Is color vision an inherited trait?

You are here

Show

Search For A Disorder

Clinical Characteristics

Ocular Features: 

Human color vision is trichromatic and requires the normal function of three classes of cones responding to wavelengths of approximately 420nm (blue cones), 530 nm (green cones), and 560 nm (red cones).  Dichromatic color vision discussed here is based on responses of red and green cones whose pigments are generated from contiguous gene regions on the X chromosome encoding OPN1MW (green pigment), and OPN1LW (red pigment).

The degree of color deficiency is variable and some males are so mildly affected that they are unaware of any defect until tested.  The human eye is capable of seeing about a million colors which is made possible in part by the wide range of comparative signal outputs from the three classes of cones.  In addition, the ratio of red and green cones varies among individuals and these factors collectively influence how each individual interprets the spectrum of wavelengths that enter the eye.  The phenotype of red-green color blindness is highly variable.  

Four subclasses of red-green color vision defects are recognized:

               Protanopia - only blue and green cones are functional (1 percent of Caucasian males) 

               Deuteranopia - only blue and red cones are functional (1 percent of Caucasian males)

               Protanomaly - blue and some green cones are normal plus some anomalous green-like cones (1  percent of Caucasian males)

               Deuteranomaly - normal blue and some red cones are normal plus some anomalous red-like cones (5 percent of Caucasian males)

Blue color blindness (tritanopia; 190900) is the result of mutations in the OPN1SW gene on chromosome 7. ERG flicker responses can be used to define the type and nature of the cone defects. 

Systemic Features: 

There are no systemic abnormalities. 

Genetics

Red-green color perception is based on gene products called opsins which, combined with their chromophores, respond to photons of specific wavelengths.  The OPN1LW and OPN1MW genes reside in a cluster with a head-to-tail configuration on the X chromosome at Xq28.  Red-green color vision defects are therefore inherited in an X-linked recessive pattern.  There is a single gene for the red cone opsin but there are multiple ones for the green pigment.  Only the red gene and the immediately adjacent green pigment gene are expressed.  All are under the control of a master switch called the locus control region, LCR.

These DNA segments undergo relatively frequent unequal crossovers which can disrupt the color sensitivity of the gene products so that red-green colorblindness in some form is the most common type of anomalous color vision.  It is found in approximately 8% of males and perhaps 0.5% of females. 

Treatment

Treatment Options: 

No treatment is available for red-green color blindness although appropriately tinted lenses may enhance the perception of certain shades for specific tasks. 

Early work in non-human primates suggest that viral-mediated gene therapy can restore trichromacy to at least some extent.

References

Neitz M, Neitz J. Curing Color Blindness-Mice and Nonhuman Primates. Cold Spring Harb Perspect Med. 2014 Aug 21. [Epub ahead of print].

Deeb SS. The molecular basis of variation in human color vision. Clin Genet. 2005 May;67(5):369-77. Review.

Neitz M, Neitz J. Numbers and ratios of visual pigment genes for normal red-green color vision. Science. 1995 Feb 17;267(5200):1013-6.

Most individuals who are color blind inherit the trait. Men are more likely to be color blind because of the way color blindness is inherited. The gene for the trait is located on the X chromosome. Men have one X chromosome and women have two. If a man inherits the gene for the trait, he will have a color vision defect. If a woman inherits a single gene for the trait, she will not, because the normal gene on her other X chromosome will dominate over the defective gene. Women must inherit the defective trait from both parents to be color blind.

Color blindness is a so-called sex-linked characteristic. This means it is a gene that occurs only on the X chromosome, which is passed to the child by the mother. The Y chromosome, which is passed to the child by the father, does not carry the defective gene. This means that children inherit color blindness only from their mothers. Children can inherit color blindness from a mother who is color blind or from a mother who is a carrier of the gene but is not color blind herself. Daughters of men who are color blind will carry the trait, but sons will not.

A more unusual way to become color blind is through disease. Cataracts are the most common cause of acquired color deficiency. In one of the most common eye diseases, cataracts, a cloudy layer in the lens or eye capsule develops. The condition can cause vision to worsen in bright sunlight. Other conditions that may cause acquired color deficiency are retinal and optic nerve diseases.

Medications such as digitalis, a common medication for heart disease, and quinine, medicine for malaria, can also make color perception change. Alcohol has also been known to change the way people see color.