Acute Alcohol Sensitivity

Genetic MONDO:0012454 Pathograph 11 Show in embeddings browser inborn error of metabolism

Acute alcohol sensitivity - the alcohol flushing response, colloquially "Asian flush" - is an inherited, exposure-conditioned disorder of acetaldehyde clearance. Ethanol is oxidised to acetaldehyde by alcohol dehydrogenase and then to acetate by mitochondrial aldehyde dehydrogenase 2 (ALDH2). When ALDH2 activity is deficient, acetaldehyde accumulates after drinking and produces facial flushing, nausea and tachycardia within minutes. The mechanism is *dominant negative*, which is why a single copy suffices. ALDH2 functions as a tetramer, and a subunit encoded by the inactive allele poisons the tetramers it joins: in gastric biopsies, neither homozygotes nor heterozygotes showed any ALDH2 activity band on isoelectric focusing, so heterotetramers containing mutant subunits are inactive or nearly so. In an alcohol challenge, rs671 (p.Glu504Lys) heterozygotes reached a six-fold higher acetaldehyde level than wild-type carriers. Two framings in the standard account of this disorder are wrong, and this entry deliberately departs from both. First, **it is not only rs671.** A 2024 alcohol-challenge study identified two further ALDH2 variants - rs747096195 (p.Arg101Gly) and rs190764869 (p.Arg114Trp) - in flushing individuals who were not of East Asian descent, each roughly doubling acetaldehyde, by mechanisms that differ from rs671's: failure of functional dimer/tetramer formation for R101G, and reduced Vmax for both. Second, **it is not a benign curiosity.** Acetaldehyde is a genotoxin; the flushing response is a clinically usable biomarker of markedly elevated oesophageal squamous cell carcinoma risk from drinking, and Brooks and colleagues wrote their landmark paper specifically to tell clinicians that a question about past flushing episodes is a cancer risk assessment. The same allele that causes this disorder is *protective* against alcohol use disorder, because the reaction is aversive. The knowledge base already curates both downstream consequences - `Alcohol_Use_Disorder` names ALDH2 as a large-effect protective locus, and the oesophageal cancer entries name it as a risk factor - without curating the disorder that sits between them. This entry supplies that shared mechanism.

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1
Inheritance
5
Pathophys.
5
Phenotypes
2
Gaps
11
Pathograph
2
Genes
2
Differentials
1
Models
2
References
1
Deep Research
🏷

Classifications

Harrison's Part
GENETICS ENVIRONMENT DISEASE
👪

Inheritance

1
Autosomal dominant HP:0000006
A single inactive ALDH2 allele produces the phenotype, because the mutant subunit inactivates the tetramers it is incorporated into rather than merely contributing nothing. Homozygotes are more severely affected than heterozygotes, so the trait is dominant but not fully so at the quantitative level - a gene-dosage gradient sits on top of the dominant-negative effect.
Autosomal dominant inheritance
Show evidence (1 reference)
PMID:8290656 SUPPORT Human Clinical
"Our results support the notion that the mutant allele is dominant and that the heterotetrameric ALDH2 molecules containing the mutant subunits are enzymatically inactive or far less active."
States both the dominance and its structural basis in one sentence.
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Discussions and Knowledge Gaps

