Ocular Albinism: X-Linked & What That Means

All types of albinism are genetic disorders, meaning they start within our DNA. The defining characteristic of albinism as a whole is an abnormality of melanin synthesis in which the amount of pigment (melanin) made by the pigment cell (melanocyte) is reduced or absent. Though the effects on the skin and hair are less or absent in those with ocular albinism, certain abnormalities are always present in the eyes of people with albinism. These include:

• Reduction in iris or retinal pigment
• Iris translucency
• Foveal hypoplasia
• Misrouting of the optic nerves at the chiasm
• Nystagmus
• Alternative strabismus

To read more about Oculocutaneous albinism and the associated symptoms and to learn more about how I see, check out my article on the topic: “Albinism: What is It and What Do I see.”

Chromosomes & Inheritance

DNA is inherited from both our biological mother and father. We have 22 sets of chromosomes, which are the cells that hold our genetic information. We get one of these sets from our mother and one from our father. One set of these chromosomes are designated as sex chromosomes meaning they dictate your assigned or biological sex. If you get two X chromosomes, you are considered a biological female, and if you get an X and a Y, you are considered a biological male.

Sex chromosomes are important because Ocular albinism (OA) is an X-linked version of albinism. This means that OA is carried on the X chromosome. Because biological females get two copies of X chromosomes, if one abnormal chromosome is passed to her, she would have one normal X chromosome to essentially default to. This means that X-linked disorders like OA occur almost exclusively in biological males.

The above graphic shows a genetic lineage that begins with an unaffected male parent and a carrier female parent. This equates to an XY set of chromosomes and an Xx with one of those X chromosomes carrying the gene for OA. With this lineage, 50% of any biological males will be affected by OA, and none of the biological female children will be affected but 50% of the females will be carriers.

Unaffected father – xy & Carrier mother Xx

• 50% male children would be affected – Xy
• 50% female children would be carriers – Xx

Alternatively, if a father is affected and has children with a mother who is not a carrier, the lineage below would be the result:

Affected father – Xy & Non-carrier mother xx

• 0% male children would be affected – xy
• 50% female children would be carriers – Xx

Though a father with OA and a mother who is a carrier would have female children with a 50% chance of having two of the mutations responsible for producing OA, a female with any X-linked disorder including Ocular Albinism is exceedingly rare.

Some females with forms of oculocutaneous albinism that result in more pigment are misdiagnosed with ocular albinism. This is something to keep in mind when you or your children get a diagnosis. OCA comes in so many different levels of pigment and levels of eye conditions and acuity. You can find more information and some helpful images in my summary of the 2020 NOAH Virtual Conference: Day 3 & 4.

I cannot stress the importance of remembering that fact as you meet others in the albinism community who may or may not look similar to you. We all share a condition, but we are still quite different. Expecting others to perform at a certain level just because you’re at that level can be detrimental to a person’s self-esteem. I’ve seen community members belittle others for using various aids and make hurtful statements that assume every person with albinism “should” be at a certain level whether that be related to acuity, level of photophobia, pigment, and more. We need to stop this behavior. Stop comparing yourself to someone else, especially on social media.

Having a community to belong to is a beautiful gift, and we should each work to make it a safe place for questions and for comments even when some of those may seem ignorant. We are all at varying levels of understanding, and the field of genetics is always shifting as we learn new things, discover more genes, and push the science forward. Let’s all remember that when replying to comments, messages, and emails.

Thanks for reading.

Stay curious.