Hi,
Just by googling aka ankylosing spondylitis I am able to find several synonyms(?) to ankylosing spondylitis. My guess is that people may be diagnosed with the alternate name, and not even know that there are support forums for their disease.

Also, there are those people who have been mis-diagnosed as well.

Then we have to consider how many of those people with AS have access to the internet. Possibly 1 in 5? Odds would be much less in poorer areas(countries).

HLA-B27+, JRA diagnosis in 1981, re-diagnosed as AS in 1988. Also iritis, colitis, and psoriasis. NSD + low carb helps me. My health makes it hard for me to post in a timely way.