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about Ablinism
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Approximately one in 17,000 people have one of the types of albinism. About 18,000 people in the United States are affected. Albinism affects people from all races. The parents of most children with albinism have normal hair and eye color for their ethnic background, and do not have a family history of albinism.
Melanin pigment is important in other areas of the body, such as the eye and the brain, but it is not known what the melanin pigment does in these areas. Melanin pigment is present in the retina (RET-n-ah), and the area of the retina called the fovea (FOE-vee-ah) does not develop correctly if melanin pigment in not present in the retina during development (see below). The other areas of the retina develop normally whether or not melanin pigment is present. The nerve connections between the retina and the brain are also altered if melanin pigment is not present in the retina during development. The iris has melanin pigment and this makes the iris opaque to light (no light goes through an opaque iris). Iris pigment in albinism is reduced, and the iris is translucent to light, but the iris develops and functions normally in albinism.
As with most metabolic pathways in our body, the first compound in a pathway is converted to the next compound by the action of an enzyme. For example, in the simple pathway A-->B-->C, the conversion of compound A to B occurs because of the action of Enzyme 1, and the conversion of B to C occurs because of the action of Enzyme 2. The formation of melanin pigment follows a pathway like this, but the pathway is more complex and not all of the steps are known.
Tyrosinase (tie-ROW-sin-ace) is the major enzyme involved in the formation of melanin pigment. Tyrosinase is responsible for converting tyrosine to DOPA and on to dopaquinone (dopa-QUIN-own). The dopaquinone then forms black-brown eumelanin or red-yellow pheomelanin. The tyrosinase enzyme is made by the tyrosinase gene on chromosome 11, and alterations (also called mutations) of this gene can produce one type of albinism because the tyrosinase enzyme made by the altered gene does not work correctly.
Two additional enzymes called tyrosinase-related protein 1 or DHICA oxidase (DEE-ca OX-eye-dase) and tyrosinase-related protein 2 or dopachrome tautomerase (dopa-chrome tow-TOM-er-ace) are important in the formation of eumelanin pigment. The gene for DHICA oxidase in on chromosome 9 and the gene for dopachrome tautomerase in on chromosome 9. Alterations of the DHICA oxidase gene are associated with a loss of function of this enzyme and this produces on type of albinism. Alterations of the gene for dopachrome tautomerase do not produce albinism.
Three other genes make proteins that are also involved in melanin pigment formation and albinism, but the exact role of these proteins remains unknown. These genes are the P gene on chromosome 15, the Hermansky-Pudlak syndrome gene on chromosome 10, and the ocular albinism gene on the X chromosome.
| Gene | Location |
| Tyrosinase | Chromosome 11 |
| P | Chromosome 15 |
| Dopachrome tautomerase (TRP2) | Chromosome 13 |
| DHICA oxidase (TRP1) | Chromosome 9 |
| Hermansky-Pudlak syndrome(HPS) | Chromosome 10 |
| Ocular albinism (OA1) | Chromosome X |
There are several less common types of albinism which involve other problems also, such as mild problems with blood clotting, or problems with hearing. (See discussion of types of albinism below.)
Albinism may cause social problems, because people with albinism look different from their families, peers, and other members of their ethnic group.
Growth and development of a child with albinism should be normal and intellectual development is normal. Developmental milestones should be achieved at the expected age. General health of a child and an adult with albinism is normal, and the reduction in melanin pigment in the skin, hair and the eyes should have no effect on the brain, the cardiovascular system, the lungs, the gastrointestinal tract, the genitourinary system, the musculoskeletal system, or the immune system. Life span is normal.
For help with visual acuity, eye doctors experienced in low vision can prescribe a variety of devices. No one device can serve the needs of all persons in all situations, since different occupations and hobbies require the use of vision in different ways. Young children may simply need glasses, and older children can sometimes benefit from bifocal glasses. Low vision clinics may prescribe telescopic lenses mounted on glasses, sometimes called bioptics, for close-up work as well as for distant vision. Recently smaller and lighter telescopes have been developed; however, ordinary glasses or bifocals with a strong reading correction may serve well for many people with albinism.
