Variety of clinical traits
Examinations of African Americans with POAG show a variety of clinical traits, including a range of visual field defects and differences in optic nerve appearance. The study is using 1.8 million single nucleotide polymorphisms to identify genes that are associated with POAG.
“Our comprehensive genetic analysis uses genome-wide, exome-wide, and mitochondrial association analysis to look at some of the genes that might be associated with glaucoma in this population,” Dr. O’Brien explained. “We suspect that those differences we see clinically will be related to some of the differences that occur genetically.”
Mitochondrial DNA analysis shows that African Americans are a widely diverse population with multiple ancestral branches, or haplogroups. A few of these haplogroups are over-represented in POAG cases within the study population.
Early analysis suggests some of these ancestral lineages may confer some degree of protection against POAG, while other lineages may increase the risk of developing POAG.
One of the clearest examples is a pair of missense variants in the mitochondrial cytochrome c oxidase subunit I (MT-CO1) gene that define a common African haplogroup. The presence of these two variants may elevate the risk of developing glaucoma and could result in more severe disease.
“Patients with this double-missense mutation appear to have worse visual field loss, higher cup-to-disc ratio, and lower IOP,” Dr. O’Brien said.”