What are Mitochondrial Diseases and the Benefits of Mitochondrial DNA Testing?
The road to diagnosing and treating genetic conditions has never been easy. In many cases, patients and their families have faced years of uncertainty, multiple misdiagnoses, and a lack of effective treatment options. For conditions with complex and diverse symptoms, identifying the root cause has been akin to searching for a needle in a haystack. Mitochondrial diseases are one group of conditions which have been more difficult to diagnose.
Mitochondrial diseases can present in a variety of ways, affecting various organ systems, and mimicking symptoms of other medical conditions. Traditional genetic testing approaches have involved testing nuclear DNA, which comprises the majority of our genome. However, this approach does not test for the DNA found within our mitochondria (mtDNA). Some mitochondrial diseases are caused by variants (mutations) within the mtDNA. If a mitochondrial disease is suspected in a patient, testing their mtDNA might help to diagnose them.
For nearly two decades, Baylor Genetics has performed mtDNA testing. Our team understands that searching for the genetic link to your patient’s complex symptoms may be challenging. With mtDNA testing, we hope to provide you with further insight into these genes and help you find the information you need so that you can best help your patients.
The Significance of Mitochondrial DNA
To understand the significance of mitochondrial DNA testing, it’s essential to grasp its unique characteristics and pivotal role in cellular function. Mitochondria, often referred to as the “powerhouses of the cell,” play a crucial role in producing energy for cells through oxidative phosphorylation (OXPHOS). As stated previously, the mitochondria have their own genetic material outside of the nuclear genome. The mitochondrial genome holds a concise set of 37 genes, which are critical for the mitochondria’s energy production process through OXPHOS. Variants in these genes can severely disrupt energy production, resulting in mitochondrial diseases.1 As there are many mitochondria within each cell that each have their own genome the amount of any variants present can be different across different cells and tissues (this is called heteroplasmy). Unlike nuclear DNA, which is inherited from both parents, mtDNA is solely maternally inherited.
Signs and Symptoms of Mitochondrial Disease
Mitochondrial DNA testing can be considered for your patient if their condition or symptoms are related to those listed below:2
• Myopathy and cardiomyopathy
• Ocular findings, including ophthalmoplegia, pigmentary retinopathy, ptosis, and optical atrophy
• Hearing loss
• Ataxia, spasticity, or dystonia
• Diabetes mellitus
• Stroke-like episodes
For individuals with diseases by variants within the mtDNA, it is important to know that the exact symptoms, their onset, and their severity can vary. This is true even among individuals with the same variant such as a patient’s family members, primarily due to differences in the amount of the variant present.
“Mitochondrial copies can have different percentages of mutations,” said Dr. Yue Wang, Clinical Director of NGS/Molecular at Baylor Genetics. “If a child has a higher percentage of a mutation, they are more likely to experience a more severe phenotype.”
Many of the symptoms seen with mitochondrial disease are related to issues with tissues that require high amounts of energy. However, given how much each patient’s experience with their mitochondrial disease differs it is important to keep in mind that their presentation may be atypical. In addition, since there is clinical overlap between mitochondrial diseases and other conditions some patients might benefit from mtDNA testing ordered in tandem with other types of genetic or other testing to best come to a diagnosis.3
How is Mitochondrial DNA Testing Performed?
To perform mtDNA testing at Baylor Genetics, biological samples must be collected by a healthcare provider and shipped to our lab. Once received, the patient’s sample is assessed for variants. These variations are analyzed to determine their potential significance in relation to mitochondrial disorders. The data collected is then reviewed for specific evidence of mtDNA variants that can indicate the presence of a disease.
Each mtDNA test offered by Baylor has specific requirements for acceptable sample types. Below are listed sample types that are acceptable for at least one test:
• Cord blood
• Cultured skin fibroblast
• Extracted DNA
• Skeletal muscle
What are the Benefits of Mitochondrial DNA Testing?
Mitochondrial DNA testing offers many unique insights, such as providing more information about an individual’s risk of disease and potential health outcomes. By taking preventative measures and utilizing this type of testing, healthcare providers can promote better medical management and significantly impact their patients’ quality of life.
Clinical benefits of mtDNA at Baylor Genetics include the following:
• A suite of test offerings, including several tests which analyze the entire mtDNA genome
• Identification of variants within the mitochondrial genome that may be missed by testing of nuclear DNA only – over one-third of patients with a mitochondrial disorder have a finding only within their mtDNA4
• Many of our mtDNA tests typically take 4 weeks to complete
• Some tests can be performed on several sample types. This can help provide additional information when previous negative results might be obtained due to heteroplasmy.
What are the Limitations of Mitochondrial DNA Testing?
While mtDNA testing can offer healthcare providers valuable insight into their patients’ medical histories, there are some limitations. Some of the limitations of mtDNA testing include:
• Testing of mtDNA will not provide information about a patient’s nuclear DNA. Baylor Genetics offers a suite of tests including nuclear genome and dual nuclear and mitochondrial genome assessment.
• Heteroplasmy can complicate interpretation of results and clinical management
• As the amount of a variant may differ between tissue types, in some cases it may be necessary to perform more invasive procedures such as a muscle biopsy to get the most accurate results
What Mitochondrial DNA Tests are Offered at Baylor Genetics?
Mitochondrial DNA testing is a powerful tool for diagnosing and guiding the treatment of genetic disorders. Uncovering the root cause of medical conditions to help tailor treatment plans for patients is valuable in providing better healthcare services. At Baylor Genetics, our goal is to supply healthcare providers with the necessary resources to diagnose, treat, and monitor the progression of inherited genetic disorders more accurately.
Some of our testing options to help detect mitochondrial disorders include:
• Comprehensive mtDNA Analysis by Massively Parallel Sequencing – 2055
• Dual Genome Panel by Massively Parallel Sequencing – 2085
• Mitochondrial Nonsyndromic Hearing Loss and Deafness Mutation Panel – 3030
Is Mitochondrial DNA Testing Right for My Patient?
At Baylor Genetics, we know that mtDNA testing can deliver additional insight into the function of mtDNA and help you find the answers you need to help your patients. Being aware of any signs and symptoms that may be linked to a mitochondrial disorder can significantly impact your patient’s health. As a reminder, our genetic counselors are here to support you in finding the best mtDNA testing option for your patients.
Through our innovative mtDNA testing, Baylor Genetics can provide answers that help you best navigate how to support your patients with mitochondrial diseases.
Learn more about Baylor Genetics’ mtDNA test offerings.
1. Mavraki, E., Labrum, R., Sergeant, K. et al. Genetic testing for mitochondrial disease: the United Kingdom best practice guidelines. Eur J Hum Genet (2022). https://doi.org/10.1038/s41431-022-01249-w
2. Chinnery PF, Adam MP, Mirzaa GM, Pagon RA, et al. Primary Mitochondrial Disorders Overview. (2021). GeneReviews®. University of Washington, Seattle; 1993-2023
3. Chial, H. & Craig, J. (2008) mtDNA and Mitochondrial Diseases. Nature Education 1(1):217
4. Falk MJ, Sondheimer N. Mitochondrial genetic diseases. Curr Opin Pediatr. (2010). https://doi: 10.1097/MOP.0b013e3283402e21