Overview
Developmental delay due to methylmalonate semialdehyde dehydrogenase (MMSDH) deficiency is an extremely rare inherited metabolic disorder. It is sometimes also called ALDH6A1 deficiency or methylmalonic semialdehyde dehydrogenase deficiency. This condition affects the body's ability to break down certain amino acids, specifically valine and thymine. When the enzyme methylmalonate semialdehyde dehydrogenase does not work properly, certain toxic substances can build up in the body, particularly in the brain and nervous system. The hallmark feature of this condition is developmental delay, meaning children may be slower to reach milestones such as sitting, walking, and talking compared to other children their age. Some affected individuals may also have intellectual disability, delays in speech and language, and mild to moderate neurological problems. The severity of symptoms can vary widely between individuals — some people may be only mildly affected while others experience more significant challenges. Because this disease is so rare, there is no specific cure or targeted treatment available. Management focuses on supportive care, including early intervention therapies such as physical therapy, occupational therapy, and speech therapy to help children reach their developmental potential. Some metabolic specialists may recommend dietary modifications to reduce the intake of certain amino acids. Monitoring by a team of specialists is important to address the various needs of affected individuals over time.
Also known as:
Key symptoms:
Delayed motor milestones such as sitting and walkingSpeech and language delaysIntellectual disabilityLow muscle tone (floppiness)Poor coordination or balanceLearning difficultiesBehavioral challengesElevated levels of certain organic acids in urineFeeding difficulties in infancySeizures in some cases
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Infantile
Begins in infancy, roughly 1 month to 2 years old
Treatments
No FDA-approved treatments are currently listed for Developmental delay due to methylmalonate semialdehyde dehydrogenase deficiency.
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Specialists
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Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
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Caregiver Resources
NORD Caregiver Resources
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Mental Health Support
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.How severe is my child's enzyme deficiency, and what does that mean for their development?,Should my child follow a special diet, and if so, what foods should we limit or avoid?,What therapies (physical, occupational, speech) do you recommend, and how often?,Are there any warning signs during illness that should prompt an emergency visit?,How often should we have metabolic testing and follow-up appointments?,Are there any clinical trials or research studies my child could participate in?,Should other family members be tested for this condition?
Common questions about Developmental delay due to methylmalonate semialdehyde dehydrogenase deficiency
What is Developmental delay due to methylmalonate semialdehyde dehydrogenase deficiency?
Developmental delay due to methylmalonate semialdehyde dehydrogenase (MMSDH) deficiency is an extremely rare inherited metabolic disorder. It is sometimes also called ALDH6A1 deficiency or methylmalonic semialdehyde dehydrogenase deficiency. This condition affects the body's ability to break down certain amino acids, specifically valine and thymine. When the enzyme methylmalonate semialdehyde dehydrogenase does not work properly, certain toxic substances can build up in the body, particularly in the brain and nervous system. The hallmark feature of this condition is developmental delay, meani
How is Developmental delay due to methylmalonate semialdehyde dehydrogenase deficiency inherited?
Developmental delay due to methylmalonate semialdehyde dehydrogenase deficiency follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Developmental delay due to methylmalonate semialdehyde dehydrogenase deficiency typically begin?
Typical onset of Developmental delay due to methylmalonate semialdehyde dehydrogenase deficiency is infantile. Age of onset can vary across affected individuals.