DNA, genes, chromosomes, and proteins

Your body is made up of 40 trillion cells, and each cell contains a copy of your unique genetic information. A genome refers to a complete set of instructions, either mitochondrial or nuclear.1 This is like having two bookcases, full of recipes, handed down through generations.

The nuclear genome is made up of the nuclear DNA (nDNA). This is like the biggest bookcase that's located within the nucleus. It is the control centre of your cells and contains most of your genetic information. nDNA is inherited from both parents and made up of 20,000-25,000 genes,2 providing the instructions (or recipes) for things like your hair or eye colour.

Your body has many genes with different roles. Genes are like the recipes within each recipe book. Around 1,100 nDNA genes help with mitochondrial function.3

In all your cells, genes are found on chromosomes. Each chromosome is like one recipe book. We usually have 46 chromosomes of nDNA to make 23 pairs within each cell's nucleus. Thousands of genes send messages to your cells to make proteins. These proteins are crucial for almost every task in your cells.1

The mitochondrial genome is made up of the mitochondrial DNA (mtDNA) which is a much smaller bookcase found in the mitochondria. The mitochondria have 37 genes. These genes give instructions (or recipes) for making energy.2

An introduction to genes, genomes, and genetic instruction are explained here.

You can think about our genome of being made up on two bookcases full of recipes. One bookcase is for nuclear DNA, one for mitochondrial DNA. You can think of each recipe being a single gene. Some of the recipes are grouped into books called chromosomes. Proteins are what made when the recipes are followed. A genetic change is when a ‘typo’ or an error occurs within the books.

Genetic testing explained

DNA is made up of a sequence of A, G, C and T. These letters pair up to form the "rungs" of the twisted ladder shape that DNA is known for. Genetic testing is when a lab examines the sequence of A, G, C and T to identify any changes.

A diagram of nuclear DNA, showing the sequence of A, G, C, and T. Which stand for adenine, thymine, guanine, and cytosine to form the twist rungs of the ladder nuclear DNA is known for.

Genetic testing is like a spell-checker for your body's instruction books. It can find 'typos' or other changes in the DNA sequence that could cause health conditions. Many changes are found in genes, and most are normal, making people different from each other. Some types of genetic changes cause genetic conditions like mito.

Health professionals use various tests to diagnose mito. This can include looking for certain chemicals in blood or urine and looking at cells from different body parts such as from a muscle biopsy. Genetic testing is a useful tool and can be used early in the process of diagnosing mito.4, 5

The results of a genetic test can also determine your chance of developing mito or passing it on to any children you have. Occasionally, a genetic change is a new occurrence in the family that hasn't been inherited, referred to as a sporadic or de novo genetic change.

Genetic testing is usually ordered by a specialist doctor, not your GP. You can speak to your specialist or ask for a referral to a clinical genetics service. Clinical genetics services can provide up-to-date information on testing options and provide genetic counselling services to help you make an informed decision about testing. Medicare funding is only available for tests ordered by a specialist doctor.

What is tested?

In most cases your health professional arranges genetic testing on a blood sample. However, a urine sample or a sample from another part of your body can sometimes give more information about genetic changes.

What are the reasons for genetic testing?

In most cases your health professional arranges genetic testing on a blood sample. However, a urine sample or a sample from another part of your body can sometimes give more information about genetic changes.

Medicare Benefit Scheme

When you have a family member who knows their genetic change

If you have a close relative with a genetic change that can cause mito, your health professional can test for this specific change. They may also recommend genetic counselling to help you understand your risk of developing mito.

What are the different types of genetic tests?

Many tests can check for changes in your genes, chromosomes, or proteins. In Australia, whole genome sequencing of nDNA and mtDNA is subsidised by Medicare and is the type of test most likely to find a genetic change if a person has mito. However, even this type of testing can sometimes not find a gene change known to cause mito.

Your health professional will consider which type of testing is best for you. They will consider your symptoms and family history. If your health professional has a good idea of the possible type of mito causing your symptoms, they may use a test that only looks at a few specific genetic changes.

Categories of genetic testing are explained here.

What are the benefits of genetic testing?

There are different ways that mito can be diagnosed. You can learn more about the categories of diagnosis here.

Benefits of a genetic diagnosis include, but are not limited to:

What else should I think about before having a genetic test?

