Cone-rod Dystrophy
Gene: OPN1MW
Associated with varying degrees of colour blindness/myopia/cone rod dystrophy due to more complex genetic pathways involving rearrangements between the OPN1LW and OPN1MW genes and/or deletion of a nearby regulatory region.
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Blue cone monochromic (BCM) is characterised by severely reduced visual acuity and colour perception (usually stationary rather than progressive). OPN1LW encodes L wavelength or red cone opsin and OPN1MW encodes for the M wavelength or green cone opsin - these are both X linked genes. BCM results from complete loss of both L and M wavelength perception. Rods and short (blue) wavelength sensitive cones (opsin encoded by OPN1SW gene on chromosome 7) are functional. This condition generally arises from complex genetic rearrangements that are not readily detected by exome/genome sequencing, often requiring more targeted sequencing approaches and long-range PCR. Colour-blindness from partial or complete loss of L wavelength/red cone opsin function is also usually a result of more complex rearrangements. Polymorphisms in these genes also result in varying degrees of colour perception.
PMID 25168334 & PMID 32860923 provide a good summary. One copy of OPN1LW and often multiple copies of OPL1MW are arranged in tandem array on the X-chromosome, and the proximity and high identity of these genes can lead to recombination events. Only the first two genes in the array appear to be expressed. There are three main mechanisms by which BCM can arise:
- deletion on the X chromosome upstream of both OPN1LW and OPN1MW, in a locus control region (LCR) required for expression of both genes
- two-step process involving recombination of the L and M opsin genes resulting in a single or often hybrid gene with a subsequent missense variant (most commonly p.(Cys203Arg)) or exon deletion in this hybrid gene
- third mechanism is due to rare haplotypes (‘L/M interchange haplotypes’) at polymorphic positions in exon 3 of the opsin genes that result from intermixing between L and M opsin genes resulting in aberrant splicing of the opsin genes and a variable degree of exon 3 skippingCreated: 29 Mar 2022, 12:11 a.m. | Last Modified: 29 Mar 2022, 12:11 a.m.
Panel Version: 0.34
Mode of inheritance
X-LINKED: hemizygous mutation in males, biallelic mutations in females
Phenotypes
Blue cone monochromacy - MIM#303700; Colorblindness, deutan - MIM#303800
Publications
Gene: opn1mw has been classified as Amber List (Moderate Evidence).
Phenotypes for gene: OPN1MW were changed from Blue cone monochromacy MIM#303700; Colorblindness, deutan MIM#303800 to Blue cone monochromacy MIM#303700; Colourblindness, deutan MIM#303800
Publications for gene: OPN1MW were set to 30679166
Gene: opn1mw has been classified as Amber List (Moderate Evidence).
Tag SV/CNV tag was added to gene: OPN1MW.
gene: OPN1MW was added gene: OPN1MW was added to Cone-rod Dystrophies. Sources: Royal Melbourne Hospital,Expert Review Green Mode of inheritance for gene: OPN1MW was set to X-LINKED: hemizygous mutation in males, biallelic mutations in females Publications for gene: OPN1MW were set to 30679166 Phenotypes for gene: OPN1MW were set to Blue cone monochromacy MIM#303700; Colorblindness, deutan MIM#303800