2
Is acute alcohol sensitivity a disease entry, or a susceptibility annotation that belongs on the alcohol-related entries rather than standing alone?
KNOWLEDGE GAP OPEN aldh2_scope_susceptibility_or_disease
Attached to
pathophysiology#Acetaldehyde Accumulation After Ethanol Exposure
MONDO flags MONDO:0012454 `subset: omim_susceptibility`, and the honest reading is that this concept sits on the boundary of what dismech curates as a Disease. The case for curating it is that it has a defined post-exposure phenotype with an onset in minutes, a measurable biochemical marker (blood acetaldehyde, six-fold elevated in rs671 heterozygotes under challenge), an OMIM entity, a causal gene with a demonstrated dominant-negative mechanism, and an actionable clinical consequence - the same footing as the existing Dihydropyrimidine_Dehydrogenase_Deficiency entry, which is likewise a pharmacogenomic/metabolic sensitivity. The case against is that its manifestations only exist under an elective exposure, which makes it look more like a trait than a disease. This entry takes the first position and records the second, rather than making the choice silently. If dismech later adopts a general policy on exposure-conditioned metabolic sensitivities, this entry should be revisited under it.
How much of ALDH2-related alcohol sensitivity outside East Asian populations is missed because both the clinical framing and the standard genetic test are built around rs671?
KNOWLEDGE GAP OPEN aldh2_ancestry_framing_is_outdated
Attached to
pathophysiology#Inactivating ALDH2 Variant
The disorder is described almost everywhere - including in MONDO's own definition, which says it is "usually found in Asians" - as an East Asian condition caused by rs671. A 2024 alcohol-challenge study found two further ALDH2 variants, rs747096195 and rs190764869, in flushing individuals who were not of East Asian descent, each roughly doubling acetaldehyde by mechanisms distinct from rs671's. An rs671-only assay returns normal for those people, and an ancestry-based clinical heuristic never prompts the test. Since the flushing history is the recommended screening question for a markedly elevated oesophageal cancer risk, a systematic blind spot here has a downstream consequence. What is not known is the population frequency of these and other ALDH2 variants outside East Asia, or what fraction of non-East-Asian flushers they explain.
Proposed experiments
Full ALDH2 sequencing in ancestry-diverse self-reported flushers
aldh2_full_gene_sequencing_in_non_east_asian_flushers
Recruit self-reported alcohol flushers across ancestries, sequence the full ALDH2 coding region rather than genotyping rs671 alone, and pair each genotype with a standardised alcohol challenge measuring acetaldehyde, heart rate and skin temperature - the protocol that identified the two known additional variants.
Readouts
Blood acetaldehyde after standardised alcohol challenge, by genotype
Acetaldehyde Accumulation After Ethanol Exposure
Direction: INCREASED
Interpretation: Elevated acetaldehyde in rs671-negative flushers would quantify how much of the phenotype an rs671-only test misses.
⚙

