Albinism in humans
|Other names: Achromia, achromasia, achromatosis|
|A boy with albinism|
|Symptoms||Pale skin, eyes, and hair|
|Complications||Vision problems, sunburns, skin cancer|
|Usual onset||Present at birth|
|Types||OCA1 to 7, OA1, syndromic|
|Diagnostic method||Based on an examination, genetic testing|
|Differential diagnosis||Piebaldism, vitiligo, phenylketonuria, homocystinuria, kwashiorkor|
|Treatment||Sun protection, screening for skin cancer, frequent eye exams|
|Prognosis||Life expectancy may be similar to general population|
|Frequency||1 in 20,000|
Albinism is present at birth and characterized by the complete or partial absence of pigment in the skin, hair, and eyes. It is associated with vision problems including decreased visual acuity, light sensitivity, binocular vision deficits, refractive errors, and nystagmus. People are also more susceptibility to sunburns and skin cancer.
Albinism is due to genetic mutations that result in either a decreased ability to make or distribute melanin. At least 7 different autosomal recessive mutations can result in albinism and the condition is also be present as part of a number of syndromes including Hermansky–Pudlak and Chédiak–Higashi syndrome. Diagnosis is generally made based on an examination and may be supported by genetic testing.
Treatment involves life long sun protection such as the use of protective clothing, sunscreen, dark glasses, and avoiding UV light. Screening for skin cancer is recommended at least yearly, with the understanding that melanomas will be pink not dark. Frequent eye exams are also recommended. About 1 in 20,000 people are affected. Stigma exists in many areas of the world. The term is from the Latin albus meaning "white".
Signs and symptoms
There are different types of oculocutaneous albinism depending on which gene has undergone mutation. With some there is no pigment at all. The other end of the spectrum of albinism is "a form of albinism called rufous oculocutaneous albinism, which usually affects dark-skinned people".
"With ocular albinism, the color of the iris of the eye may vary from blue to green or even brown, and sometimes darkens with age. However, when an optometrist or ophthalmologist examines the eye by shining a light from the side of the eye, the light shines back through the iris since very little pigment is present."
Because individuals with albinism have skin that entirely lacks the dark pigment melanin, which helps protect the skin from the sun's ultraviolet radiation, their skin can burn more easily from overexposure.
The human eye normally produces enough pigment to color the iris blue, green or brown and lend opacity to the eye. In photographs, those with albinism are more likely to demonstrate "red eye", due to the red of the retina being visible through the iris. Lack of pigment in the eyes also results in problems with vision, both related and unrelated to photosensitivity.
Those with albinism are generally as healthy as the rest of the population (but see related disorders below), with growth and development occurring as normal, and albinism by itself does not cause mortality, although the lack of pigment blocking ultraviolet radiation increases the risk of melanomas (skin cancers) and other problems.
Development of the optical system is highly dependent on the presence of melanin. For this reason, the reduction or absence of this pigment in people with albinism may lead to:
- Misrouting of the retinogeniculate projections, resulting in abnormal decussation (crossing) of optic nerve fibres
- Sensitivity to light and decreased visual acuity due to light scattering within the eye (ocular straylight) Photophobia is specifically when light enters the eye, unrestricted – with full force. It is painful and causes extreme sensitivity to light.[unreliable source]
- Reduced visual acuity due to foveal hypoplasia and possibly light-induced retinal damage.
Eye conditions common in albinism include:
- Nystagmus, irregular rapid movement of the eyes back and forth, or in circular motion.
- Amblyopia, decrease in acuity of one or both eyes due to poor transmission to the brain, often due to other conditions such as strabismus.
- Optic nerve hypoplasia, underdevelopment of the optic nerve.
The improper development of the retinal pigment epithelium (RPE), which in normal eyes absorbs most of the reflected sunlight, further increases glare due to light scattering within the eye. The resulting sensitivity (photophobia) generally leads to discomfort in bright light, but this can be reduced by the use of sunglasses or brimmed hats.
Oculocutaneous albinism is generally the result of the biological inheritance of genetically recessive alleles (genes) passed from both parents of an individual such as OCA1 and OCA2. A mutation in the human TRP-1 gene may result in the deregulation of melanocyte tyrosinase enzymes, a change that is hypothesized to promote brown versus black melanin synthesis, resulting in a third oculocutaneous albinism (OCA) genotype, "OCA3". Some rare forms are inherited from only one parent. There are other genetic mutations which are proven to be associated with albinism. All alterations, however, lead to changes in melanin production in the body. Some of these are associated with increased risk of skin cancer