Trio-based exome sequencing arrests de novo mutations in early-onset high myopia

Abstract

The etiology of the highly myopic condition has been unclear for decades. We investigated the genetic contributions to early-onset high myopia (EOHM), which is defined as having a refraction of less than or equal to -6 diopters before the age of 6, when children are less likely to be exposed to high educational pressures. Trios (two nonmyopic parents and one child) were examined to uncover pathogenic mutations using whole-exome sequencing. We identified parent-transmitted biallelic mutations or de novo mutations in as-yet-unknown or reported genes in 16 probands. Interestingly, an increased rate of de novo mutations was identified in the EOHM patients. Among the newly identified candidate genes, a BSG mutation was identified in one EOHM proband. Expanded screening of 1,040 patients found an additional four mutations in the same gene. Then, we generated Bsg mutant mice to further elucidate the functional impact of this gene and observed typical myopic phenotypes, including an elongated axial length. Using a trio-based exonic screening study in EOHM, we deciphered a prominent role for de novo mutations in EOHM patients without myopic parents. The discovery of a disease gene, BSG, provides insights into myopic development and its etiology, which expands our current understanding of high myopia and might be useful for future treatment and prevention.

Keywords: BSG; de novo mutations; early-onset high myopia; rare inherited mutations.

Fig. 1.

Patterns of de novo mutations in HM patients and their contribution to disease risk. (A) Plot of the mean de novo mutation rate of HM patients (HM) and normal individuals (control). The de novo mutation rate for normal individuals was calculated based on 982 normal individuals from the NPdenovo database (www.wzgenomics.cn/NPdenovo/). The statistical significance of the differences in the de novo mutation rates between the HM patients and the controls was tested using a two-sample Poisson rate test. (B) The relationship between the number of de novo mutations and the paternal age. (C) The relationship between the number of de novo mutations in the proband and the diopter sphere–oculus dexter (DS-OD). (D) The relationship between the number of de novo mutations in the proband and the diopter sphere–oculus sinister (DS-OS). (E) A scatter diagram of the total damaging scores and the expected de novo mutation rate (expected DNMR) of the genes with de novo mutations. The total damaging score was calculated by 14 generic functional prediction tools, and the expected DNMR was used for each gene DNMR average from the mirDNMR database (www.wzgenomics.cn/mirdnmr/).

Fig. 2.

Identification of mutations in the BSG gene. (A) Identification of mutations in the BSG gene in five unrelated patients. (B) Schematic of the BSG gene and its domains with the sites of the variants identified in this study. (C) Both missense mutations (G297S and P221S) are located in highly conserved regions.

Fig. 3.

Clinical features of the Bsg mutant mice. Comparisons of the ALs in the WT and mutant mice at each time point [week 6 (w6)–w4, w8–w6, w10–w8]. HET, heterozygous mutant mice; WT, wild-type mice.

Fig. S1.

Bsg knockin mutant mice were generated by a homologous recombination approach and genotyped by PCR using tail genomic DNA.

Fig. S2.

Comparisons of the ALs in the WT and mutant mice at each time point [week 6 (w6)–w4, w8–w6, w10–w8]. HET, heterozygous mutant mice; WT, wild-type mice.

Fig. S3.

The electroretinogram responses in the mutant mice were normal compared with their WT siblings. (A) The scotopic ERG response of the WT and mutant mice. (B) The photopic ERG response of the WT and mutant mice.

Fig. S4.

Bsg expression patterns. (A) Expression patterns of the Bsg gene in different mouse tissues. (B and C) Expression patterns of known myopia-related genes in different mouse tissues.

Fig. 4.

PPI of the HM genes. PPI network of the genes related to HM identified in this study and previous studies.