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What is LCA?

LCA is a rare genetic disorder that results in the progressive loss of vision. Those with LCA eventually go blind, typically in their late teens to early twenties. 15 genes have been found to cause LCA when they are mutated. One of these genes is Retinal Dehydrogenase 12 or RDH12. RDH12 typically works by recycling molecules known as retinols that are important in the eye's ability to detect light. RDH12 is also important in detoxifying chemicals that are produced by light and can damage cells if left unaltered. Without a functioning RDH12, the cells of the retina die.

RDH12 Visual Cycle

The Visual Cycle and the Role of Vitamin A in RDH12-LCA

How do you get diagnosed?

Individuals with LCA have very reduced or no vision at birth depending on what form of LCA they have. A variety of other eye-related abnormalities including roving eye movements, deep-set eyes, and sensitivity to bright light also occur with this disease. Some patients with LCA also experience central nervous system abnormalities. Within an infant's first few months of life, parents usually notice a lack of visual responsiveness and unusual roving eye movements, known as nystagmus. Eye examinations of infants with LCA can reveal normal appearing retinas or abnormal changes depending on which gene is causing the LCA. However, electroretinography (ERG) tests, which measure visual function, detect little if any activity in the retina. A low level of retinal activity, measured by ERG, indicates very little visual function. ERG tests are key to establishing a diagnosis of LCA along with genetic testing. It is vital to get genetically tested once you receive a diagnosis of LCA or Retinitis Pigmentosa (RP) from your doctor, as each gene has a different cause, progression and visual expectation. Genetic testing also allows for the success of research as it helps provide more information about each individual disease and possible cures. RDH12–LCA children tend to have periods of stability followed by periods of vision loss related to the death of the rods and cones in the eye. No child is exactly alike in the progression of the disease which makes this diagnosis even more difficult. The expectation is that most people diagnosed with RDH12–LCA will lose most if not all of their usable vision by their teens to twenties.

How do genes work in RDH12?

Chart-1.webp

The most frequent retinal phenotype in patients with RDH12 mutations is an autosomal recessive inherited retinal degeneration (IRD). ​

To have an autosomal recessive disorder, you inherit two mutated genes, one from each parent. These disorders are usually passed on by two carriers. Their health is rarely affected, but they have one mutated gene (recessive gene) and one normal gene (dominant gene) for the condition. With each pregnancy, two carriers have a 25% chance of having an unaffected child with two normal genes (bottom left), a 50% chance of having an unaffected child who is also a carrier (top left, bottom right), and a 25% chance of having an affected child with two recessive genes (top right).

In rare cases, RDH12 can segregate with a milder phenotype in an autosomal dominant fashion.

In an autosomal dominant disorder, the mutated gene is a dominant gene located on one of the nonsex chromosomes (autosomes). You need only one mutated gene to be affected by this type of disorder. A person with an autosomal dominant disorder — in this case, the father has a 50% chance of having an affected child with one mutated gene (dominant gene) and a 50% chance of having an unaffected child with two normal genes (recessive genes).

Chart-2.webp

Why Get Tested?

If you suspect that yourself or someone in your family may have LCA or RP you need to consult with your local eye doctor. They should be able to do a retinal exam to see if there is any evidence of disease. If there is, your next step should be an ERG and/or genetic testing. Genetic confirmation is important because a patient with Body Cell Mass (BCM) needs to understand how the disease spreads, and what the chances are of passing the disease to future children.

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If you or a family member have a clinical diagnosis of RDH12–LCA, there are many reasons to perform a DNA test, for example:

  • to have a genetic confirmation of the diagnosis

  • to help scientific research to find all the possible genetic mutations that lead to disease

  • to know possible experimental therapies that often depend on the particular genetic mutation that you have

For an introduction to the problem of genetic testing please visit Foundation Fighting Blindness or My Retina Tracker.

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