Quantitative trait locus mapping for age-related cataract severity and synechia prevalence using four-way cross mice

PURPOSE. The goal of this study was to map mouse quantitative trait loci (QTL) that influence the development of murine age-related cataract and synechia, by using a genetically heterogeneous mouse population bred by a four-way cross. METHODS. The test population consisted initially of 510 mice bred as the progeny of (BALB/cJ x C57BL/6J)F1 females and (C3H/HeJ x DBA/2J)F1 males. Each mouse was examined by slit lamp at 18 and 24 months of age and scored for degree of lens opacity on a 0 to 4+ scale, and the presence or absence of additional anterior chamber disease was noted. The presence of synechia was confirmed by histology. Each mouse was genotyped at 96 maternal and 92 paternal loci, and the significance of association between genotype and eye lesions was tested by permutation analysis. RESULTS. Significant QTL with effects on lens opacity at 24 months were detected on mouse chromosomes 4, 11, and 12. The effects were additive, and severe cataracts were seen in 80% of the mice with all three high-risk alleles, but in only 28% of the mice with all three low-risk alleles. The risk of synechia was associated with paternal chromosome I and on both the maternal and paternally inherited chromosome 4. Mice with all three high-risk alleles had a 68% risk of synechia, compared with a 0% incidence in mice with all three counteralleles. CONCLUSIONS. A four-way cross population of mice can be used to map polymorphic loci that influence cataract severity and synechia prevalence in late life. The results provide a first step toward identification of the individual genes involved and may help to guide the search for homologous human genes.