Genetic Testing and You at VisionAmerica

What is genetic testing and how can it be helpful?

What is genetic testing and how can it be helpful? Many eye disorders “run in families” and are genetic — that is to say, they are passed on from parents to their offspring by genes. We also say these conditions are hereditary and that those who are affected have inherited the condition. It is possible to test someone’s genes to look for changes that can cause an eye disease and that is one type of genetic testing. These changes to genes are called mutations. To do this test, a sample of blood is collected from the arm, just like at your annual physical exam, and sent to a laboratory where it is analyzed. The results are returned to the doctor and then discussed with the patient or family. Genetic testing may be helpful in many ways. Here are some of them:

• It can establish a definite diagnosis that might not be possible otherwise
• It might rule out a condition that your eye doctor was considering since some can look very much like each other
• It can identify people who might be eligible to participate in a clinical trial, or a new treatment
• It might help determine how the condition will progress since different gene mutations affect people differently

Some other possible outcomes you should know about are:

• Sometimes, nothing is found with genetic testing and you need to be prepared for that possibility
• Genetic testing may confirm that a person has a specific disease that they were hoping they did not have and that can cause distress
• Genetic testing may confirm that a parent has passed the disease to an offspring and that can be distressing

You should discuss the pros and cons of genetic testing with your eye doctor and the genetics doctor before deciding whether or not to have the test done. Here is what usually happens — your primary eye doctor will make a referal to a genetics specialist at VisionAmerica of Birmingham. The specialist will do a detailed eye exam, may repeat some of the tests you have had previously and may do some additional special testing. He will also do an extensive family history and draw a pedigree which is a diagram of your family. When he has all the information needed he will talk with you about genetic testing, the pros and cons, expense and possible outcomes. It is then up to you whether or not you want to have it done. If you do, he will collect a blood sample from your arm, send it to a lab and have you back to discuss the results. He will also send the results of his exam and the genetic testing to your eye doctor so he or she stays involved in what happens and may recommend further counseling with a genetic counselor.
 

One Family’s Story

A woman in her 30’s had a routine eye exam but mentioned that she had an uncle who was blind and who lived elsewhere. She did not know the diagnosis but knew that her son also had an eye disease that might be the same as the uncle’s but he did not have an exact diagnosis either. Eventually both the uncle and the son had genetic consultation and it was established they they both had a hereditary disease called choroideremia. There are clinical trials underway now trying gene therapy for this condition. The uncle’s condition is likely too advanced for that therapy to be effective but the son is not and he and his parents can decide if they want to try and enroll in a trial or not. The son’s eligibility depends on knowing his exact diagnosis and that was accomplished with genetic testing. If he does enter a clinical trial that results in improved vision it will be a very happy outcome that would not have been possible without genetic testing.
 

Genetic Eye Disease

Many eye disorders are hereditary and can be passed from one or both parents to an offspring. Some of the more common ones that we see include:

• Achromatopsia
• Albinism — Oculocutaneous
• Albinism — Ocular
• Aniridia
• Autosomal Dominant Optic Atrophy
• Best Disease
• Cataracts (Usually the types seen in children)
• Choroideremia
• Color Vision Deficiency (not really color “blindness” but some people call it that)
• Corneal Dystrophy
• Cone-Rod Dystrophy
• Doyne Honeycomb Dystrophy (Autosoaml Dominant Drusen)
• Glacuoma (Usually the typesseen in children)
• Juvenile X-Linked Retinoschisis
• Leber Hereditary Optic Neuropathy
• Leber Congenital Amaurosis (a type of retinitis pigmentosa)
• Pattern Dystrophy
• Retinitis Pigmentosa
• Stargardt Juvenile Macular Dystrophy

 

Clinical Trials

A clinical trial or clinical study is a research project using people with and without eye disease to try and answer important questions about what causes the disease, how it affects vision and how it might be treated or cured. Some clinical trials involve gene therapy or other treatments but not all of them. For a list of trials put together by the National Institutes of Health, see the link below. Keep in mind that this list is for all trials, not just those about eyes, but you can search within for a term or word that will show trials related to specific eye disorders, if there are any.
 

Gene Therapy

Gene therapy is a procedure intended to correct or lessen the effects of gene mutations by replacing the defective gene with a normal one. A very simple example might be the following: a gene is supposed to make a product like a protein but it can’t because it has a mutation that prevents it from doing so. If we could replace it with a normal gene the problem would be solved. We do not have to literally replace one with the other provided the normal one can become active and produce the missing or altered protein where it is needed. To make this happen, the normal gene is attached to a virus that is then injected inside the eye. Viruses are very good at entering living cells. The virus enters the cells and the normal gene is now where it can be active and produce the missing product. The process is more complicated than that but the idea is the same.

For more information please visit: https://nei.nih.gov/news