Kidney diseases caused by glomerular basement membrane typeIVcollagen defects in dogs

Abstract

To review the pathogenesis, as well as the clinical and pathologic features of canine glomerular diseases caused by genetic type IV collagen defects. Original studies and review articles from human and veterinary medical fields. Presence in glomerular basement membranes (GBM) of a network composed of α3.α4.α5 heterotrimers of type IV collagen is required to maintain structure and function of glomerular capillary walls. Hereditary nephropathy (HN) is the most commonly used name for kidney diseases that occur in dogs due to genetic type IV collagen abnormalities. To date, 4 different collagen IV gene mutations have been identified in dogs with HN; 2 are COL4A5 mutations that cause X-linked HN (XL-HN), and 2 are COL4A4 mutations that cause autosomal recessive HN (AR-HN). Affected males with XL-HN and affected males and females with AR-HN develop juvenile-onset kidney disease manifested by proteinuria typically starting at 3-6 months of age and followed by progressive kidney disease leading to terminal failure usually at 6-24 months of age. Carrier female dogs with XL-HN also develop proteinuria starting at 3-6 months of age, but progressive disease causing kidney failure is uncommon until they are >5 years old. The distinctive pathologic lesions of HN are extensive multilaminar splitting and thickening of the GBM, as demonstrated by electron microscopy, and abnormal type IV collagen α-chain content of basement membranes, as demonstrated by immunolabeling. Identification of the underlying gene mutations has permitted genetic testing and selective breeding practices that currently are minimizing HN in breeds known to be at risk. Canine HN is a rare disease that should be considered whenever a dog exhibits a juvenile-onset kidney disease characterized partly by proteinuria, but highly specialized methods are required to pursue a definitive diagnosis.