An organism lacking the pigmentation normal to its kind.
Depending on the type of albinism, the skin
and hair of albino animals (including humans)
may be uncolored while the irises of the
eyes appear pink. Albinism, which may be total or only partial, is generally
inherited. Albino plants contain no chlorophyll
and thus, being unable, to perform photosynthesis,
|A female and male both carrying a recessive
gene (green) for albinism (A) will have three normally pigmented children
(B, D, and E) to every one albino (C). The corresponding normal gene
(orange or purple) in both produces normal skin color. This is due
to an amino acid phenylalanine
(1), which has been converted to tyrosine
and then to the pigment melanin. However, a recessive gene in double
quantity only allows the conversion of phenylalanine to tyrosine (F)
resulting in albinism.
Albinism in humans and other animals occurs when one of several genetic
defects makes the body unable to produce or distribute melanin,
a natural substance that gives color to the hair, skin, and iris of the
eye. The defects may be passed down through families.
There are two main types of albinism:
The most severe form of albinism is called oculocutaneous
albinism. People with this type of albinism have white or pink
hair, skin, and iris color, as well as vision problems.
- Type 1 albinism is caused by defects that affect production
- Type 2 albinism is due to a defect in the "P" gene. People with this
type have slight coloring at birth.
Another type of albism, called ocular albinism type 1 (OA1),
affects only the eyes. The person's skin and eye colors are usually in the
normal range. However, an eye exam will show that there is no coloring in
the retina, at back of the eye.
Hermansky-Pudlak syndrome (HPS) is a form of albinism caused
by a single gene. It can occur with a bleeding disorder, as well as with
lung and bowel diseases.
Other complex diseases may lead to loss of coloring in only a certain area
(localized albinism). These conditions include:
- Chediak-Higashi syndrome (lack of coloring all over
the skin, but not complete)
- Tuberous sclerosis (small areas without skin coloring)
- Waardenburg syndrome (often a lock of hair that grows
on the forehead, or no coloring in one or both irises)
Source: MedLine Plus (US National Library
of Medicine & NIH)