Who's at risk for birdshot?

Uveitis is a rare eye disease, and birdshot uveitis is even more rare. It is generally understood that fewer than one in 200,000 Americans ever receive a diagnosis of birdshot.

Beyond that, which populations are more likely to come down with this potentially blinding eye disease? And which ones are less prone? Perhaps the less prone are more vulnerable than we realize.

Scientists have studied many patients in an effort to learn the who and why of birdshot. There is no doubt that middle-aged Caucasian women are the likeliest to be diagnosed. Some say they account for 89% of known cases.

As rare as birdshot is among certain groups of people, such as Asians and Africans, it's only a matter of time before we see more such cases. The populations of the world are not as isolated as they once were, and our DNA tells our story. Researchers are finding genetic commonalities among "birdies", but they still have many questions.

Why is birdshot uveitis so rare in these groups of people? We don't exactly know, but the more relevant question may be... Is it possible? And what makes it more likely?

Since Puerto Ricans are of European descent, researchers had wondered why no cases had been documented. It wasn't until 2016 that a paper revealed nine such cases. Perhaps it was a matter of not considering the possibility? Could birdshot have been there all along? As in other locations, the patients in Puerto Rico were overwhelmingly women and the median age at diagnosis of 52. (references listed below.)

Not until 2016 was the first African American documented as having birdshot chorioretinopathy. The 51-year-old woman was diagnosed after ten years of birdshot symptoms including a decrease in visual acuity, macular edema, and diffuse chorioretinal atrophy. Might her doctors have not considered birdshot earlier because no other African Americans had been so diagnosed? One Caucasian person in the line of ancestry would be enough for her, or any other African American, to acquire the requisite HLA-A29 genetic marker.

Researchers are actively investigating why only a small fraction of those with the HLA-A29 marker ever come down with birdshot, but anyone who inherits the gene is at risk. Consider, if you will, the high percentage of African Americans who have European ancestry.

According to data released by Ancestry.com, 23andme.com, FamilyTree.com, National Geographic Genographic Project and AfricanDNA, the average African American genome is between 19% and 29% European. Even considering that birdshot chorioretinopathy is a very rare disease, the math tells us that there must be more African Americans with this disease who remain undiagnosed.

As we move into the 21st century we assume that ophthalmologists, retina specialists and uveitis specialists are considering all of their patients for birdshot uveitis. The importance of looking beyond averages and embracing the reality of each individual cannot be overstated.

The more we learn and share, the sooner we’ll understand the many facets of birdshot uveitis.

Alexander Knezevic, Marion R. Munk, Frankie Pappas, Pauline T. Merrill, Debra A. Goldstein*. (2016, January 1). HLA-A29-Positive birdshot Chorioretinopathy in an African American patient. Northwestern Scholars. https://www.scholars.northwestern.edu/en/publications/hla-a29-positive-birdshot-chorioretinopathy-in-an-african-america

Frances M Marrero 1, Edgar De Jesus 1, Samuel Alvarez 2, Israel J Mendez Bermudez 3, Mariam Vila 1, Carmen Santos 1, Armando L Oliver 1. (2021, June 19). Characteristics, Upon Presentation, of a Cohort of Hispanic Patients with Birdshot Retinochoroidopathy. PubMed.

Henry Louis Gates Jr. (2013, February 11). Exactly how ‘Black’ is Black America? The Root. https://www.theroot.com/exactly-how-black-is-black-america-1790895185

KatarzynaBryc12Eric Y.Durand2J. MichaelMacpherson3DavidReich145Joanna L.Mountain2. (2021, June 19). The genetic ancestry of African Americans, Latinos, and European Americans across the United States. ScienceDirect.com | Science, health and medical journals, full text articles and books. https://www.sciencedirect.com/science/article/pii/S0002929714004765

Nelson, S. (2019, September 8). My heritage is mixed race. Chances are decent that yours is, too. The Daily Beast. https://www.thedailybeast.com/my-heritage-is-mixed-race-chances-are-decent-that-yours-is-too