For nystagmus, research has searched for an effective treatment which helps in all cases. Attempted treatments to control nystagmus have included biofeedback, contact lenses, and surgery. The most promising may be eye muscle surgery that reduced the movement of the eyes; however, vision may not improve in all cases due to other associated eye abnormalities. People with albinism may find ways of reducing nystagmus while reading, such as placing a finger by the eye, or tilting the head at an angle where nystagmus is dampened.
For strabismus, ophthalmologists prefer to treat infants starting at about six months age, before the function of their eyes has developed fully. They may recommend that parents patch one eye to promote the use of the non-preferred eye. In other cases, the alignment of the eyes improves with the wearing of glasses. Correction of strabismus by surgery or by injection of medicine into the muscles around the eyes does not completely correct the problem with both eyes fixing on one point. Although these treatments may improve the alignment of the eyes and enhance psycho-social development and interpersonal interactions, they cannot correct the improper routing of the nerves to the brain. Depth perception is not improved with eye muscle surgery.
For photophobia, eye doctors can prescribe dark glasses that shield the eyes from bright light, or photochromic lenses that darken on exposure to brighter light. There is no proof that dark glasses will improve vision, even when used at a very early age, but they may improve comfort. Many children and adults with albinism do not like tinted lenses, and benefit more from wearing a cap or a visor when outdoors in the sun.
Children with albinism often prefer to read with a head tilt and usually hold the page close to the eyes. Occasionally it can be difficult to get them to use their glasses, as they do not notice significant improvement in their vision when glasses are used. Furthermore, use of glasses or books with large print can be difficult because of peer pressure.
Various classroom aids help children with albinism:
Prescription of appropriate classroom visual aids requires teamwork of the student, parent, classroom teacher, vision resources teacher, and an optometrist or ophthalmologist experienced in working with persons with low vision. The American Foundation for the Blind (15 West 16th Street, New York, NY 10011) maintains a directory of low vision clinics in the United States.
Sunburn is skin damage from exposure to ultraviolet light, which is a part of sunlight that is not visible to the human eye. Redness develops 2 to 6 hours after exposure to ultraviolet light, and sunburn may not turn completely red until as long as 24 hours after the exposure. As a result a sunburn can worsen after a person leaves the sun. Prolonged sun exposure in a person who does not tan well is associated with the development of skin cancer. This can be prevented with correct protection of the skin from the ultraviolet radiation of the sun.
It is difficult to state a general rule for the number of hours in the sun that people with albinism can tolerate, since the intensity of the ultraviolet light varies a great deal, depending upon the time of day and year, and the environmental conditions:
A sensitive hairbulb tyrosinase enzyme activity assay was developed in an attempt to improve the specificity of the hairbulb test. Unfortunately, biochemical studies of hairbulb tyrosinase activity also proved to be unreliable and did not have the specificity necessary for accurate diagnosis. The hairbulb tyrosinase assay test is no longer used in the evaluation of an individual with OCA.
In the 1980's the classification of OCA was expanded using very careful skin, hair, and eye examinations. The reason for this was the knowledge that there were more than 50 gene loci that controlled pigmentation in the mouse, and it was suggested that careful analysis of skin, hair, and eye pigmentation of individuals with OCA could help identify the human equivalent of each of these genes. A number of types of OCA were identified, including platinum OCA, minimal pigment OCA, yellow OCA, temperature-sensitive OCA, autosomal recessive ocular albinism and brown OCA, and it was hoped that each would be caused by a different gene. In the 1990's, we have been able to identify the genes involved in most types of OCA, and have found that the classifications based on hair, skin and eye color is not accurate and that it was better to classify OCA types based on the specific gene involved.
