COL4A4 and focal segmental glomerulosclerosis: The GBM was found to be significantly thinner in patients with a mono-allelic variant in COL4A3/COL4A4 (median of 0.29 μm (interquartile range 0.22-0.35 μm) compared to patients with idiopathic FSGS and other hereditary causes (median of 0.36 μm [interquartile range 0.29-0.45 μm]) (P < 0.01).