Mutations in SCO2 are associated with autosomal-dominant high-grade myopia

Abstract

Myopia, or near-sightedness, is an ocular refractive error of unfocused image quality in front of the retinal plane. Individuals with high-grade myopia (dioptric power greater than -6.00) are predisposed to ocular morbidities such as glaucoma, retinal detachment, and myopic maculopathy. Nonsyndromic, high-grade myopia is highly heritable, and to date multiple gene loci have been reported. We performed exome sequencing in 4 individuals from an 11-member family of European descent from the United States. Affected individuals had a mean dioptric spherical equivalent of -22.00 sphere. A premature stop codon mutation c.157C>T (p.Gln53*) cosegregating with disease was discovered within SCO2 that maps to chromosome 22q13.33. Subsequent analyses identified three additional mutations in three highly myopic unrelated individuals (c.341G>A, c.418G>A, and c.776C>T). To determine differential gene expression in a developmental mouse model, we induced myopia by applying a -15.00D lens over one eye. Messenger RNA levels of SCO2 were significantly downregulated in myopic mouse retinae. Immunohistochemistry in mouse eyes confirmed SCO2 protein localization in retina, retinal pigment epithelium, and sclera. SCO2 encodes for a copper homeostasis protein influential in mitochondrial cytochrome c oxidase activity. Copper deficiencies have been linked with photoreceptor loss and myopia with increased scleral wall elasticity. Retinal thinning has been reported with an SC02 variant. Human mutation identification with support from an induced myopic animal provides biological insights of myopic development.

Figure 1

A Family with High-Grade Myopia Segregation of SCO2 mutation (c.157C>T) in a high-grade myopia family. Abbreviations are as follows: + indicates DNA available for this study, and § indicates samples used for exome sequencing. Where available, the genotype of each individual is shown as a “WT” for the wild-type allele and as an “M” for the mutated allele.

Figure 2

Immunofluorescent Labeling of Sco2 in Mouse Ocular Tissues in Induced Myopic Eyes, Fellow Eyes, and Independent Control Eyes Immunofluorescent labeling of Sco2 in mouse retina, retinal pigment epithelium, and sclera in induced myopic eyes, fellow eyes, and independent control eyes. The florescence intensity labeled of the green color shows the localization of proteins, and blue color indicates the nuclei that were stained with DAPI. Lower level of abundance was determined for myopic retina and RPE, whereas a higher level of abundance was found in myopic sclera. The following abbreviations represent the retinal layers: NFL, nerve fiber layer; GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer; PRL, photo receptor layer; and RPE, retinal pigment epithelium.

Figure 3

Transcription Quantification of Sco2 in Mouse Retina and Sclera in Induced Myopic Eyes, Fellow Eyes, and Independent Control Eyes Experimental myopia was induced in B6 wild-type (WT) mice (n = 36) by applying a −15.00 D spectacle lens on the right eye (experimental eye) for 6 weeks since postnatal day 10. The left eyes were uncovered and served as contra-lateral fellow eyes. Age-matched naive mice eyes were used as independent control eyes (n = 36). Primer sequences to conduct qRT-PCR were forward 5′ ATC GCA CAG CCC TAA GTC TC 3′ and reverse 5′ CAG TAG CAT CGT GGA CCT GA 3′ (NM_001111288.1). The bar represents the fold changes of mRNA for Sco2 after normalization by using GAPDH as reference. The mRNA levels of sco2 in myopic and fellow retina and sclera are compared with independent controls. Relative fold change—the values are shown in log values (2¹⁰). n = 36; ^*p < 0.05, ^**p < 0.01 and ^***p < 0.001.