Medical Conditions

Metachromatic Leukodystrophy (MLD) in Babies

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

Content reviewed against published NIH, FDA, NIH guidelines

Editorial policy

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If your baby has been diagnosed with or you suspect metachromatic leukodystrophy (mld) in babies, here is what the evidence says.

The short answer

Metachromatic leukodystrophy (MLD) is a rare inherited lysosomal storage disorder affecting about 1 in 40,000 to 160,000 people, caused by deficiency of the enzyme arylsulfatase A (ARSA). This leads to progressive destruction of myelin (the protective white matter coating on nerves) in the brain and peripheral nerves. The late infantile form is the most common and severe, typically presenting between ages 1-2 with loss of motor skills and progressive neurological decline. Gene therapy (atidarsagene autotemcel/Lenmeldy) has been approved for presymptomatic or early symptomatic patients, offering the first disease-modifying treatment option.

Key takeaways

  • Metachromatic leukodystrophy (MLD) is a rare inherited lysosomal storage disorder affecting about 1 in 40,000 to 160,000 people, caused by deficiency of the enzyme arylsulfatase A (ARSA). This leads to progressive destruction of myelin (the protective white matter coating on nerves) in the brain and peripheral nerves. The late infantile form is the most common and severe, typically presenting between ages 1-2 with loss of motor skills and progressive neurological decline. Gene therapy (atidarsagene autotemcel/Lenmeldy) has been approved for presymptomatic or early symptomatic patients, offering the first disease-modifying treatment option.
  • Usually normal when: Your baby is developing on schedule with no signs of regression, and you are monitoring because of a family history
  • Call your doctor if: Your child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation
  • 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)

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What Parents Should Know

According to NIH, FDA guidelines, metachromatic leukodystrophy (MLD) is a rare inherited lysosomal storage disorder affecting about 1 in 40,000 to 160,000 people, caused by deficiency of the enzyme arylsulfatase A (ARSA). This leads to progressive destruction of myelin (the protective white matter coating on nerves) in the brain and peripheral nerves. The late infantile form is the most common and severe, typically presenting between ages 1-2 with loss of motor skills and progressive neurological decline. Gene therapy (atidarsagene autotemcel/Lenmeldy) has been approved for presymptomatic or early symptomatic patients, offering the first disease-modifying treatment option. At 0-6 months, babies with MLD typically appear completely normal in the first months of life. Development proceeds normally, and there are usually no early signs. MLD is not currently included in standard newborn screening in most states, though some states are adding it. If there is a known family history of MLD, prenatal or newborn testing for ARSA enzyme activity and genetic confirmation should be pursued immediately, as early treatment (before symptoms begin) offers the best outcomes with gene therapy. It is generally considered normal when your baby is developing on schedule with no signs of regression, and you are monitoring because of a family history. However, you should contact your pediatrician promptly if your child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation.

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

Normal vs. Concerning

Usually Normal
Worth Discussing
Your baby is developing on schedule with no signs of regression, and you are monitoring because of a family history
Your child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation
Your child was treated with gene therapy before symptoms appeared and continues to develop
Your child is having seizures or episodes of stiffness with arching of the back
Your child is meeting milestones and MRI shows stable findings after treatment
Your toddler who was previously walking well is becoming increasingly clumsy or unsteady

By Age

What to expect by age

0-6 months

Babies with MLD typically appear completely normal in the first months of life. Development proceeds normally, and there are usually no early signs. MLD is not currently included in standard newborn screening in most states, though some states are adding it. If there is a known family history of MLD, prenatal or newborn testing for ARSA enzyme activity and genetic confirmation should be pursued immediately, as early treatment (before symptoms begin) offers the best outcomes with gene therapy.

6-12 months

In the late infantile form of MLD, babies typically continue to develop normally through this period, reaching milestones such as sitting, babbling, and sometimes cruising. However, subtle signs may begin to emerge toward the end of this period in some children, including clumsiness, difficulty with walking or standing, or irritability. Most children are not yet diagnosed at this stage unless there is a family history.

1-2 years

This is when the late infantile form of MLD most commonly becomes apparent. Children who had been walking may begin to stumble, fall frequently, or lose the ability to walk. Other early signs include stiffness or floppiness in the legs, difficulty with speech, and behavioral changes such as increased irritability. The regression of previously acquired motor skills is a key warning sign. An MRI showing white matter abnormalities, low ARSA enzyme activity, and elevated urine sulfatides confirm the diagnosis.