We have now identified five genes that are associated with the development of OCA and one gene that is involved in OA.
| Gene | Type of Albinism |
| Tyrosinase gene | OCA1 (OCA1A and OCA1B) |
| P gene | OCA2 |
| TRP1 gene | OCA3 |
| HPS gene | Hermansky-Pudlak Syndrome |
| CHS gene | Chediak Higashi Syndrome |
| OA1 gene | X-linked ocular albinism |
The pigmentation (phenotype) range for OCA at each gene locus is broad. Most of the various types or subtypes of OCA that were defined over the past 20 years can now be associated with a specific genetic locus.
Many different mutations of the tyrosinase gene have been identified in individuals and families with OCA1. Most mutations lead to the production of tyrosinase enzyme that does not work. As a result, the first two critical conversions in the melanin pathway (tyrosine-->dopa-->dopaquinone) are not made and no melanin pigment forms; the pathway is "blocked" at the start. Mutations that produce an inactive enzyme or no enzyme at all are called "null" mutations.
Some tyrosinase gene mutations are not null mutations but are called "leaky" mutations. These mutations lead to the production of a tyrosinase enzyme that has a little activity but nowhere near the normal amount of activity (often in the range of 1-10% of normal activity). Leaky mutations and the resultant tyrosinase enzyme allow some melanin to form. The formation of melanin can be very small (the minimal pigment type of OCA) or can range to nearly normal (the type of OCA that was mistakenly called autosomal recessive ocular albinism).
An important distinguishing characteristic of OCA1 is the presence of marked hypopigmentation at birth. Most individuals affected with a type of OCA1 have white hair, milky white skin, and blue eyes at birth. The irides can be very light blue and translucent such that the whole iris appears pink or red in ambient or bright light. During the first and second decade of life, the irides usually become a darker blue and may remain translucent or become lightly pigmented with reduced translucency. The skin remains white or appears to have more color with time. Sun exposure produces erythema and a burn if the skin is has little pigment and is unprotected, but may tan well if cutaneous pigment has developed. Pigmented lesions (nevi, freckles, lentigines) develop in the skin of individuals who have developed pigmented hair and skin.
Visual acuity for OCA1A is usually in the legally-blind range, 20/200 to 20/400, although near vision may be better if the print is held close to the eyes. Vision usually does not improve with age. Photophobia and nystagmus cause more problems with OCA1A than with other types. Vision often does not correct well with glasses, but low vision aids help.
The original OCA1B phenotype was called yellow albinism because of the yellow blond or golden color of the melanin that develops in the hair of affected individuals. It is now known that the hair color is the result of pheomelanin synthesis (see pathway above), and the formation of this type of melanin is related to the reduced tyrosinase function. Only small amounts of dopaquinone form and these combine quickly with sulfur-containing compounds present in the cell and produce the pheomelanins. Other types of OCA1B have been described as minimal pigment OCA, platinum OCA, temperature-sensitive OCA, and autosomal recessive ocular albinism.
All variations of OCA1B are characterized by having very little or no pigment present at birth followed by the development of varying amounts of melanin in the hair and the skin in the first or second decade. In some cases, the melanin develops within the first year. The hair color changes to light yellow, light blond or golden blond first, and may eventually turn dark blond or brown in the adolescent and the adult. One interesting feature of OCA1B is the development of dark eyelashes. Eyelash hair pigment is often darker than that of the scalp hair. The irides can develop hazel, light tan or brown pigment, sometimes limited to the inner third of the iris, and iris pigment can be present on globe transillumination. Some degree of iris translucency, as demonstrated by slit-lamp examination, is usually present. Visual acuity is in the range of 20/90 to 20/400, and may improve with age.
Many individuals with OCA1B will tan with sun exposure while it is more common to burn without tanning after sun exposure. Pigmented nevi can develop with time, although most developing nevi are amelanotic. Very few freckles develop.
