A neurologist or geneticist can order a muscle biopsy. For the most part these days, many mitochondrial diseases are found via blood work.
Genetics have come a long way, and a knowledgeable geneticist or neurologist can run mtDNA and nDNA bloodwork to find out if you have a mutation that is linked to various forms of mito disease.
Mitochondrial dysfunction is a secondary finding in many many different disease processes(learn more at UMDF and MitoAction.org). If the specialists feel strongly they know what the primary disorder is that is causing the mitochondrial findings they often won’t test further.
However, if the findings don’t seem to have a primary they will continue to test.
Depletions are a little different- they have isolated around 12 different nDNA mutations that cause depletions, but that covers less then 20 percent of patients who have depletions found on muscle biopsy. So, unless you are one of the 20 percent, have clinical findings that encourage a Dr. to test for those known mutations it is statistically more difficult to identify a depletion without it being found on muscle biopsy.
Depletions can be caused by certain medications and illnesses- but with Abby because she was symptomatic from birth, the feeling always leaned toward genetic.
Because Abby’s constellation of clinical findings were so odd ball and metabolic blood work did not indication much we opted for the second muscle biopsy- she clearly had some sort of neuro muscular issues but all the less invasive options were not showing anything.
Finding a lab that knows how to handle a biopsy to diagnosis Mito is a whole other ball of wax. I know there is one center in the UK that was listed as number 1 for years for identifying myopathies and have read that in general the UK is moving along quickly for mito diagnostics. I know the different labs with good reputations for diagnostics in the US but don’t know who would be recommended in the UK.
I know Dr. Theo recently discovered that Mast cells can cause damage to mitochondria- I am hopeful he will research this further. It in my mind is a break through finding that may explain a lot not just for us, but many who suffer Mast with extreme fatigue etc(Mitochondria as you know are how our bodies make energy).
Hoping that answered your questions? If not I will try again 🙂 Not the greatest at explaining this stuff 🙂