2-3 years

In untreated late infantile MLD, progression continues with loss of speech, swallowing difficulties, vision loss, and eventual loss of all voluntary movement. This is a devastating trajectory for families. Gene therapy (Lenmeldy/atidarsagene autotemcel) is FDA-approved for presymptomatic and early symptomatic late infantile MLD and has shown the ability to slow or halt disease progression in many treated children. Hematopoietic stem cell transplant may also be considered. Supportive care including physical therapy, feeding support, and seizure management is essential.

What to Tell Your Pediatrician

  • Describe when you first noticed metachromatic leukodystrophy (mld) 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 toddler who was previously walking well is becoming increasingly clumsy or unsteady.
  • Mention if your child is losing previously acquired motor or language skills.
  • 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 is developing on schedule with no signs of regression, and you are monitoring because of a family history
  • Your child was treated with gene therapy before symptoms appeared and continues to develop
  • Your child is meeting milestones and MRI shows stable findings after treatment
Mention at your next visit when...
  • Your toddler who was previously walking well is becoming increasingly clumsy or unsteady
  • Your child is losing previously acquired motor or language skills
  • You have a family history of MLD and want to discuss testing for your baby
  • Your child has been diagnosed with MLD and you want to discuss treatment options including gene therapy
Act now when...
  • Your child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation
  • Your child is having seizures or episodes of stiffness with arching of the back

What You Can Do at Home

  • Keep track of when you notice metachromatic leukodystrophy (mld) in babies — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your baby is developing on schedule with no signs of regression, and you are monitoring because of a family history — this is generally within the range of normal.
  • At 0-6 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 child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation.

Abnormal Newborn Screening Results

An abnormal or positive newborn screening result means that further testing is needed, not that your baby definitely has a condition. Most positive screens turn out to be false positives after confirmatory testing. Newborn screening tests are intentionally sensitive to avoid missing any affected babies, so follow-up testing is essential to determine whether the result is a true positive.

My Baby Lost Skills They Previously Had

Temporary regression in skills can be normal during periods of rapid growth, illness, stress, or when a baby is intensely focused on developing a new skill. However, true developmental regression - the sustained loss of previously acquired skills such as words, social engagement, or motor abilities - is always a reason to seek prompt medical evaluation. This is especially concerning if multiple skill areas are affected simultaneously.

