COL4A4 and hematuria, benign familial, 1: Considering that a relevant amount of heterozygous disease-causing variants in COL4A3 and COL4A4 also cause thin basement membrane nephropathy (now mostly described as autosomal dominant Alport syndrome) with a lower frequency of classic symptoms and a lower probability of causing end-stage kidney disease, the actual lifetime risk would be even higher.7