Alport syndromes: phenotypic heterogeneity of progressive hereditary nephritis

Alport syndrome is a primary genetic disease of basement membranes, manifested clinically as a progressive nephropathy variably associated with sensorineural deafness and a plethora of ocular abnormalities. The long-recognized phenotypic heterogeneity of Alport syndrome may be considered on several levels, including basement membrane biochemistry, basement membrane ultrastructure, the natural history of the nephropathy, and the occurrence of extrarenal abnormalities. This review discusses the possible molecular bases for the heterogeneity. The discussion draws upon recent insights into the molecular genetics of Alport syndrome, and the biochemistry of normal and Alport syndrome basement membranes, in order to provide a framework for understanding the variable renal and extrarenal manifestations of the disease.