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When it comes to diagnosing TK2 deficiency (TK2D), the debate between muscle biopsy and genetic testing — and which genetic test to use — has real clinical stakes. Experts now lean toward whole exome sequencing as a first-line approach in the U.S., warning that stopping at a gene panel risks missing the diagnosis and delaying treatment. Time, access, and a broad differential all factor into the decision.
Diagnosing TK2 deficiency (TK2D), a rare mitochondrial muscle disease, requires navigating a tricky choice: start with a muscle biopsy, a gene panel, or go straight to whole exome sequencing? Experts Dr. Michio Hirano and Dr. Zarazuela Zolkipli-Cunningham break it down, noting that while most centers favor genetic testing first, biopsies can provide valuable functional evidence — especially when showing respiratory chain defects and mitochondrial DNA depletion consistent with TK2 variants.
The catch? A biopsy without depletion doesn't rule out TK2D, since depletion depends on disease phase. And on the genetic side, stopping at a panel isn't enough — a panel followed by exome sequencing can eat up six months, potentially delaying treatment that works better when started earlier.
Key Takeaways
Why it matters: TK2D is now a treatable condition, and earlier intervention appears to improve outcomes. Getting the diagnosis right — and fast — is no longer just academic; it directly shapes patient prognosis.
