PurposeThe R345W mutation in EFEMP1 causes malattia leventinese, an autosomal dominant eye disease with pathogenesis similar to an early-onset age-related macular degeneration. In mice, Efemp1R345W does not cause detectable degeneration but small subretinal deposits do accumulate. The purpose of this study was to determine whether there were abnormal responses to light at this presymptomatic stage in Efemp1R345W mice.MethodsResponses to light were assessed by visual water task, circadian phase shifting, and negative masking behavior. The mechanism of abnormal responses was investigated by anterior eye exam, electroretinogram, melanopsin cell quantification, and multielectrode recording of retinal ganglion cell activity.ResultsVisual acuity was not different in Efemp1R345W mice. However, amplitudes of circadian phase shifting (P = 0.016) and negative masking (P < 0.0001) were increased in Efemp1R345W mice. This phenotype was not explained by anterior eye defects or amplified outer retina responses. Instead, we identified increased melanopsin-generated responses to light in the ganglion cell layer of the retina (P < 0.01).ConclusionsEfemp1R345W increases the sensitivity to light of behavioral responses driven by detection of irradiance. An amplified response to light in melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) is consistent with this phenotype. The major concern with this effect of the malattia leventinese mutation is the potential for abnormal regulation of physiology by light to negatively affect health.

Chédiak-Higashi syndrome (CHS) is a lethal disorder caused by mutations in the LYST gene that involves progressive neurologic dysfunction. Lyst -mutant mice exhibit neurologic phenotypes that are sensitive to genetic background. On the DBA/2J-, but not on the C57BL/6J-background, Lyst -mutant mice exhibit overt tremor phenotypes associated with loss of cerebellar Purkinje cells. Here, we tested whether assays for ataxia could measure this observed strain-dependency, and if so, establish parameters for empowering phenotype- and candidate-driven approaches to identify genetic modifier(s). A composite phenotypic scoring system distinguished phenotypes in Lyst -mutants and uncovered a previously unrecognized background difference between wild-type C57BL/6J and DBA/2J mice. Accelerating rotarod performance also distinguished phenotypes in Lyst -mutants, but at more advanced ages. These results establish that genetic background, Lyst genotype, and age significantly influence the severity of CHS-associated neurologic deficits. Purkinje cell quantifications likewise distinguished phenotypes of Lyst -mutant mice, as well as background differences between wild-type C57BL/6J and DBA/2J mice. To aid identification of potential genetic modifier genes causing these effects, we searched public datasets for cerebellar-expressed genes that are differentially expressed and/or contain potentially detrimental genetic variants. From these approaches, Nos1 , Prdx 2, Cbln3 , Gnb1 , Pttg1 were confirmed to be differentially expressed and leading candidates.

Central corneal thickness is a quantitative trait with important associations to human health. In a phenotype-driven approach studying corneal thickness of congenic derivatives of C57BLKS/J and SJL/J mice, the critical region for a quantitative trait locus influencing corneal thickness, Cctq1a, was delimited to a 10-gene interval. Exome sequencing, RNAseq, and studying independent mutations eliminated multiple candidate genes and confirmed one. Though the causative gene, Tyr, has no obvious direct function in the transparent cornea, studies with multiple alleles on matched genetic backgrounds, both in isolation and genetic complementation crosses, confirmed allelism of Tyr-Cctq1a; albino mice lacking Tyr function had thin corneas. Albino mice also had increased axial length. Because albinism exposes eyes to increased light, the effect of dark-rearing was tested and found to rescue central corneal thickness. In sum, the results point to an epiphenomenon; developmental light exposure interacts with genotype as an important determinate of adult corneal thickness.