COL4A5 and X-linked hydrocephalus with stenosis of the aqueduct of Sylvius: Alport syndrome (AS) has been reported as the second most common IKD following ADPKD in Europe and the US during adulthood (Groopman et al., 2019; Oberdhan et al., 2022), with most of them (about 80%) being XLAS caused by the pathogenic variants in the COL4A5 gene (Nozu et al., 2020), which leads to heterogeneous renal manifestations from hematuria alone to end-stage kidney disease.