What is albinism?
Albinism is a disease in which a person has partial or complete loss of pigmentation (coloring) of the skin, eyes and hair.
What causes it?
Genetic mutations that affect the production of a pigment called melanin. There is a cell called the melanocyte that is responsible for giving skin, hair, and eyes pigmentation. In albinism, the melanocytes are present, but genetic mutations interfere with their pigment production or their ability to distribute it to keratinocytes, the major cell type comprising the epidermis, or outer layer of the skin. There are currently five known genetic types of albinism, the most common being oculocutaneous type 1 (OCA1) and type 2 (OCA2). Oculocutaneous means affecting the eyes and skin ("oculo" meaning eye and "cutaneous" meaning skin).
Patients with OCA1 have mutations in a gene called TYR that is responsible for creating the enzyme tyrosinase, used by cells to convert the amino acid tyrosine into pigment molecules that color the skin, hair, and eyes. OCA2, the most common form of albinism in Africa, results from a mutation in the OCA2 gene, which encodes the P protein. We don't know what this P protein does.
What are the symptoms of albinism?
People with albinism will have the following symptoms:
an absence of color in the hair, skin, or eyes
lighter than normal coloring of the hair, skin, or eyes
patches of skin that have an absence of color
Albinism occurs with vision problems, which may include:
strabismus (crossed eyes)
photophobia (sensitivity to light)
nystagmus (involuntary rapid eye movements)
impaired vision or blindness.
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What does a person with albinism look like?
Most people with OCA1 have snow-white skin, snow-white hair, and no pigment in their eyes. The iris (colored part of the eye that encircles the pupil) is a pale bluish pinkish color, while the pupil may actually be red. This redness comes from light entering the pupil and reflecting off of blood vessels in the retina, the light-sensitive layer of tissue lining the back of the eyeball. Normally, the pupil appears black because pigment molecules in the retina absorb light entering the eye, preventing it from bouncing back to the outside world.
Those with OCA2 can make a small amount of pigment and thus may have light blond to brown hair color. Their irises are blue to light gray and their pupils dark red to light gray.
How does this lack of pigment in the eyes affect vision?
People with albinism are legally blind because photoreceptors (cells in the retina that detect light) get oversaturated with light and send confusing messages to the brain. If you look at a person with albinism, you'll see a nystagmus, or fluttering, in their eyes; the eyes are sort of bouncing in their sockets because they are getting a confusing visual stimulus.
What are some other conditions associated with albinism?
Without pigment in the skin, you are more susceptible to non-melanoma skin cancers in keratinocytes. Normally, melanocytes distribute pigment molecules to keratinocytes, where they act sort of like umbrellas shielding the nucleus (and the DNA inside) from the sun's UV radiation. Albinos are particularly at risk for squamous cell carcinoma, a cancer of the outermost layer of skin, and basal cell carcinoma affecting deeper layers. They also may experience premature skin aging. Melanin helps prevents wrinkles and elastosis (breakdown of elasticity) by blocking UV radiation.
Are there any treatments for albinism?
No, there are not. Patients with albinism are advised to protect themselves from the sun.
Are there any treatments in the pipeline?
Some researchers, such as Richard King at the University of Minnesota, are trying to develop gene therapies, or drugs that would go into the cells and correct DNA mutations responsible for albinism. So far, scientists have had some success in correcting patches of depigmented skin and hair in mice, but they are a long way from translating this research to humans.
What animals, besides humans, can be albinos?
Any animal that has melanocytes can get albinism. That means virtually all mammals. Reptiles, amphibians and lower vertebrates can also be albinos, but these organisms may also have other types pigment production cells besides melanocytes, so they may not appear colorless. In the zoo here in Cincinnati, we had an albino alligator.
According to the National Organization of Albinism and Hypopigmentation (NOAH), one in every 17,000 people in the U.S. has some type of albinism, but the incidence is much higher in East Africa (about 1 in 3000, according to some estimates). Why this disparity?
The mutation in OCA2, which is responsible for most albinism cases in Africa, is probably the oldest mutation causing albinism and, putatively, originated during mankind's development in Africa. For some reason, it's retained there.
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References
https://www.healthline.com/health/albinism https://www.scientificamerican.com/article/killing-albinos-tanzania-albinism/