HLA-A29-POSITIVE BIRDSHOT CHORIORETINOPATHY IN AN AFRICAN AMERICAN PATIENT

Birdshot chorioretinopathy in an HLA-A29 positive Asian patient

Purpose

To present a case of birdshot chorioretinopathy (BCR) in a Chinese patient with HLA-A29 positivity.

Observations

A 45-year-old Chinese female presented at a tertiary Ophthalmology Clinic with complaints of frequent headaches as well as blurred vision, photophobia, and pressure in the left eye (OS). The patient had a significant ocular history of left orbital cavernous hemangioma status post lateral orbitotomy and resection. Uncorrected visual acuity was 20/20 in the right eye (OD) and 20/40 in OS (pinhole 20/30). Funduscopic examination demonstrated optic disc edema, left eye worse than right eye, and vascular tortuosity in both eyes (OU). Late phase fluorescein angiography (FA) showed extensive perivascular and optic disc leakage and peripheral capillary leakage in OU. Laboratory evaluations were positive for human leukocyte antigen-A29 (HLA-A29). The patient was started on 40 mg prednisone daily; mycophenolate mofetil 500 mg twice daily was subsequently added.At the 3-month consultation visit to the Uveitis Clinic, dilated funduscopic examination revealed 1+ vitreous cells and improved optic disc edema in OU. FA showed improved vascular and optic disc leakage in OS but worsened leakage in OD. At this point, indocyanine green angiography (ICGA) was ordered which revealed hypocyanescent lesions throughout the choroid that were centered on the optic disc, supporting and confirming the diagnosis of BCR.

Conclusions and Importance

The index patient is the first reported case of BCR in an HLA-A29 positive Asian patient.

HLA-A29 and Birdshot Uveitis: Further Down the Rabbit Hole

HLA class I alleles constitute established risk factors for non-infectious uveitis and preemptive genotyping of HLA class I alleles is standard practice in the diagnostic work-up. The HLA-A29 serotype is indispensable to Birdshot Uveitis (BU) and renders this enigmatic eye condition a unique model to better understand how the antigen processing and presentation machinery contributes to non-infectious uveitis or chronic inflammatory conditions in general. This review will discuss salient points regarding the protein structure of HLA-A29 and how key amino acid positions impact the peptide binding preference and interaction with T cells. We discuss to what extent the risk genes ERAP1 and ERAP2 uniquely affect HLA-A29 and how the discovery of a HLA-A29-specific submotif may impact autoantigen discovery. We further provide a compelling argument to solve the long-standing question why BU only affects HLA-A29-positive individuals from Western-European ancestry by exploiting data from the 1000 Genomes Project. We combine novel insights from structural and immunopeptidomic studies and discuss the functional implications of genetic associations across the HLA class I antigen presentation pathway to refine the etiological basis of Birdshot Uveitis.