<unk>  is inherited from the X chromosome. The genes involved in the BCM are on chromosome X, at position Xq28, at the end of the q arm of the X chromosome. The genes’ names are: Type OMIM Gene Locus Locus Control Region Xq28 opsin Xq28 opsin Xq28 LCR is the Locus Control Region, and acts as a promoter of the expression of the two opsin genes thereafter. In the absence of this gene, none of the following two opsin genes are expressed in the human retina. In addition, it ensures that only one of the two opsin genes (red or green) is expressed exclusively in each<unk> . OPN1LW and OPN1MW are respectively the genes that contain the genetic code for protein opsin needed for the<unk>  pigments which select red or green light. The gene responsible for the formation of the<unk>  photopigment is in a position far away, on chromosome 7 and the gene responsible for the formation of rhodopsin (the rod photopigment) is located on chromosome 3. There are many genetic mutations that can affect this group of genes, LCR, OPN1LW and OPN1MW that lead to the BCM: a deletion of the LCR , intragenic deletion of exons within the genes OPN1LW and OPN1MW and a 2 steps mechanism with an homologous recombination and a punctual inactivation. The point mutation is the so-called C203R. The name of the point mutations indicates the position at which mutation has occurred, in this case the amino acid position 203 and which has been replaced, in this case a C = Cysteine with an R = Arginine. The C203R mutation causes the opsin protein once formed does not carry the folding, that is it doesn't take the proper three-dimensional form. Other point mutations are the P307L and R247X. The last one replaces arginine with the Stop codon, prematurely stopping at position 247 the formation of the protein (nonsense mutation). Other mutations on genes OPN1LW and OPN1MW that lead to the<unk>  are constituted by a set of point mutations called for example LIAVA.<unk>  will be caused by the production of new hybrid gene, like in the previous case, from the homologous recombination of OPN1LW and OPN1MW. Exon 3 of the hybrid gene contains the following amino acids in the positions indicated: 153 Leucine, 171 Isoleucine, 174 Alanine, 178 Valine and 180 Alanine. This genotype has the abbreviated name LIAVA. Another disease of the retina that is associated with the position Xq28 is Bornholm Eye Disease (BED). Finally note there is also a particular mutation of the two genes OPN1LW and OPN1MW which causes a different disease from the<unk> . This type of mutation is named W177R and is a misfolding mutation that, if present on both opsin genes cause<unk>  dystrophy with evidence of degeneration and cell death of the<unk> s.
Blue cone monochromacy
Optic nerve hypoplasia
Quadrantanopia
Macular hypoplasia
Congenital stationary night blindness
Cortical visual impairment
Cerebral achromatopsia
Associative visual agnosia