Albinism

December 31, 2014

Synonyms

Overview

Albinism is a group of inherited disorders that results in little or no production of the pigment melanin, which determines the color of the skin, hair and eyes due to absence or defect of tyrosinase, a copper-containing enzyme involved in the production of melanin. Melanin also plays a role in the development of certain optical nerves, so all forms of albinism cause problems with the development and function of the eyes. It is the opposite of melanism. Unlike humans, other animals have multiple pigments and for these, albinism is considered to be a hereditary condition characterised by the absence of melanin in particular, in the eyes, skin, hair, scales, feathers or cuticle.

Symptoms

Other symptoms can include light skin or changes in skin color; very white to brown hair; very light blue to brown eye color that may appear red in some light and may change with age; sensitivity to sun exposure; and increased risk of developing skin cancer.

In humans, there are two principal types of albinism: oculocutaneous, affecting the eyes, skin and hair, and ocular affecting the eyes only.

Most people with oculocutaneous albinism appear white or very pale, as the melanin pigments responsible for brown, black, and some yellow colorations are not present. Ocular albinism results in light blue eyes,and may require genetic testing to diagnose.

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 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 afflicted 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.

Visual problems

Development of the optical system is highly dependent on the presence of melanin, and the reduction or absence of this pigment in sufferers of albinism may lead to:

Misrouting of the retinogeniculate projections, resulting in abnormal decussation (crossing) of optic nerve fibres
Photophobia and decreased visual acuity due to light scattering within the eye (ocular straylight)
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.

Some of the visual problems associated with albinism arise from a poorly developed retinal pigment epithelium (RPE) due to the lack of melanin.This degenerate RPE causes foveal hypoplasia (a failure in the development of normal foveae), which results in eccentric fixation and lower visual acuity, and often a minor level of strabismus.

The iris is a sphincter formed from pigmented tissue that contracts when the eye is exposed to bright light, to protect the retina by limiting the amount of light passing through the pupil. In low light conditions, the iris relaxes to allow more light to enter the eye. In albinistic subjects, the iris does not have enough pigment to block the light, thus the decrease in pupil diameter is only partially successful in reducing the amount of light entering the eye. Additionally, the improper development of the 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 and/or brimmed hats.

Causes

Albinism is caused by a mutation in one of several genes and most types are inherited in an autosomal recessive manner. Each of these genes provides instructions for making one of several proteins involved in the production of melanin. Melanin is produced by cells called melanocytes, which are found in your skin and eyes. A mutation may result in no melanin at all or a significant decline in the amount of Melanin.

Prevention

If a family member has albinism, a genetic counselor can help to understand the chances of having a future child with albinism.

Diagnosis

Genetic testing can confirm albinism and what variety it is, but offers no medical benefits except in the cases of non-OCA disorders that cause albinism along with other medical problems which may be treatable. There is no 'cure' for Albinism. The symptoms of albinism can be assisted by various methods detailed in treatment chapter.

Prognosis

The prognosis is largely positive. Albinism does not affect the lifespan of the Person. However, persons suffering from Hermansky-Pudlak syndrome (a type of albinism) can developpe bleeding problems and lungs diseases and therefore tend to have shorter life spans.

Treatment

Although there's no cure, people with the disorder can take steps to improve vision and avoid too much sun exposure. This can be done by

avoiding prolonged exposure to the sun,
using sunscreen with a high SPF rating (20 or higher),
covering up completely with clothing when exposed to the sun,
wearing sunglasses with UV protection.

It is managed through lifestyle adjustments. People with Albinism need to take care not to sun-burn and should have regular healthy skin checks by a dermatologist. Individuals with vision problems may need corrective lenses. They should also have regular follow-up exams with an ophthalmologist.

For the most part, treatment of the eye conditions consists of visual rehabilitation. Surgery is possible on the extra-ocular muscles to decrease strabismus.Nystagmus-damping surgery can also be performed, to reduce the "shaking" of the eyes back and forth.The effectiveness of all these procedures varies greatly and depends on individual circumstances.

Glasses and other vision aids, large-print materials as well as bright but angled reading lights, can help individuals with albinism, even though their vision cannot be corrected completely. Some people with albinism do well using bifocals (with a strong reading lens), prescription reading glasses, and/or hand-held devices such as magnifiers or monoculars.

Albinism is often associated with the absence of an iris in the eye. Contact lenses may be colored to block light transmission through the aniridic eye. Some use bioptics, glasses which have small telescopes mounted on, in, or behind their regular lenses, so that they can look through either the regular lens or the telescope. Newer designs of bioptics use smaller light-weight lenses. Some US states allow the use of bioptic telescopes for driving motor vehicles. (See also NOAH bulletin "Low Vision Aids").