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 metachromatic leukodystrophy (mld) in babies normal?
Metachromatic leukodystrophy (MLD) is a rare inherited lysosomal storage disorder affecting about 1 in 40,000 to 160,000 people, caused by deficiency of the enzyme arylsulfatase A (ARSA). This leads to progressive destruction of myelin (the protective white matter coating on nerves) in the brain and peripheral nerves. The late infantile form is the most common and severe, typically presenting between ages 1-2 with loss of motor skills and progressive neurological decline. Gene therapy (atidarsagene autotemcel/Lenmeldy) has been approved for presymptomatic or early symptomatic patients, offering the first disease-modifying treatment option.
When should I call the doctor about metachromatic leukodystrophy (mld) in babies?
Your child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation Your child is having seizures or episodes of stiffness with arching of the back
When is metachromatic leukodystrophy (mld) in babies normal?
Your baby is developing on schedule with no signs of regression, and you are monitoring because of a family history Your child was treated with gene therapy before symptoms appeared and continues to develop Your child is meeting milestones and MRI shows stable findings after treatment
What causes metachromatic leukodystrophy (mld) in babies?
Metachromatic leukodystrophy (MLD) is a rare inherited lysosomal storage disorder affecting about 1 in 40,000 to 160,000 people, caused by deficiency of the enzyme arylsulfatase A (ARSA). This leads to progressive destruction of myelin (the protective white matter coating on nerves) in the brain and peripheral nerves. The late infantile form is the most common and severe, typically presenting between ages 1-2 with loss of motor skills and progressive neurological decline. Gene therapy (atidarsagene autotemcel/Lenmeldy) has been approved for presymptomatic or early symptomatic patients, offering the first disease-modifying treatment option. Common explanations include: Your baby is developing on schedule with no signs of regression, and you are monitoring because of a family history. Your child was treated with gene therapy before symptoms appeared and continues to develop.
What should I mention to my pediatrician about metachromatic leukodystrophy (mld) in babies?
You should mention metachromatic leukodystrophy (mld) in babies at your next visit if: Your toddler who was previously walking well is becoming increasingly clumsy or unsteady. Your child is losing previously acquired motor or language skills. You have a family history of MLD and want to discuss testing for your baby.
Is metachromatic leukodystrophy (mld) in babies normal at 0-6 months?
Babies with MLD typically appear completely normal in the first months of life. Development proceeds normally, and there are usually no early signs. MLD is not currently included in standard newborn screening in most states, though some states are adding it. If there is a known family history of MLD, prenatal or newborn testing for ARSA enzyme activity and genetic confirmation should be pursued immediately, as early treatment (before symptoms begin) offers the best outcomes with gene therapy.
Is metachromatic leukodystrophy (mld) in babies normal at 6-12 months?
In the late infantile form of MLD, babies typically continue to develop normally through this period, reaching milestones such as sitting, babbling, and sometimes cruising. However, subtle signs may begin to emerge toward the end of this period in some children, including clumsiness, difficulty with walking or standing, or irritability. Most children are not yet diagnosed at this stage unless there is a family history.
Should I go to the ER for metachromatic leukodystrophy (mld) in babies?
Seek emergency care if your child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation, or if your child is having seizures or episodes of stiffness with arching of the back. When in doubt, call your pediatrician's after-hours line for guidance.
Does metachromatic leukodystrophy (mld) in babies go away on its own?
In many cases, metachromatic leukodystrophy (mld) in babies resolves on its own, especially when your baby is developing on schedule with no signs of regression, and you are monitoring because of a family history. By 2-3 years, in untreated late infantile MLD, progression continues with loss of speech, swallowing difficulties, vision loss, and eventual loss of all voluntary movement. This is a devastating trajectory for families. Gene therapy (Lenmeldy/atidarsagene autotemcel) is FDA-approved for presymptomatic and early symptomatic late infantile MLD and has shown the ability to slow or halt disease progression in many treated children. Hematopoietic stem cell transplant may also be considered. Supportive care including physical therapy, feeding support, and seizure management is essential.
NIHFDANIH

References

  1. [1]National Library of Medicine. Metachromatic Leukodystrophy. GeneReviews, 2023. NIH
  2. [2]U.S. Food and Drug Administration. FDA Approves First Gene Therapy for Metachromatic Leukodystrophy. FDA News Release, March 2024. FDA
  3. [3]National Library of Medicine. Metachromatic Leukodystrophy. MedlinePlus Genetics, 2023. NIH

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss Metachromatic Leukodystrophy (MLD) in Babies.

Things to mention

  • Describe when you first noticed metachromatic leukodystrophy (mld) 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 toddler who was previously walking well is becoming increasingly clumsy or unsteady.
  • Mention if your child is losing previously acquired motor or language skills.
  • 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 toddler who was previously walking well is becoming increasingly clumsy or unsteady
  • Your child is losing previously acquired motor or language skills
  • You have a family history of MLD and want to discuss testing for your baby

Urgent signs to report immediately

  • Your child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation
  • Your child is having seizures or episodes of stiffness with arching of the back

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

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Bottom line

Most cases of metachromatic leukodystrophy (mld) in babies are normal. Talk to your pediatrician if your child is rapidly losing motor skills, has difficulty swallowing, or is choking on food or liquids — seek urgent neurological evaluation.

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

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An abnormal or positive newborn screening result means that further testing is needed, not that your baby definitely has a condition. Most positive screens turn out to be false positives after confirmatory testing. Newborn screening tests are intentionally sensitive to avoid missing any affected babies, so follow-up testing is essential to determine whether the result is a true positive.

My Baby Lost Skills They Previously Had

Temporary regression in skills can be normal during periods of rapid growth, illness, stress, or when a baby is intensely focused on developing a new skill. However, true developmental regression - the sustained loss of previously acquired skills such as words, social engagement, or motor abilities - is always a reason to seek prompt medical evaluation. This is especially concerning if multiple skill areas are affected simultaneously.

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