Every cell in the body contains a matched pair
of genes, one inherited from each parent. These genes act as a
sort of "blueprint" that guides the development of a
fetus.
Albinism is an inherited problem caused by a flaw
in one or more of the genes that are responsible for directing
the eyes and skin to make melanin (pigment). As a result, little
or no pigment is made, and the child's skin, eyes and hair may
be colorless.
In most types of albinism, a recessive trait,
the child inherits flawe d genes for making melanin from both
parents. Because the task of making melanin is complex, there
are many different types of albinism, involving a number of different
genes.
It's also possible to inherit one normal gene
and one albinism gene. In this case, the one normal gene provides
enough information in its cellular blueprint to make some pigment,
and the child will have normal skin and eye color. They "carry"
one gene for albinism. About one in 70 people are albinism carriers,
with one flawed gene but no symptoms; they have a 50% chance of
passing the albinism gene to their child. However, if both parents
are carriers with one flawed gene each, they have a 1 in 4 chance
of passing on both copies of the flawed gene to the child, who
will have albinism. (There is also a type of ocular albinism that
is carried on the X chromosome and occurs almost exclusively in
males because they have only one X chromosome and, therefore,
no other gene for the trait to override the flawed one.)
Symptoms of albinism can involve the skin, hair,
and eyes. The skin, because it contains little pigment, appears
very light, as does the hair.
Although people with albinism may experience a variety of eye
problems, one of the myths about albinism is that it causes people
to have pink or red eyes. In fact, people with albinism can have
irises varying from light gray or blue to brown. (The iris is
the colored portion of the eye that controls the size of the pupil,
the opening that lets light into the eye.) If people with albinism
seem to have reddish eyes, it's because light is being reflected
from the back of the eye (retina) in much the same way as happens
when people are photographed with an electronic flash.
People with albinism may have one or more of the following
eye problems:
They may be very far-sighted or near-sighted,
and may have other defects in the curvature of the lens of the
eye (astigmatism) that cause images to appear unfocused.
They may have a constant, involuntary movement
of the eyeball called nystagmus.
They may have problems in coordinating the eyes
in fixing and tracking objects (strabismus), which may lead to
an appearance of having "crossed eyes" at times.
Strabismus may cause some problems with depth
perception, especially at close distances.
They may be very sensitive to light (photophobia)
because their irises allow "stray" light to enter their
eyes. It's a common misconception that people with albinism shouldn't
go out on sunny days, but wearing sunglasses can make it possible
to go outside quite comfortably.
In addition to the characteristically light skin
and eye problems, people with a rare form of albinism called Hermansky-Pudlak
Syndrome (HPS) also have a greater tendency to have bleeding disorders,
inflammation of the large bowel (colitis), lung (pulmonary) disease,
and kidney (renal) problems.