Medical Conditions

Signs of Mitochondrial Disease in Babies

Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist

Content reviewed against published NIH, AAP, Mayo Clinic guidelines

Editorial policy

Last reviewed:

If your baby has been diagnosed with or you suspect signs of mitochondrial disease in babies, here is what the evidence says.

The short answer

Mitochondrial diseases affect the body's ability to produce energy at the cellular level and can affect virtually any organ system. Signs in babies include low muscle tone, poor growth, developmental delays or regression, seizures, vision or hearing loss, exercise intolerance, and multi-organ involvement (brain, muscles, heart, liver). These conditions are rare but important to consider when a baby has progressive symptoms affecting multiple organ systems. Diagnosis requires specialized testing.

Key takeaways

  • Mitochondrial diseases affect the body's ability to produce energy at the cellular level and can affect virtually any organ system. Signs in babies include low muscle tone, poor growth, developmental delays or regression, seizures, vision or hearing loss, exercise intolerance, and multi-organ involvement (brain, muscles, heart, liver). These conditions are rare but important to consider when a baby has progressive symptoms affecting multiple organ systems. Diagnosis requires specialized testing.
  • Usually normal when: Your baby has an isolated developmental delay that is improving with therapy
  • Call your doctor if: Your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction
  • Varies by age — see the age-by-age breakdown below
“Fever itself is not an illness — rather, it is a sign or symptom that the body is fighting an infection. Fever stimulates certain defenses, such as the white blood cells, which attack and destroy invading bacteria.”
— Fever and Your Child, American Academy of Pediatrics (AAP)

Thousands of parents search for this exact thing. You are not alone.

What Parents Should Know

According to NIH, AAP, Mayo Clinic guidelines, mitochondrial diseases affect the body's ability to produce energy at the cellular level and can affect virtually any organ system. Signs in babies include low muscle tone, poor growth, developmental delays or regression, seizures, vision or hearing loss, exercise intolerance, and multi-organ involvement (brain, muscles, heart, liver). These conditions are rare but important to consider when a baby has progressive symptoms affecting multiple organ systems. Diagnosis requires specialized testing. At 0-3 months, severe mitochondrial disease can present at birth with lactic acidosis, low muscle tone, seizures, liver dysfunction, or cardiomyopathy. Some babies appear well at birth and develop symptoms over weeks. Multi-organ involvement is a hallmark: a combination of neurological, cardiac, and metabolic symptoms should raise suspicion. It is generally considered normal when your baby has an isolated developmental delay that is improving with therapy. However, you should contact your pediatrician promptly if your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction.

Sources: [1], [2], [3]

Normal vs. Concerning

Usually Normal
Worth Discussing
Your baby has an isolated developmental delay that is improving with therapy
Your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction
Your baby recovers normally from illnesses
Your baby develops sudden new neurological symptoms like stroke-like episodes, vision loss, or severe weakness
Your baby has normal growth and energy levels
Your baby has symptoms affecting multiple organ systems without a clear unifying diagnosis

By Age

What to expect by age

0-3 months

Severe mitochondrial disease can present at birth with lactic acidosis, low muscle tone, seizures, liver dysfunction, or cardiomyopathy. Some babies appear well at birth and develop symptoms over weeks. Multi-organ involvement is a hallmark: a combination of neurological, cardiac, and metabolic symptoms should raise suspicion.

3-6 months

Signs may include poor growth, feeding difficulties, low muscle tone, motor delays, and episodes of metabolic decompensation during illness. Elevated lactate levels in blood or spinal fluid may be a clue. Some mitochondrial diseases present with specific patterns of brain involvement visible on MRI.

6-12 months

Developmental delays or failure to achieve milestones may become apparent. Some mitochondrial diseases cause progressive symptoms, while others fluctuate. Episodes of worsening during illness (metabolic decompensation) are common. A metabolic genetics specialist can guide evaluation and testing.

12-24 months

Developmental regression (losing previously acquired skills) is an important red flag for mitochondrial disease. Toddlers may show increasing fatigue, feeding problems, or new neurological symptoms. Heart involvement (cardiomyopathy) may become apparent with poor stamina or breathing difficulties.

2-3 years

Later-presenting mitochondrial disease may show as exercise intolerance, stroke-like episodes, seizures, hearing loss, or vision problems. These children often seem to have "more than their share" of problems affecting multiple organs. A mito specialist coordinates multidisciplinary care.

What to Tell Your Pediatrician

  • Describe when you first noticed signs of mitochondrial disease in babies and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby has symptoms affecting multiple organ systems without a clear unifying diagnosis.
  • Mention if your baby has developmental delays with unexplained elevated lactate levels.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

What Should You Do?

