DEFINITION
Albinism: A group of genetic disorders in which there is partial or total lack of the pigment melanin in the eyes, skin, and hair.
See also: Albinism, oculocutaneous; Hermansky-Pudlak syndrome.
Albinism is a defect of melanin production that results in little or no color (pigment) in the skin, hair, and eyes.
Albinism is a recessively inherited condition affecting about one in 17,000 people. A person who inherits albinism usually inherits a recessive gene for the condition from each parent, though this is not the case in ocular albinism.
Albinism appears in different forms and may be inherited by one of several modes: autosomal recessive, autosomal dominant, or X-linked inheritance.
Albinism refers to a group of genetic defects that cause decreased levels of the pigment, melanin, which forms color in skin, hair, and eyes. Low levels of melanin cause very light skin tone and blond-white hair.
Albinism is a defect of melanin production. This defect results in the partial or full absence of pigment (color) from the skin, hair, and eyes.
Albinism
Dr Trisha Macnair
Albinism is a group of conditions characterised by a lack of colour in the skin, hair and eyes.
Albinism, an inherited disorder, is caused by the absence of the pigment melanin and results in no pigmentation in skin, hair, or eyes. In albinos, their body has an abnormal gene, which restricts the body from producing melanin.
Albinism is present at birth, although some types of the disorder may not be easily identified in infants. Although there's no cure for albinism, people with the disorder can take steps to improve vision and avoid too much sun exposure.
Albinism
This rare, inherited disorder is characterized by a total or partial lack of melanin in the skin, compared to the pigmentation of siblings and parents. Albinos (people with albinism) have white hair, pale skin, and pink eyes.
Albinism refers to a group of inherited conditions. People with albinism have absent or reduced pigment in their eyes, skin or hair. They have inherited genes that do not make the usual amounts of a pigment called melanin which is essential for the full development of the retina. Lack of melanin in development of the retina is the primary cause of visual impairment in albinism. In the USA it is estimated that one person in 17,000 has some type of albinism.
There are two major categories of albinism (overlap of these categories often occurs):
Ocular Albinism (OA) is divided into two types according to the inheritance pattern:
autosomal recessive OA occurring equally in males and females, and X-linked OA with symptoms occurring primarily in males. In the X-linked cases, mothers carry the gene and pass it to their sons. Although the mothers usually have normal vision, they have subtle eye changes that can be identified by an ophthalmologist. If a woman does carry the gene, with each pregnancy there is a one in two chance of having a son with X-linked ocular albinism. For specific information, families should seek the advice of a qualified genetic counselor.
Oculocutaneous Albinism (OCA, involves the lack of pigment in the hair, skin and eyes. Each parent must carry the gene for this form which follows an autosomal recessive inheritance pattern, meaning there is a one in four chance at each pregnancy that the baby will be born with albinism. Within OCA there are two primary types of albinism.
Type 1 (formerly known as Tyrosinase Negative) involves the complete lack of pigment. These children have white skin and hair and moderate to severe visual impairment. Children with
Type 2 (formerly known as Tyrosinase Positive) have various amounts of pigmentation, yellow or blonde hair and usually less severe visual impairment.
Secondary OCA
The appearance of albinism may indicate the presence of other rare conditions that require special management. Hermansky-Pudlak Syndrome (HPS) involves a platelet defect that results in susceptibility to bleeding and bruising. Aspirin and aspirin-like drugs should be avoided, as they may convert a mild bleeding disorder into a severe one. HPS can be identified by a specialized test involving electron microscopy of the platelets. Chediak-Higashi Syndrome is associated with a white blood cell problem leading to a susceptibility to bacterial infections. Prior to a surgical procedure for persons with these rare forms of albinism, specific tests for bleeding dysfunction and white blood cell abnormalities should be performed.
Albinism, oculocutaneous: An hereditary disorder characterized by deficiency of the pigment melanin in the eyes, skin and hair. The lack of eye pigment causes photophobia (sensitivity to light), nystagmus, and decreased visual acuity.
