Nephrotic syndrome within the first three motnhs of life, characterized initially by increased mesangial matrix, with or without hypertrophy and hyperplasia of podocytes, and eventual glomerular sclerosis. The disease is MONDO_0009733 (nephrotic syndrome, type 4). Also known as: WT1 nephrotic syndrome, congenital nephrotic syndrome - diffuse mesangial sclerosis, nephrotic syndrome caused by mutation in WT1.