Recent findings by us and others showed that about 50% of patients with COL4A3/COL4A4 heterozygous mutations, a prevalent cause of familial microscopic hematuria due to TBMN, develop proteinuria with secondary focal segmental glomerulosclerosis (FSGS), after their third decade of life. Here, COL4A3 is linked to focal segmental glomerulosclerosis.