When to take action

Probably normal when...
  • Your baby has an isolated developmental delay that is improving with therapy
  • Your baby recovers normally from illnesses
  • Your baby has normal growth and energy levels
Mention at your next visit when...
  • Your baby has symptoms affecting multiple organ systems without a clear unifying diagnosis
  • Your baby has developmental delays with unexplained elevated lactate levels
  • Your baby becomes disproportionately ill during minor infections
Act now when...
  • Your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction
  • Your baby develops sudden new neurological symptoms like stroke-like episodes, vision loss, or severe weakness

What You Can Do at Home

  • Keep track of when you notice signs of mitochondrial disease in babies — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your baby has an isolated developmental delay that is improving with therapy — this is generally within the range of normal.
  • At 0-3 months, focus on observation rather than intervention unless your pediatrician advises otherwise.
  • Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
  • While monitoring at home, seek immediate care if your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction.

Signs of a Metabolic Disorder in Babies

Metabolic disorders (inborn errors of metabolism) occur when the body cannot properly process certain nutrients or chemicals. Many are detected through newborn screening. Signs can include poor feeding, vomiting, lethargy, seizures, unusual body or urine odor, failure to thrive, developmental regression, and metabolic crises triggered by illness or fasting. Early detection and treatment are crucial, as many metabolic disorders are manageable with dietary modifications and medical treatment.

Signs of Lysosomal Storage Disease in Babies

Lysosomal storage diseases are a group of rare inherited conditions where the body lacks enzymes needed to break down certain substances, causing them to accumulate in cells. Signs may include developmental regression, enlarged liver or spleen, coarsening facial features, skeletal abnormalities, corneal clouding, and progressive neurological decline. Early diagnosis is important because some conditions now have enzyme replacement therapy or other treatments that can slow disease progression.

When Is Genetic Testing Recommended for a Baby?

Genetic testing may be recommended when a baby has multiple birth defects, developmental delays without clear cause, dysmorphic features, a family history of genetic conditions, abnormal newborn screening results, or when a specific genetic condition is suspected. Types of testing include chromosomal microarray, whole exome sequencing, and targeted gene panels. Results can guide treatment, predict outcomes, and inform family planning.

Milestone

Month-by-Month Development

Detailed monthly development guides from birth through 24 months.

Guide

When to Call the Doctor

General guide on when to call the pediatrician, visit urgent care, or go to the ER.

Frequently asked questions

Is signs of mitochondrial disease in babies normal?
Mitochondrial diseases affect the body's ability to produce energy at the cellular level and can affect virtually any organ system. Signs in babies include low muscle tone, poor growth, developmental delays or regression, seizures, vision or hearing loss, exercise intolerance, and multi-organ involvement (brain, muscles, heart, liver). These conditions are rare but important to consider when a baby has progressive symptoms affecting multiple organ systems. Diagnosis requires specialized testing.
When should I call the doctor about signs of mitochondrial disease in babies?
Your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction Your baby develops sudden new neurological symptoms like stroke-like episodes, vision loss, or severe weakness
When is signs of mitochondrial disease in babies normal?
Your baby has an isolated developmental delay that is improving with therapy Your baby recovers normally from illnesses Your baby has normal growth and energy levels
What causes signs of mitochondrial disease in babies?
Mitochondrial diseases affect the body's ability to produce energy at the cellular level and can affect virtually any organ system. Signs in babies include low muscle tone, poor growth, developmental delays or regression, seizures, vision or hearing loss, exercise intolerance, and multi-organ involvement (brain, muscles, heart, liver). These conditions are rare but important to consider when a baby has progressive symptoms affecting multiple organ systems. Diagnosis requires specialized testing. Common explanations include: Your baby has an isolated developmental delay that is improving with therapy. Your baby recovers normally from illnesses.
What should I mention to my pediatrician about signs of mitochondrial disease in babies?
You should mention signs of mitochondrial disease in babies at your next visit if: Your baby has symptoms affecting multiple organ systems without a clear unifying diagnosis. Your baby has developmental delays with unexplained elevated lactate levels. Your baby becomes disproportionately ill during minor infections.
Is signs of mitochondrial disease in babies normal at 0-3 months?
Severe mitochondrial disease can present at birth with lactic acidosis, low muscle tone, seizures, liver dysfunction, or cardiomyopathy. Some babies appear well at birth and develop symptoms over weeks. Multi-organ involvement is a hallmark: a combination of neurological, cardiac, and metabolic symptoms should raise suspicion.
Is signs of mitochondrial disease in babies normal at 3-6 months?
Signs may include poor growth, feeding difficulties, low muscle tone, motor delays, and episodes of metabolic decompensation during illness. Elevated lactate levels in blood or spinal fluid may be a clue. Some mitochondrial diseases present with specific patterns of brain involvement visible on MRI.
Should I go to the ER for signs of mitochondrial disease in babies?
Seek emergency care if your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction, or if your baby develops sudden new neurological symptoms like stroke-like episodes, vision loss, or severe weakness. When in doubt, call your pediatrician's after-hours line for guidance.
Does signs of mitochondrial disease in babies go away on its own?
In many cases, signs of mitochondrial disease in babies resolves on its own, especially when your baby has an isolated developmental delay that is improving with therapy. By 2-3 years, later-presenting mitochondrial disease may show as exercise intolerance, stroke-like episodes, seizures, hearing loss, or vision problems. These children often seem to have "more than their share" of problems affecting multiple organs. A mito specialist coordinates multidisciplinary care.
NIHAAPMAYO CLINIC

