What's causing this former jockey's nephrotic syndrome?

A patient presents complaining of increasing tiredness and weight gain
Jockey horse trainer
When the oedema in his legs cleared up, it revealed something unusual.

Nicholas is a 38-year-old retired jockey who attends regularly for prescriptions for timolol and latanoprost eye drops to control his longstanding glaucoma.

Today he presents complaining of increasing tiredness over the past month and, in his own words, “just generally slowing up and putting on weight alarmingly”.