Renal dysplasia: new approaches to an old problem.

Renal dysplasia is a clinically important consequence of abnormal nephrogenesis. Various forms are encountered in clinical practice; however, renal dysplasia may represent the final common end point of defects in the normal cascade of fetal kidney development. Typical histopathologic changes characterize renal dysplasia, including architectural distortion, metaplasia, and primitive glomeruli and tubules. Cystic changes are not universal but can be found in most situations. The advent of recent molecular techniques, including gene targeting and positional cloning, has expanded our knowledge of the molecular control of normal mammalian nephrogenesis and with it our understanding of the pathogenesis of renal dysplasia. A defect in the ability of the branching ureteric duct and the undifferentiated metanephric blastema to communicate appears to be the basic underlying principle for the formation of dysplasia. Mutation, defective regulation of transcription, and alteration in spatial or temporal expression of a number of classes of genes, including growth factors, have been implicated in the development of renal dysplasia. Numerous examples, both experimental and in nature, highlight this point.