COL4A4 and Alport syndrome: The remaining 15% of patients with Alport syndrome, in descending order of the number of cases reported, include autosomal recessive Alport syndrome (ARAS) caused by pathogenic variants in both alleles of either COL4A3 or COL4A4 genes [7–9], autosomal dominant Alport syndrome (ADAS) caused by heterozygous pathogenic variants in COL4A3 or COL4A4 genes [10, 11] and digenic Alport syndrome caused by coexisting pathogenic variants in COL4A3, COL4A4, or COL4A5 genes [12, 13].