NPHS2 and focal segmental glomerulosclerosis: Collectively, these data support the hypothesis that certain heterozygous podocin variants, which on their own would not lead to perceptible clinical effects, aggravate the phenotype when co-inherited on the background of heterozygous COL4A3/A4 pathogenic variants, by predisposing to focal segmental glomerulosclerosis and kidney function decline.