Summary

PEMT makes your own choline by converting PE to PC — three SAM-consuming methylation steps. The rs7946 Met variant reduces this enzyme's activity, increasing dietary choline dependence. This matters most for women after menopause (estrogen normally rescues PEMT) and when stacked with MTHFR variants that reduce SAM supply.

Genotype spectrum

CC (Val/Val — ancestral)

You're in a small minority with full PEMT function. Your liver can synthesise choline efficiently, giving you more buffer when dietary choline is low.

CT (Val/Met — heterozygous)

Most common genotype. You have one copy of functional PEMT, providing partial endogenous choline synthesis.

TT (Met/Met — homozygous variant)

Actually the majority genotype in Europeans. You share this with over half the population.

Practical takeaway

For TT Carriers (Moderate Attention)
• Dietary choline priority: Eggs (147 mg each — 2-3/day covers ~60% of AI), liver (356 mg/3oz), salmon, shrimp, chicken, soybeans. Target: 550 mg/day men, 425 mg/day women.
• Choline supplement: If dietary intake is consistently low, phosphatidylcholine or choline bitartrate 250-500 mg/day. Postmenopausal TT women: 500 mg/day is reasonable.
• Pregnancy critical: Choline requirements increase to 450 mg/day (lactating: 550 mg/day). TT carriers have reduced endogenous synthesis — dietary adequacy during pregnancy is a genuine priority for fetal brain development.
• Liver health: If you have other NAFLD risk factors (obesity, insulin resistance, alcohol use), choline adequacy matters more for you than for CC carriers. Consider ALT/AST monitoring.
• If stacked with MTHFR CT or TT: Double attention to choline — both because MTHFR reduces your alternative remethylation capacity (increasing reliance on betaine/choline pathway) AND because reduced SAM may further limit PEMT output.
For CT Carriers (Low Priority Alone)
• Standard dietary choline adequacy. Eggs remain the single best food source.
• Pregnancy: ensure choline-rich diet. Prenatal supplements vary widely in choline content (many contain none).
• Becomes relevant in compound with MTHFR variants or postmenopausal status.
For CC Carriers (Genuine Advantage)
• Full PEMT function — robust endogenous choline synthesis. Standard dietary guidance.
• Your liver's choline factory runs at full capacity. You have more buffer for periods of low dietary choline intake.

Evidence detail

What This Gene Does

PEMT (phosphatidylethanolamine N-methyltransferase) is primarily expressed in the liver. It converts phosphatidylethanolamine (PE) to phosphatidylcholine (PC) through three sequential methylation reactions, each consuming one SAM molecule and producing one SAH. This is the ONLY endogenous route for de novo choline synthesis in mammals — all other choline must come from diet.

PC is essential for VLDL particle assembly and hepatic lipid export. When PC synthesis is insufficient (low dietary choline + reduced PEMT activity), fat accumulates in hepatocytes — the mechanism underlying PEMT-related non-alcoholic fatty liver disease.

PEMT consumes approximately 5 mmol SAM per day, making it one of the largest consumers of methyl groups in the body. This directly connects PEMT to the broader methylation cycle: MTHFR makes methylfolate → MTR makes methionine → MAT makes SAM → PEMT consumes SAM for PC synthesis.

The rs7946 variant (Val175Met) produces a loss-of-function enzyme. Song et al. 2005 confirmed this directly: V175M-transfected cells showed significantly diminished PEMT activity compared to wild-type (p<0.01).

Critical allele frequency note: The Met allele (reduced function) is the MAJORITY allele in European populations (~73%). This means the "variant" genotype is actually the most common one. The "wild-type" Val/Val (CC) genotype is the minority (~7% of Europeans). This has implications for how we frame risk — see Genotype Spectrum.

Mechanism

PEMT performs the endogenous choline synthesis pathway:

PE + 3 SAM → PC + 3 SAH (three sequential methylation steps)

The Val175Met substitution reduces enzyme activity. Here's what this means in practice:

1. Reduced endogenous choline production. PEMT normally provides ~30% of hepatic PC. With V175M, this fraction drops. Dietary choline must make up the difference.

2. The SAM connection. PEMT consumes ~5 mmol SAM/day. When PEMT activity is reduced, less SAM is consumed for PC synthesis. Paradoxically, this means more SAM is available for other methylation reactions. But the trade-off is clear: less choline produced endogenously = higher dietary choline requirement.

3. The estrogen rescue. Estrogen upregulates PEMT through an estrogen response element in intron 1A (Resseguie 2011). Premenopausal women with the Met variant are partially protected — estrogen compensates for reduced enzyme function by increasing PEMT transcription. After menopause, this protection disappears.

4. The VLDL-liver fat link. PC is required for VLDL particle assembly. Without adequate PC, the liver cannot export triglycerides efficiently → fat accumulation → NAFLD. This is why PEMT variants associate with fatty liver, especially when dietary choline is low.

5. The MTHFR compound effect. MTHFR C677T reduces SAM production (less methylfolate → less methionine → less SAM). PEMT requires SAM as its substrate. But PEMT V175M actually reduces SAM demand (less enzyme activity = less consumption). The net interaction is complex — MTHFR impairs the supply, PEMT impairment reduces the demand from one consumer but also reduces choline output. The practical compound effect: both pathways converge on choline insufficiency, because MTHFR-impaired individuals also rely more on choline/betaine for alternative homocysteine remethylation (via BHMT).

Think of it as: PEMT is your liver's choline factory. The Met variant is like running the factory at 60% capacity. When the raw materials (SAM) are also reduced (MTHFR variants), and the backup supply line (estrogen-mediated upregulation) is offline (menopause), you're relying almost entirely on dietary choline to keep the operation running.

PEMT G5765A

Summary

Genotype spectrum

Practical takeaway

Evidence detail

Sources (11)