Pathophysiology

5
Inactivating ALDH2 Variant
A heterozygous or homozygous variant reducing ALDH2 catalytic capacity. The dominant allele worldwide is rs671 (p.Glu504Lys, historically written E487K in mature-protein numbering); rs747096195 (p.Arg101Gly) and rs190764869 (p.Arg114Trp) are further variants identified in flushing individuals of non-East-Asian descent.
Genetic context allele_type: SNV variant_origin: GERMLINE functional_impact_category: DOMINANT_NEGATIVE
Downstream
Loss of Tetrameric ALDH2 Catalytic Activity The variant subunit inactivates the tetramer. The route differs by allele: rs671 subunits assemble but the resulting heterotetramers are inactive, whereas p.Arg101Gly fails to form functional dimers/tetramers at all and p.Arg114Trp reduces Vmax.
Show evidence (2 references)
PMID:39075523 SUPPORT Human Clinical
"In East Asian descendants, an inactive genetic variant in ALDH2, rs671, triggers an alcohol flushing response due to acetaldehyde accumulation."
Names the canonical variant and the causal chain in one sentence.
PMID:39075523 SUPPORT Human Clinical
"We identified two additional ALDH2 variants in humans causing facial flushing and acetaldehyde accumulation after alcohol consumption."
Establishes that the allelic basis is broader than rs671, which is why this node is named for the class of variant rather than for rs671.
Loss of Tetrameric ALDH2 Catalytic Activity
The mitochondrial low-Km aldehyde dehydrogenase that oxidises acetaldehyde to acetate loses activity. Because ALDH2 is the low-Km enzyme, it is what normally keeps circulating acetaldehyde near zero during drinking, and there is no redundant activity that substitutes at physiological concentrations. No GO annotation for tetramer assembly is attached to this node, and the omission is deliberate: assembly behaves *oppositely* across the alleles that reach this node. The dominant rs671 subunit assembles normally and poisons the tetramer it joins - that is precisely what "dominant negative" means here, and annotating decreased homotetramerization would state the opposite. p.Arg101Gly, by contrast, does show a lack of functional dimer/tetramer formation. A single-valued modifier cannot carry both, so the distinction is stated here and in the two downstream evidence items rather than flattened into one wrong annotation.
ethanol catabolic process GO:0006068 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased ethanol catabolic process (GO:0006068). GO:0006068 is a biological process from the Gene Ontology. ↓ DECREASED
aldehyde dehydrogenase (NAD+) activity GO:0004029 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased aldehyde dehydrogenase (NAD+) activity (GO:0004029). GO:0004029 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Acetaldehyde Accumulation After Ethanol Exposure With the clearing enzyme disabled, acetaldehyde produced from ethanol accumulates instead of being oxidised onward to acetate.
Show evidence (1 reference)
PMID:8290656 SUPPORT Human Clinical
"About half of Chinese individuals lack mitochondrial aldehyde dehydrogenase-2 (ALDH2) activity, which is responsible for the oxidation of acetaldehyde produced during ethanol metabolism."
Names the enzyme, its substrate, and the scale of the deficiency in the population where it was characterised.
Ethanol Oxidation to Acetaldehyde by Alcohol Dehydrogenase
Ingested ethanol is oxidised to acetaldehyde by alcohol dehydrogenase before ALDH2 has anything to clear. This node exists because acetaldehyde exposure is set by the *ratio* of two enzyme steps, not by ALDH2 alone: the fast-metabolizing ADH1B*2 allele raises the production rate, and the slow-metabolizing ADH1B*1/*1 genotype lowers it. That is why ADH1B genotype modifies risk on top of ALDH2, and why the combination is far more informative than either alone.
alcohol dehydrogenase (NAD+) activity GO:0004022 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves alcohol dehydrogenase (NAD+) activity (GO:0004022). GO:0004022 is a molecular function from the Gene Ontology.
Downstream
Acetaldehyde Accumulation After Ethanol Exposure Acetaldehyde produced here is what accumulates when ALDH2 cannot clear it. The two-enzyme balance is why ADH1B genotype modifies the phenotype.
Show evidence (2 references)
PMID:19320537 SUPPORT Other
"Ethanol is first metabolized primarily by alcohol dehydrogenase (ADH) into acetaldehyde (Figure 2), a mutagen and animal carcinogen that causes DNA damage and has other cancer-promoting effects"
States this node's claim exactly - the ADH-catalysed step - and names acetaldehyde's genotoxicity in the same sentence. Tagged OTHER because the source is a review article stating established biochemistry rather than reporting a study of its own.
PMID:19320537 SUPPORT Other
"It should be noted that ADH is also polymorphic, and genetic variants in ADH1B interact with the ALDH2 variant to modify risk"
The interaction claim that justifies curating ADH1B as a modifier and giving this production step its own node.
Acetaldehyde Accumulation After Ethanol Exposure
Systemic acetaldehyde rises after drinking. This node is the hinge of the entry: everything upstream is constitutive genetics, everything downstream requires an ethanol exposure to have occurred. A carrier who never drinks has the genotype and none of the phenotype.
Animal models
Aldh2 knockout mouse Mouse recapitulates Knockout mice exposed to ethanol or acetaldehyde show higher blood acetaldehyde and greater toxicity than wild-type, which is the defining biochemical feature of the human disorder.
Downstream
Flushing Acetaldehyde is a vasodilator; the cutaneous vasodilation it causes is the visible sign the syndrome is named for.
Tachycardia Part of the acute physiological response, measured as heart rate in the alcohol-challenge protocol.
Nausea The third element of the acute triad.
Acetaldehyde Genotoxicity and Oxidative Stress The same accumulated acetaldehyde is a genotoxin, so the acute symptomatic arm and the long-term carcinogenic arm share one upstream node.
Show evidence (1 reference)
PMID:39075523 SUPPORT Human Clinical
"human subjects were given an alcohol challenge (0.25 g/kg) while quantifying acetaldehyde levels and the physiological response (heart rate and skin temperature) to alcohol"
Establishes that the accumulation is measured under a defined exposure, which is what makes this node exposure-conditioned rather than constitutive.
Acetaldehyde Genotoxicity and Oxidative Stress
Accumulated acetaldehyde damages DNA - measurable as micronucleus formation in lymphocytes - and alcohol metabolism in cells carrying reduced-activity ALDH2 variants generates excess reactive oxygen species. This is the mechanistic bridge from a transient flushing reaction to a durable cancer risk.
reactive oxygen species metabolic process GO:0072593 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased reactive oxygen species metabolic process (GO:0072593). GO:0072593 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Esophageal squamous cell carcinoma risk Repeated genotoxic acetaldehyde exposure of the upper aerodigestive epithelium over years of drinking raises squamous carcinoma risk. The intermediates - mutation accumulation, clonal expansion, dysplasia - are the standard carcinogenesis sequence and are curated in the oesophageal cancer entries rather than duplicated here.
Show evidence (2 references)
PMID:15840430 SUPPORT In Vitro
"Alcohol-induced facial flushing was also associated with an increased frequency of micronuclei in lymphocytes treated with acetaldehyde."
Links the clinical sign directly to measured genotoxicity in the same subjects.
PMID:39075523 SUPPORT In Vitro
"the R101G and R114W variants had a 2-3-fold increase in reactive oxygen species formation with respect to wild type ALDH2"
The oxidative-stress arm, measured for the two newer variants.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Acute Alcohol Sensitivity Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

