The age at onset of renal failure was also the same for homozygous and for compound heterozygous COL4A3 and COL4A4 mutations (21.5 ± 7.2, 95%CI 17.2–25.9, n = 13; and 21.8 ± 7.0, 95% CI 19.8 to 23.7, n = 52). This evidence concerns the gene COL4A4 and kidney failure.