Type IV collagen α5 chain: Normal distribution and abnormalities in X-linked Alport syndrome revealed by monoclonal antibody

Although the evidence indicates that mutation of the gene for the α5 chain of type IV collagen, α5-(IV), is the primary defect in X-linked Alport syndrome, protein data for the α5(IV) chain with regard to its normal distribution and its distribution in patients with Alport syndrome is lacking. We produced a rat monoclonal antibody (H51) by immunizing rats with a synthetic peptide corresponding to the nonconsensus amino acid sequence of α5(IV) NC1 domain. H51 reacted by Western blotting with 26-kd cationic monomers and associated dimers of human type IV collagen NC1 domain. Immunohistochemical studies demonstrated that in normal human kidney α5(IV) was present in the glomerular basement membrane and basement membranes of the Bowman's capsule and in some tubules (collecting ducts). The α5(IV) chain was also detected in the basement membranes of normal skin, eye, and lung. Male patients with X-linked Alport syndrome revealed no reactivity of renal and epidermal basement membranes with H51, whereas α5(IV) staining was normal in the glomerular basement membrane of patients with other types of glomerular diseases, including benign familial hematuria, The staining was also normal in the skin of nonaffected males in X-linked Alport families. Female heterozygous for Alport syndrome exhibited a discontinuous or mosaic pattern in the immunofluorescent staining of the epidermal basement membrane. These findings confirm that in patients with X-linked Alport syndrome there are abnormalities in α5(IV) in renal and epidermal basement membranes at the protein level Immunofluorescent staining of skin biopsies with this antibody may be of value in making a diagnosis of Alport syndrome, and, furthermore, may aid in detecting carrier females in whom urinary abnormalities are often mild or silent.