Another type of OCA1B is temperature-sensitive OCA. Affected individuals are thought to have OCA1A during the first years of life, with white hair and skin, and blue eyes. With further development, some of the body hair develops pigment. The hair under the arms remains white and the scalp hair remains white but may develop a slight yellow tint. In contrast to this is the arm and leg hair that develop light to dark pigment. The eyes stay blue and the skin remains white and does not tan. This type of OCA1B is caused by a mutation of the tyrosinase gene that produces an enzyme that does not work at regular body temperature (scalp and under the arms) but does work in cooler parts of the body (arms and legs). As a result, melanin synthesis occurs in the cooler but not the warmer areas of the body such as the arms and legs.
In Caucasian individuals with OCA2, the amount of pigment present at birth varies from minimal to moderate. The hair can be very lightly pigmented at birth, having a light yellow or blond color, or more pigmented with a definite blond, golden blond or even red color. The normal delayed maturation of the pigment system in northern European individuals (i.e., very blond or towheaded as a child with later development of dark blond or brown hair) and lack of long hair can make the it difficult to distinguish OCA1 from OCA2 in the first few months of life. The skin is white and does not tan on sun exposure. Iris color is blue-gray or lighted pigmented, and the degree of iris translucency correlates with the amount of pigment present. With time, pigmented nevi and lentigines may develop and pigmented freckles are seen in exposed areas with repeated sun exposure. The hair in Caucasian individuals may slowly turn darker through the first two or more decades of life.
There is a distinctive OCA2 phenotype in African-American and in African individuals. The hair is yellow at birth and remains yellow through life, although the color may turn darker. Interestingly, the hair can turn lighter in older individuals, and this probably represents the normal graying with age. The skin is white at birth with little change over time, and no tan develops. Localized pigmented lesions such as pigmented nevi, lentigines and freckles can develop in some individuals. The irides are blue/gray or lightly pigmented.
There appears to be a wide OCA2 pigment phenotypic range in African-Americans, in that some individuals with OCA2 (defined as having pigmented hair at birth and the ocular features of albinism) have brown, ginger, auburn or red hair. Some of this variation may reflect genetic admixture in this population, and some may result from different mutations of the P gene and their different effect on the function of the P protein. Some individuals who were previously thought to have autosomal recessive ocular albinism have now been shown to have OCA2.
Brown OCA is part of the spectrum of OCA2, resulting from alterations of the P gene. These gene alterations are associated with the development of yellow or red pheomelanin and a lack of development of brown or black eumelanin. As with OCA1B, Brown OCA may arise from a mutation that reduces ("leaky" mutation)the function of the P gene product while the more common OCA2 results from completely knocking out ("null" mutation) the function of the P protein.
Angelman syndrome is a complex developmental disorder that includes developmental delay and severe mental retardation, microcephaly, neonatal hypotonia, ataxic movements, and inappropriate laughter. In Angelman syndrome, the hypopigmentation is characterized by light skin and hair. There may be a history of nystagmus or strabismus, and iris translucency and reduced retinal pigment may be present. No analysis of the optic tract organization is available. It is expected that individuals with Angelman syndrome having OCA2 will be described, because of the location of the P gene in the Prader-Willi/Angelman syndrome region of chromosome 15.
Rufous or red OCA has only been partially documented. Individuals with OCA who have red hair and reddish-brown pigmented skin have been reported in Africa and in New Guinea, but clinical descriptions are incomplete, and similar individuals in the U.S. population have not been identified and reported. The cases are described in the literature as 'red', 'rufous', or 'xanthous' albinism. Individuals with red hair who have either OCA1 or OCA2 are also recognized, but the reddish-brown skin pigment is usually not present, and they should not be confused with Rufous OCA.
The pigment phenotype in South African individuals includes red or reddish brown skin, ginger or reddish hair, and hazel or brown irides. The ocular features are not fully consistent with the diagnosis of OCA, however, as many do not have iris translucency, nystagmus, strabismus, or foveal hypoplasia. Furthermore, no misrouting of the optic nerves has been demonstrated by a visual evoked potential, suggesting either that this is not a true type of albinism, or that the hypopigmentation is not sufficient to consistently alter optic nerve development. At this time, the phenotype for TRP1-related OCA in the Caucasian and the Asian populations is unknown.
