What to consider before taking a Genetic Test

There are many reasons why a person with an IRD may consider having a genetic test for an IRD, for example your eye doctor may think that you have an eye disease caused by genetic condition and wants to confirm the diagnosis they may advise you to take a genetic test. There may also be a history of an IRD caused by a genetic mutation in your family and so you may want to know if you are at high risk of developing the condition during your lifetime.

An eye doctor may be able to diagnose condition through a clinical examination, or tell you about your risk by looking at a detailed family history, but a genetic test is required to confirm a gentic dignosis. Depending on the purpose of the test, genetic tests can be categorised as diagnostic tests, carrier tests or predictive tests. It is the case in some countries that in order to get access to mobility aids and devices that improve accessibility, you may need to have a genetic test.

If you would like to learn more about mobility and visual aids for the vision impaired click here http://www.retina-international.org/resources

The decision to take a genetic test requires consideration by the affected individual themselves and their families, ultimately it is the individual’s choice. If you decide to take a genetic test it is important that you have access to all of the available information in order to help you make an informed decision.

It is important also that you have the opportunity to discuss all of the options with your eye doctor or a genetic counsellor as they are perfectly placed to provide you with clarity and the best information for you.

Genetic testing can bring great benefits, but it is also important that you understand the benefits and the risks before making your final decision.

Here are some of the benefits and the risks to discuss with your family and health care provider in order to help you make a choice that is appropriate for you.  

A genetic test has the potential to tell you about the cause of an Inherited Retinal Disease (IRD). When you have an accurate diagnosis it is then possible for you to participate in an appropriate clinical trial, if one is available.

Your information can be stored on a register that will help to not only populate clinical trials in the future but aids researchers to better understand the course of the condition affecting you. With the emergence of therapies for IRDs it also gives you the opportunity to access a suitable treatment in the future.

For some, the results of a genetic test can assist in family planning decisions. Knowing that you have an increased risk of having a child with an IRD can give you the opportunity to, talk with your doctor to establish if there is any pre natal technique that would diminish the possibility of an affected son or give you the opportunity to be prepared.

In some cases the risk of having a baby with retinal dystrophy is not for the affected person but for a relative, the best example of this is in the case of X-linked diseases.

As most genetic conditions are inherited, running through many generations of a family, information about your genetic makeup can be useful to other family members. If it is known that a genetic condition runs in your family, it may prevent individuals from being misdiagnosed. This information might also be of use to them when they are planning their education and career, allowing them to make up their minds which career to pursue from the outset.  

It must be stressed that taking a genetic test and waiting for and ultimately receiving the results can cause stress and lead to a lot of emotion in families. Patients with IRDs often describe the actual diagnosis as a relief at having a definitive answer and of a feeling of empowerment at having options. However they have also described feelings of anxiety and guilt, some have described it as like being diagnosed with an IRD all over again. With this in mind the need to talk through the possible outcomes, be they positive or negative, with your loved ones is critical.
As many treatments for IRDs are still in the development phase, a genetic confirmed diagnosis may not lead to an intervention or treatment now or in the future.

Although there are over 260 genes described that can be mutated in persons with IRDs, they explain only 60% of the potentially causative genes. It is very important to note that in some families a defective gene cannot be found just yet. This does not necessarily mean there is no change. Some genetic mutations are very difficult to find with current laboratory techniques. For those trying to get a diagnosis to enable access to information on inheritance and disease pathways this can be very frustrating indeed.
As genetic mutations are often passed through generations of families the results of your genetic test may reveal information about other family members, in particular their genetic risk of a condition. You must consider this, will other family members want to be made aware of this?

The laws with respect to right to privacy on genetic conditions differ in many countries and regions. Retina International strongly recommends that you examine the position in your own country so that you establish how the results of a genetic test could affect your ability to access a mortgage or the impact it might have on an insurance policy.

Again the nature of genetic testing means that in some cases family secrets involving paternity and adoption may come to light. This is why preparation and open discussion is key.