5
Cardiovascular 1
Tachycardia HP:0001649 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Tachycardia (HP:0001649), qualified as temporality acute. HP:0001649 is a phenotype from the Human Phenotype Ontology.
Temporal: ACUTE
Show evidence (1 reference)
PMID:19320537 SUPPORT Human Clinical
"characteristic physiological response to drinking alcohol that includes facial flushing (see Figure 1), nausea, and tachycardia"
Names tachycardia in the characteristic response.
Digestive 1
Nausea HP:0002018 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nausea (HP:0002018), qualified as temporality acute. HP:0002018 is a phenotype from the Human Phenotype Ontology.
Temporal: ACUTE
Show evidence (1 reference)
PMID:19320537 SUPPORT Human Clinical
"facial flushing (see Figure 1), nausea, and tachycardia"
Names nausea in the characteristic response.
Integument 1
Flushing HP:0031284 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Flushing (HP:0031284), qualified as temporality acute. HP:0031284 is a phenotype from the Human Phenotype Ontology.
Temporal: ACUTE
Show evidence (2 references)
PMID:19320537 SUPPORT Human Clinical
"show a characteristic physiological response to drinking alcohol that includes facial flushing (see Figure 1), nausea, and tachycardia"
Names facial flushing as the leading element of the response.
PMID:15840430 SUPPORT Human Clinical
"A significant association was observed between the ALDH2 genotype and alcohol-induced facial flushing."
Genotype-phenotype association measured directly rather than assumed.
Other 2
Esophageal squamous cell carcinoma risk Esophageal carcinoma HP:0011459 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Esophageal carcinoma (HP:0011459). HP:0011459 is a phenotype from the Human Phenotype Ontology.
Show evidence (7 references)
PMID:19320537 SUPPORT Human Clinical
"ALDH2-deficient individuals are at much higher risk of esophageal cancer (specifically squamous cell carcinoma) from alcohol consumption than individuals with fully active ALDH2"
The central risk claim, with its restriction to squamous cell carcinoma and its conditioning on alcohol consumption both stated.
PMID:24477652 SUPPORT Human Clinical
"the adjusted ORs for flushing response of GCA and ESCC was 2.03 (95% CI 1.15-3.56, p=0.014) and 2.32 (95% CI 1.34-4.03, p=0.003), respectively, compared with those reporting no flushing response"
Quantifies the risk for both oesophageal squamous carcinoma and gastric cardia adenocarcinoma using flushing as the exposure variable.
PMID:24477652 SUPPORT Human Clinical
"There is no significant association between GCA risk and alcohol consumption."
The negative result that makes the positive one interesting: in this cohort the risk tracked flushing status rather than drinking quantity.
+ 4 more references
Reduced heavy drinking
Show evidence (4 references)
PMID:15840430 SUPPORT Human Clinical
"The frequency of heavy drinking was significantly higher among subjects with the ALDH2(1)/ALDH2(1) genotype than among subjects with the ALDH2(2) allele (ALDH2(1)/ALDH2(2) and ALDH2(2)/ALDH2(2) genotypes)."
Measures the behavioural difference by genotype in the same cohort where flushing and micronuclei were measured.
PMID:8290656 SUPPORT Human Clinical
"The ALDH2 deficiency in Chinese has been implicated in alcohol flush reaction and reported to be a negative risk factor for development of alcohol dependence."
States the protective relationship with alcohol dependence.
PMID:34310648 SUPPORT Human Clinical
"Current alcohol flushing, the inactive ALDH2*1/*2 genotype, and the fast-metabolizing ADH1B*2 allele were less frequently found in the AD groups."
A dedicated case-control study measuring the protective direction for flushing and for both genotypes.
+ 1 more reference
🧬

