Abstract
Blue cone monochromacy (BCM) is characterized by loss of function of both OPN1LW (the first) and OPN1MW (the downstream) genes on the X chromosome. The purpose of this study was to investigate the first and downstream genes in the OPN1LW/OPN1MW array in four unrelated Japanese males with BCM. In Case 1, only one gene was present. Abnormalities were found in the promoter, which had a mixed unique profile of first and downstream gene promoters and a −71A > C substitution. As the promoter was active in the reporter assay, the cause of BCM remains unclear. In Case 2, the same novel mutation, M273K, was present in exon 5 of both genes in a two-gene array. The mutant pigments showed no absorbance at any of the wavelengths tested, suggesting that the mutation causes pigment dysfunction. Case 3 had a large deletion including the locus control region and entire first gene. Case 4 also had a large deletion involving exons 2–6 of the first gene. As an intact LCR was present upstream and one apparently normal downstream gene was present, BCM in Case 4 was not ascribed solely to the deletion. The deletions in Cases 3 and 4 were considered to have been caused by non-homologous recombination.
Highlights
The human retina contains three types of cone photoreceptors: long-wavelength sensitive cones (L cones), medium-wavelength sensitive cones (M cones), and short-wavelength sensitive cones (S cones)
Cases of blue cone monochromacy (BCM) typically present with severely impaired color discrimination, reduced visual acuity, nystagmus, photophobia, and diminished L/M cone function despite retention of rod and blue cone function[6,7]
From the results of repeated long-range polymerase chain reaction (PCR) analysis of downstream genes, we concluded that this subject had a single gene in the array
Summary
The human retina contains three types of cone photoreceptors: long-wavelength sensitive cones (L cones), medium-wavelength sensitive cones (M cones), and short-wavelength sensitive cones (S cones). Cases of BCM typically present with severely impaired color discrimination, reduced visual acuity, nystagmus, photophobia, and diminished L/M cone function despite retention of rod and blue cone function[6,7]. The dysfunction in both L and M cones in BCM is reportedly caused by one of the three genotypes. Neither gene is expressed in the absence of the LCR Another genotype involves a deleterious mutation in a single-gene array (either the L or M gene present alone in the array). The purpose of this study was to investigate their genotypes in the L/M pigment gene array, which could be categorized into one of the three above-mentioned genotypes, but others were unreported mechanisms and differed from each other
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