Albinism

background

Albinism refers to a group of inherited conditions marked by decreased or absent pigmentation (coloring) of the skin, hair, and eyes. In some cases, albinism includes other eye problems, such as decreased vision, sensitivity to light, involuntary eye movements, problems with the iris (the colored part of the eye), and decreased pigment in the retina (the cells at the back of the eye that detect light).
Albinism is an inherited condition, meaning that it is passed from parents to children. Individuals receive two copies of most genes, one from the mother and one from the father. Albinism is caused by mutations in genes that provide instructions for making melanin, the pigment that provides color to hair, skin, and eyes. Melanin also absorbs ultraviolet light from the sun to protect the skin. Because melanin is absent or decreased, people with albinism are at increased risk of skin damage caused by the sun.
Because different mutations affect the production of melanin in slightly different ways, the type of albinism is determined by the specific genetic mutation that is present. The different types of albinism include oculocutaneous albinism (OCA) types 1, 2, 3, and 4; ocular albinism (OA); Chediak-Higashi syndrome (CHS); Hermansky-Pudlak syndrome (HPS); and Griscelli syndrome (GS).
The worldwide prevalence of OCA type 1 is about one in 40,000. The worldwide prevalence of OCA type 2 is about one in 15,000. The worldwide prevalence of OCA type 3 is unknown. OCA type 4 is extremely rare, except in Japan, where it accounts for about 24% of cases of OCA. The worldwide prevalence of OA is about one in 50,000. CHS and GS are extremely rare, with unknown prevalence. HPS is rare, except in Puerto Rico, where its prevalence is about one in 1,800.
Albinism generally affects males and females in equal numbers. One exception is OA, which is far more common in males. Albinism generally affects people of all races and ethnicities equally. Exceptions include OCA type 2, which is more common among Africans and African-Americans than among Caucasians, and OCA type 3, which has been confirmed only in Africans and African-Americans.
Most people with albinism live long, normal lives. OCA types 1, 2, 3, and 4 are not associated with premature death, and complications are typically limited to skin and vision problems.
People with CHS may bruise and bleed easily and are prone to lung and sinus infections. About 85% of people with CHS experience severe complications and may die by age 10. People with HPS often have bleeding problems, lung problems, heart conditions, and kidney problems. Lung problems often cause death by the fourth or fifth decade of life. People with GS have weakened immune systems and typically die from infections during the first decade of life.

Related Terms

AIED, Aland Island eye disease (X-linked), albinism, albinoidism, albinoism, autosomal dominant albinism, autosomal recessive forms of ocular albinism, black locks-albinism-deafness of sensoneural type (BADS), brown albinism, Chediak-Higashi syndrome, congenital achromia, Cross syndrome, Forsius-Eriksson syndrome (X-linked), Hermansky-Pudlak syndrome, hypopigmentation, Nettleship Falls syndrome (X-linked), ocular albinism, oculocutaneous albinism, rufous albinism, tyrosinase negative albinism (type I), tyrosinase positive albinism (type II), yellow mutant albinism.