Once you have seen the appropriate medical professional in your country and you receive the test result there is no going back so it is important to be very sure about the decision you make. 

Consanguinity describes a situation where a couple who are hoping to have children together are related to each other by blood.

There may be consanguinity in previous generations if the couple comes from a small isolated population.

We inherit one copy of a gene from our mother, and one from our father. We all carry between six to seven recessive non-working genes, but we are healthy because the other copy of the gene compensates. These recessive non-working genes only become a problem if a child inherits two of these.

Doctors see higher rates of recessive genetic disorders amongst children from relationships where the parents are related and this is known as consanguinity. It is much more likely to occur in the case of cousins, due to shared grandparents or great grandparents.
If both parents carry the same non-working gene and both pass on the non-working copy to a child, the child will have no normal gene to compensate. In this case, the child will be affected by an autosomal recessive disorder.
If both parents carry the same non-working gene and both pass on the non-working copy to a child, the child will have no normal gene to compensate. In this case, the child will be affected by an autosomal recessive disorder.
Autosomal recessive inheritance describes a situation where both parents are carriers of a defective copy of a gene that does them no harm as they have a normal gene to compensate.
If both parents pass on a copy of a defective gene then the child will be affected by an autosomal recessive disorder. Everyone carries copies of altered genes, in fact recent research suggests that each of us carry 6-7 altered genes.

You are more likely to carry the same altered gene as your cousin, because you share grandparents in common, than with someone who is not related, which is why AR disorders crop up more frequently in cousin marriages.

When adults, or children, with an inherited retinal disease (IRD) first show signs of having some degree of difficulty with their eyesight, they may seek a diagnosis from an optometrist or ophthalmologist. These specialists may work in private practice or in association with a public or private hospital or a research facility linked to a university.

The choice between an optometrist, or ophthalmologist, in the first instance may depend on the financial capacity of the individual, or family, to pay for specialist services. If an individual, or family, has private health insurance they may opt for the ophthalmologist because the fees may be reimbursed. The choice may also depend on whether the individual, or family, live in a large capital city or a small country town. Often an optometrist will refer the individual or family members to an ophthalmologist at a large hospital, in the capital city, because they generally have more expertise in dealing with inherited retinal diseases.

A typical appointment or series of appointments at the optometrist or ophthalmologist would include:

Collecting information from the individual, or if a child is involved, the information is collected from the parents:
1. Ocular:
- Symptoms: night blindness, vision loss, glare, colour vision, driving (dates should be included)
- Other ophthlamic conditions
2. Medical conditions:
- deafness, diabetes, developmental delay, heart, skeletal, kidney etc
- other medical issues
3. Medications currently, or in previous year, being taken.

Obtaining information about the relevant family history or pedigree

This is followed by a Clinical eye examination which would test for:

  • Vision
  • Visual Fields
  • Colour
  • Vision Electrophsyiology – mfERG, PERG, Full Field ERG
  • Fundus examination
  • Imaging:

- Colour photos
- Fundus autofluorescence

When all available information is collected, the diagnosis is discussed with the individual and in the case of a child, with their parents. Given that in most instances, there is no optometrical assistance available, unless the individual also is myopic or has another condition where spectacles may be of some benefit , advice is provided in relation to:

  • Genetic Counselling
  • Genetic testing options which include:

- Referral to the Australian Inherited Retinal Disease Register & DNA Bank
- State-based Genetic Clinics associated with the large public hospitals
- Referral to Genetics Clinics for those who would consider self-funding of genetic testing
- Referral to Clinical Genetic Services who may fund a small percentage of genetic testing for inherited retinal disease on a case by case basis

  • Possible human clinical trials, gene therapy, stem cells, bionic eye and other current research

After all of the specific referrals relating to inherited retinal disease have been made, the individual may be referred to other organisations for peer support or for practical support with daily living and workplace assistance. Such organisations would include:

  • Retina Australia
  • Vision Australia
  • Guide Dogs Australia
  • Other support agencies

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