Yes, you're correct that it is rare. We have in the clinic about 18 patients, which is probably more than you would expect from the supposed frequency of the disease. It's actually not too difficult to make the diagnosis once the patient gets to the nephrology clinic, but sometimes patients will go through a series of other health care providers who just haven't thought about the issue or have recognized something but not referred.
Making the diagnosis once the patient gets to the provider who knows about the disease is actually not that difficult, but in certain patients there can certainly be delays, which is always rather troubling.