A Proposed Taxonomy for the Podocytopathies

Abstract

A spectrum of proteinuric glomerular diseases results from podocyte abnormalities. The understanding of these podocytopathies has greatly expanded in recent years, particularly with the discovery of more than a dozen genetic mutations that are associated with loss of podocyte functional integrity. It is apparent that classification of the podocytopathies on the basis of morphology alone is inadequate to capture fully the complexity of these disorders. Herein is proposed a taxonomy for the podocytopathies that classifies along two dimensions: Histopathology, including podocyte phenotype and glomerular morphology (minimal-change nephropathy, focal segmental glomerulosclerosis, diffuse mesangial sclerosis, and collapsing glomerulopathy), and etiology (idiopathic, genetic, and reactive forms). A more complete understanding of the similarities and differences among podocyte diseases will help the renal pathologist and the nephrologist communicate more effectively about the diagnosis; this in turn will help the nephrologist provide more accurate prognostic information and select the optimal therapy for these often problematic diseases. It is proposed that final diagnosis of the podocytopathies should result from close collaboration between renal pathologists and nephrologists and should whenever possible include three elements: Morphologic entity, etiologic form, and specific pathogenic mechanism or association.Clin J Am Soc Nephrol 2: 529-542, 2007. doi: 10.2215/CJN.04121206 T he spectrum of primary nephrotic syndrome includes a variety of causes, presentations, histopathologic findings, and outcomes. These disorders may appear at any age, may be exquisitely sensitive or highly resistant to therapy, and have varied implications for long-term renal function. Past efforts to develop an organized approach to these diseases have largely centered on histopathology. Although these approaches were helpful in defining lesions, for each morphologic entity there is a wide range in response to treatment and outcome. This observation suggests that traditional pathologic description alone is insufficient to classify these disorders.Here, we propose a new taxonomy for podocyte diseases. The word "taxonomy" was coined by Carl Linnaeus, the 18th century Swedish scientist who proposed the system for naming and classifying organisms that remains in use today. A taxonomy is organized into multiple levels, each of which represents a taxon with one or more elements. The ideal taxonomy separates the elements of each taxon (the taxa) into mutually exclusive, unambiguous, and all-encompassing categories. In practice, a good taxonomy should be simple, easy to remember, and easy to use. Taxonomies provide classification and frequently more: A conceptual framework for analysis, discussion, and hypothesis generation. Our proposed podocyte taxonomy has two dimensions-histopathology and etiology-and includes additional modifiers related to biomarkers that have been identified through recent progress in the genetics, cell biology, and pathophysiol...

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