Albinism - types, symptoms, causes and treatment
Albinism is a genetic disorder in which the melanocytes do not produce, or produce reduced amounts of, melanin, the chemical that deposits pigment in cells of the SKIN, HAIR, and structures of the EYE. Without melanin, the skin, eyes, and hair have little or no pigment and consequently lack color. People who have albinism typically have light to white skin and hair, and light or no color to the irises of the eyes (the pigmented rings around the center of the eyes). Albinism reduces or eliminates the skin’s ability to protect itself from exposure to ultraviolet light, greatly increasing the risk for damage such as SUNBURN and SKIN CANCER.
The lack of pigmentation characteristic of albinism extends to the interior of the eye as well, resulting in VISION IMPAIRMENT. In the normal eye the RETINA, the inner lining of the back of the eye that receives light images and encodes them as NERVE signals for the OPTIC NERVE to carry to the BRAIN, is highly pigmented such that it appears black. The pigment suppresses extraneous light and supports the functions of rods and cones, the specialized cells of vision that line the retina. Without the protection of pigment, unfocused lightwaves bombard the retina. The brain cannot sort the resulting nerve signals into images and consequently fails to properly establish the neurologic pathways that make vision (the interpretation of patterns of light as images) possible.
There are a number of INHERITANCE PATTERNS for albinism, nearly all of which are recessive (require a defective pigmentation GENE from each parent). Researchers have identified several types of gene mutations that cause most forms of albinism.
Oculocutaneous albinism (OCA)
The three types of OCA involve the skin, hair, and eyes to varying degrees.
- OCA type 1 results from a MUTATION of the gene that encodes tyrosinase, an enzyme necessary to convert the essential amino acid tyrosine to melanin. OCA type 1 features nearly complete absence of pigmentation and usually legal blindness (refractive correction can achieve vision no better than 20/200).
- OCA type 2 results from a mutation of the P gene, which encodes proteins that participate in pigmentation. OCA type 2 features moderate pigmentation and moderate vision impairment (usually correctable to 20/60).
- OCA type 3 results from a mutation of the TRP-1 gene, which encodes proteins that have incompletely understood roles in the formation of pigment.
Ocular albinism (OA)
Ocular albinism results from an X-linked mutation of an as-yet unidentified gene. People who have OA have normal or minimally affected skin and hair pigmentation but lack pigment in the structures of the eye, resulting in vision impairment.
Other forms of albinism
Other forms of albinism are less common or may be part of a larger complex of symptoms. Among them are
- Chédiak-Higashi syndrome (CHS), a variation of OCA in which there are also immune and neurologic dysfunctions
- Hermansky-Pudlak syndrome (HPS), a multisystem disorder that involves PLATELET dysfunction resulting in excessive bleeding, vision impairment, and inappropriate fat storage in tissues throughout the body as well as absence of pigmentation in the skin and hair
- Waardenburg’s syndrome, a complex of symptoms involving HEARING LOSS and partial albinism (often a lock of white hair in the front of the head with the rest of the hair normal color); people with this disorder may also have pale blue eyes or different color in each eye
Symptoms of Albinism and Diagnostic Path
The most obvious symptom of albinism, pale coloration of the skin and hair, is apparent at birth. Light-colored eyes and vision problems such as STRABISMUS (inability of the eyes to focus in unison), NYSTAGMUS (involuntary rapid eye movements), and PHOTOPHOBIA (extreme sensitivity to light) are common and also manifest early in infancy.
The characteristic absence of pigmentation is fairly conclusive for diagnosis of albinism. A thorough OPHTHALMIC EXAMINATION with OPHTHALMOSCOPY reveals the retina’s hypopigmentation. A VISUAL ACUITY test demonstrates the degree of vision impairment. GENETIC TESTING can identify the causative gene mutation, which helps define the inheritance pattern.
Albinism Treatment Options and Outlook
There are no treatments for albinism itself. CORRECTIVE LENSES and methods to correct strabismus or nystagmus, if present, can improve vision to the extent possible. Many people who have albinism have functional vision, even if they have legal blindness, and can participate in most activities that require basic vision though may not be able to drive.
Albinism, particularly OCA type 1, may limit outdoor activities in areas that receive intense sunlight. The sun presents a risk for sunburn and related damage as well as harm to the eyes. Photophobia nearly always accompanies albinism and can make it difficult to remain in bright light, even wearing sunglasses, for any substantial length of time. People who have albinism should wear protective clothing, sunglasses, hats, and high-SPF sunscreen whenever they are outdoors.
Albinism Risk Factors and Preventive Measures
The sole risk factor for albinism is genetic mutation. Doctors recommend genetic testing and counseling for families in which members have albinism. Though there is no treatment for albinism, early diagnosis helps minimize the extent of vision impairment that may result from nystagmus or strabismus. People who have albinism also should undergo frequent screening for skin cancer, beginning in childhood.
See also AMBLYOPIA; MELANOCYTE.
