De novo intrachromosomal gene conversion from OPN1MW to OPN1LW in the male germline results in Blue Cone Monochromacy.

Elena Buena-Atienza,Nicole Weisschuh,Thomas Rosenberg,Susanne Kohl,Klaus Rüther,Peter Gustavsson,Zornitza Stark,Britta Baumann,Astrid S Plomp,Bernd Wissinger,Elfride De Baere,Ditta Zobor,Jan Willem R Pott,Richard Bergholz,Bart P Leroy,Marie T Greally,John R Heckenlively,Katherine Rose,Richard G Weleber ,Joanne Verheij ,Hélène Dollfus ,David G Birch ,Christian Hamel

doi:10.1038/srep28253

Abstract

X-linked cone dysfunction disorders such as Blue Cone Monochromacy and X-linked Cone Dystrophy are characterized by complete loss (of) or reduced L- and M- cone function due to defects in the OPN1LW/OPN1MW gene cluster. Here we investigated 24 affected males from 16 families with either a structurally intact gene cluster or at least one intact single (hybrid) gene but harbouring rare combinations of common SNPs in exon 3 in single or multiple OPN1LW and OPN1MW gene copies. We assessed twelve different OPN1LW/MW exon 3 haplotypes by semi-quantitative minigene splicing assay. Nine haplotypes resulted in aberrant splicing of ≥20% of transcripts including the known pathogenic haplotypes (i.e. ‘LIAVA’, ‘LVAVA’) with absent or minute amounts of correctly spliced transcripts, respectively. De novo formation of the ‘LIAVA’ haplotype derived from an ancestral less deleterious ‘LIAVS’ haplotype was observed in one family with strikingly different phenotypes among affected family members. We could establish intrachromosomal gene conversion in the male germline as underlying mechanism. Gene conversion in the OPN1LW/OPN1MW genes has been postulated, however, we are first to demonstrate a de novo gene conversion within the lineage of a pedigree.

Highlights

X-linked cone dysfunction disorders such as Blue Cone Monochromacy and X-linked Cone Dystrophy are characterized by complete loss or reduced L- and M- cone function due to defects in the OPN1LW/OPN1MW gene cluster
MW gene cluster in twenty-four affected subjects from sixteen families diagnosed with BCM or X-linked Cone Dystrophy (XLCD) not carrying mutations commonly reported in BCM
For consistency we designate haplotypes according to the amino acid residues they encode (i.e. ‘LIAVA’ for p.[L153-I171-A174-V178-A180])

Summary

Introduction

X-linked cone dysfunction disorders such as Blue Cone Monochromacy and X-linked Cone Dystrophy are characterized by complete loss (of) or reduced L- and M- cone function due to defects in the OPN1LW/OPN1MW gene cluster. A particular combination of common polymorphisms in LW exon 3 segregating in a single BCM family was first noted by Nathans and colleagues but not considered as disease-causing at that time[9] This haplotype, referred to as ‘LIAVA’ in the literature, comprises the following SNPs: c.(453A >G; 457A >C; 465C >G; 511G >A; 513G >T; 521C; 532A >G; 538T >G) and a thereof deduced cone pigment variant with a certain combination of amino acid exchanges: p.[(=); M153L; (=); V171I; A174A; I178V; S180A]. In a recent study involving subjects with protan colour vision defects, the ‘LIAVA’ haplotype and other rare exon 3 haplotypes in LW were found to induce exon 3 skipping in vitro[20] These findings have lately been corroborated and extended to patients with severe cone disorders including BCM and the identification of two further haplotypes, ‘LVAVA’ and ‘MIAVA’, that impair splicing[21]

Methods

Results

Conclusion