APLP2 and hyperopia: Mice homozygous for a null allele of the Aplp2 gene (Aplp2-/- mice) were found to develop high degrees of hyperopia (+11.5 ± 2.2 D, p < 1.0 × 10−4) compared to both heterozygous (Aplp2+/-) (-0.8 ± 2.0 D, p < 1.0 × 10−4) and wild-type (Aplp2+/+) (+0.3 ± 2.2 D, p < 1.0 × 10−4) littermates (Fig 4A), consistent with the finding that APLP2 expression is suppressed in hyperopia in monkeys (Fig 1).