Alport syndrome (ATS) initially described as a likely autosomal dominant condition, with males being more severely affected than females, [1–5] has been redefined as an X-linked semi-dominant condition [6, 7] after the discovery in 1990 of the causative gene COL4A5 on the X chromosome (Xq22.3). This evidence concerns the gene COL4A5 and Andersen-Tawil syndrome.