Mitochondrial disease symptoms

Because mitochondria are present in almost every cell in our body, people can develop a wide range of symptoms depending on which cells are affected by faulty mitochondria. Even within members of the same family, people can be affected in completely different ways, with one person much more severely affected than another. This is why we sometimes use the phrase ‘any symptom, any organ, any age’.

This page explains the types of symptoms that may be seen in mitochondrial disease, how they can differ by life stage and body system, and when to seek medical advice. It does not provide a diagnosis. Only specialist healthcare professionals can diagnose mitochondrial disease.

If you’re concerned about symptoms, you should speak to your GP, who can refer to appropriate NHS specialists where needed.

Why mitochondrial disease symptoms can be so different

Mitochondria are structures inside our cells that convert energy into a form that the cell can use. Because nearly all cells rely on energy to function, mitochondrial disease can affect many different organs and systems, including the brain, muscles, heart and digestive system.

Symptoms can vary because:

• Different genetic changes affect mitochondria in different ways
• Organs have different energy demands
• Symptoms may develop gradually or change over time

Even people with the same genetic condition can experience very different symptoms and levels of severity.

People are sometimes diagnosed with a mitochondrial ‘syndrome’, which means a recognised pattern or collection of symptoms that tend to occur together. These syndromes are frequently named after the doctors who first described or classified them. However, a diagnosis doesn’t mean that every individual will develop all the associated symptoms or experience them to the same degree.

Symptoms by life stage

Symptoms in babies and young children

In babies and young children, mitochondrial disease often affects development and growth. Symptoms may appear in infancy or early childhood and can involve more than one system.

Symptoms may include:

• Developmental delay or loss of previous skills (regression)
• Low or high muscle tone (hypotonia or dystonia)
• Feeding and swallowing difficulties or poor weight gain
• Frequent vomiting
• Seizures
• Movement, co-ordination or balance difficulties
• Recurrent or severe illness, particularly during infections
• Abnormal breathing patterns – panting without previous exertion, long pauses in breathing
• Sudden collapse due to cardiac arrhythmia or cardiac failure (cardiomyopathy)

Symptoms in children and teenagers

In childhood and adolescence, mitochondrial disease symptoms may become more noticeable as physical and cognitive demands increase.

Symptoms may include:

• Muscle weakness or fatigue during activity
• Difficulty with balance or co-ordination
• Learning difficulties
• Headaches or migraines
• Hearing or vision problems, drooping of eyelids
• Delayed puberty or growth issues

Symptoms in adults

Adults with mitochondrial a disorder may experience symptoms that develop slowly and can initially affect a single body system.

Symptoms may include:

• Persistent fatigue or reduced exercise tolerance
• Muscle weakness, pain or cramps
• Drooping of the eyelids and restriction of eye movements
• Hearing loss
• Visual changes – sudden loss of central vision in some cases
• Migraines
• Gastrointestinal problems – severe constipation, early fullness and loss of appetite
• Diabetes or other endocrine issues
• Balance problems or peripheral neuropathy – decreased sensation and/or power as a result of nerve involvement, typically affecting the feet more than the hands

Some adults live with mild or unexplained symptoms for many years before mitochondrial disease is considered.

Symptoms by body system

Neurological symptoms

The nervous system has high energy demands and is commonly affected.

Symptoms may include:

• Seizures or epilepsy
• Migraines or recurrent headaches
• Developmental delay
• Movement disorders
• Stroke‑like episodes
• Tingling, numbness or weakness due to nerve involvement

Muscular symptoms

Muscle symptoms are common and may affect everyday activity.

Symptoms may include:

• Muscle weakness
• Rapid fatigue with exercise
• Muscle pain or cramps
• Drooping eyelids (ptosis)

Cardiac symptoms

The heart relies heavily on energy and may be affected in some people.

