Introduction
This post was inspired by the news I read, that a popular Nigerian Nollywood actor is set to divorce his wife for giving birth to an albino baby.
On reading this headline, any learned fellow would see it as a ridiculous thing, but the saddening truth is that in Africa and many other parts of the world, a large number of people still do not understand the concept behind albinism. In this article, I will try to shade light on the disorder called albinism from a biochemical perspective.
Definition of Albinism
Albinism is a congenital (hereditary) autosomal disorder characterized by the complete absence or a deficiency in the production of melanin pigment. This disorder is not peculiar to humans; it is obtainable in all vertebrates.
To fully understand this disorder, we need to briefly talk about Melanin
The main culprit, Melanin, is a generic name given to some pigments found in the skin, eyes and hair of vertebrates. Basically, melanin exists in three variants namely:
Eumelanin: This is the most popularly kind of melanin which and is largely responsible for black and brown color of the skin and hair. In the hair, black eumelanin would cause the production of black hair, brown eumelanin would cause production of blonde hair, while a mixture of brown eumelanin mixed with red phemelanin causes the production of strawberry blonde hair.
Pheomelanin: Pheomelanin is mainly responsible for red, pink and other colors. It is more concentrated in areas like the nipples, lips and the genital organs.
Neuromelanin: The function of neuromelanin is yet to be extensively studied, and the main thing known about it is that it is found in the brain.
Melanin gives the skin its color, and protects us from the UV radiation of the sun. It actively absorbs the light from the sun and darkens the skin, thereby protecting it from UV radiation damage.
Production of Melanin
Melanin is produced from the catabolism of the aromatic amino acid, tyrosine. It is produced in specialized cells called melanocytes, which are densely packed in the dermis and epidermis of the skin, the uvea (iris-containing part of the eyes), inner ear, hair follicles and around the leptomeninges of the brain and spinal cord.
The enzyme tyrosinase is chiefly in charge of the melanin biosynthesis pathway. The synthesis of melanin starts in the liver where phenylalanine hydroxylase converts phenylalanine to tyrosine.
Next, tyronsine is then transported to the pigment granules (melanosomes) of the melanocytes where tyrosinase oxidizes L-tyrosine to dihydrophenylalanine (DOPA). Tyrosinase then converts DOPA to DOPAquinone, from which two varients of melanin, the pheomelanins (red and yellow polymers) and the eumelanins (black and brown polymers) can be obtained.
The production of pheomelanin requires glutathione or cysteine which converts DOPAquinone to cysteinyl DOPA, from which pheomelanin is made.
To produce eumelanine, DOPAquinone is sponteanously converted to LeocoDOPAchrome and DOPAchrome respectively, from where it goes through several other reactions to result in eumelanine.
So What Causes Albinism?
Albinism is primarily caused by defect or complete absence of tyrosinase, which is the rate-limiting enzyme in the production of melanin. Generally, it is caused by a genetic mutation which either affects the melanin-producing proteins, the melanin receptor cells or the cells involved in packaging and distributing melanin, and it is inherited as a recessive allele.
Types of Albinism
There are two types of albinism- oculocutaneous albinism and ocular albinism. Oculocutaneous albinism affects the skin, eyes and hair, whereas ocular albinism only affects the eyes, while skin and hair coloring remains normal.
How Does Albinism Affect the Eyes?
As we have established, both types of albinism will affect sight. It reduces the pigmentation of the iris and the retinal pigment epithelial cells, which is located between the choroid and retina. This lack of pigmentation causes the vessels of the retina to assume an abnormal shape, while the vessels of the choroid becomes more visible.
Ultimately, this abnormality causes light sensitivity because there is no or not enough pigments to absorb light.
Also, albinos have an underdeveloped fovea. Fovea is the part of the eye mainly responsible for clarity of vision.
Apart from light sensitivity, underdevelopment of the fovea is the primary cause of impaired vision in albinos. Depending on the level of underdevelopment of the fovea, sight defect may be either mild or severe.
Albinism also causes a misrouting of visual signal in the pathway that connects the eyes to the brain. This obstructs the movement of nerve impulse from the retina to the brain, thereby further affecting vision acuity.
Albinos also have defective eye conditions called Nystagmus and Strabismus. Nystagmus causes involuntary side-to-side, circular or up-to-down movement of the eyes, while strabismus is a condition where the eye muscles do not work in sync with each other. In this condition, it is difficult to direct both of the eyes at the object simultaneously.
These two conditions strain the eyes of the albino, and causes them to squint tilt their head in an unusual manner before they can get a fairly good view of their surroundings.
Can Two Non-Albino Parents Have an Albino Baby?
This is where many persons get it twisted. It is true that albinism is an inherited disorder, but it is also true that it can be inherited from two non-albino parents. I will try to explain this in the most simplistic manner.
Two different genes called the OCA2 gene and the TYR (Tyrosinase) genes are important in pigmentation. Remember that genes are stored in strands of DNA called chromosomes. Each person has two of these chromosomes (OCA2 and TYR), one of each is inherited from either parents.
A mutation (alteration) in any of these genes is what causes albinism, and for one to be an albino, the two copies of chromosomes, inherited from both parents must be mutated. If one has one mutated copy and one normal copy, the person wouldn’t be an albino. Instead, they will be carriers of the albino gene. Carriers of albinism have normal skin pigmentation, and may not have albino children unless if their partners are also carriers of the albinism gene, and the two mutated genes get “mixed up” in their child.
There is however a little complication in the inheritance pattern of ocular albinism. It is an X-linked disorder, which means that the mutated gene is carried on the X-chromosomes. This implies that, considering that males have only one X-chromosomes, a single copy of the mutated gene is enough to cause ocular albinism. In females however, because they have two X-chromosomes, a single mutated copy of the gene is not enough to cause the disorder.
What all of these mean is that two perfectly non-albino parents can have an albino baby.
Treatment and Management
For now, there is no known cure for albinism. However, the following can be done to manage the condition.
Proper diagnosis can identify refractive errors, so they can be treated to increase vision acuity.
Wearing of absorptive sunglasses helps reduce light sensitivity and eye strain.
Patients can be given contact lenses with colored components at the regions overlapping the iris. These lenses reduces light sensitivity by blocking the entry of light into the iris. They also reduce refractive error.
Surgical operations can be done to correct ocular misalignment in very severe cases of strabismus and nystagmus.
Having established these, it is necessary to state that on-going studies using animal models promises a possible solution via gene therapy, in which abnormal genes can be replaced with normal ones. These studies have however not been evaluated in human subjects.
Dispelling some myths about albinism
Some myths you may have heard about albinos are mostly false.
For starters, albinism is not contagious. You cannot contract it from interacting with albinos. It can only be passed from parents to children if both parents are carriers of albinism gene. Also, albinos can have non-albino children, as long as their partners do not also have (or transfer) the albinism gene to the offspring.
Albinism is not a curse or punishment, so do not believe any religious myth that says such and suggests the use of albinos for any religious ritual.
Conclusion
In conclusion, I want to state that albinos are normal people. They have normal brain function, and are not less intelligent than people with proper pigmentation. Two non albino parents can have an albino baby, and it doesn’t mean that the woman cheated.
References
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