This trichrome stain of a glomerulus in a patient with focal segmental glomerulosclerosis (FSGS) demonstrates blue collagen deposition. FSGS accounts for about a sixth of cases of nephrotic syndrome in adults and in children. FSGS is most often a primary disease, but it can be secondary to other conditions. Some cases are familial and linked to mutations in NPHS1 (nephrin) and NPHS2 (podocin) genes encoding for proteins forming the slit pores.