Genetics and mito

How long does genetic testing take?

The time it takes to receive a genetic test result for mito can vary depending on the type of test and the lab. Generally, it can take several months. For example, the Victorian Clinical Genetics Services (VCGS) states that tests can take 3-4 months.

The time taken can be shorter if there is urgent medical care that can be informed by the results of the genetic test. Testing may be prioritised if the outcome of the genetic test will inform reproductive options or if symptom progression is significant. In some research projects, urgent  genetic testing can be done in just a few days.12, 13

The time taken to receive results can also be longer when a genetic change is found, but it is not yet clear whether this change causes mito. You should ask your health professionals about the expected times when the sample is provided for testing.

What does my genetic test result mean?

The test result will explain if a genetic change has been found and if this change is likely to cause mito. Test results are complex and difficult to understand. You should speak to a health professional to understand what your genetic test result means for you.

A pathogenic change is a genetic change known to stop the gene from working correctly. Pathogenic means that it can cause disease. Therefore, this means that the genetic change can lead to mito.

Genetics and mito images

Genetic testing might find a genetic change that does not cause mito. This is called a benign change. These changes are usually not detailed in the genetic report.

Sometimes, the genetic test result will be uncertain. An uncertain variant means a genetic change has been found, but whether it causes mito is unclear. DNA contains a lot of information, making interpreting the genetic information challenging.

Genetic test results can be reclassified, meaning the result might change over time. This happens when additional information or research gives the lab new clues about a genetic change. If the test result is uncertain, this result might change in the future.

A health professional specialising in genetics will interpret the genetic test results and consider other test results, such as blood or tissue tests and family history.

It's recommended to talk to your health professional for more detailed, personalised advice based on your unique circumstances and needs. They can also guide you through any decisions that need to be made based on the results. Learn more about genetic counselling and mito.

How much does genetic testing cost?

The best way to access genetic testing in Australia is by seeing a specialist. They should be experienced in this area, such as a mito clinic or a clinical genetics service.

If you are being seen in a public hospital, you do not have to pay for any testing. You may pay some out-of-pocket costs for testing if you are being seen in a private hospital or seeing a specialist privately.

cost of a genetic test for mito will be different depending on:

  • Which type of testing is best suited for each situation
  • Which lab is doing the test
  • Whether you are eligible for funding under Medicare or through your private health insurance.

You should discuss the cost of genetic testing with your health professional to understand whether the test will cost you any money.

Which Australian labs offer genetic testing for mito?

This list may be useful for health professionals when requesting a genetic test. This list is based on information provided to Mito Foundation and my be incomplete. We encourage pathology services to contact us with any additional or updated information.

Summary

  • Your body is made of 40 trillion cells, each with a copy of your unique genetic code, like a collection of recipes passed down through generations.
  • Genetic testing acts like a spell-checker for your genetic instructions, finding "typos" that could lead to diseases.
  • Tests include Whole Genome Sequencing (WGS), Whole Exome Sequencing (WES) and Mitochondrial genome sequencing. Changes in both nuclear and mitochondrial DNA can be detected by performing either WGS alone or WES plus mtDNA sequencing.
  • A genetic diagnosis can provide certainty, faster diagnosis, and enables monitoring, proactive management, and early intervention for better quality of life.
  • Before testing, consider fears of discrimination, emotional impact, and costs. Test results can indicate pathogenic changes causing disease, benign changes, or uncertain variants, requiring consultation with a genetics specialist.

Helpful resources

Disclaimer: Resources provided by the Australian Mitochondrial Disease Foundation Limited (Mito Foundation), offers general information and is not a substitute for medical advice. It is essential to assess the suitability of the content for your individual circumstances and make decisions based on your medical condition. The information’s accuracy is subject to change, and we do not guarantee ongoing currency or availability. While efforts are made to ensure accuracy, Mito Foundation is not obligated to provide updated information. The copyright for this document and its content belongs to, or is licensed to, Mito Foundation, and reproduction without prior written consent is prohibited.

Author(s): Mito Foundation
Reviewer(s): David Thorburn BSc(Hons) PhD FHGSA FFSc(RCPA) FAHMS,  Suzanne Sallevelt MD PhD FRACP and members of the mito community.
Version: 2.1
Date published:  9 April 2024    

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