A 6-year-old boy had had a quinsy. 9 days later, there appeared edemata of the face, extremities and trunk, general health condition deteriorated. Urine became turbid. Objectively: expressive edemata, ascites. AP-100/55 mm Hg, diuresis - 0,2 l of urine per day. Results of the biochemical blood analysis: total protein - 50 g/l, cholesterol - 11,28 mmol/l, urea - 7,15 mmol/l, creatinine - 0,08 mmol/l. Urinalysis results: leukocytes - 3-5 per HPF, red blood cells are absent. What is the provisional diagnosis?