kidney biopsies (FFPE) to interrogate for p.E545V. Methods: DNA analysis via next generation sequencing (NGS) was performed on residual renal biopsy FFPE tissue on 13 renal AFib cases. 10/13 cases were known to have p.E545V by LC-MS/MS. Results: The cohort consisted of 10 M and 3 F, all white, with a median age of 61 years. Proteinuria was present in 100% and 85% had increased serum creatinine (median 4 mg/dL). Family history was present in 42% and 23% had monoclonal gammopathy. The 1-, 2-, and 5-year kidney survival rates (from diagnostic kidney biopsy) were 44%, 33%, and 11%, respectively, whereas the 1-, 2-, and 5-year patient survival rates were 92%, 82%, and 64%, respectively. All kidney biopsies showed massive glomerular involvement by Congo red-positive amyloid; 15% and 23% also showed vascular and interstitial involvement, respectively. NGS detected FGA p.E545V in 7/13 residual biopsy FFPE samples. The remaining cases (6/13) had low input or degraded DNA and/or showed low coverage of the area of interest. 3 patients underwent NGS from peripheral blood, which confirmed FGA p.E545V. In 3 cases, LC-MS/MS did not detect the variant but, for 2 cases, p.E545V was detected in the biopsy and peripheral blood, respectively. Conclusion: NGS can successfully be performed on DNA extracted from readily available FFPE kidney tissue, allowing for prompt confirmation of diagnosis of AFib p.E545V renal amyloidosis. This would also remove the burden of further testing for the patient and nephrologist. Additional studies are needed to test this approach in other forms of hereditary renal amyloidosis.