Oculocutaneous albinism is conventionally classified as to whether it is tyrosinase-negative or tyrosinase-positive. In the tyrosinase-negative class, there is absence of the enzyme tyrosinase. In the tyrosinase-positive class, tyrosinase is present but it cannot enter pigment cells to do its job and make melanin.
There are a number of specific types of oculocutaneous albinism, all of which are inherited in an autosomal recessive manner:
* Type IA is characterized by absence of tyrosinase with complete absence of melanin, marked photophobia, and nystagmus. It is due to mutation of the tyrosinase gene (TYR) on chromosome 11q.
* Type IB has reduced activity of tyrosinase. It has been called yellow albinism. The child looks "dead white" at birth and has the usual eye problems, but soon develops normal skin pigmentation and yellow hair.
* Type II has normal tyrosinase activity. It is the most common type of oculocutaneous albinism. The hair darkens and freckles and nevi (moles) develop normally on the skin. The disorder is due to mutation of the oculocutaneous albinism gene (OCA2) on chromosome 15q.
* Type III is characterized by absence of tyrosinase with the presence of pigmentation of the iris in the first decade of life. It is due to mutation of the tyrosine-related protein-1 gene (TYRP1) on chromosome 9p.
* Type IV is characterized by normal tyrosinase and is due to mutation of the MATP gene on chromosome 5p. MATP stands for membrane-associated transporter protein.
Hermansky-Pudlak syndrome: Abbreviated HPS. A genetic disorder characterized by albinism (with lack of pigment in the skin or eye), bruising and prolonged bleeding (due to defective blood platelets), and fibrosis of the lungs. There is occasionally also inflammatory bowel disease and impaired kidney function. All HPS patients suffer from varying degrees of albinism. The lack of pigment in the eye impairs their vision and often leads to involuntary rhythmic eye movements called nystagmus. The most serious health problems in HPS are the tendency to bruise easily and bleed and the progressive deterioration in lung function.
The reason HPS patients bleed too easily is that their blood platelets are deficient in so-called dense bodies. These subcellular organelles release their contents to make other platelets stick together and form a clot. Without dense bodies, the time needed for a clot to form is abnormally slow. Women with HPS may therefore need medical intervention during their menstrual cycles or at childbirth. HPS patients are advised to avoid blood anticoagulants such as aspirin. Drugs are needed to prevent excessive bleeding during dental extractions and other surgical procedures. Inflammatory bowel disease with the onset of symptoms between 10 and 30 years of age can complicate HPS and usually responds poorly to therapy. The lung problems in HPS begin with restrictive disease and then progress inexorably to death, usually in the fourth or fifth decade.
HPS patients have a biochemical storage disorder. They accumulate a fatty product called ceroid lipofuscin. This causes inflammation in tissues such the lungs. Prolonged inflammation leads to fibrosis, which in the case of the lung impairs its ability both to expel air and to exchange carbon dioxide for oxygen.
HPS is inherited as an autosomal recessive condition. HPS occurs in many countries. It is especially common in certain areas in the Swiss Alps and Puerto Rico. In NW Puerto Rico, 1 in every 1800 individuals is affected with HPS and 1 in 21 persons carries the HPS gene. HPS is genetically heterogenous. It is not a single genetic entity. Mutations in different genes on different chromosomes are now known to lead to HPS. Gene loci for HPS have been identified on chromosomes 3, 5 and 10. Puerto Ricans with HPS have been found to have mutations in the HPS1 gene and, less often, in the HPS3 gene. Only half of individuals with HPS not from Puerto Rico have mutations in HPS1 and very few do in HPS3; and a number have mutations in another locus, HPS4.
Patients with HPS2 have mutations in a protein called AP-3, which is involved in directing the movement of proteins inside cells. AP-3 is needed by T cells to kill infected cells. T cells deficient in AP-3 due to HSP-2 cannot kill target cells. The lytic granules required for killing fail to move towards the contact site between the T cell and the target cell. AP-3 therefore appears to be involved in mediating granule movement inside killer T cells.
