COL4A5 and X-linked Alport syndrome: This variant was even more frequent in another study of 269 Polish children enrolled into a National Registry for children with persistent glomerular hematuria, where the COL4A5:c.1871G>A variant was the most prevalent, accounting for 39% (44/113) of genetically confirmed X-linked Alport syndrome in unrelated Polish families, thus making it the predominant variant in this national cohort [7].