types of the disease

General: The type of albinism is determined based on the specific genetic mutation that is present. The different types of albinism include oculocutaneous albinism (OCA) types 1, 2, 3, and 4; ocular albinism (OA); Chediak-Higashi syndrome (CHS); Hermansky-Pudlak syndrome (HPS); and Griscelli syndrome (GS).
Oculocutaneous albinism type 1: OCA type 1 is caused by mutations in the tyrosinase (TYR) gene. This gene provides instructions for making an enzyme necessary for the production of melanin. OCA type 1 is inherited as an autosomal recessive trait. People who have OCA type 1 have white hair, milky white skin, and blue eyes.
OCA type 1 is divided into two subtypes: type 1A and type 1B. OCA 1A, also known as classic tyrosinase-negative OCA, is the most severe form of OCA. People with OCA 1A have white hair and skin and blue eyes. These individuals are at high risk of sunburn and skin cancer. People with OCA 1A have extremely poor vision. In addition, sensitivity to light and involuntary movement of the eyes can be severe in this form of OCA.
OCA type 1B is also called yellow mutant OCA, Amish albinism, or xanthous albinism. Although they are typically born with complete lack of pigment, individuals with OCA 1B may have pigmentation that ranges from very little to near normal. People with OCA 1B tend to show more pigment during the first few years of life, with yellow hair pigment and eyelashes that may be darker than the hair on the scalp. The eyes may be hazel or light brown. Vision may be moderately impaired and may improve with age. People with OCA 1B may also develop nevi, harmless pigmented lesions on the skin.
A subtype of OCA 1B is temperature-sensitive OCA 1B. In this form of OCA, the enzyme involved in melanin creation has different activity in different parts of the body depending upon their temperature. Melanin is produced in cooler areas of the body; therefore, the arms and legs tend to have darker pigment, whereas warmer parts of the body (i.e., those closer to the heart) do not have melanin activity and are therefore lighter in color.
Oculocutaneous albinism type 2: OCA type 2 is the most common type of albinism in all races and is caused by mutations in the P gene. The P gene provides instructions for making a protein essential to the production of melanin, although its exact role is not yet known. OCA type 2 is inherited as an autosomal recessive trait. Most people with OCA type 2 do not have any black pigment in the skin, hair, or eyes at birth. Pigmentation and vision may improve with age.
Caucasians with OCA type 2 may have a range of pigmentation at birth. The hair may be light yellow or dark blond. The skin tends to be white and does not tan. The eyes tend to be blue-gray. Africans and African-Americans with OCA type 2 usually have yellow hair at birth that remains this color throughout life. The skin is white and does not tan, and the eyes are blue-gray.
A subtype of OCA type 2 is brown OCA, which is seen only in Africans and African-Americans. In this type of OCA, the skin and hair are light brown and the eyes are gray. Hair and eye color may darken with time.
Oculocutaneous albinism type 3: OCA type 3 is caused by mutations in the tyrosinase-related protein-1 (TRP1) gene. This gene provides instructions for making a protein essential to the production of melanin, although its exact role is not yet known. OCA type 3 is inherited as an autosomal recessive trait and may be referred to as red, rufous, or xanthous albinism. In this form of OCA, black pigment is typically replaced with brown pigment. African people with OCA type 3 tend to have light brown or reddish skin and hair and blue-brown eyes. People with this type of OCA may also have eye problems.
Oculocutaneous albinism type 4: OCA type 4 is caused by mutations in the membrane-associated transporter protein (MATP) gene. The function of the protein created by this gene is not clear. OCA type 4 is inherited as an autosomal recessive trait. OCA type 4 may be the most common form of albinism seen in people from Japan and Korea. However, information concerning this type of OCA is currently limited.
Ocular albinism: OA is caused by mutations in the OA1 gene (also called GPR143), which is located on the X chromosome. The role of the protein created by the OA1 gene is currently unknown. OA is an X-linked recessive trait that primarily affects the eyes. Eye problems are similar to those seen in OCA. Males are primarily affected by OA, because a female must carry the genes on both X chromosomes in order to have the condition. People with this type of albinism are often identified by the presence of macromelanosomes, which are dense collections of melanin in the skin that can be detected with a biopsy.
Chediak-Higashi syndrome (CHS): CHS is caused by mutations in the LYST gene (also known as the CHS1 gene). This gene provides instructions for making a protein important for the normal functioning of melanin cells. CHS is inherited as an autosomal recessive trait. People with CHS are at an increased risk of infections, especially of the lungs, nose, sinuses, and throat. Hair, skin, and eye pigment tends to be reduced, but albinism is not obvious. The hair may be light brown to blonde in color and have a metallic sheen, the skin may be creamy white to gray, and eye problems are variable.
Hermansky-Pudlak syndrome (HPS): HPS is caused by mutations in the HPS gene. There are eight distinct types of HPS, all of which are inherited as autosomal recessive traits. People with HPS have pigmentation that ranges from none to near normal. Other symptoms include involuntary eye movements, crossed eyes, underdevelopment of part of the retina, and decreased vision. Abnormal bleeding may occur in infants with HPS (in males, this is often discovered at the time of a circumcision). Throughout life, people with HPS are more susceptible to bleeding and bruising. Later in life, people with HPS may experience lung problems, inflammatory bowel disease, kidney problems, and a heart condition called cardiomyopathy.
Griscelli syndrome (GS): GS is caused by mutations in the RAB27A gene, which provides instructions for making the GTP-binding protein RAB27a, and the MYO5A gene, which provides instructions for making the myosin motor protein myosin 5a. These proteins are important for the proper production and transport of melanin. GS is inherited as an autosomal recessive trait. People with GS tend to have a milder form of albinism, with pale skin and silvery gray hair at birth.