Genetic Associations

2
ALDH2
Gene: ALDH2 hgnc:404 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is ALDH2 (hgnc:404). hgnc:404 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
PMID:19320537 SUPPORT Human Clinical
"we estimate that there are at least 540 million ALDH2-deficient individuals in the world, representing approximately 8% of the population"
The population scale of the deficient genotype.
PMID:39075523 SUPPORT Human Clinical
"As alcohol flushing is not exclusive to those of East Asian descent, we questioned whether additional ALDH2 genetic variants can drive facial flushing and inefficient acetaldehyde metabolism using human testing and biochemical assays."
The premise that led to the two additional variants, and the reason ancestry cannot be used to rule the diagnosis out.
ADH1B
Gene: ADH1B hgnc:250 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is ADH1B (hgnc:250). hgnc:250 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: MODIFIER variant_origin: GERMLINE
Show evidence (3 references)
PMID:30629674 SUPPORT Human Clinical
"The combination of ADH1B*1/*1 and ALDH2*1/*2 markedly increased the risk of esophageal DIULs ≥5 mm (39.3 [10.6-146])."
The joint-genotype odds ratio, far above the ORs for either genotype separately in the same model - the quantitative basis for curating ADH1B as a modifier rather than ignoring it.
PMID:30629674 SUPPORT Human Clinical
"Although the inactive heterozygous ALDH2*1/*2 genotype was more common (33.3% vs. 11.4%, p = 0.002) in the group with DIULs ≥5 mm than in the group without DIULs ≥5 mm"
The ALDH2 half of the same model, quoted from a sentence that survives snippet matching. The separate odds ratios for each genotype (ADH1B*1/*1 12.5 and 9.89; ALDH2*1/*2 2.94 and 3.79) are in the same abstract but cannot be quoted here, because their bracketed confidence intervals are stripped by snippet matching; they are reported in the `features` text above instead.
PMID:34310648 SUPPORT Human Clinical
"The combination of the alcohol flushing status and the ALDH2 and ADH1B genotypes can provide a better new strategy for AD risk assessment than the alcohol flushing status alone or the genotypes alone in Asian men and women."
Independent statement that the two genotypes plus flushing status are jointly more informative than any of them alone.
🗃️

External Assertions

1
OMIM acute alcohol sensitivity
OMIM disease record OMIM:610251
OMIM entry for alcohol sensitivity, acute (ALDH2-related).
🌍

Environmental Factors

1
Ethanol Ingestion
exposure to ethanol ECTO:9000027 Environmental Conditions, Treatments and Exposures Ontology (ECTO) Relation: this environmental factor is this exposure This environmental factor is exposure to ethanol (ECTO:9000027). ECTO:9000027 is an exposure from the Environmental Conditions, Treatments and Exposures Ontology.
Drinking ethanol is a necessary condition for every symptomatic feature of this disorder. The entry is named for a *sensitivity*, so the exposure is not a risk factor sitting alongside the genotype - it is the other half of the cause. The exposure term is bound to the chemical rather than the drinking-behaviour term because the mechanism curated here is ethanol chemistry: oxidation to acetaldehyde and failure of its clearance.
Show evidence (1 reference)
PMID:39075523 SUPPORT Human Clinical
"human subjects were given an alcohol challenge (0.25 g/kg) while quantifying acetaldehyde levels and the physiological response (heart rate and skin temperature) to alcohol"
A controlled, dosed ethanol exposure producing the measured response - the exposure itself, evidenced.
Mechanism Target:
TRIGGERS Ethanol Oxidation to Acetaldehyde by Alcohol Dehydrogenase — Ethanol is the substrate this step oxidises. Attaching here rather than at the downstream accumulation node is the literal reading: the exposure supplies substrate to the production step, and the accumulation follows from production outrunning a defective clearance step. Without the exposure there is no production, no accumulation, and no phenotype.
Show evidence (1 reference)
PMID:39075523 SUPPORT Human Clinical
"Aldehyde dehydrogenase 2 (ALDH2) is critical for alcohol metabolism by converting acetaldehyde to acetic acid."
Places ethanol metabolism upstream of the acetaldehyde step this exposure triggers.
🔬

