CBS Gene
The sulfur pathway gatekeeper. CBS (cystathionine beta-synthase) diverts homocysteine away from methylation toward the transsulfuration pathway. Upregulations speed this process, potentially causing sulfur sensitivity, ammonia buildup, and glutathione imbalances. A key SNP in functional medicine.
Understanding CBS
Normal Function
Converts homocysteine to cystathionine. First step in transsulfuration. Makes cysteine.
CBS Upregulation
Faster enzyme activity. Pulls more homocysteine through. Common variants: C699T, A360A.
Ammonia Production
Transsulfuration produces ammonia. Fast CBS means more ammonia. Detox burden.
Sulfite/Sulfate Issue
More cysteine means more sulfur metabolites. SUOX enzyme next. Molybdenum matters.
Glutathione Impact
Cysteine is rate-limiting for glutathione. CBS affects GSH production dynamics.
Methylation Drain
Fast CBS pulls homocysteine away. Less available for methionine recycling.
Signs of CBS Upregulation
Sulfur Sensitivity
React to eggs, garlic, onions, cruciferous, MSM, NAC, ALA.
Brain Fog
Ammonia crosses blood-brain barrier. Cognitive effects. Fatigue.
Supplement Reactions
React to high-sulfur supplements. NAC, glutathione, taurine problematic.
Wine/Alcohol Issues
Sulfites in wine problematic. Histamine overlap. Headaches.
Management Strategies
Low Sulfur Trial
Temporary reduction to clear sulfur. Not long-term—sulfur is essential.
Molybdenum
Cofactor for SUOX. Helps convert sulfite to sulfate. Often deficient.
Ammonia Support
BH4 helps. Ornithine, charcoal may help. Yucca root traditional.
B6 (P5P Form)
CBS cofactor. Too much can speed CBS more. Balance important.
Protein Moderation
Methionine from protein feeds pathway. Moderate, don't restrict severely.
Address Root Causes
Gut issues, oxidative stress worsen picture. CBS isn't the whole story.
Key Connections
Genes don't act alone.
CBS doesn't determine your fate. It reveals where the system might need support.
Where it matters
CBS is mainly expressed in the liver, kidney, and brain. Liver CBS handles most systemic transsulfuration. Brain CBS may play a role in hydrogen sulfide signaling.
Expression depends on
- • Nutrient availability
- • Sunlight exposure
- • Toxin burden
- • Cell turnover rate
- • Age and hormonal status
SNPs are throttles, not defects
Genetic variants often slow down pathways to protect the system from overwhelm. They reveal where you need to go slower, not that you're broken.
The real question
Not "what does this gene do?" but "what is this pathway already struggling with that makes this gene relevant?"
Related patterns
"Genes don't cause outcomes. They reveal where the system is already under pressure."