There are 3 allergens associated with coffee allergy. Cof a 1 is a chitinase protein. Chitinase proteins are usually associated with Latex Food Syndrome, but in this case the allergen is an inhalant allergen and not a food allergen, so does not need to be avoided if suffering from this syndrome.
Cof a 2 and Cof a 3 are both metallothionein proteins. Again these are inhalant allergens and not food allergens and they are used in the plant to bind metals such as zinc.
Coffee allergy has been linked to asthma, rhinoconjunctivitis and atopic dermatitis, especially in patients who work with coffee occupationally.
I have put together some more comprehensive resources at http://www.allergyresources.co.uk/Coffee.php
The allergy resources page for coffee allergy covers the key allergens, which allergic syndromes are linked to this allergy and other foods which are commonly cross reactive with coffee allergy.
There is also regularly updated links to useful websites specifically for coffee allergies and the latest research papers on the topic.
If you have multiple allergies and are interested in how they are linked or want to find out more about food allergies outside the usual top 14 then you can follow me on Facebook or Twitter, where I share a food allergy card every day of the week.