I don't have the gene, however I have been diagnosed with AS. My understanding is that a large majority of people who have AS have the gene but it is not a requirement for diagnosis, as a smaller percentage of people don't have the gene.
Then with regard to having the gene, it also doesn't mean that you have AS, it means that you have a higher likelihood of having it and there are other symptoms and diagnosis criteria required to diagnose AS.
Hope that helps :)

After being misdiagnosed for many years, the second rheumatologist I saw told me the usual diagnostic markers for AS are: positive for HLA-B27 gene, elevated sed rate, elevated CRP, possible damage seen on x-ray or MRI and symptoms. In my case, damage was not seen by x-ray, so technically, my diagnosis is non-radiographic axial spondyloarthritis (an early form of Ankylosing Spondylitis), but my doc gave me the diagnosis of AS since I'm positive for the genes and my history of symptoms went back decades.

I have the gene and AS

Yup just diagnosed in march and start simponi treatment april 6th
Ive been telling people for years something os wrong and now its so bad to reverse , i wanna sue 2018 xray notes say Evidence of AS ... So heres me !, In pain 😭🤣

Hi, new here. I have the gene and was finally diagnosed with AS after years of blood test showing some kind of inflammation. I was treat will all kinds of antibiotics which didn’t help. Finally it got so bad I couldn’t walk and the pain was unbearable. Being hospitalized, draining the inflammation from my hip and the many test including MRI gave me the answer. Pray all goes well with you.