HPS is a pigmenting type of OCA and skin and eye pigment develop in many affected individuals, but the amount of pigment that forms is quite variable. Some affected individuals have marked hypopigmentation of their skin and hair similar to that of OCA1A, others have white skin and yellow or blond hair similar to OCA1B or OCA2, and others have only moderate hypopigmentation suggesting that they may have OA rather than OCA. The variation can be seen within families as well as within families.
Individuals with HPS in the Puerto Rican population have hair color that varies from white to yellow to brown. Skin color is creamy white and definitely lighter than individuals without HPS in this population. Freckles are often present in the sun exposed regions (face, neck, arms and hands), often enlarging and overlapping into large areas that look like normal dark skin pigment, but tanning does not occur. Pigmented nevi are common. Iris color varies from blue to brown, and all of the ocular features of albinism are present. Visual acuity ranges from 20/60 to 20/400.
Affected individuals have been identified in other populations infrequently, and the phenotype shows the same degree of variation in pigmentation as is found in Puerto Rico. Hair color varies from white to brown, and this correlates with the ethnic group. The skin is white and does not tan. Eye color varies from blue to pigmented.
The most important medical problems in HPS are usually related to the lung and the gastrointestinal tract changes. Interstitial lung fibrosis (or scarring of the lungs) develops in many individuals with HPS, although the actual prevalence is unknown. The fibrosis results in an inability of the lungs to expand and contract, reducing their ability to take in oxygen and exhale carbon dioxide. This is called restrictive lung disease. Fewer individuals with HPS develop colitis of inflammation of the intestinal tract. This is called granulomatous colitis, and the medical problems include abdominal pain and bloody diarrhea in a child or an adult. The presence of ceroid material in the lungs and the intestines suggest that this material may be involved in the development of these complications, but this has not been proven.
The bleeding problem in HPS is related to a deficiency of granules in the platelets (i.e. storage pool-deficient platelets) that store material needed for normal platelet function. Platelets are cells in the blood that are responsible for forming the initial clot after a blood vessel is cut or opened. Platelets work by first attaching to exposed material in the blood vessel wall, and then sticking together and contracting into a small plug to close the hole. Platelets stick together because they secrete chemicals from storage compartments that are inside each platelet. In HPS, these storage compartments do not form (storage granules do not form) and the platelets are unable to secrete this necessary chemicals. The platelets first stick to the cut blood vessel wall but do not aggregate and contract and do not form a firm plug at the hole. This produces mild bleeding episodes in many affected individuals, including easy brusibility, epistaxis (bloody nose), hemoptysis (bloody sputum), bleeding of the gums with brushing or dental extraction, and postpartum bleeding. Occasional severe bleeding is observed which in part may be related to normal variation in von Willibrand factor.
Visual acuity in X-Linked albinism is in the range of 20/50 to 20/400.
It is often possible to identify females who carry the gene by examining their eyes. "X-Linked" means that the gene for ocular albinism is passed from mothers who carry the gene to sons who have ocular albinism. See appendix, "Understanding Genetics", for an explanation of the way X-Linked inheritance works.
The most accurate test for determining the specific type of albinism is a gene test. A small sample of blood is obtained from the affected individual and the parents as a source of DNA, the chemical that carries the 'genetic code' of each gene. By a complex process, a genetic laboratory can "sequence" the code of the DNA, to identify the changes (mutations) in the gene that cause albinism in the family. The test is useful only for families that contain individuals with albinism, and cannot be performed practically as a screening test for the general population. None of the tests available are capable of detecting all of the mutations of the genes that cause albinism, and responsible mutations cannot be detected in a small number of individuals and families with albinism.
The test can be used to determine if a fetus has albinism. For this purpose a sample would be obtained by amniocentesis, a procedure which involves using a needle to draw fluid from the uterus, at 16 to 18 weeks gestation. Those considering such testing should be aware that given proper support children with albinism can function well and have normal life spans.
