A boy, aged 7, is under treatment during 1 month. On hospitalization: significant edema, proteinuria - 7,1 g/L, protein in daily urine - 4,2 g. Blood biochemical profile: stable hypoproteinaemia (43,2 g/L), hypercholesterinaemia (9,2 mmol/L). Which variant of glomerulonephritis is the most probable in this case?