To understand genetic testing, we need to look more in depth at DNA, genes, and genomes.
Your DNA is like a collection of cookbooks on how to make you. It contains all the recipes needed to build, grow, and develop each person.
A gene is a single recipe in your cookbook. Genes are sections of DNA storing information on how to make specific parts of you. Changes or mutations in a gene are common and don’t necessarily cause problems, although they can lead to genetic disorders or illnesses.
The genome contains all your DNA and controls the activity of each gene. The human genome is made up of around 22,000 genes.
Inheritance is the process of genetic information being passed from parent to child. If you have a change in one of your genes, it may be passed on to your child.
Who should be referred for macular disease genetic testing?
Diagnosing macular disease has traditionally relied on clinical testing by an ophthalmologist. This involves examining the retina and macular, electrophysiology (assessing the pathway from the retina to the brain) and testing peripheral vision. If an eye disease is thought to be inherited then genetic testing may also be recommended.
Genetic testing is most useful when the inherited eye disease is thought to be caused by variations in a single gene (monogenic) and are referred to as Inherited Retinal Diseases (IRDs), which includes retinitis pigmentosa. Macular Dystrophies are one group of IRDs that specifically affect the macular, such as Stargardt disease, adult vitelliform macular dystrophy, and Best disease.
Inherited retinal diseases and macular dystrophies are rare. Your eye care professional will advise if you have a suspected macular dystrophy or IRD and may recommend you see an ophthalmologist who specialises in retinal conditions.
Genetic testing for AMD is currently not advised
Age-related macular degeneration (AMD) is influenced by many gene variations (known as polygenetic) and individuals with the highest genetic risk for developing AMD may only develop mild changes and never lose vision.
There are currently private laboratories offering predictive DNA screening for AMD. Due to the complexity of multiple gene variations and the environmental risk factors associated with disease progression, interpreting results for AMD is especially challenging.
Current advice is that if you have a family history of AMD, you should ensure you have regular eye exams and modify your lifestyle and behaviours, such as stopping smoking, ensuring a healthy diet, and regular exercise.
Each state and territory provides genetic services. A team of geneticists (a doctor specialising in genetics), molecular scientists, ophthalmologists and often a genetic counsellor work together to find which of your genes has a variation that causes your disease. You will need to have seen an ophthalmologist for diagnosis and will require a referral from either an ophthalmologist or GP to access genetic services.
There can be long wait times for an appointment at a genetic clinic and to receive your genetic results (from months to years). Priority is given to more urgent tests that may be associated with disorders that can be life-threatening and affect other parts of the body. Your test may also be prioritised if you are considering having children, or if a treatment is available for your suspected condition.
Currently the affected gene or genes can be found in around 70% of cases. With this information doctors can give you a better understanding of how your condition will change over time. You may also have access to research trials and any future treatments.
If you are suspected of having an inherited retinal disease, it may also affect other members of your immediate and extended family. A genetic counsellor can help you talk to your family about genetic information and make decisions around your health care and future children.
Genetic testing is a complex process and the information you receive may feel overwhelming. MDFA has developed a comprehensive checklist of questions to ask when first diagnosed with a genetic eye disease.
What happens if no genetic diagnosis is found?
Remember around 30% of people will not find a genetic answer to their condition.
No genetic answer does not mean it isn’t a genetic condition. Science doesn’t have all the answers and researchers continue to discover rare new conditions and genetic variants.
Variants of uncertain significance mean a difference was found in a gene but it is unknown whether it affects the function of that gene.
Remember genomic research is constantly evolving, and new breakthroughs are happening all the time. Your ophthalmologist may recommend genetic testing again in the future.
Genetic vs genomic testing
What is the difference between genetic and genomic testing?
While the technology used in the actual testing differs between the two, the concepts are similar.
- Genomic testing examines many genes while genetic testing examines a few (1–5) genes.
- If an eye disease is suspected as being inherited, genetic or genomic testing may be recommended to identify the mutation or variation in your DNA.
If you are experiencing difficulties accessing ophthalmology or genetic services for a suspected inherited macular or retinal disease you can call our National Helpline on 1800 111 709 for further information and support.