For information about these tests, contact:
612-624-0144.
Each cell in the body has two copies of each gene- one version from the mother and one version from the father. For OCA, the individual with albinism has received an albinism gene from both parents, and both versions of his blueprint for making pigment are incorrect.
If a person carries one normal copy of a gene and one altered or albinism copy of a gene, he or she still has one blueprint that will provide enough information to make pigment. That means that he or she will have normal eye and skin color. For OCA, parents carry an albinism gene with an incorrect version of the blueprint, but they have normal pigmentation, because they still have one normal gene with a normal version of the blueprint.
About 1 in 70 people carries a gene for OCA. Suppose a man and a woman each carry an altered copy of the same gene and have normal coloration. They each have a normal copy and an albinism copy of the gene, and will pass one of these two copies when they conceive a baby. They each have a 1 in 2 chance of passing on the albinism copy of the gene to their baby. As a result, for each pregnancy there is a 1 in 4 chance (1/2 x 1/2) that their baby will get two copies of the gene for albinism, in which case the baby will have no normal blueprint for making pigment, and will have albinism. This description of the inheritance of albinism applies to the different types of OCA. See the section "Understanding Genetics", for a more detailed discussion. There are five genes known that can cause OCA, and there many be several additional OCA genes that have not been identified to date. If you wish specific information about your chances for having a child with albinism, seek advice from a qualified genetics counselor.
Figure 4 and Figure 5 are pictures of human chromosomes. The first 22 pairs of chromosomes are called autosomes. They are numbered according to size, with chromosome #1 being the largest chromosome and chromosome 22 the smallest chromosome. These are the non-sex chromosomes. The 23rd pair is the sex chromosome pair. Females have two X chromosomes, and males have one X and one Y chromosome.
Each chromosomes is composed of many hundreds or thousands of genes. Genes are biochemical blueprints which code for products needed to produce and maintain human life. Genes account for physical traits as well as cellular chemical reactions, which direct the production and maintenance of our body systems. As we have two of each of the autosomes, one from each parent, we have two of each of the genes located on the autosomes, one from each parent. Females have two copies of every gene located on the X chromosome, while males have one copy of the genes on the X chromosome and one copy of the genes on the Y chromosome.
If a person carries one gene of a pair that has an altered blueprint and the other of the pair has an unaltered blueprint, then the effects of the altered blueprint do not show. This person is an unaffected carrier. Carriers make enough of the gene product to produce pigment. Therefore, people who carry only one gene responsible for albinism do not know they are carriers. If, however, a person carries two copies of an altered gene, then the product of that gene cannot be made correctly. Such persons have albinism because they cannot produce pigment.
When two people who carriers for the same gene have a child together, then the child has one out of four chances of getting two copies of the albinism gene and having albinism. The child has one out of four chances of getting the two copies of the normal gene and having normal pigment and not being a carrier. The child has two out of four chances of getting one normal gene and one albinism gene and having normal pigment but being a carrier. See Diagram 6.
Since females have two X chromosomes, they will have two copies of all genes on the X chromosome. Males have one X chromosome and one Y chromosome. Because of this difference, males will have only one copy of each gene on the X chromosome. A female can carry one copy of an altered gene on one of her X chromosomes and not show it, because she also carries a second unaltered copy on her other X chromosome. If a male carries one copy of an altered gene on his X chromosome, he does not carry an unaltered copy. As a result, he will show the effects of this gene. See Diagram 7.
If a woman carries the gene responsible for X-linked ocular albinism, the risk for her to give birth to an affected son is 50% or one in two for each birth. None of her daughters will be affected but for each birth of a daughter there is a one in two chance that the daughter will be a carrier.
Children of a man with X-linked ocular albinism will not have ocular albinism, but all of his daughters will be carriers.
These risk figures hold true in each and every pregnancy. They are not changed by the outcome of a previous pregnancy.
