Definition, Symptoms, Gene Defect, and Therapeutics
|Photo courtesy of The Guardian Opens in new window|
Albinism, one of the most widely recognized and striking of all genetic conditions, describes a group of inherited metabolic disorders characterized by a reduction or absence of a pigment (called melanin Opens in new window) in the skin, hair and eyes. In addition to a lack of pigment, common features in affected individuals are visual abnormalities, including decreased visual acuity, rapid, involuntary back and forth darting of the eyes (nystagmus), increased sensitivity to light (photophobia), and crossed eyes, caused by a muscle imbalance of the eyes (strabismus).
The term albino is used to designate individuals manifesting the symptoms of albinism. It was first used in about 1660 by a Portuguese explorer in describing white Negroes he had observed in Africa, and comes from the Latin albus, meaning white. Early explorers to the New World found a high frequency of albinism in several Indian tribes.
The English Rev. Dr. Spooner, a brilliant classicist whose amusing errors of speech became known as spoonerisms Opens in new window, was an albino. His errors of speech are thought to be related to his nystagmus, which caused a jumbling of information from the printed page, leading to a verbal jumbling of speech.
Albinos are popularly thought to have red eyes, but actually most have blue or grayish eyes. In some types, the iris appears to have a violet or reddish hue, because light is reflected back from the reddish retina, similar to the effect seen in some flash photos where eyes appear red.
Albinism also occurs in plants, insects, fish, reptiles, amphibians, birds, marsupials and mammals. The Greeks referred to it as “leukoethiopes,” from leuko, the word for white.
Pliny and Aulus Gellius described the condition in the first century. Historically, people with albinism have been singled out and occupied social positions ranging from outcasts to semigods.
Gene Defect and Associated Symptoms
Albinism is a genetic disorder caused by a defect in the genes that are involved in the production of the pigment called melanin Opens in new window. Albinism consists in several types and almost all result from both parents carrying the gene for the condition.
Everybody carries two copies of most genes (except for the sex chromosome genes)—one set from each parent. If a person carries one gene for normal pigmentation and one gene for albinism, s/he will have enough genetic material to produce normal pigmentation and therefore will not have albinism.
However, if a person has inherited two albinism genes (one from each parent) and therefore has no gene for normal pigmentation, s/he will have albinism. When both parents carry an albinism gene, even though neither parent has the disorder, there is a one in four risk that any offspring of theirs will manifest albinism.
Affected individuals may be far-sighted (hyperopia) or near-sighted (myopia), and often have astigmatism, a condition wherein light focuses poorly on the retina due to abnormal curvature of the cornea. Some forms may be associated with other problems such as difficulties with blood clothing or hearing impairment.
Note: Albinism should be differentiated from hypopigmentation Opens in new window, in which there is a reduction of the normal amount of pigment, but vision is unaffected. Many forms of hypopigmentation are associated with deafness.
Visual problems are caused by pigmentary deficiency. The eye needs pigment to develop normal vision, though the reason for this requirement is unknown.
The retina develops improperly during fetal life, and vision cannot be totally corrected, even with corrective lenses. Nerve signals from the retina to the brain do not travel along the proper nerve routes.
Normally light enters the eye only through the pupil—the dark opening at the center of the iris. But in albinism, the iris doesn’t have enough pigment to screen out excess light, and it passes through the iris, as well.
Albinism is often obvious at birth from the symptoms—lack of pigmentation. It can be verified with a DNA test to determine the presence of the albinism gene. Associated visual problems can be detected through eye examinations.
Treatment for albinism generally consists of attempts to alleviate ocular deficiencies. Surgery, though sometimes helpful for cosmetic reasons, does not seem to improve vision.
Corrective and tinted lenses and specialized magnifiers and small telescopes may be helpful in addressing vision problems.
Albinism generally does not affect life span, though there is an increased incidence of skin cancer due to the lack of pigmentation, which serves to protect the skin from damage caused by ultraviolet radiation. Sunscreens are recommended for reducing exposure to the harmful ultraviolet rays.
- Adapted from The Encyclopedia of Genetic Disorders and Birth Defects By James Wynbrandt, Mark D. Ludman