Ultrastructural Characterization of Proteinuric Patients Predicts Clinical Outcomes
Authors: Royal Virginie , Zee Jarcy , Liu Qian , Avila-Casado Carmen , Smith Abigail R. , Liu Gang , Mariani Laura H. , Hewitt Stephen , Holzman Lawrence B. , Gillespie Brenda W. , Hodgin Jeffrey B. , Barisoni Laura 
Published: February 2020

Significance Statement
Glomerular features ascertained by electron microscopy are underreported in clinical practice, and their value in predicting outcome is unclear. This study is the first comprehensive investigation of the association of clinical outcomes with 12 glomerular electron microscopy descriptors reflecting the status of podocytes, endothelial cells, and glomerular basement membranes, individually and as electron microscopy profiles after descriptor-based consensus clustering. The authors demonstrate that severe effacement and microvillous transformation, individually and as a component of clusters, were associated with proteinuria remission, whereas prominent endothelial cell and glomerular basement membrane abnormalities were associated with loss of renal function. These findings highlight the importance of a standardized and comprehensive ultrastructural analysis, and that use of quantifiable structural changes in assessing patients with proteinuria might have important clinical implications.

Background
The analysis and reporting of glomerular features ascertained by electron microscopy are limited to few parameters with minimal predictive value, despite some contributions to disease diagnoses.

Methods
We investigated the prognostic value of 12 electron microscopy histologic and ultrastructural changes (descriptors) from the Nephrotic Syndrome Study Network (NEPTUNE) Digital Pathology Scoring System. Study pathologists scored 12 descriptors in NEPTUNE renal biopsies from 242 patients with minimal change disease or FSGS, with duplicate readings to evaluate reproducibility. We performed consensus clustering of patients to identify unique electron microscopy profiles. For both individual descriptors and clusters, we used Cox regression models to assess associations with time from biopsy to proteinuria remission and time to a composite progression outcome (≥40% decline in eGFR, with eGFR<60 ml/min per 1.73 m2, or ESKD), and linear mixed models for longitudinal eGFR measures.

Results
Intrarater and interrater reproducibility was >0.60 for 12 out of 12 and seven out of 12 descriptors, respectively. Individual podocyte descriptors such as effacement and microvillous transformation were associated with complete remission, whereas endothelial cell and glomerular basement membrane abnormalities were associated with progression. We identified six descriptor-based clusters with distinct electron microscopy profiles and clinical outcomes. Patients in a cluster with more prominent foot process effacement and microvillous transformation had the highest rates of complete proteinuria remission, whereas patients in clusters with extensive loss of primary processes and endothelial cell damage had the highest rates of the composite progression outcome.

Conclusions
Systematic analysis of electron microscopic findings reveals clusters of findings associated with either proteinuria remission or disease progression.