Birdshot Chorioretinopathy is a rare form of bilateral posterior Uveitis, accounting for between 1 – 3% of all Uveitis cases. A slight female predominance has been reported. The disease is uncommon in children. Birdshot Chorioretinopathy causes severe, progressive inflammation of both the choroid and the retina. The name of the disease stems from the hypopigmentation pattern of the lesion on the retina, which resembles the impacts from a shotgun. Symptoms of Birdshot Chorioretinopathy include retinal vasculitis, particulate matter in the vitreous or vitreous inflammation, macular oedema, flashing lights in the eyes, night blindness and loss of colour vision. A frequent prognosis is complete loss of visual acuity.
Birdshot Chorioretinopathy is the disease with the strongest association to a HLA class I antigen. More than 95% of patients carry the HLA-A29 antigen with the relative risk of HLA-A29 carriers developing Birdshot Chorioretinopathy being estimated at between 50 and 250. HLA-A*29:02, which is the most frequent A29 allele in the Caucasian population is also the allele most frequently associated with Birdshot Chorioretinopathy in Caucasians. The disease has however been observed in HLA*29:01 Caucasian patients. Birdshot Chorioretinopathy is extremely rare in Asia where the most frequent HLA-A29 allele is A*29:01. The mechanism by which HLA-A29 confers susceptibility to Birdshot Chorioretinopathy is unknown. Proposals include antigen specific molecular mimicry following an infection or a role for retinal S-Antigen.
The presence of HLA-A*29 alone is not sufficient for a diagnosis of Birdshot Chorioretinopathy, as there are many cases of patients who do not carry HLA-A*29. Indeed the prevalence of HLA-A29 in the Caucasian population (around 7%) is far higher than the disease frequency and it is likely, as with many HLA disease associations, that other factors are involved. Nonetheless the strong association suggests that genetic testing for HLA-A*29 and A*29 alleles, over serological testing, is useful as a supportive finding as part of the diagnosis.
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