The syndrome was first described in 1959 and is named after its discoverers, the Czech internists F. Hermansky and P. Pudlak who described 2 unrelated albinos with a lifelong bleeding tendency and peculiar pigmented cells in the bone marrow. One patient was male and the other female, both 33 years old.
HPS is also known as albinism with hemorrhagic diathesis and pigmented reticuloendothelial cells and as delta-storage pool disease.
DIAGNOSIS
The diagnosis of albinism can be challenging. If albinism is suspected, concerns should be communicated to the pediatrician who will refer the family to a pediatric ophthalmologist. If a child has OCA, diagnosis will often be based first on the fair color of the child's skin and hair. A diagnosis of albinism may be suspected when a child develops rhythmic, involuntary eye movements (nystagmus) within the first few weeks of life and the eye exam identifies:
* if light passes through the iris (transillumination)
* the underdevelopment of the central retina (foveal hypoplasia), and
* the absence of melanin pigment in the eye.
While hair bulb testing has been used as a diagnostic test for albinism in the past, newer, more accurate genetic tests are now available for diagnosis, classification, and prenatal genetic counseling. The visual evoked potential test (VEP), designed to identify the misrouting of retinal fibers of the optic nerve, can be valuable in providing a specific diagnosis.
CHARACTERISTICS
* Low Vision (visual acuity between 20/50 and 20/800)
* Sensitivity to bright light and glare (photophobia)
* Rhythmic, involuntary eye movements (nystagmus)
* Absent or decreased pigment in the skin and eye and sensitivity to sunburn (ultraviolet light) that could lead to skin cancers or cataracts in later life
* "Slowness to see" in infancy
* Farsighted, nearsighted, often with astigmatism
* Underdevelopment of the central retina (foveal hypoplasia)
* Decreased pigment in the retina (blonde fundus)
* Inability of the eyes to work together (absence of stereo vision)
* Misrouting of the nerve pathways from the retina to the brain
* Light colored eyes ranging from lavender to hazel, with the majority being blue
* Strabismus, with both vertical and horizontal deviations
VISUAL AND BEHAVIORAL CHARACTERISTICS
* Infants with albinism may behave as if they are not seeing during the first weeks of life and gradually become visually attentive. This is now a well-documented condition.
* Additional energy and effort a child uses to process visual information can cause fatigue and irritability, worsening nystagmus.
* Children typically exhibit an eye and/or head position that allows them to slow down or stop their nystagmus (null point).
* Children may use one eye at a time for looking.
* They may have an absence of stereo vision contributing to depth perception problems.
* Children bring objects close to their eyes to see more clearly.
* Even with glasses or contacts, vision will not correct to normal.
* Occasionally a child's eyes will look pink or red due to a reflection on the back of the eye (retina).
* The following environmental factors can have a significant influence on the child's ability to see: changes in lighting from various light sources, the position of the light source, and glare from reflecting surfaces. Looking directly into a bright light or window creates a silhouetting effect, diminishing the ability to see detail. Children are also slow to adjust to changes in lighting, such as from outdoors to indoors or sunny light to shadows.
MYTHS
The following statements are NOT TRUE, according to current knowledge in the field:
* Persons with albinism always have red eyes.
* Persons with albinism are totally blind.
* Albinism is contagious.
* Persons with albinism are the result of evil spirits or wrongdoing.
* Persons with albinism are retarded or deaf.
* Albinism results from inbreeding or the mixture of two races.
* Persons with albinism have magical powers.
SOCIAL AND EMOTIONAL ISSUES
Persons with albinism often have quite normal lives. The support of family, teachers, and friends is crucial in order for a child with albinism to grow up with a positive self image. Sometimes, however, the appearance of the person with albinism becomes a focus, rather than the individual. A person with albinism may try to minimize the differences caused by albinism, resulting in a great deal of stress at continually trying to maximize visual ability and/or denying altogether that one even has albinism. Families of children with albinism may experience prejudice, rejection, or frustration. They may become caught in isolation and denial. As well, the myths related to albinism can interfere with the family's free discussion of the condition.
