Thanks David, that's really interesting.

I'm HLA-B27+, early onset (20 years), mixed - axial and peripheral. And I have:

Rs30187(C;T) -;T)
Rs27044(C;G) -;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.