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Andrei V Tkatchenko, Tatiana V Tkatchenko, Virginie JM Verhoeven, Pirro G Hysi, Pawan Kumar Singh, Ashok Kumar, Jeremy A Guggenheim, Cathy Williams, ; APLP2 Regulates Refractive Error and Myopia Development in Mice and Humans. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4568.
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We recently identified APLP2 as one of the genes linked to myopia in monkeys. The purpose of this study was to evaluate the role of APLP2 in refractive error development in humans and mice.
Results for the APLP2 locus from a genome-wide association study in 3,819 children (ALSPAC) were analyzed and replicated in the CREAM dataset, which included 45,756 individuals from 27 Caucasian and 5 Asian cohorts. Refractive eye development was also analyzed in Aplp2 knockout mice.
Numerous SNPs in the 5’ end of APLP2 were strongly associated with refractive error in the ALSPAC cohort (top SNP rs188663068; P = 0.0005). Analysis of SNPs within 100 kb of APLP2 in the CREAM dataset revealed that multiple SNPs in the 5’ end of APLP2 also showed association with refractive error (P = 0.007 for rs7127037). Analysis of Aplp2 knockout mice revealed that Aplp2 is expressed in the amacrine cells of the retina and that the Aplp2 knockout mice developed hyperopia (+11.5 ± 2.2 D) compared to both heterozygous (-0.8 ± 2.0 D, P < 0.0001) and wild-type (+0.3 ± 2.2 D, P < 0.0001) littermates. Knockout mice developed -1.2 ± 0.6 D of myopia upon form-deprivation, whereas myopic refractive shift was -5.8 ± 1.0 D in heterozygous and -11.4 ± 0.8 D in the wild-type littermates. Lack of Aplp2 did not have any effect on visual acuity (F(2, 20) = 0.56, P = 0.58), but resulted in a dose-dependent reduction in contrast sensitivity (F(12, 120) = 3.57, P = 0.00015). Analysis of scotopic ERGs in the Aplp2 knockouts revealed a dose-dependent decrease in b-wave amplitude (F(2, 18) = 6.85, P = 0.006) and an increase in b-wave implicit time (F(2, 18) = 6.08, P = 0.0096). The amplitude of the oscillatory potentials (OP) exhibited a dose-dependent decrease in the Aplp2 heterozygous and knockout mice, while the OP implicit time was increased in both heterozygous and knockout animals compared to wild-type littermates.
Genetic variation in APLP2 is associated with refractive error and myopia in the human population. Aplp2 plays critical role in refractive eye development as revealed by the hyperopic phenotype and reduced susceptibility to form-deprivation myopia in Aplp2 knockout mice. In situ hybridizations and ERG revealed that Aplp2 is primarily expressed in retinal amacrine cells and that reduced expression of Aplp2 affects visual responses mediated by the inner retina in mice.
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