rs72547516 — CYP1A2 Ile386Val

Rare CYP1A2 missense variant (Ile386Val) associated with potentially reduced enzyme activity and altered metabolism of caffeine, clozapine, theophylline, and other CYP1A2 substrates

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CYP1A2 Ile386Val — A Rare Variant Affecting Drug and Caffeine Metabolism

CYP1A2 is one of the most abundant drug-metabolizing enzymes in the liver, responsible for breaking down approximately 10–15% of clinically used medications, including caffeine11 caffeine
CYP1A2 processes ~95% of ingested caffeine, clozapine (antipsychotic), theophylline (asthma), olanzapine, tizanidine, and melatonin. The rs72547516 variant causes an isoleucine-to-valine substitution at position 386 of the CYP1A2 protein (p.Ile386Val), a missense change that may alter enzyme structure and reduce its metabolic capacity.

The Mechanism

The isoleucine at codon 386 sits within the substrate-binding region of CYP1A2. The Ile386Val substitution22 Ile386Val substitution
Valine's smaller side chain and slightly different steric profile may reduce the precision of substrate positioning or alter active-site geometry, affecting catalytic efficiency is predicted to reduce enzyme activity, though in-vivo data in large populations are lacking due to the variant's rarity. CYP1A2 is also highly inducible: cigarette smoke, charcoal-grilled meat, and cruciferous vegetables upregulate its expression via the aryl hydrocarbon receptor (AhR) pathway. Carriers of the G allele who are non-smokers would be expected to have reduced basal CYP1A2 activity, with limited compensatory induction.

The Evidence

This variant is extremely rare globally33 extremely rare globally
G allele frequency 0.04–0.07% across major population databases; homozygous GG genotype essentially unobserved in population studies, with the highest observed frequencies in small Northern European cohorts (up to ~0.7% in Finnish samples and 2.5% in a small Danish sample). No ClinVar entry exists, and no CPIC or DPWG clinical guideline specifically addresses this variant.

The broader pharmacogenomics context is well-established: reduced CYP1A2 function, from any cause, leads to slower clearance of CYP1A2 substrates. A pathway-targeted pharmacogenomics study of 150 human liver samples44 pathway-targeted pharmacogenomics study of 150 human liver samples
Klein K et al. Frontiers in Pharmacology, 2010 showed that genetic and environmental factors together explain about 42% of CYP1A2 activity variation, with both cis and trans regulatory polymorphisms contributing. Missense variants that alter active-site residues are classified as potentially impacting enzyme function in this framework.

The clinical relevance of CYP1A2 metabolizer status was demonstrated for caffeine and cardiovascular risk: Cornelis et al. (JAMA, 2006)55 Cornelis et al. (JAMA, 2006)
Cornelis MC et al. Coffee, CYP1A2 Genotype, and Risk of Myocardial Infarction. JAMA, 2006 showed that slow metabolizers consuming 4+ cups of coffee daily had a 64% increased myocardial infarction risk (OR 1.64, 95% CI 1.14–2.34). For medications, CYP1A2 metabolizer status matters most for narrow-therapeutic-index drugs like clozapine and theophylline, where even a 30–50% reduction in clearance can push plasma concentrations into toxic ranges.

Practical Actions

If you carry the G allele (AG genotype), your CYP1A2 activity may be somewhat reduced compared to the AA majority. The most actionable steps involve monitoring drugs with narrow therapeutic windows, limiting caffeine especially if combining it with CYP1A2-inhibiting substances, and informing prescribers of your genotype before starting clozapine or theophylline.

CYP1A2 activity is strongly modifiable by lifestyle: smokers have 2–3× higher CYP1A2 induction, while cruciferous vegetables (broccoli, cabbage, Brussels sprouts) cause moderate induction. If you stop smoking, expect CYP1A2 activity to fall over several days, potentially raising levels of any CYP1A2-metabolized medications to clinical significance.

Interactions

The Ile386Val variant interacts with the well-characterized CYP1A2 inducibility variant rs762551 (*1F). Carriers of both the rs762551 slow-metabolizer C allele and this rs72547516 G allele could carry a compounded reduction in CYP1A2 baseline activity and inducibility, though this combination is expected to be vanishingly rare given the frequency of each allele. Smoking status is a major environmental modifier for both variants.

Drug Interactions

caffeine dose_adjustment literature
clozapine increased_toxicity literature
theophylline dose_adjustment literature
olanzapine dose_adjustment literature
tizanidine increased_toxicity literature
melatonin dose_adjustment literature

Nutrient Interactions

caffeine altered_metabolism

Genotype Interpretations

What each possible genotype means for this variant.

AA Normal Metabolizer Normal

Normal CYP1A2 enzyme activity

You carry the common ancestral allele at rs72547516 (AA), meaning you have the standard isoleucine at position 386 of the CYP1A2 protein. CYP1A2 function at this position is unaffected. This genotype is found in nearly all individuals worldwide — over 99.9% of people carry it.

Your CYP1A2 activity will still vary based on environmental factors (smoking, diet, medications), but is not reduced by this particular variant. Other CYP1A2 variants such as rs762551 (*1F) are far more common determinants of your caffeine and drug metabolism speed.

AG Heterozygous Variant Carrier Intermediate

One copy of the Ile386Val variant — possible modest reduction in CYP1A2 activity

CYP1A2 is the primary enzyme responsible for metabolizing caffeine (~95%), clozapine, theophylline, olanzapine, tizanidine, and melatonin. A missense change at a functionally important codon like 386 may reduce the precision of substrate binding or catalytic efficiency. In heterozygous carriers, one functional copy remains, so any reduction would be partial rather than complete — but for drugs with narrow therapeutic windows, even partial reduction matters.

The absolute risk increase is difficult to quantify given the rarity of this variant in published cohorts. The Ile386Val change is more conserved in pharmacogenomics databases as potentially functional compared to synonymous or UTR changes.

GG Homozygous Variant Poor

Two copies of the Ile386Val variant — substantially reduced CYP1A2 activity expected

Homozygous carriers of reduced-function CYP1A2 variants show pharmacokinetic profiles analogous to other CYP poor metabolizers — reduced drug clearance, elevated drug exposure at standard doses, and increased risk of dose-dependent adverse effects. Because this specific homozygous state has not been characterized in clinical cohorts, all recommendations are derived from the known pharmacology of CYP1A2 deficiency and from analogy with other characterized CYP1A2 reduced-function alleles.

The CYP1A2 enzyme also bioactivates certain pro-carcinogens found in grilled meats (heterocyclic amines, polycyclic aromatic hydrocarbons). Reduced CYP1A2 activity may lower carcinogen bioactivation from these dietary sources.