Muscle biopsy is no longer the gold standard for diagnosing Mitochondrial disease.

There are a number of diagnostic tools used.

Metabolic Labs-urine and blood(some very specialized)

Genetics-

Clinical examination(more then 2 organ systems involved)

Ruling out any other possible disease process.

Mito is one of the most difficult diseases to diagnosis. Sometimes Mito can be primary or secondary(secondary to nutrition,diabetes,cancer,medications etc). Currently, only a small percent of the overall population of Mito Patients has a gene mutation identified as disease causing. Mito can be because of either mutations/deletions/depletions in mtDNA or nDNA. It can cause poor function of the mitochondria(Function I,II, III, etc).

Muscle biopsy for Mito is though the only way to definitely diagnose Mitochondrial Depletion, for 80 percent of those with a depletion. Only 20 percent of have gene identified. The best part about a biopsy is that it can rule out many other diseases of the muscle.

They are now using swab testing of saliva even for testing.

The specialist are really working hard to find less invasive ways to diagnose. For many with Mitochondrial disease something like a muscle biopsy is incredibly difficult on their energy and ability to heal and recover.

For our daughter, all metabolic labwork was normal. Nothing indicated a Mitochondrial Disease, so we went ahead and did the biopsy(second one) more to see if there was another disease of the muscle- to our surprise they found the depletion.