Finding a top specialist in a particular condition

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My DS has been diagnosed with a rare hormone related condition and while we await the NHS consultant appointment I'm trying to find out more about the condition, treatments, long term implications etc . This includes finding out whether there is an endocrinologist in the uk who has a special interest in it, is right on the ball in terms of research etc. it's pretty rare I think and a generalist might not know that much about it.
So how do I find this out? It could apply to any condition really ... I need a directory of some sort...
Google isn't really helping me.
Any tips?

I'm in the same boat. I've been looking for a private endo due to very long waiting lists to see a NHS one. I have suspected Cushing's Disease. I have all the symptoms including high cortisol in multiple tests, the buffalo hump, weight gain etc. Apparently most endo's aren't clued up on Cushing's as much as they should be and often dismiss patients who eventually end up getting diagnosed with it by another endo. I've come across a few good ones both in The UK and abroad but none in my local area, sadly. It would maybe a good idea to join a FB group of your DS's condition as they can often help you find specialists and give you great advice and support.