Publicly funded genome sequencing is providing meaningful diagnoses for people with suspected mitochondrial disease, including conditions such as thymidine kinase 2 deficiency (TK2d), although access to testing remains uneven, according to a study published recently in the European Journal of Human Genetics.
An evaluation of the first 19 months of publicly funded genome sequencing in Australia found that the technology delivered definitive genetic diagnoses for 20% of patients tested. Researchers concluded that while genome sequencing can significantly improve detection of mitochondrial disorders such as TK2d, efforts are needed to ensure patients in regional and remote areas can access the testing.
“There is a clear need for a framework to systematically review the implementation of genomic tests into standard clinical practice, including the definition of what constitutes appropriate outcome measures to drive future policy and practice to ensure equitable, timely and sustainable implementation,” explained this study’s authors.
The analysis included the first 300 individuals who underwent publicly funded genome sequencing for suspected mitochondrial disease between November 2023 and May 2025. The program became available nationwide through the Medicare Benefits Scheme in November 2023. Patients ranged from 3 months to 96 years old, with a median age of 25 years. The cohort included 159 females and 167 adults. Sequencing results were typically returned in a median of 84 days.
Read more about testing and diagnosis for TK2d
Among the patients tested, 61 received a definitive diagnosis. Thirty-four of these diagnoses involved mitochondrial disease genes, conditions that can include disorders such as TK2d that affect how mitochondria generate energy in cells. Twenty-four of the mitochondrial diagnoses were caused by mutations in mitochondrial DNA, while 10 were in nuclear genes that control mitochondrial function.
Genome sequencing also uncovered diagnoses that earlier tests had missed. Seventeen patients who received a diagnosis had previously undergone genetic testing without success, including exome sequencing or targeted gene panels. In some cases, genome sequencing identified complex genetic changes or mitochondrial DNA deletions that older tests could not reliably detect. These findings show how advanced sequencing can reveal the underlying cause of symptoms in mitochondrial diseases such as TK2d.
The testing also identified 27 patients with non-mitochondrial genetic disorders. Many of these involved neurodevelopmental syndromes, while others included conditions such as epilepsy, cardiomyopathy or metabolic diseases. Some of these diagnoses were considered actionable or treatable, including GLUT1 deficiency and certain cancer predisposition syndromes.
However, the study also highlighted disparities in access. Most testing occurred in major cities, which accounted for 80% of cases, while very remote areas represented only 0.3%. Even after adjusting for population size, testing rates remained lower in remote regions. Researchers say addressing these gaps is essential so that patients with mitochondrial disorders such as TK2d can benefit equally from genomic advances.
For patients and families affected by mitochondrial disease, the findings suggest genome sequencing could shorten the diagnostic journey and reveal causes that might otherwise remain unknown. Expanding access to testing and integrating it into routine clinical care may allow more patients with conditions such as TK2d to receive earlier diagnoses and more targeted care.
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