Overview
Disorders of the methionine cycle and sulfur amino acid metabolism are a group of rare inherited conditions that affect how the body processes certain building blocks of protein called sulfur-containing amino acids — mainly methionine, homocysteine, and cysteine. These amino acids play important roles in many body functions, including building proteins, protecting cells from damage, and helping the brain and nervous system work properly. When the enzymes or proteins that manage these chemical steps are missing or not working correctly, harmful substances can build up in the blood and tissues, causing damage over time. The most well-known condition in this group is homocystinuria (also called classical homocystinuria), caused by a deficiency of the enzyme cystathionine beta-synthase (CBS). Other related conditions include methionine adenosyltransferase (MAT) deficiency, cystathioninuria, and hypermethioninemia. Symptoms vary depending on the specific disorder but often include problems with the eyes (such as lens dislocation), bones (tall stature, curved spine), blood clots, and intellectual or developmental delays. Treatment depends on the specific condition but may include special low-protein diets, vitamin B6 (pyridoxine) supplements, betaine, folate, or vitamin B12. Many patients respond well to treatment, especially when the condition is caught early through newborn screening. With proper management, many people with these disorders can live relatively healthy lives, though lifelong monitoring and dietary care are usually needed.
Key symptoms:
Dislocation of the eye lens (ectopia lentis), causing blurry or poor visionUnusually tall height with long limbs and fingers (Marfanoid body shape)Curved or sideways spine (scoliosis or kyphosis)Blood clots in veins or arteries, which can cause stroke or pulmonary embolismIntellectual disability or learning difficultiesDevelopmental delays in childhoodOsteoporosis or weak, brittle bonesPsychiatric symptoms such as anxiety, depression, or behavioral problemsElevated levels of homocysteine or methionine in the bloodFlushing of the cheeksSeizures in some casesLiver problems (in some subtypes like MAT deficiency)Neurological problems such as movement difficulties
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Variable
Can begin at different ages, from infancy through adulthood
Treatments
No FDA-approved treatments are currently listed for Disorder of methionine cycle and sulfur amino acid metabolism.
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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
No travel grants are currently matched to Disorder of methionine cycle and sulfur amino acid metabolism.
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Caregiver Resources
NORD Caregiver Resources
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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.Which specific disorder in the methionine cycle does my child or I have, and which gene is affected?,Is my condition likely to respond to vitamin B6 treatment, and how will we find out?,What diet changes are needed, and can we work with a metabolic dietitian?,What are the signs of a blood clot, and should I take any preventive medication?,How often do I need blood tests, and what levels are we trying to keep in the normal range?,Are there any restrictions on physical activity, surgery, or pregnancy?,Should other family members be tested for this condition?
Common questions about Disorder of methionine cycle and sulfur amino acid metabolism
What is Disorder of methionine cycle and sulfur amino acid metabolism?
Disorders of the methionine cycle and sulfur amino acid metabolism are a group of rare inherited conditions that affect how the body processes certain building blocks of protein called sulfur-containing amino acids — mainly methionine, homocysteine, and cysteine. These amino acids play important roles in many body functions, including building proteins, protecting cells from damage, and helping the brain and nervous system work properly. When the enzymes or proteins that manage these chemical steps are missing or not working correctly, harmful substances can build up in the blood and tissues,
How is Disorder of methionine cycle and sulfur amino acid metabolism inherited?
Disorder of methionine cycle and sulfur amino acid metabolism follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.