TEACHING STRATEGIES
* Since not all children with albinism have the same visual acuity or use their vision with the same efficiency, it is important to consider each child as an individual.
* Early and ongoing assessment of the child's vision is crucial. As children progress through the educational system, they face increased visual demands and smaller print size and thus can benefit from suitable magnifiers, telescopes, or large print materials.
* It is important that the child, parent, teacher, vision resource teacher, ophthalmologist, and optometrist work as a team. The team should consider positioning, seating, lighting, glare, toys and materials, along with social/emotional growth of each child.
* The condition of "slowness to see" calls for an approach that uses all the senses for learning (multisensory) with the very young child.
* Allow the child to use the head and eye position that is comfortable and works the best.
* Provide good indirect lighting or position a light source behind the child. Never position a child directly facing the light source. Also, parents or teachers should always position themselves so that the child is not looking toward a light source.
* A child who may be poorly organized may benefit from predictable environments and routines.
* A child should be able to hold toys and objects as close as he would like and should be allowed to move to the most advantageous viewing position.
* A careful "walk-through" of the house or classroom will identify the areas of highest glare. Using indoor lighting, even during the day, can equalize lighting from indoor and outdoor sources and reduce the effects of glare on the eyes. A hat or visor can eliminate glare from overhead lighting.
* To compensate for missed nonverbal cues such as facial expression, and everyday social gestures, etc., a child should be given verbal and/or tactual information.
* Lack of depth perception can be compensated for by learning to use information from the environment. Provide a child with repeated opportunities for exploration and movement in a variety of settings and lighting conditions.
* When the environment makes it difficult to see, a child must learn to rely on other senses. Bright glare from snow, sand, water, or pavement, or dappled light where sun and shadows continually change, can reduce a child's visual world.
* Open discussion and support at home for a child with albinism encourages him to acknowledge his feelings and to begin the process of self-advocacy.
* The following qualities make a significant difference in the child's ability to see printed materials:
o High contrast Uncluttered background
o Well defined pictures
o Large print Primary colors
GLOSSARY
1. Electron Microscopy: examination by a microscope which uses a beam of electrons to form an enlarged image of a specimen.
2. Platelets: one of three types of blood cells. The platelet is the smallest cellular element of the blood and is needed for proper clotting.
3. Refractive Error: an eye defect that causes decreased visual acuity.
4. Stereo Vision: the perception of objects in space and their relative position to one another.
5.HPS is also known as albinism with hemorrhagic diathesis and pigmented reticuloendothelial cells and as delta-storage pool disease.
RESOURCES
Haefemeyer, J. (1997). Visual Problems in Albinism, NOAH News, Winter.
Haefemeyer, J. (1996). X-Linked Ocular Albinism Researched, NOAH News, Winter.
Haefemeyer, J., Kind, R., LeRoy, B. (1992). Facts About Albinism
Johnson Printing Company (1996). Transactions of the American Ophthalmological Society Annual Meeting -1996.
King, R. A., Summers CG. (1988). Albinism, Dermatologic Clinics, 6,217-227.
Kinnear, P., Barrie, J., Witkop, C. (1985). Albinism, Survey of Ophthalmology, 30 (2),75-101.
Waugh, J. (1990). Social and Emotional Aspects of Albinism, NOAH News, Spring.
Moore, Dennis (1991). Another View: Albino vs. Person With Albinism, NOAH News, Spring.
National Organization for Albinism and Hypopigmentation (1992). Assisting Students with Albinism, NOAH pamphlet.
National Organization for Albinism and Hypopigmentation (1992). What is Albinism, NOAH pamphlet. NOAH, 1530 Locust St. #29, Philadelphia, PA 19102, 1-800-473-2310
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