Diagnosis

3
Flushing history
Asking whether alcohol has previously caused facial flushing identifies ALDH2 deficiency without a laboratory test, because the reaction is intense enough that affected people are aware of it. The authors of the landmark paper propose this explicitly as a clinical screening question and the basis for counselling and, in high-risk patients, endoscopic screening. Its performance is good but population-dependent, and the dependence runs the wrong way for the people most at risk. In male clinic patients aged 50 and over, a validated flushing questionnaire had 96.1% sensitivity and 79.0% specificity for inactive ALDH2 - better on both counts than the ethanol patch test (72.4% / 71.4%), which is worth stating because the patch test is sometimes proposed as the more objective alternative. But in 472 Japanese *alcohol-dependent women*, sensitivity fell to 50.0%, against 88% previously reported in the Japanese general female population. The authors' inference is the mechanistically interesting one: a *lack* of flushing may itself be what allows a woman with inactive ALDH2 to become alcohol-dependent, so the screen fails selectively in exactly the group whose drinking puts them at highest oesophageal-cancer risk. A negative flushing history in a heavy drinker should not be taken to exclude ALDH2 deficiency; genotyping should be.
medical history taking NCIT:C18020 NCI Thesaurus (NCIT)
Show evidence (8 references)
PMID:9419411 SUPPORT Human Clinical
"When all three categories of flushing (current always, former always, and sometimes) were collapsed into one, the questionnaire's sensitivity and specificity for identifying inactive ALDH2 were 96.1 and 79.0%, respectively, compared with 72.4 and 71.4% for the ethanol patch test."
Quantifies the questionnaire and shows it outperforms the ethanol patch test on both sensitivity and specificity.
PMID:30629674 SUPPORT Human Clinical
"the sensitivity and specificity of current or former flushing to identify the presence of inactive ALDH2 were 50.0% and 93.5%, respectively; these values were previously reported to be 88% and 92%, respectively, in a Japanese general female population"
The failure mode. Graded PARTIAL because it qualifies the screening recommendation rather than supporting it: sensitivity halves in alcohol-dependent women.
PMID:30629674 SUPPORT Human Clinical
"The low sensitivity in the present study suggests that a lack of alcohol flushing may play a crucial role in the development of alcohol dependence in women with inactive ALDH2."
The authors' interpretation, which explains why the failure is selective rather than random - and connects it to the Reduced heavy drinking phenotype curated above.
+ 5 more references
Endoscopic screening with esophageal iodine staining
Lugol chromoendoscopy detects distinct iodine-unstained lesions (DIULs) in the oesophageal squamous mucosa - a marker of field cancerization, and in one Japanese series of 472 alcohol-dependent women, lesions that proved on histology to be low-grade intraepithelial neoplasia in 26 patients and superficial squamous cell carcinoma in 9. This is the secondary-prevention step that the flushing history and genotype are used to select for.
esophageal iodine staining chromoendoscopy NCIT:C16546 NCI Thesaurus (NCIT)
Show evidence (3 references)
PMID:30629674 SUPPORT Human Clinical
"we investigated the results of screening using esophageal iodine staining and the identification of determinants for esophageal DIULs in 472 Japanese alcohol-dependent women"
Documents iodine-staining endoscopic screening applied to an ALDH2-relevant at-risk population.
PMID:30629674 SUPPORT Human Clinical
"DIULs ≥5 mm were histologically diagnosed as low-grade intraepithelial neoplasia in 26 patients and superficial squamous cell carcinoma in 9 patients."
Shows the screen detects real neoplasia rather than an incidental staining artefact, which is what makes it worth performing.
PMID:30629674 SUPPORT Human Clinical
"The presence of large or multiple esophageal distinct iodine-unstained lesions (DIULs) is a strong predictor of field cancerization in the upper aerodigestive tract."
States what the finding means - field cancerization, not a single lesion.
ALDH2 genotyping
Molecular testing for rs671 and, where the history suggests flushing in a non-East-Asian individual, wider ALDH2 sequencing - since two further flushing-causing variants have been described that an rs671-only assay would miss.
molecular genetic analysis NCIT:C19770 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:8290656 SUPPORT Human Clinical
"determined the genotypes from leukocytes of the same individuals by using polymerase-chain-reaction amplification and hybridization with allele-specific oligonucleotide probes"
Describes the genotyping approach in the study that paired genotype with enzyme phenotype.
PMID:39075523 SUPPORT Human Clinical
"the methodology developed here to characterize ALDH2 genetic variant response to alcohol can lead the way precision medicine strategies to further understand the interplay of alcohol consumption, ALDH2 genetics, and cancer"
The authors' framing of genotype-guided assessment, which is the rationale for testing beyond rs671.
📊

