Deletions in the COL 4 A 5 Collagen Gene in X - linked Alport Syndrome

The type IV collagen a5 chain (COL4A5) gene of88 unrelated male patients with X-linked Alport syndrome was tested for major gene rearrangements by Southern blot analysis, using COL4A5 cDNA probes. 14 different deletions were detected, providing a 16% deletion rate in the COL4A5 gene in the patient population. The deletions are dispersed all over the gene with different sizes, ranging from 1 kb to the complete absence of the gene (> 250 kb) in one patient. In four patients with intragenic deletions, absence of the a3(IV) chain in the glomerular basement membrane was demonstrated by immunohistochemical studies. This finding supports the hypothesis that abnormalities in the a5(IV) chain may prevent normal incorporation of the a3(IV) chain into the glomerular basement membrane. Direct sequencing ofcDNA amplified from lymphoblast mRNA of four patients with internal gene deletions, using appropriate combinations of primers amplifying across the predicted boundaries of the deletions, allowed us to determine the effect of the genomic rearrangements on the transcripts and, by inference, on the a5(IV) chain. Regardless of the extent of deletion and of the putative protein product, the 14 deletions occur in patients with juvenile-type Alport syndrome. (J. Clin. Invest. 1994. 93:1195-1207.)