Melanin Production in Cells
If you stood at the shoulder of a doctor examining someone with albinism, you'd find that most everything -- the brain (except for vision centers), heart, lungs, digestive system, muscles and immune system -- looked healthy. Lifespan, except in untreated skin cancer, is unchanged. Intelligence is also unaffected.
That said, you might want to think of albinism as a manufacturing problem. The problem starts in the melanocytes -- cells located in several places throughout the body. They are located in:
- the bottom layer of the skin's epidermis
- the uvea, the part of the eye containing the iris and other nearby tissues
- the inner ear
- the leptomeninges, a membrane around the brain and spinal cord
- hair follicles
Generally, people with albinism have a problem with melanin production along the way.
Melanocytes manufacture melanin. Manufacturing begins when melanocytes, following instructions in DNA, construct melanin-making enzymes -- you can think of these as production-line workers -- and the amino acid tyrosine. Production happens inside sacs called melanosomes. Melanosomes take in the enzymes and tyrosine. Inside melanosomes, the enzymes, acting as catalysts within the cells, begin a long series of chemical reactions in order to convert tyrosine into the two types of melanin humans have. These are eumelanin, which is brown or black, and pheomelanin, which is red or yellow. Once melanosomes are packed with melanin, melanocytes ship them away -- to keratinocytes, barrier cells in the topmost layer of the skin and the iris in the eye -- and into our hair. How many are shipped, and the mix of pigments carried, determine our baseline skin, eye and hair colors. When melanocytes in the hair follicles don't make enough melanin, hair color can range from white, to yellow, to brown. This has no health consequences [source: King et al].
As the sun beats down on our skin, cells are hard at work protecting it from the heat and from harmful ultraviolet rays. Inside the keratinocytes, melanosomes respond to this assault in a curious way: They cover the nucleus like a beach umbrella, protecting the DNA. Ultraviolet rays can damage DNA and other cell parts, but melanin absorbs the rays. For people with albinism, there are not enough melanosomes available in skin cells to fight off the harmful rays. The resulting lack of melanin leaves the skin vulnerable to sun damage, increasing the risk of sunburn and skin cancer.
In the next section, we will discuss how this breakdown in melanin production affects the sight and physical appearance of those with albinism.