The link between HLA- A29 and Birdshot Chorioretinopathy is one that interests many people and the paper published by:  Brézin AP, Monnet D, Cohen JH, Levinson RD, on this subject asks the question:

Why do people of European descent tend to get Birdshot, whilst other ethnic groups who also carry the HLA A29 antigen do not?

The paper explains that there are two different subtypes of HLA29A:- HLA29:02 is most frequent in caucasians, whilst HLA29:01 is most frequent in Asians.

It used to be thought that the disease only appeared in people with the HLA-A29:02 version of the antigen.  The paper tells us that is no longer a valid argument.   It suggests that another factor, probably not HLA linked, is either protective in Asians and in Africans or, alternatively, triggers an autoimmune reactivity that is possibly present in Caucasians of european descent and absent in Asians and in Africans.

We might start to make progress if scientists can find the answer to what this might be.

We are trying to get hold of the full research paper so that we can review it in detail.