Facts About Ocular Albinism


Albinistic man portrait, Image from Wikimedia CommonsOcular albinism is an inherited genetic disorder in which the eyes lack melanin, the substance that gives pigmentation to the irises (colored part of the eye), skin, and hair. Unlike a person with oculocutaneous albinism, a person with ocular albinism has skin and hair that show normal or near-normal coloration. Eye pigmentation is important for normal vision.

The most common form of ocular albinism is the Nettleship-Falls type or ocular albinism type 1. There are other forms of ocular albinism but they are much rarer and may be associated with additional symptoms, like hearing loss.

Symptoms for Ocular Albinism

The main symptom of ocular albinism is the complete or partial absence of pigmentation in the iris and the retina, the light sensitive membrane in the back of the eye. The color of the eye iris can vary from blue to green or even brown, and sometimes darken with age. When a doctor examines the eye of an affected individual by shining light from the side of his/her eye, the light shines back through the iris because very little melanin pigment is present.

Other symptoms for ocular albinism include rapid, involuntary movements of the eye (nystagmus), increased sensitivity to light (photophobia), eyes that are not aligned in parallel or do not see in the same direction (strabismus), stereoscopic vision or problems with combining vision from both eyes to perceive depth, and severely impaired sharpness of vision (visual acuity).

The pattern of routing of nerves from the back of the eye to the brain in an individual with ocular albinism is different from that of a normal person. This creates a problem in vision and in the way the eyes function.

With regards to skin color, an individual with ocular albinism may have lighter skin tone than other members of his/her family but this difference is usually negligible.

Treatment for Ocular Albinism

For treatments of ocular albinism, read the article on cures for albinism.

Prevalence of Ocular Albinism

According to a statistics from NIH, at least 1 in 60,000 males suffer from ocular albinism. The condition is more common in males than in females.[ad#co-1]

What Causes Ocular Albinism – The Genetics of Ocular Albinism

Ocular albinism type 1 is caused by a mutation in the GPR143 gene. This gene provides the instruction for the production of protein that plays a role in skin and eye pigmentation. The protein helps control the growth of melanosomes, which are cellular structures that manufacture and store the pigment melanin. Melanin gives color to eyes, hair, and skin. It is also found in the retina and plays a role in normal vision.

How Ocular Albinism is Inherited?

The GPR143 gene is located in X chromosome, a sex chromosome found in both males and females. Females carry two X chromosomes while males carry only one (the other is Y chromosome). Since the gene is located in the X chromosome, ocular albinism type 1 is inherited in an X-linked pattern.

Males develop ocular albinism just by inheriting an X chromosome with the mutated gene from their mothers. Females on the other hand, should inherit two X chromosomes with the mutated GPR143 gene from their fathers and mother in order to develop ocular albinism.

If a female only inherited one affected X chromosome, she may not develop ocular albinism but she is considered a carrier of the defective gene. She can pass it to her children. All her male children develop ocular albinism because they only have one X chromosome. The female children will develop ocular albinism if their father also carries the mutated gene in his X chromosome. In other words, females develop ocular albinism if both of their parents carry the mutated GPR143 gene. This is the reason why ocular albinism is less common in females than in males.

Carrier females or those who carry only one X chromosome with the mutated form of GPR143 do not experience vision loss or other significant eye abnormalities but they may have mild changes in retinal pigmentation that can be detected during an eye examination.[ad#afterpost]

Reference

Ocular Albinism – Genetics Home Reference