EPHA2 Segregates with Microphthalmia and Congenital Cataracts in Two Unrelated Families.

Philippa Harding,Ian Christopher Lloyd,Ian Christopher Lloyd,Ian Christopher Lloyd,Nicholas Owen,Elena Schiff,Maria Toms,Maria Toms,Mariya Moosajee,Mariya Moosajee,Mariya Moosajee,Mariya Moosajee,Suzannah Bell

doi:10.3390/ijms22042190

Abstract

EPHA2 is a transmembrane tyrosine kinase receptor that, when disrupted, causes congenital and age-related cataracts. Cat-Map reports 22 pathogenic EPHA2 variants associated with congenital cataracts, variable microcornea, and lenticonus, but no previous association with microphthalmia (small, underdeveloped eye, ≥2 standard deviations below normal axial length). Microphthalmia arises from ocular maldevelopment with >90 monogenic causes, and can include a complex ocular phenotype. In this paper, we report two pathogenic EPHA2 variants in unrelated families presenting with bilateral microphthalmia and congenital cataracts. Whole genome sequencing through the 100,000 Genomes Project and cataract-related targeted gene panel testing identified autosomal dominant heterozygous mutations segregating with the disease: (i) missense c.1751C>T, p.(Pro584Leu) and (ii) splice site c.2826-9G>A. To functionally validate pathogenicity, morpholino knockdown of epha2a/epha2b in zebrafish resulted in significantly reduced eye size ± cataract formation. Misexpression of N-cadherin and retained fibre cell nuclei were observed in the developing lens of the epha2b knockdown morphant fish by 3 days post-fertilisation, which indicated a putative mechanism for microphthalmia pathogenesis through disruption of cadherin-mediated adherens junctions, preventing lens maturation and the critical signals stimulating eye growth. This study demonstrates a novel association of EPHA2 with microphthalmia, suggesting further analysis of pathogenic variants in unsolved microphthalmia cohorts may increase molecular diagnostic rates.

Highlights

EPHA2 (OMIM:176946) encodes a 976 amino acid transmembrane tyrosine kinase receptor [1]
We identified through next-generation sequencing (NGS) autosomal dominant EPHA2 variants segregating congenital cataracts and bilateral microphthalmia in two unrelated families: (i) missense variant c.1751C>T, p.(Pro584Leu) and (ii) splicing variant c.2826-9G>A
We identified functional variants of EPHA2 in two unrelated families with bilateral mild microphthalmia and cataracts, and demonstrated a significant reduction in eye size of epha2a/b morphant zebrafish at 3 dpf

Summary

Introduction

EPHA2 (OMIM:176946) encodes a 976 amino acid transmembrane tyrosine kinase receptor [1]. EPHA2 is part of the ephrin (Eph) family of receptors, which are known to be widely expressed during early embryogenesis, where they play a key role in the development of neuronal and vascular networks, as well as epithelial tissues [2]. The Eph family contains 16 receptors, grouped into EphA and EphB, and eight ephrin ligands [3]. Eph receptors and ephrin ligands are both membrane-bound, mediating cell-contact-dependent bidirectional signalling [2]. They regulate several cellular processes, including adhesion, migration, morphology, proliferation, differentiation, survival, and secretion [4]. EPHA2 is important for the correct formation of multiple organs, and is highly expressed in the developing kidney, inner ear, and lens [3,6,8,9]

Methods

Discussion

Conclusion