The genetics of strabismus

Identification of 2 Potentially Relevant Gene Mutations Involved in Strabismus Using Whole-Exome Sequencing

Background

The etiology of strabismus has a genetic component. Our study aimed to localize the candidate causative gene mutant in a Chinese family with strabismus and to describe its underlying etiology.

Material/Methods

Genomic DNA was extracted from the affected individual and his parents in a Chinese pedigree with strabismus. The resulting exomes were sequenced by whole-exome sequencing. After variant calling and filtering, the candidate causative gene mutations were selected for the rarity and predicted damaging effect, which complied with the model of recessive disease transmission.

Results

We examined a Chinese strabismus pedigree with the parents unaffected and 2 offspring affected. Whole-exome sequencing and bioinformatics filtering identified 2 variants including Abelson helper integration site 1 (AHI1) gene and nebulin (NEB) gene. The variant in the AHI1 gene, c.A3257G (p.E1086G), and the altered amino acid had a damaging effect on the encoded protein predicted by Polyphen2. Moreover, this change was located in the conserved SH3 domain of AHI1. Biallelic pathogenic variant in AHI1 gene can cause Joubert syndrome-related disorders with oculomotor apraxia characteristics. Additionally, c.A914G mutation was found in nebulin (NEB) gene. Therefore, we concluded that AHI1 c.3257A>G and NEB c.914 A>G were potential causal variants in this strabismus pedigree.

Conclusions

We detected an AHI1 homozygous mutation in the affected individual. Whole-exome sequencing is a powerful way to identify causally relevant genes, improving the understanding of this disorder.

A strabismus susceptibility locus on chromosome 7p

Strabismus has been known to have a significant genetic component, but the mode of inheritance and the identity of the relevant genes have been enigmatic. This paper reports linkage analysis of nonsyndromic strabismus. The principal results of this study are: (i) the demonstrated feasibility of identifying and recruiting large families in which multiple members have (or had) strabismus; (ii) the linkage in one large family of a presumptive strabismus susceptibility locus to 7p22.1 with a multipoint logarithm of odds score of 4.51 under a model of recessive inheritance; and (iii) the failure to observe significant linkage to 7p in six other multiplex families, consistent with genetic heterogeneity among families. These findings suggest that it will be possible to localize and ultimately identify strabismus susceptibility genes by linkage analysis and mutation screening of candidate genes.