Brooklynella and Uronema haven't been as thoroughly researched as Cryptocaryon and Amyloodinium. The latters are a major threat to the aquaculture industry and thus, worthy of extensive study. Since brook & uronema are mostly host-specific diseases, and nobody really wants to eat clownfish or chromis damselfish... :p
Even anecdotal accounts differ with these diseases. With brook, I've seen cases where it only afflicts the clownfish, no other fish are affected, etc. While other times it wipes out an entire fish population like velvet. Symptoms of this disease can also vary - from skin peeling or sloughing off, to excessive white mucous forming around the affected area(s), to sometimes looking very similar to ich-like sprinkles. As mentioned above, only a skin scrape viewed under a scope can conclusively ID.
It is even a big mystery WHY clownfish are so susceptible to this disease. Following a velvet outbreak, clownfish are often the only fish left standing - presumably because of their incredibly thick mucous coat. But brook tears thru them like hot butter. o_O