rs641738 — MBOAT7

Regulatory variant that reduces MBOAT7 expression in the liver, impairing phosphatidylinositol remodeling and increasing risk of NAFLD, liver fibrosis, and hepatocellular carcinoma

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MBOAT7 rs641738 — When Phospholipid Remodeling Falters, the Liver Pays the Price

Your liver cells constantly remodel the fatty acid tails of membrane phospholipids, swapping in and out different acyl chains to maintain proper membrane composition and signaling. The MBOAT7 gene11 MBOAT7 gene
membrane-bound O-acyltransferase domain-containing 7, also known as LPIAT1 (lysophosphatidylinositol acyltransferase 1) encodes the enzyme responsible for one specific and critical step in this process: re-acylating lysophosphatidylinositol (lyso-PI)22 lysophosphatidylinositol (lyso-PI)
a phospholipid stripped of its sn-2 fatty acid tail with arachidonoyl-CoA to produce PI(18:0/20:4), the dominant phosphatidylinositol species in hepatocyte membranes. The rs641738 variant reduces MBOAT7 expression in the liver, depleting this key phospholipid and tipping the balance toward hepatic fat accumulation and inflammation.

The Mechanism

MBOAT7 operates within the Lands cycle33 Lands cycle
a phospholipid remodeling pathway where phospholipase A2 cleaves the sn-2 fatty acid from a phospholipid, creating a lysophospholipid, and an acyltransferase re-esterifies it with a new fatty acid. What makes MBOAT7 unique among the MBOAT family is its exquisite substrate selectivity: it preferentially esterifies arachidonoyl-CoA (C20:4, an omega-6 fatty acid) into the sn-2 position of lyso-PI. This selectivity means MBOAT7 is the primary enzyme determining how much arachidonic acid ends up in phosphatidylinositol pools.

The rs641738 T allele sits in the regulatory region between MBOAT7 and TMC4 on chromosome 19. It does not change the MBOAT7 protein sequence, but it reduces MBOAT7 mRNA and protein expression in hepatocytes. Lipidomic profiling of human liver biopsies shows that T allele carriers have markedly reduced PI species containing arachidonoyl chains — primarily PI(18:0/20:4) — and elevated levels of the precursor 18:0-lyso-PI and 18:1-lyso-PI44 Lipidomic profiling of human liver biopsies shows that T allele carriers have markedly reduced PI species containing arachidonoyl chains — primarily PI(18:0/20:4) — and elevated levels of the precursor 18:0-lyso-PI and 18:1-lyso-PI
Luukkonen et al. The MBOAT7 variant rs641738 alters hepatic phosphatidylinositols and increases severity of non-alcoholic fatty liver disease in humans. J Hepatol, 2016. The functional consequence is a deficit in arachidonoyl-PI, which disrupts membrane signaling, lipid droplet dynamics, and inflammatory tone in the liver.

When MBOAT7 activity falls, the accumulation of lyso-PI and the depletion of mature PI species promote de novo lipogenesis and triglyceride accumulation in hepatocytes. MBOAT7 also appears to shape the availability of arachidonic acid for downstream eicosanoid production, linking phospholipid remodeling to inflammatory signaling in Kupffer cells and hepatic stellate cells.

The Evidence

The variant was first identified as a NAFLD risk locus in the landmark study by Mancina et al.55 landmark study by Mancina et al.
The MBOAT7-TMC4 Variant rs641738 Increases Risk of Nonalcoholic Fatty Liver Disease in Individuals of European Descent. Gastroenterology, 2016, which examined 3,854 participants in the multi-ethnic Dallas Heart Study and 1,149 European liver biopsy patients. Each T allele increased risk of hepatic steatosis (OR 1.42 in the biopsy cohort), NASH (OR 1.18), and significant fibrosis (OR 1.30). In European Americans specifically, the per-allele OR for steatosis was 1.37.

The definitive evidence came from a meta-analysis of 42 studies encompassing over one million participants (9,688 with liver biopsies)66 meta-analysis of 42 studies encompassing over one million participants (9,688 with liver biopsies)
Teo et al. rs641738C>T near MBOAT7 is associated with liver fat, ALT and fibrosis in NAFLD: A meta-analysis. J Hepatol, 2021. This analysis confirmed that the T allele increases risk of NAFLD diagnosis (OR 1.17), advanced fibrosis under a recessive model (OR 1.22), and elevated ALT, while lowering serum triglycerides. Crucially, the association was robust in European adults but was not replicated in children or in non-European populations, suggesting the effect may be modulated by environmental or developmental factors.

Beyond NAFLD, rs641738 T increases risk of liver inflammation and accelerated fibrosis progression in chronic hepatitis C77 rs641738 T increases risk of liver inflammation and accelerated fibrosis progression in chronic hepatitis C
Thabet et al. MBOAT7 rs641738 increases risk of liver inflammation and transition to fibrosis in chronic hepatitis C. Nat Commun, 2016 (n=2,051), and increases hepatocellular carcinoma risk in non-cirrhotic patients with liver disease88 increases hepatocellular carcinoma risk in non-cirrhotic patients with liver disease
Donati et al. MBOAT7 rs641738 variant and hepatocellular carcinoma in non-cirrhotic individuals. Sci Rep, 2017 (OR 2.10 in combined non-cirrhotic cohort).

