Albinism


The word "albinism" refers to a group of inherited conditions. People
with albinism have little or no pigment in their eyes, skin, or hair. They have
inherited genes that do not make the usual amounts of a pigment called melanin.
One person in 17,000 has some type of albinism. Albinism affects people from all
races. Most children with albinism are born to parents who have normal hair and
eye color for their ethnic backgrounds. Albinism is found on the eleventh
chromosome, section q, loci 14-21.
Oculocutaneous albinism involves the eyes, hair, and skin. Ocular albinism
involves primarily the eye. People with ocular albinism may have slight
lightening of hair and skin colors as well, compared to other family members. At
present researchers have found 10 different types of oculocutaneous albinism,
and five types of ocular albinism. Newer laboratory research studying DNA has
shown that there are numerous types of changes in the genes of those with
albinism, including within families.
The most common types of oculocutaneous albinism are called "ty-negative"
and "ty-positive". Persons with ty-negative albinism have no melanin
pigmentation, and more difficulty with vision. Those with ty-positive albinism
have very slight pigmentation, and generally less severe visual difficulties.
Tests were done on the hair roots of individuals with albinism, to tell these
types of albinism apart. However, these hair tests cannot identify types of
albinism, particularly in young children, whose pigment systems are immature.
Therefore hair tests are not helpful in predicting the extent of visual
disability of a child.
"Ty-Neg" (also called Type 1A) albinism results from a genetic defect in
an enzyme called tyrosinase. Tyrosinase helps the body to change the amino acid
tyrosine into pigment. The genetic defect that causes albinism in other types of
albinism is unknown, but it is speculated that it involves other enzymes used to
make pigment.
Albinism is passed from parents to their children through genes. For
nearly all types of albinism both parents must carry an albinism gene to have a
child with albinism. Parents may have normal pigmentation but still carry the
gene. When both parents carry the gene, and neither parent has albinism, there
is a one in four chance at each pregnancy that the baby will be born with
albinism. This type of inheritance is called autosomal recessive inheritance.
If a parent has a child with albinism, it means the parent must carry
the albinism gene. Until recently, unless a person has albinism or has a child
with albinism, there was no way of knowing whether he or she carries the gene
for albinism. Recently a test has been developed to identify carriers of the
gene for ty-negative albinism and for other types in which the tyrosinase enzyme
does not function. The test uses a sample of blood to identify the gene for the
tryrosinase enzyme by its DNA code. A similar test can identify ty-negative or
similar albinism in unborn babies, by aminiocentesis.
People with albinism have very normal lives. They play sports, have
normal intelligence, and can have babies. The only difference between normal
people and albino is that they don\'t have pigment in their skin.

Category: Science