References

  1. [1]National Institute of Neurological Disorders and Stroke. Mitochondrial Myopathies. NIH
  2. [2]American Academy of Pediatrics. Mitochondrial Disorders. HealthyChildren.org. AAP
  3. [3]Mayo Clinic. Mitochondrial disease. Mayo Clinic

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss Signs of Mitochondrial Disease in Babies.

Things to mention

  • Describe when you first noticed signs of mitochondrial disease in babies and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby has symptoms affecting multiple organ systems without a clear unifying diagnosis.
  • Mention if your baby has developmental delays with unexplained elevated lactate levels.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

Observations to share

  • Your baby has symptoms affecting multiple organ systems without a clear unifying diagnosis
  • Your baby has developmental delays with unexplained elevated lactate levels
  • Your baby becomes disproportionately ill during minor infections

Urgent signs to report immediately

  • Your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction
  • Your baby develops sudden new neurological symptoms like stroke-like episodes, vision loss, or severe weakness

My notes

From ismybabyalright.com — free, evidence-based baby health guides

All content follows our editorial policy and is reviewed against published clinical guidelines.

2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members

Related Resources

Well-Baby Visit PrepBaby Sign Language GuideBaby Tracker

Bottom line

Most cases of signs of mitochondrial disease in babies are normal. Talk to your pediatrician if your baby has a metabolic crisis with severe lethargy, seizures, or organ dysfunction.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.

Share:FacebookX

Was this page helpful?

Related Medical Concerns

Signs of a Metabolic Disorder in Babies

Metabolic disorders (inborn errors of metabolism) occur when the body cannot properly process certain nutrients or chemicals. Many are detected through newborn screening. Signs can include poor feeding, vomiting, lethargy, seizures, unusual body or urine odor, failure to thrive, developmental regression, and metabolic crises triggered by illness or fasting. Early detection and treatment are crucial, as many metabolic disorders are manageable with dietary modifications and medical treatment.

Signs of Lysosomal Storage Disease in Babies

Lysosomal storage diseases are a group of rare inherited conditions where the body lacks enzymes needed to break down certain substances, causing them to accumulate in cells. Signs may include developmental regression, enlarged liver or spleen, coarsening facial features, skeletal abnormalities, corneal clouding, and progressive neurological decline. Early diagnosis is important because some conditions now have enzyme replacement therapy or other treatments that can slow disease progression.

When Is Genetic Testing Recommended for a Baby?

Genetic testing may be recommended when a baby has multiple birth defects, developmental delays without clear cause, dysmorphic features, a family history of genetic conditions, abnormal newborn screening results, or when a specific genetic condition is suspected. Types of testing include chromosomal microarray, whole exome sequencing, and targeted gene panels. Results can guide treatment, predict outcomes, and inform family planning.

My Baby's Head Shape Looks Abnormal

Many babies develop temporary head shape irregularities that are completely normal. A cone-shaped head from vaginal delivery reshapes within days. Mild positional flattening (plagiocephaly) from sleeping on the back is very common and usually improves with repositioning and tummy time. However, head shape changes involving ridges, a persistently bulging fontanelle, or rapid head growth changes should be evaluated to rule out craniosynostosis.

Achondroplasia (Dwarfism) in Babies

Achondroplasia is the most common form of short-limbed dwarfism, affecting about 1 in 15,000 to 40,000 births. It is caused by a mutation in the FGFR3 gene and is usually apparent at birth with characteristic features including short limbs, a larger head, and a prominent forehead. Intelligence is normal. With monitoring for specific complications and supportive care, children with achondroplasia lead full, active, and independent lives.

Adenoid Hypertrophy and Breathing

Adenoids are lymphoid tissue located behind the nose that help fight infection in young children. When adenoids become enlarged (adenoid hypertrophy), they can block the nasal airway, causing chronic mouth breathing, snoring, nasal speech, and sleep-disordered breathing. Enlarged adenoids are most common between ages 2-7 and are a leading cause of obstructive sleep apnea in young children. Treatment ranges from watchful waiting and nasal steroids to surgical removal (adenoidectomy) if breathing or sleep is significantly affected.