June recalls

A 5-year-old has a week of puffy eyes and swollen ankles and is otherwise well with a normal blood pressure. His parents first noticed the swelling around his eyes on waking, and by evening his socks leave deep imprints on his ankles. He has been growing and developing normally, with no rash, joint pain, fevers, or recent medication changes, and there is no family history of kidney disease. On examination he has mild peri-orbital and bilateral pitting ankle oedema with a soft, non-tender abdomen. Urine dipstick shows heavy protein (4+) with no blood. What is the most likely diagnosis?