Symptoms may include:

• Cardiomyopathy (heart muscle disease) – usually thickening of heart muscle
• Heart rhythm problems
• Reduced exercise tolerance

Heart involvement may not produce symptoms early and is often monitored through specialist tests.

Gastrointestinal symptoms

Digestive symptoms can affect nutrition and growth.

Symptoms may include:

• Feeding difficulties
• Reflux or vomiting
• Diarrhoea or constipation
• Abdominal pain
• Poor weight gain

Vision and hearing symptoms

Vision and hearing problems may occur at any age.

Symptoms may include:

• Hearing loss
• Visual impairment – can be sudden central vision loss
• Optic nerve involvement
• Difficulty with night or peripheral vision

Endocrine and metabolic symptoms

Energy disruption can affect hormone systems.

Symptoms may include:

• Diabetes
• Growth problems
• Problems with temperature regulation
• Thyroid or hormonal imbalance

Symptoms can change over time

Mitochondrial disease symptoms may progress, remain stable or fluctuate. Some people notice symptoms worsen during periods of illness, stress or physical exertion. Others experience long periods with little change.

There is no single pattern that applies to everyone.

When symptoms may need specialist assessment

The following features do not confirm mitochondrial disease, but may prompt consideration for specialist review:

• Symptoms in more than one organ system, for example muscle weakness plus hearing loss
• Unexplained neurological symptoms, such as seizures or stroke-like episodes, especially at a young age
• A condition called lactic acidosis (an increase in lactic acid concentration in the body) on blood tests without another clear cause. This can cause nausea and vomiting, fatigue, fast, deep breathing and muscle cramps
• A family history of similar symptoms, sudden visual loss, hearing loss or unexplained early deaths
• Recurrent episodes of severe fatigue or regression after an illness

Red flags like these are a guide, not a diagnosis. If any of these sound familiar, keep a simple symptom diary and share it with your GP. It can help move you to the right tests more quickly.

Getting medical advice and support

The Lily Foundation does not diagnose mitochondrial disease. Diagnosis is carried out by specialist NHS teams, such as neurologists, clinical geneticists and metabolic doctors working in either paediatric or adult practice and sometimes within the NHS Highly Specialised Services for Rare Mitochondrial Disorders.

If you’re concerned about symptoms:

• Speak to your GP
• Share a clear symptom history
• Ask whether specialist referral may be appropriate

You can learn more about the diagnostic process on our page about mitochondrial disease diagnosis.

Frequently asked questions

Can mitochondrial disease symptoms be mild?

Yes. Some people have mild or non‑specific symptoms that can be difficult to recognise, especially in early stages.

Can mitochondrial disease start in adulthood?

Yes. Although mitochondrial disorders are genetic, symptoms may first appear in adolescence or adulthood.

Are symptoms the same for everyone?

No. Symptoms, severity and progression vary widely, even between people with the same genetic condition.

Can mitochondrial disease be misdiagnosed?

Yes. Because symptoms overlap with other conditions, misdiagnosis can occur, particularly before specialist assessment.

What should I do if I’m worried about symptoms?

Speak to your GP. They can assess your concerns and refer to appropriate NHS specialists if needed.

Support beyond medical care

Living with uncertainty around symptoms can be challenging. Many people benefit from emotional support, patient organisations and reliable information alongside medical care.

If you or someone you know has a suspected mitochondrial disorder, The Lily Foundation are here to offer compassion, community and ongoing support every step of the way. We’re here to help you navigate the questions you inevitably have, offering resources, guidance and a caring community so you don’t have to face these challenges alone.

We invite you to learn more about our work, our mission and how you can connect with others who share your journey. Explore our website and our information on understanding mitochondrial disease, as well as reading our mitochondrial disease guide. Why not read all about The Lily Foundation’s research and, most importantly, take a look at all the ways we can offer mitochondrial disease support.

Important note: This page provides general information only and does not confirm or rule out any condition. Always seek advice from a qualified healthcare professional.