In many families a cause is not identified, however, in 40–50% cases, TBMN is linked with a heterozygous mutation of the COL4A3, COL4A4 or COL4A5 genes that encode type IV collagen, and the clinical features overlap with the carrier state for autosomal recessive or X-linked Alport syndrome [3–5]. This evidence concerns the gene COL4A4 and Alport syndrome.