Genetic modifiers of secondary glaucoma

Abstract

Purpose: : Exfoliation syndrome and pigment dispersion syndrome are important glaucoma risk factors with strong hereditary components. C57BL/6J mice with the Lyst^bg-J and Dct^Slt-lt3J mutations recapitulate aspects of exfoliation syndrome and pigment dispersion syndrome, respectively. The purpose of the current experiments was to determine the extent to which phenotypes of these mice are sensitive to genetic background by generating and analyzing congenic strains of mice in which these mutations have been bred onto the DBA/2J background.

Methods: : Inbred C57BL/6J strains carrying either the Lyst^bg-J or Dct^Slt-lt3J mutations were reiteratively backcrossed to DBA/2J mice for 10 generations and then individually intercrossed to produce two distinct congenic strains homozygous for the Lyst^bg-J or Dct^Slt-lt3J mutations. Anterior chamber phenotypes were assessed using slit lamp photography. Iris transillumination defects (iris-TID) were quantified and averaged among mice identical genotype, with experimental and control cohorts tested for potential differences using Student’s t-test. Eyes and optic nerves were also compared histologically. To test strain sensitivities to oxidative stress, strains were injected with a replication deficient Ad5 adenovirus expressing wild-type catalase followed by subsequent analysis of iris-TID. All analyses were performed using age-matched DBA/2J controls.

Results: : Lyst^bg-J and Dct^Slt-lt3J iris phenotypes were both highly sensitive to genetic background. For Lyst^bg-J, compared to C57BL/6J, the DBA/2J genetic background resulted in a significant enhancement of the "Marcel-like" iris-TID defects common in exfoliation syndrome. Quantification of iris transilluminance revealed a 4-fold increase in defect severity in Lyst^bg-J irides on the DBA/2J compared to C57BL/6J background (n=8 eyes each strain). Mice receiving adenoviral transduction of wild-type catalase exhibited a 30% reduction in iris-TID compared to sham injected controls (n=10 eyes each group). For Dct^Slt-lt3, the DBA/2J genetic background caused a striking enhancement of iris atrophy and pigment dispersion. Interestingly, histologic analyses demonstrated that the Dct^Slt-lt3J mutation influenced the type and size of cellular infiltrate in the anterior chambers of DBA/2J mice. Surprisingly, neither of the DBA/2J congenic strains developed optic nerve degeneration.

Conclusions: : These results indicate that the anterior chamber phenotypes associated with the Lyst^bg-J and Dct^Slt-lt3J mutations are highly sensitive to genetic background. This finding may explain why genetic studies of pigment dispersion syndrome and exfoliation syndrome in human populations have been a challenge; genetic background is a significant confounding factor.

Keywords: iris • genetics • optic nerve