Overview

Mitochondria are known as our body's power plants. They burn the sugars, fats and proteins in our diet to generate the energy that our body needs to function normally. When our mitochondria don't function correctly this can impact our health.

Disorders of mitochondrial energy generation can be caused by primary mutations in mitochondrial DNA (point mutations and single deletions) and by nuclear gene disorders. A subset of nuclear gene disorders result in secondary mutations in mitochondrial DNA (multiple deletions or depletion of mitochondrial DNA).

What is this test?

Testing for mitochondrial disorders is performed using molecular DNA testing and biochemical/enzymology methods.

The best method for testing depends on the age of onset, clinical symptoms, family history and results of screening tests (metabolic and imaging). Expert input from a clinical geneticist or suitable specialist is usually needed to determine which testing is the most appropriate.

Testing is performed on blood, urine, saliva, skeletal muscle, liver, cardiac muscle, chorionic villus (CVS) or cultured skin fibroblasts depending on the clinical presentation.

What conditions does this test look for?

Our tests detect a number of different mitochondrial disorders, including:

  • Leigh syndrome
  • Alpers syndrome
  • Kearns Sayre syndrome
  • Pearson syndrome
  • MELAS
  • MERRF
  • Leber hereditary optic neuropathy,
  • CPEO
  • Mitochondrial hepatopathy
  • Mitochondrial cardiomyopathy
  • Other mitochondrial encephalopathies

VCGS offers a range of different test options, shown below.
See our test option summary table for all sample requirements, reporting times and costs.

Mitochondrial

Relatives of a patient previously diagnosed with a specific mutation may be tested for the same mutation.
Testing depends upon the mutation type identified in the relative:

Nuclear DNA: cascade testing is via Sanger sequencing on an EDTA blood sample

mtDNA: cascade testing is via NGS panel for the specific mutation- blood, liver, muscle or urine samples are suitable depending upon the condition.

View Test & Specification requirements

Mutations in more than 290 different nuclear genes can cause mitochondrial disease. Clinical exome or genome sequencing will typically be the appropriate choice for nuclear gene testing.

View Test & Specification requirements

a) Deletion quantitation - second tier test

This is a second-tier test to accurately quantitate the heteroplasmy levels of previously identified mtDNA deletions in samples where there is a concern regarding whether the amount of deleted mtDNA is likely to be sufficiently high to cause symptoms.

Please contact the laboratory to discuss the sample requirements and pricing for this test prior to request.

b) Depletion quantitation

View Test & Specification requirements

Respiratory chain enzyme testing in biopsies or perimortem samples of muscle, liver or heart or in cultured skin fibroblasts has traditionally been the first line diagnostic method used for most children with suspected mitochondrial disease.

An accurate enzyme diagnosis can guide subsequent testing of single genes or to confirm that mutations in a candidate gene are truly causative. In recent years it has become common to offer exome sequencing or mtDNA sequencing or both prior to enzyme testing.

View Test & Specification requirements

This test is the most comprehensive test to identify variants in the one analysis. Whole Genome Sequencing enables the identification of single nucleotide and copy number variants in more than 290 nuclear encoded genes, as well as genes in the mitochondrial genome.

Accurate quantitation of heteroplasmy levels of large (>1kb) mtDNA deletions is possible with this assay.

DNA extracted from EDTA blood or muscle biopsy are the most suitable samples for analysis (urine and saliva samples are not suitable).

View Test & Specification requirements

Amplicon based, high coverage next generation sequencing (NGS) provides sensitive analysis of mtDNA. This assay detects any heteroplasmic or homoplasmic single nucleotide variant (SNV) as well as large deletions in a single assay.

Please note: Heteroplasmy levels of large deletions are an estimate only, they cannot be accurately determined due to inherent PCR bias.

This assay is not validated for the detection of large duplications.

View Test & Specification requirements
How do I arrange a test?

Testing is performed when an individual is suspected of having a mitochondrial disorder. This can be at any age but often occurs in the newborn period or infancy. Testing can also be performed in early childhood, adolescence, in young adults or in middle age. This is a specialised test that is usually ordered by a paediatrician or other medical specialist.

Please provide the following clinical details (if available) to enable optimal interpretation:

  • Patient name, medical record no., date of birth, date of sample, delay between death and freezing if relevant.
  • Full clinical summary and family history with pedigree.
  • Include copies of relevant investigations
    • urine organic & amino acids
    • tissue histology (including electron microscopy & enzyme histochemistry)
    • summary of CT, MRI or MRS studies of brain.
  • Paired plasma lactate & pyruvate levels; multiple estimations preferred.
  • Paired CSF lactate & pyruvate levels, preferably with blood levels obtained at about the same time.
Frequently asked questions

What are mitochondria?

Mitochondria are organelles in all our cells that take part in a wide range of metabolic pathways. They are the body's power plants that burn fuels (sugars, fats and proteins) to generate energy in the form of a small molecule called ATP.

The mitochondrial respiratory chain or oxidative phosphorylation system is the central energy generating pathway in cells. It comprises five enzyme complexes located in the mitochondrial inner membrane. More than 1000 genes are required for normal mitochondrial function. However, a unique feature of the mitochondrion is that it contains an additional genome (mitochondrial DNA), located within the mitochondrion itself.

What are the symptoms of a mitochondrial disorder?

The symptoms of mitochondrial disorders vary widely. Some symptoms of inherited mitochondrial disorders include lethargy, failure to gain weight, developmental delay, seizures, diabetes, muscle weakness, deafness and loss of vision.

What treatments are available for a mitochondrial disorder?

Treatment focuses on management of specific symptoms, ensuring good nutrition, aggressive management of infections and identifying patients for whom specific treatment options are available. For some mitochondrial disorders, there are no effective treatments.

How much experience does the VCGS Mitochondrial laboratory have?

The laboratory has acted as the Australasian referral centre for diagnosis of mitochondrial disease in children for more than two decades. We have diagnosed more than 600 children. The laboratory is tightly integrated with the Murdoch Childrens Research Institute and has a high international profile in mitochondrial disease. Our achievements include translating knowledge of mitochondrial DNA genetics into reproductive options for families, defining the most widely used diagnostic criteria for mitochondrial disorders, defining the epidemiology of childhood mitochondrial diseases and improving diagnosis and discovery of new 'disease' genes through Next Generation DNA sequencing. Either in house or through collaboration with national and international colleagues, we have identified mutations in more than 60 different disease genes, 20 of which we were the first to identify.