rs67784355 — CYP3A4 *11 (Thr363Met)

CYP3A4*11 — A Rare Variant with Real Consequences for Drug Clearance

CYP3A4 is the dominant drug-metabolizing enzyme in the human liver and intestine, processing approximately half of all prescription medications¹¹ approximately half of all prescription medications
Including statins, immunosuppressants, benzodiazepines, calcium channel blockers, HIV antiretrovirals, antifungals, and many anticancer agents. The CYP3A4*11 allele, defined by rs67784355 (c.1088C>T on the coding strand; p.Thr363Met), is one of the rarest functionally characterized CYP3A4 variants — but when it occurs, it produces a measurably compromised enzyme.

Threonine at position 363 sits within the substrate recognition site 5 (SRS-5)²² substrate recognition site 5 (SRS-5)
One of six substrate-recognition sites lining the CYP3A4 active site; SRS-5 contributes to the hydrogen-bonding network that stabilizes the active site architecture and positions substrates for catalysis. Replacing this threonine with a bulkier methionine disturbs the local protein structure, reducing both how much enzyme is produced and how stable it is once made.

The Mechanism

CYP3A4 is encoded on the minus (antisense) strand of chromosome 7. The *11 allele introduces a C→T change at position 1088 of the coding sequence (NM_017460.6:c.1088C>T), which on the genomic plus strand corresponds to a G→A substitution at rs67784355. The encoded threonine (polar, hydroxyl side chain) at codon 363 is replaced by methionine (hydrophobic, larger side chain). This is not a conservative substitution — methionine cannot fulfill the hydrogen-bonding role of threonine in the SRS-5 network.

In vitro expression studies³³ In vitro expression studies
Using baculovirus-insect cell and mammalian expression systems to produce recombinant CYP3A4 protein consistently find that CYP3A4*11 produces substantially less functional apoprotein than wild-type CYP3A4*1. The carbon monoxide-difference spectra⁴⁴ carbon monoxide-difference spectra
A spectrophotometric test of functional CYP content that measures correctly folded heme-containing protein of *11-expressing cells show reduced signal — meaning fewer active enzyme molecules, not just impaired ones.

The Evidence

Four independent in vitro studies characterize CYP3A4*11 across different substrates:

Loperamide: Wang et al. (2019)⁵⁵ Wang et al. (2019)
Functional characteristics of CYP3A4 allelic variants on the metabolism of loperamide in vitro found that CYP3A4*11's intrinsic clearance (CLint) for N-demethylation of loperamide was approximately 5.7-fold lower than wild-type, placing it among the most functionally impaired alleles tested. The authors attributed the deficit to protein instability from the bulky methionine substitution disrupting the tertiary structure at position 363.

Quinine: Gao et al. (2019)⁶⁶ Gao et al. (2019)
Enzymatic activities of CYP3A4 allelic variants on quinine 3-hydroxylation in vitro showed that CYP3A4*11 expressed at particularly low apoprotein levels compared to wild-type, consistent with reduced protein stability, and displayed reduced quinine hydroxylation activity. Five variants in total showed this pattern of low expression — *11 was among the most severely affected.

Midazolam and testosterone: Kato et al. (2021)⁷⁷ Kato et al. (2021)
Functional characterization of 40 CYP3A4 variants by assessing midazolam 1'-hydroxylation and testosterone 6β-hydroxylation confirmed reduced T363M expression in mammalian cells, noting that this substitution affects either protein expression or stability. The kinetic analysis placed *11 among the variants with meaningfully reduced catalytic efficiency.

Original identification: Sata et al. (2000)⁸⁸ Sata et al. (2000)
CYP3A4 allelic variants with amino acid substitutions in exons 7 and 12 first identified *11 from human liver samples and demonstrated its altered catalytic activity, establishing residue 363 as functionally important.

The limitation of all current evidence is that it is exclusively in vitro. The 2023 joint consensus genotyping recommendation⁹⁹ 2023 joint consensus genotyping recommendation
From AMP, CPIC, CAP, DPWG, ESPT, and PharmGKB explicitly excluded CYP3A4*11 from its Tier 1 and Tier 2 clinical assay recommendations because of this limitation — no pharmacokinetic studies in human carriers have been published. The variant is too rare to recruit sufficient carriers for in vivo trials under normal circumstances.

Practical Implications

Because clinical pharmacokinetic data are absent, prescribers cannot rely on published dosing guidelines for *11 carriers as they can for CYP3A4*22 or CYP3A5*1/*3. However, the consistent direction of the in vitro evidence — reduced enzyme levels, reduced clearance across multiple chemically distinct substrates — makes it reasonable to apply the same precautions used for other CYP3A4 reduced-function alleles.

The drugs of greatest concern are those with narrow therapeutic windows metabolized primarily by CYP3A4: tacrolimus and cyclosporine (transplant immunosuppressants), statins particularly atorvastatin and simvastatin, midazolam and other benzodiazepines, and cardiotoxic drugs like loperamide (at high doses). For each of these, standard doses may produce higher-than-expected plasma concentrations in *11 carriers.

Importantly, CYP3A4 inhibitors (grapefruit, clarithromycin, ketoconazole, ritonavir) compound an already-reduced enzyme capacity — the additive effect of genetic reduction plus pharmacological inhibition can push drug levels into the toxic range.

Interactions

CYP3A4*11 exists in the same genetic neighborhood as the more common and better-studied CYP3A4 variants. The CYP3A4*22 allele (rs35599367)¹⁰¹⁰ CYP3A4*22 allele (rs35599367)
An intronic splice variant causing ~50% reduced CYP3A4 mRNA, with established clinical guidelines for tacrolimus dosing is the most clinically relevant partner. CYP3A4*38 was defined precisely because rs67784355 was found in cis with the CYP3A4*3-defining variant in some haplotypes, meaning the same chromosome can carry multiple reduced-function alleles simultaneously.

CYP3A5 status (rs776746) is critical context for CYP3A4*11 carriers. CYP3A5 is a closely related enzyme that partially compensates for reduced CYP3A4 activity. If a *11 carrier is also a CYP3A5 non-expresser (*3/*3, the case for ~85% of Europeans), total CYP3A enzyme capacity is substantially diminished. A CYP3A5 expresser who carries *11 may show near-normal overall CYP3A clearance because CYP3A5 compensates — the opposite is true in non-expressers.

Gene-drug interactions are equally important. Strong CYP3A4 inhibitors added to an already-impaired metabolizer create additive metabolic suppression. Any patient carrying CYP3A4*11 who starts an azole antifungal, macrolide antibiotic, or ritonavir-boosted HIV regimen while on a narrow-therapeutic-index CYP3A4 substrate should be monitored intensively.