Larry, a book for children about a child with albinism going to school, available from the National Association for the Visually Handicapped, 305 East 24 Street, New York City, NY 10010, (212)-889-3141.
NOAH News, the newsletter of the National Organization of Albinism and Hypopigmentation, 1500 Locust Street, Suite 1816, Philadelphia, PA 19102. NOAH also publishes Information about Albinism bulletins which on various topics related to albinism. Phone 800-473-2310.
The Student with Albinism, published by NOAH and the National Association for Parents of Visually Impaired, may also be obtained through NOAH, for $3.00 This booklet provides more information on helping the child with albinism to function in the classroom. It was written by Julia Ashley, a PhD student at Nova University who surveyed teachers of students with albinism.
Albinism: A group of inherited conditions which
include a decrease in the amount of pigment in the eyes alone, or in both the
eyes and skin. The term albino comes from a Portuguese explorer of Africa who
saw both dark- and light-skinned natives, and called them "Negroes" (from the
word for black) and "Albinos" from the word for white) -- he erred in thinking
that they were of different races.
Amino Acid: A natural substance found in all living
animals and plants. Amino acids are the "building blocks" for protein. When the
body takes in protein in food, it breaks the protein down into amino acids, and
then uses the amino acids to build other proteins. The body can also change
amino acids into certain other substances, including melanin pigment. The term
"albino" should be avoided because it calls upon appearance or genetic condition
to label a person.
Astigmatism: An eye condition which causes decreased
sharpness of vision because the lens does not focus light evenly on the retina
so that the image is distorted.
Autosomal: Referring to a chromosome other than one of
the sex (X or Y) chromosomes. See "Understanding Genetics."
B.A.D.S.: Black Locks Albinism Deafness Syndrome: A rare
form of albinism which includes a black forelock (an area of the hair at the top
of the forehead) and deafness from birth.
Bioptic: A special lens mounted on a pair of glasses
to aid low vision.
Braille: A system for writing for the blind that uses
characters made up from raised dots which a person can read with his fingertips.
Carrier: A person who has an altered gene but does not
show characteristics of it because he or she also has a normal gene. Such a
person appears normal but can pass the altered gene on to his or her offspring.
Chediak-Higashi Syndrome: A very rare type of albinism
which includes a defect in white blood cells, so that resistance to infection is
reduced.
Chromosome: A microscopic structure, made out of DNA,
which carries the genes. All cells within the body have a set of chromosomes.
The sperm and the ovum contain the chromosomes which parents pass on to their
child. During growth both before and after birth the child's body copies these
chromosomes into each new cell. Each chromosome contains a large number of
genes.
DNA: Deoxyribonucleic acid, a natural substance which
stores genetic information as an intertwined double chain. The body reads the
code stored in this chain to learn how to assemble proteins from amino acids.
DOPA: Dihydroxyphenylalanine, a natural chemical which
the body makes as a step in the process of making the pigment melanin.
Enzyme: A specialized protein in the body that helps
the body convert one chemical substance to another.
Eumelanin: A darker brown or black form of the pigment
melanin. See also "phaeomelanin."
Fovea: The area of the retina of the eye which contains
the nerve fibers which allow the sharpest vision.
Gene: A piece of information, stored in a code in DNA,
which tells the body how to make a particular protein. Genes are passed on in
the sperm and the egg that combine during conception.
Hairbulb: A "root" of a human hair, from which growth
and coloration of the hair develops. Human hairbulbs go through cycles, and when
the bulb dies out or is pulled out a new one grows in its place.
Hairbulb pigmentation (incubation) test: A laboratory
test in which a hairbulb is incubated in the amino acid tyrosine to see whether
or not the hairbulb will make pigment. Also used to test the activity of the
enzyme tyrosinase in hairbulbs. This test is not considered to be an accurate
measurment of tyrosinase activity and is no longer used.
