The advantages of molecular diagnostics are particularly evident in female carriers of Alport syndrome, where distinguishing between a heterozygous variant in the X-linked COL4A5 gene and a heterozygous variant in COL4A3 and COL4A4 genes has significant implications for genetic counselling, especially in prenatal contexts, and long-term prognosis. The gene discussed is COL4A4; the disease is Alport syndrome.