Choroideremia

Choroideremia is an X-linked genetic condition that causes progressive vision loss that mainly affects males. Becuase Choroideremia is X-linked it primarily affects males. Female carriers are not usually affected, however, some may develop night blindness and loss of visual field later in life.

The first symptom of this condition is usually difficulty with night vision (night blindness), which can occur in early childhood. A progressive narrowing of the field of vision (tunnel vision) follows, as well as a decrease in the ability to see details (visual acuity).

These vision problems are caused by the progessive loss of cells in the specialised light-sensitive tissue that lines the back of the eye (retina) and a nearby network of blood vessels.

The degree of vision impairment in choroideremia worsens over time, however, memebrs of the same family can be affected in different ways and show different rates of decline. However, all individuals with this condition will develop blindness, most commonly in late adulthood.

Quick facts about choroideremia
Genes: CHM
Inheritance: X-linked
Relevant resources for choroideremia

A quick genetics rundown

As humans we have about 23,000 genes. These genes are like tiny instruction manuals that influence our health, growth and development. We inherit half of our genes from our biological mum and the other half from our biological dad. These genes are lined up on structures called chromosomes. Most of us have 23 pairs of chromosomes. The first 22 pairs are called autosomes and for the most part - these are the same among men and women. The 23rd pair determine our sex - two X chromosomes for a female and one X and one Y chromosome for males.

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How is choroideremia inherited?

choroideremia is an X-linked condition. X-linked conditions occur when there is a genetic variation on the X-chromosome. For these conditions, the sex of the parent who passes on the gene variation influences the risk for the children.

If the father is affected, all his daughters will have a variation on one of their X-chromosomes and be healthy carriers. Sons can only inherit these x-linked conditions from their mother and therefore, in this situation, will not be affected by the disease.

If the mother is a healthy carrier of an X-linked variation and has a son, there is a 50% chance that they could inherit this variant and be affected by the disease. If they have a daughter, there is a 50% chance that they will be a healthy carrier (just like her mum).

Another way of looking at this is that there is a 25% chance of having an affected son and a 75% chance that the child will not be affected by the disease.

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What is carrier screening?

Carrier testing is like a checkup for your genes. It tests to see if you carry a gene variation that could cause a serious genetic disease in your child. Eugene offers an inclusive genetic carrier screening panel that includes choroideremia, but there's a total 301 conditions that can be tested.

Eugene’s carrier test is a clinical grade test that can be done from the comfort of your own home — it’s just a saliva test. You're also paired with a genetic counsellor who provides mindful support and guidance every step of the way.

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Should parents screen for choroideremia before or early in pregnancy?

The biggest benefit of screening for choroideremia is that it can help future parents understand their reproductive risk so they can be ready and empowered to make more informed decisions. If neither partner are carriers, it provides reassurance and peace of mind that the risk of having a child with a genetic disease is low.

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