Abstract: TH-PO483
Diagnostic Utility of Characterizing Glomerular Basement Membrane (GBM) Collagen IV Changes by Quantitative Immunofluorescence in Paraffin Sections from FSGS Patients Carrying COL4A3/4/5 Variants
Session Information
- Genetic Diseases: Glomerulopathies - I
November 02, 2023 | Location: Exhibit Hall, Pennsylvania Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Genetic Diseases of the Kidneys
- 1202 Genetic Diseases of the Kidneys: Non-Cystic
Authors
- Puapatanakul, Pongpratch, Washington University in St Louis, St Louis, Missouri, United States
- Isaranuwatchai, Suramath, Chulabhorn Hospital, Bangkok, Thailand
- Chanakul, Ankanee, Chulalongkorn University, Bangkok, Bangkok, Thailand
- Surintrspanont, Jerasit, Chulalongkorn University, Bangkok, Bangkok, Thailand
- Iampenkhae, Kroonpong, Chulalongkorn University, Bangkok, Bangkok, Thailand
- Suphapeetiporn, Kanya, Chulalongkorn University, Bangkok, Bangkok, Thailand
- Charu, Vivek, Stanford University School of Medicine, Stanford, California, United States
- Suleiman, Hani, Washington University in St Louis, St Louis, Missouri, United States
- Praditpornsilpa, Kearkiat, Chulalongkorn University, Bangkok, Bangkok, Thailand
- Miner, Jeffrey H., Washington University in St Louis, St Louis, Missouri, United States
Background
Variants in COL4A3/4/5 genes are the most common genetic abnormalities associated with FSGS patients without typical Alport syndrome (AS), linking glomerular basement membrane (GBM) collagen IV (colIV) aberrations and podocytopathy. However, variant pathogenicity is often unclear.
Methods
We developed a new method of immunofluorescence staining for collagen α5(IV) and α1/2(IV) on kidney paraffin sections and used Airyscan confocal microscopy to assess colIV levels in 17 idiopathic FSGS patients with pathogenic/likely pathogenic (P/LP) variants, variants of uncertain significance (VUS), and likely benign (LB) variants in COL4A3/4/5 genes, respectively. Samples from 2 nephrectomies, 3 transplant surveillance biopsies, and 6 biopsies from FSGS patients without COL4A variants were used as controls.
Results
Our approach demonstrated collagen α3α4α5(IV) and α1α1α2(IV) in the GBM as two distinct layers, which enabled quantitative comparisons (Figure 1). The ratios of the mean fluorescence intensities of collagen α5(IV) to α1/2(IV) (α5:α1/2 FI ratios) and the ratios of the thicknesses of α5(IV) to α1/2(IV) (α5:α1/2 thickness ratio) were calculated to represent the level of collagen α3α4α5(IV) in relation to α1α1α2(IV). α5:α1/2 FI and thickness ratios were comparable across the control samples (mean ratios 1.36±0.9 and 1.97±0.63, respectively), while both ratios were drastically decreased in all patients with P/LP variants (mean ratios 0.19±0.08 and 0.94±0.48, respectively) confirming the validity of the approach. We then identified 3 VUS patients with significantly reduced α5:α1/2 FI and thickness ratios, suggesting these variants could in fact be pathogenic.
Conclusion
Our approach can serve as a new diagnostic tool to identify the subgroup of FSGS patients with underlying pathogenic COL4A variants, which can be confirmed with genetic testing. This may help guide immunosuppressive therapy for FSGS.
Funding
- NIDDK Support