Thanks David, that's really interesting.
I'm HLA-B27+, early onset (20 years), mixed - axial and peripheral. And I have:
Rs30187(C;T) - http://www.snpedia.com/index.php/Rs30187(C;T)
Rs27044(C;G) - http://www.snpedia.com/index.php/Rs27044(C;G)
So if I'm reading the study correctly I have an Rs30187 allele that is associated only with the axial form, and a Rs27044 allele that is associated with the mixed form. And both of those are also associated with early onset.