Methionine Synthase Deficiency
What is Methionine Synthase Deficiency?
Methionine synthase deficiency is a rare inherited metabolic disorder. It occurs when your body cannot produce enough of an enzyme called methionine synthase. This enzyme plays a critical role in processing amino acids, which are the building blocks of proteins.
The enzyme helps convert homocysteine into methionine, an essential amino acid your body needs. When this conversion fails, homocysteine builds up in your blood and tissues. High homocysteine levels can damage blood vessels, affect brain development, and disrupt normal growth.
This condition is genetic, meaning it passes from parents to children through genes. Most cases appear in infancy or early childhood. Early detection through blood testing allows families to manage the condition and prevent serious complications.
Symptoms
- Delayed developmental milestones in infants and children
- Feeding difficulties and failure to gain weight normally
- Low muscle tone or weakness
- Seizures or unusual movements
- Intellectual disability or learning difficulties
- Vision problems or abnormal eye movements
- Anemia or pale skin
- Fatigue and low energy levels
- Balance and coordination problems
- Blood clots or stroke in severe cases
Some infants may appear healthy at birth. Symptoms often emerge gradually during the first months or years of life. Early symptoms can be subtle and may resemble other childhood conditions.
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Causes and risk factors
Methionine synthase deficiency is caused by genetic mutations passed from parents to children. Both parents must carry a copy of the mutated gene for a child to develop the condition. The affected gene provides instructions for making the methionine synthase enzyme. When this gene has errors, the enzyme cannot work properly or may not be made at all.
Risk factors include having parents who are related by blood, which increases the chance of inheriting two copies of the same mutated gene. Family history of unexplained developmental delays or metabolic disorders also raises risk. Certain populations with higher rates of carrier status may see more cases. The condition is present from birth but may not show symptoms immediately.
How it's diagnosed
Doctors diagnose methionine synthase deficiency through blood tests that measure homocysteine levels. Elevated homocysteine is a key marker of this condition. Additional tests may check methionine levels, which are typically low when the enzyme is not working. Genetic testing can confirm the specific mutation causing the deficiency.
Rite Aid offers homocysteine testing as an add-on to our flagship health panel. This makes it easy to screen for elevated levels at over 2,000 Quest Diagnostics locations nationwide. If you have a family history of metabolic disorders or your child shows unexplained developmental delays, talk to a doctor about getting tested.
Treatment options
- Vitamin B12 supplements, often in high doses or through injections
- Betaine supplementation to help lower homocysteine levels
- Folate supplements to support the methylation pathway
- Methionine supplements to replace what the body cannot produce
- Protein-modified diet to reduce homocysteine production
- Regular monitoring of blood homocysteine and methionine levels
- Physical therapy for developmental delays and muscle weakness
- Early intervention programs for children with learning difficulties
- Avoiding fasting, which can worsen metabolic imbalance
- Working with a metabolic specialist or geneticist for ongoing care
Need testing for Methionine Synthase Deficiency? Add it to your panel.
- Simple blood draw at your nearest lab
- Results in days, not weeks
- Share results with your doctor
Frequently asked questions
Methionine synthase deficiency is a specific genetic disorder affecting one enzyme. Other causes of high homocysteine include vitamin B12 or folate deficiency, kidney disease, and certain medications. Genetic testing can confirm if elevated homocysteine is due to this rare enzyme deficiency. The pattern of amino acid levels in blood tests also helps distinguish between causes.
There is no cure for this genetic condition. However, early diagnosis and treatment can prevent many complications. Lifelong supplementation with B12, betaine, and methionine can keep homocysteine levels under control. Many people with proper treatment can lead relatively normal lives with careful monitoring and dietary management.
This condition follows an autosomal recessive pattern. Both parents must carry one copy of the mutated gene. Each child of carrier parents has a 25 percent chance of having the condition, a 50 percent chance of being a carrier, and a 25 percent chance of inheriting two normal genes. Genetic counseling can help families understand their risks.
People with methionine synthase deficiency typically have severely elevated homocysteine levels, often above 100 micromoles per liter. Normal homocysteine levels are usually below 15 micromoles per liter. However, the specific level varies by age and severity. Any significantly elevated result should be followed up with additional metabolic and genetic testing.
Most cases are diagnosed in infancy or early childhood because symptoms appear early. However, milder forms might go undetected until later in life. Adults with unexplained high homocysteine levels, developmental history concerns, or unusual neurological symptoms should consider metabolic testing. Late diagnosis is rare but possible in less severe cases.
People with methionine synthase deficiency may need to limit high-protein foods that contain large amounts of methionine. This includes meat, fish, eggs, dairy products, and certain nuts and seeds. A metabolic dietitian can create a balanced meal plan that provides enough protein for growth while keeping homocysteine levels stable. Dietary needs vary based on individual enzyme activity and supplement response.
Monitoring frequency depends on age, symptom severity, and treatment response. Newly diagnosed patients may need testing every few weeks until levels stabilize. Once stable, testing every three to six months is common. More frequent testing may be needed during growth spurts, illness, or treatment changes.
Untreated or late-diagnosed cases can result in permanent neurological damage. High homocysteine levels are toxic to developing brain tissue. However, early treatment can prevent or minimize brain injury. Starting supplements and dietary therapy in infancy gives the best chance for normal development and cognitive function.
Yes, prenatal genetic testing is available if both parents are known carriers. Amniocentesis or chorionic villus sampling can test fetal DNA for the specific mutations. Families with a previously affected child or known carrier status should discuss prenatal testing options with a genetic counselor. Early diagnosis allows treatment planning before symptoms appear.
Chronically high homocysteine increases risk of blood clots, stroke, and heart disease. It can cause ongoing neurological problems including seizures and cognitive decline. Bone health may suffer, leading to osteoporosis or fractures. Vision problems and kidney damage are also possible. Consistent treatment to lower homocysteine reduces these long-term risks significantly.