Editor—Alport syndrome (AS) is a hereditary nephritis characterised by haematuria, proteinuria, and chronic renal failure associated with progressive high tone sensorineural deafness and characteristic eye lesions (macular flecks and anterior lenticonus1). At the molecular level, X linked AS, which is the most common form, is caused by mutations inCOL4A5, a type IV collagen gene expressed in the glomerular basement membrane of the kidney.2 Mutations in COL4A5 cause progressive kidney damage usually leading to renal failure in affected males in early adulthood (20-25 years, juvenile form). A small proportion ofCOL4A5 mutations cause a later onset form of AS with ESRF in males at >31 years, although nephritis is apparent much earlier than this. Heterozygous females are generally mildly affected and often do not develop renal failure. We report here the identification of three apparently mosaic parents (two mothers and one father) of affected subjects. In the case of the mosaic father, an unusually mild AS phenotype was observed which may be a consequence of his mosaicism.

The COL4A5 gene is composed of 51 exons spread over 250 kb of genomic DNA, which generate a 6.5 kb transcript encoding a 1685 amino acid protein3 and has been the subject of several large mutation studies.4-6 We have …