Autosomal recessive AS (ARAS) has been defined by biallelic pathogenic variants in COL4A3 or COL4A4. Individuals with a pathogenic heterozygous COL4A3 or COL4A4 variant are diagnosed as a carrier state of ARAS, autosomal dominant AS (ADAS), or thin basement membrane nephropathy. Here, COL4A4 is linked to hematuria, benign familial, 1.