By Jessie Wright
Normally, there are three kinds of
cones (each one sensitive to a
specific range of wavelengths):
"red" cones (64%)
"green" cones (32%)
"blue" cones (2%)
The normal human retina contains two kinds of light sensitive cells: the rod cells (active only in low light) and the cone cells (active in normal daylight and responsible for color perception).
Let there be light!!!
The different kinds of inherited color blindness result from partial or complete loss of function of one or more of the different cone systems.
Monochromacy: occurs when two or all three of the cone pigments are missing and color and lightness vision is reduced to one dimension.
Total color blindness
Dichromacy: occurs when only one of the cone pigments is missing and color is reduced to two dimensions.
Partial color blindness
Also known as rod monochromacy, complete achromatopsia, and
A rare, non-progressive inability to distinguish any colors as a
result of absent or nonfunctioning retinal cones.
See everything as white, black, or some shade of gray
Typically caused by a missense mutation (a switched amino acid)
in the CNGB3 gene.
CYCLIC NUCLEOTIDE-GATED CHANNEL, BETA-3 (CNGB3)
Classic achromatopsia results from a complete loss of CNGB3 function.
CNGB3 encodes for the beta subunit of the cone cyclic nucleotide-gated cation channel, found photoreceptor plasma membranes.
Upon activation by cGMP, it leads to an opening of cation channels which thereby cause a depolarization of rod photoreceptors. This gene is essential for the generation of light-evoked electrical responses in cones.
CNGB3 is not required for vital processes outside the visual system.
The human CNGB3 gene consists of 18 exons
distributed over 200 kb of genomic sequence.
Gene type: protein coding
Domain: similar to ion transport protein
Cytogenetic locus: chromosome: 8; Location: 8q21-q22
Length: 809 aa
"MFKSLTKVNKVKPIGENNENEQSSRRNEEGSHPSNQSQQTTAQE ENKGEEKSLKTKSTPVTSEEPHTNIQDKLSKKNSSGDLTTNPDPQNAAEPTGTVPEQK EMDPGKEGPNSPQNKPPAAPVINEYADAQLHNLVKRMRQRTALYKKKLVEGDLSSPEA SPQTAKPTAVPPVKESDDKPTEHYYRLLWFKVKKMPLTEYLKRIKLPNSIDSYTDRLY LLWLLLVTLAYNWNCWFIPLRLVFPYQTADNIHYWLIADIICDIIYLYDMLFIQPRLQ FVRGGDIIVDSNELRKHYRTSTKFQLDVASIIPFDICYLFFGFNPMFRANRMLKYTSF FEFNHHLESIMDKAYIYRVIRTTGYLLFILHINACVYYWASNYEGIGTTRWVYDGEGN EYLRCYYWAVRTLITIGGLPEPQTLFEIVFQLLNFFSGVFVFSSLIGQMRDVIGAATA NQNYFRACMDDTIAYMNNYSIPKLVQKRVRTWYEYTWDSQRMLDESDLLKTLPTTVQL ALAIDVNFSIISKVDLFKGCDTQMIYDMLLRLKSVLYLPGDFVCKKGEIGKEMYIIKH GEVQVLGGPDGTKVLVTLKAGSVFGEISLLAAGGGNRRTANVVAHGFANLLTLDKKTL QEILVHYPDSERILMKKARVLLKQKAKTAEATPPRKDLALLFPPKEETPKLFKTLLGG TGKASLARLLKLKREQAAQKKENSEGGEEEGKENEDKQKENEDKQKENEDKGKENEDK DKGREPEEKPLDRPECTASPIAVEEEPHSVRRTVLPRGTSRQSLIISMAPSAEGGEEV