What are the symtoms?

When we think of the symptoms that might present in mitochondrial disease, we need to think of the organ systems that work the hardest and the longest and so require the most energy. Also, the complex specialisation of mitochondria within each cell causes a dizzying array of symptoms that mitochondrial specialists have come to recognise as characteristic of this illness. 

Symptoms may be absent in healthy people who have silent genetic defects, or can be complex and multiple in a person with advanced disease. Many combinations of symptoms are also possible, even in those people with exactly the same genetic defect!

Therefore, with so many illnesses looking like mitochondrial disease and mitochondrial disease looking like so many illnesses, how do we know which is which?

 Firstly, we must suspect mitochondrial disease when: 

  1. a ‘common diseas’ has atypical features; and/or
  2. three or more organ systems are involved; and/or
  3. recurrent setbacks or flare-ups occur with infections in a ‘normal’ chronic illness.

The most common symptom is fatigue. This is not the type of fatigue one experiences after a busy day. Rather it feels like ‘hitting the wall’. Often when mitochondria are well rested, a person can achieve what they want and appear ‘normal’. However, in times of excess energy loss, high physical stresses or poor energy input, the person may feel extremely fatigued and often struggles to simply get out of bed.

These energy level fluctuations can make it difficult for a person to present their case to a practitioner. Overall, like most mitochondrial symptoms, the fatigue will progress over time, although at vastly different rates for different people.

The highest energy user in our body is our brain. The brain works constantly in the background, monitoring and controlling most of our bodily functions to the point where it requires 20% of our total energy input. The main neurological symptoms of mitochondrial disease include developmental delays, mental retardation or regression, dementia, seizures (especially atypical or refractory ones), coma, neuro-psychiatric disturbances, atypical cerebral palsy, myoclonus (brief, involuntary muscle twitching), movement disorders, ataxia (poor coordination), migraines and strokes.

Symptoms relating to muscles and nerves include weakness (may be intermittent), altered nerve sensation, fainting, temperature regulation problems, low muscle tone, muscle cramping or pain, and recurrent rhabdomyolysis (rapid muscle breakdown).

As our ears and eyes rarely rest, visual loss or blindness, and deafness (often intermittent) are another common feature of mitochondrial disease. Weak eye muscles may present as droopy eyelids (ptosis), and difficulty in moving the eyes together. Night blindness and colour-vision deficits are other less common but possible symptoms.

The bowel can show symptoms such as gastro-oesophageal reflux (indigestion), delayed gastric emptying (feeling full a lot), constipation, pseudo-obstruction, chronic or recurrent vomiting, and sometimes difficulties in swallowing. Unfortunately, these complaints are common so it is hard to determine their cause.


The kidney, heart and liver are often the forgotten high energy organs, but are very significant because their deterioration plays vital roles in the patient’s prognosis. Nephrotic syndrome, the loss of important electrolytes in ‘leaky kidneys’, heart arrhythmias, heart blocks, cardiomyopathy (large heart), and unexplained liver abnormalities are some of the earlier signs that could lead to the events of kidney, heart or liver failure.

Diabetes, short stature, an underactive thyroid or parathyroid, excess body hair, exercise intolerance not in proportion to weakness, hypersensitivity to general anaesthetics, and symmetrical fatty lumps in the skin are other symptoms to alert someone of possible mitochondrial disease.

In children, symptoms such as IUGR (poor growth inside the womb), unexplained low muscle tone, weakness, failure to thrive, infantile spasms, unexplained seizures/fits, microencephaly, and a family history of SIDS should be investigated further, especially if the child does not progress or seems to be slowly deteriorating.

The diagram on the right shows a summary of possible mitochondrial symptoms. Over time as we study and further understand this illusive illness, we will be better equipped to diagnose it.