Mitochondrial haplogroup L1c2 is associated with increased disease severity in African American patients with primary open-angle glaucoma

Abstract

Objective: The purpose of this study is to evaluate the role mitochondrial inheritance plays in primary open-angle glaucoma (POAG) characteristics in African Americans.

Methods: POAG cases from the L1c2 and L1b mitochondrial haplogroups were compared in a retrospective case-case study. Twenty-six pairs of self-identified African American POAG cases from L1c2 and L1b mitochondrial haplogroups matched on age (mean [SD] = 71.2 [9.6] and 71.3 [9.6] years, respectively; p = 0.97), sex (21 female and 5 male pairs), and family history of glaucoma (positive in 15/26 [58%] pairs) were included.

Results: L1c2 subjects displayed higher vertical cup-to-disc ratio (0.75 [0.12] and 0.67 [0.16], respectively; p = 0.01, Bonferroni-corrected p = 0.08), worse pattern standard deviation on visual field (VF) testing (5.5 [3.5] and 3.5 [2.7]; p = 0.005, Bonferroni-corrected p = 0.02), and more severe glaucoma based on American Glaucoma Society staging criteria (p = 0.04, Bonferroni-corrected p = 0.32) compared to L1b subjects. L1c2 also trended towards worse mean deviation on VF compared to L1b (-8.2 [7.6] and -5.8 [6.8], respectively, p = 0.17). Best corrected visual acuity, central corneal thickness, maximum intraocular pressure (IOP), and cataract severity were comparable between L1c2 and L1b haplogroups (p ≥ 0.49), as was retinal nerve fiber layer thickness on optical coherence tomography (75.1 [14.1] and 75.1 [13.0]; p = 0.99).

Conclusion: Results demonstrated worse glaucomatous cupping and more severe VF loss in the L1c2 compared to the L1b haplogroup despite comparable IOP. Findings implicate mitochondrial inheritance as a factor affecting POAG severity and may ultimately contribute to stratifying POAG patients into phenotypically and genotypically distinct subgroups.

Keywords: African Americans; Glaucoma; Primary open-angle glaucoma; mitochondrial genetics; mitochondrial haplogroups.

Figure 1:

(A) Distribution of vertical cup-to-disc ratio (CDR): the L1c2 haplogroup trended towards more severe glaucomatous cupping compared to L1b (P = 0.01, Bonferroni-corrected P = 0.08). (B) Distribution of glaucoma severity based on American Glaucoma Society staging criteria: the L1c2 haplogroup trended towards more severe glaucoma compared to L1b (P = 0.04, Bonferroni-corrected P = 0.32).