Hermansky-Pudlak Syndrome: A type of albinism which
includes (1) a defect of platelets, which are a small type of blood cell that
help the blood clot, and (2) accumulation of a waxy material in various body
tissues, sometimes harming the lungs, or intestines. See text for details.
Hypopigmentation: A general term for decreased
pigmentation or coloration.
Iris: The colored part of the eye, which closes in and
opens out around the pupil, to help screen the amount of light that comes into
the eye.
Melanin: A type of pigment or coloring substance made
in the eye and skin of humans and many other animals.
Melanocyte: A type of cell specialized to make the
pigment melanin. Melanocytes are located in the lower layers of skin and pass
pigment up to the higher layers. Melanocytes also are located in the eye and in
hairbulbs. Researchers have found melanocytes in the skin, hair and eyes of
persons with albinism.
Melanosome: A package of pigment within the melanocyte.
Nevus: A mole or birthmark.
Nystagmus: Involuntary movement of the eyes back and
forth.
Phaeomelanin: A yellowish-broth or reddish form of the
pigment melanin. Some persons with albinism seem to produce this pigment in
areas such as beards. See also "Eumelanin."
Photochromic: Referring to glasses that change to a
darker color (usually gray or orange) when exposed to bright light.
Photophobia: A condition in which bright light makes the
eyes particularly uncomfortable.
Pigment: A coloring matter. Pigments block the passage of
light and absorb light. The eye sees the light that is not absorbed but
reflected back.
Platelet: A small type of white blood cell which helps
the blood to clot.
Recessive: Referring to an altered gene which does not
show its effect if the person carrying that gene also has an unaltered gene. See
"Understanding Genetics."
Retina: The surface on the inside of the back of the eye.
Light enters the eye through the pupil, and the lens focuses the light on the
retina. The retina converts the light to a message to the brain.
Transillumination: A test to determine how much light
"leaks" through the iris. In a darkened room, a penlight is placed against the
side of the eye. Light coming from behind the iris shines out. In persons with
albinism, more light shines out because the iris has little pigment, and is
translucent.
Tyrosine: An amino acid, or protein building block.
Tyrosine comes from a wide variety of foods, and deficiency is rare except in
extreme protein malnutrition. The system uses tyrosine to make melanin.
Tyrosinase: An enzyme or specialized protein substance
in the pigment cell which promotes the conversion of amino acid tyrosine to DOPA
in the process of making pigment.
Ty-Neg: Tyrosinase negative, which refers to a type of
albinism in which hairbulbs incubated in a chemical solution of tyrosine do not
make pigment. See text for details. Also called Type 1A albinism.
Ty-Pos: Tyrosinase positive, which refers to a type of
albinism in which hairbulbs incubated in a chemical solution of tyrosine make
pigment. See text for details. Also called Type 2 albinism.
Ultraviolet (UV): a "color" of light not visible to the
human eye. Ultraviolet light causes tanning, burning and skin damage.
Yellow Albinism: A type of albinism similar to ty-neg
albinism at birth. It is sometimes called "yellow mutant" albinism, though the
term "mutant," which refers to a spontaneous (not inherited) change in genes, is
inappropriate. This term is no longer used to classify albinism. See text for
details.
X-Linked: Referred to a gene that is passed on with the
X chromosome. Females have two X chromosomes, while males have one X chromosome
and one Y chromosome. See "Understanding Genetics" for details.
Richard A. King, M.D., Ph.D., Professor of Medicine and in the
Institute of Human Genetics at the University of Minnesota, has conducted
research on albinism for more than fifteen years, and coordinates the
International Albinism Center.
C. Gail Summers, M.D., Associate Professor of Ophthalmology at the
University of Minnesota, is involved in research on vision and albinism, and is
co-director of the International Albinism Center.
James W. Haefemeyer, M.D., M.S., is a family practice physician in
Minneapolis, Minnesota, who has albinism and is a NOAH Scientific Advisor.
Bonnie S. LeRoy, M.S., is a Genetic Counselor at the University of
Minnesota.
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