The effect size of rs641738 is modest compared to PNPLA3 rs738409 (the strongest NAFLD risk variant), but it acts through an independent pathway — phospholipid remodeling rather than triglyceride hydrolysis — making it a complementary risk factor with additive effects when combined with PNPLA3 and TM6SF2 risk alleles.

Practical Actions

For T allele carriers, the key insight is that your liver's phosphatidylinositol remodeling is compromised. MBOAT7 preferentially incorporates arachidonic acid (an omega-6 PUFA) into PI, and when this process is impaired, the ratio of omega-6 to omega-3 fatty acids in hepatic membranes shifts. Dietary strategies that increase EPA and DHA intake can partially compensate by providing alternative substrates for membrane phospholipid composition and by dampening the inflammatory signaling that MBOAT7 deficiency amplifies.

Monitoring liver enzymes (ALT, GGT) is particularly relevant because the T allele independently raises ALT. A mildly elevated ALT in a TT homozygote may reflect the genetic predisposition rather than acute liver injury, but it also signals that the liver is under more metabolic stress than the same ALT value would indicate in a CC individual.

Interactions

MBOAT7 rs641738 interacts additively with PNPLA3 rs738409 and TM6SF2 rs58542926. In a multicenter biopsy-based study of 515 NAFLD patients99 multicenter biopsy-based study of 515 NAFLD patients
Krawczyk et al. Combined effects of the PNPLA3 rs738409, TM6SF2 rs58542926, and MBOAT7 rs641738 variants on NAFLD severity. J Lipid Res, 2017, the three variants contributed through distinct mechanisms: PNPLA3 drove both steatosis and fibrosis, TM6SF2 primarily steatosis, and MBOAT7 selectively fibrosis (OR 1.77 in multivariate analysis). Increasing numbers of risk alleles across all three loci correlated with progressively higher liver enzymes.

The MTARC1 protective variant (rs2642438) operates in a complementary pathway — while MBOAT7 deficiency impairs phospholipid remodeling, MTARC1 loss-of-function enhances hepatic fat oxidation. Carriers of MBOAT7 risk alleles who also carry MTARC1 protective alleles may experience partial offset of their fibrosis risk, though this specific interaction has not yet been directly quantified.

HSD17B13 rs72613567 (a protective splice variant) also interacts with MBOAT7 risk through complementary mechanisms: HSD17B13 loss-of-function reduces hepatic lipid droplet toxicity while MBOAT7 deficiency increases it, making the presence or absence of HSD17B13 protection relevant for MBOAT7 risk carriers.

Nutrient Interactions

arachidonic acid altered_metabolism
omega-3 fatty acids increased_need

Genotype Interpretations

What each possible genotype means for this variant.

CC Normal Phospholipid Remodeling Normal

Full MBOAT7 expression — standard hepatic phosphatidylinositol metabolism

With two C alleles at rs641738, your liver produces full levels of MBOAT7 protein, the enzyme that selectively esterifies arachidonoyl-CoA into the sn-2 position of lysophosphatidylinositol. This maintains normal levels of PI(18:0/20:4), the dominant phosphatidylinositol species in hepatocyte membranes. In the 1,066,175-participant meta-analysis by Teo et al. (2021), CC homozygotes served as the reference group with baseline NAFLD risk, lower ALT levels, and normal serum triglyceride levels. Your MBOAT7 genotype does not independently increase your liver disease risk, though other genetic and environmental factors remain relevant.

CT Reduced Phospholipid Remodeling Intermediate

One risk allele — modestly lower MBOAT7 expression with slightly increased NAFLD risk

One copy of the T allele reduces MBOAT7 mRNA and protein expression enough to alter your hepatic phospholipid profile. Lipidomic studies show intermediate levels of PI(18:0/20:4) in heterozygotes compared to CC and TT individuals. In the Teo et al. meta-analysis (2021), each T allele increased NAFLD risk by approximately 17% (OR 1.17, 95% CI 1.05-1.30) and was associated with higher liver fat on imaging (+0.03 SD) and elevated ALT. The effect is additive, so one copy confers roughly half the risk of two copies. Interestingly, T allele carriers also have slightly lower serum triglycerides — likely because more fat is retained in the liver rather than exported as VLDL particles.

TT Impaired Phospholipid Remodeling High Risk

Two risk alleles — substantially reduced MBOAT7 expression with increased NAFLD and fibrosis risk

With two T alleles, your hepatocytes produce the lowest levels of MBOAT7 protein, maximally depleting PI(18:0/20:4) and accumulating lysophosphatidylinositol species. In the definitive meta-analysis of over one million participants (Teo et al., J Hepatol 2021), TT homozygotes showed the highest liver fat on imaging, the highest ALT levels, and significantly increased odds of advanced fibrosis (OR 1.22, 95% CI 1.03-1.45) compared to CC/CT individuals under a recessive model. In the biopsy-based study by Krawczyk et al. (2017), MBOAT7 was the variant most selectively associated with fibrosis rather than steatosis alone (multivariate OR 1.77), suggesting TT homozygotes face a distinct risk of fibrosis progression even beyond what hepatic fat content alone would predict.

The TT genotype also increases risk of hepatocellular carcinoma in non-cirrhotic patients (OR 2.10 in combined European cohorts) and accelerates fibrosis progression in chronic hepatitis C (Thabet et al., Nat Commun 2016). If you carry additional liver risk alleles at PNPLA3 or TM6SF2, the combined genetic burden is substantial, as these three genes affect hepatic lipid metabolism through independent mechanisms.