Prevalence

3
East Asian (Japanese, Chinese, Korean)
Point Prevalence 36000.0 per 100,000 >1 in 1,000
Approximately 36% of East Asians show the alcohol flushing response. Entered as 36,000 per 100,000. This is the prevalence of the flushing *response* in that population, which the source attributes predominantly - not exclusively - to ALDH2 deficiency.
Show evidence (1 reference)
PMID:19320537 SUPPORT Human Clinical
"Approximately 36% of East Asians (Japanese, Chinese, and Koreans) show a characteristic physiological response to drinking alcohol that includes facial flushing"
The population figure, with the ancestry group it applies to.
Worldwide
Point Prevalence 8000.0 per 100,000 >1 in 1,000
An estimated 540 million ALDH2-deficient individuals globally, about 8% of the world population - entered as 8,000 per 100,000. This is the authors' extrapolation from East Asian population sizes and expected genotype frequencies, not a direct worldwide measurement, and it predates the identification of the non-East-Asian variants, so it is likely an underestimate of ALDH2-related flushing overall.
Show evidence (1 reference)
PMID:19320537 SUPPORT Human Clinical
"we estimate that there are at least 540 million ALDH2-deficient individuals in the world, representing approximately 8% of the population"
The worldwide figure. The surrounding sentence, which cannot be quoted here because it contains an inline citation marker that snippet matching strips, states the derivation: it is extrapolated from Japanese, Chinese and Korean population sizes and expected genotype frequencies - the basis for the caveat in this record's note.
Chinese subjects sampled by gastroendoscopic biopsy
Carrier Frequency >1 in 1,000
Of 30 subjects, 16 were ALDH2*1 homozygotes, 13 heterozygotes and 1 an ALDH2*2 homozygote - 14 of 30 carrying at least one inactive allele. A very small convenience sample from a mechanistic study, recorded because it is the cohort in which the dominant-negative biochemistry was demonstrated, not as a population estimate.
Show evidence (1 reference)
PMID:8290656 SUPPORT Human Clinical
"Sixteen subjects were homozygous for the ALDH2(1) allele, one was homozygous for ALDH2(2), and thirteen were the heterozygous genotype."
The genotype breakdown of the cohort behind the mechanism claim.
🔀

Differential Diagnoses

2

Conditions with similar clinical presentations that must be differentiated from Acute Alcohol Sensitivity:

Alcohol Use Disorder MONDO:0007079
Overlapping Features Not a diagnostic confusion so much as the mechanistic mirror image, and the reason this entry matters to the rest of the knowledge base. The same inactive ALDH2 allele that *causes* acute alcohol sensitivity is one of the two largest-effect *protective* loci against alcohol use disorder, because the reaction is aversive. `Alcohol_Use_Disorder` already curates ALDH2 in that protective role; this entry curates the disorder that produces the aversion.
Distinguishing Features
  • Opposite direction of the same allele - carriers are less likely, not more likely, to develop dependence.
  • Acute alcohol sensitivity is an exposure-triggered metabolic reaction with an onset in minutes; alcohol use disorder is a chronic behavioural condition.
  • A carrier who abstains has neither condition; a carrier who drinks despite the reaction carries elevated cancer risk without necessarily meeting dependence criteria.
Show evidence (1 reference)
PMID:8290656 SUPPORT Human Clinical
"reported to be a negative risk factor for development of alcohol dependence"
States the protective direction explicitly.
Disulfiram-ethanol reaction
Overlapping Features A pharmacologically identical syndrome produced on purpose. Disulfiram inhibits ALDH2, so a patient taking it who drinks develops flushing, nausea and tachycardia by the same acetaldehyde-accumulation mechanism curated here. Cyanamide is another ALDH inhibitor used the same way. The distinguishing feature is drug exposure, not phenotype - which is a useful reminder that the mechanism, not the genotype, produces the syndrome.
Distinguishing Features
  • Acquired and reversible on stopping the drug, rather than lifelong.
  • No family history; onset coincides with starting an ALDH-inhibiting drug.
  • Genotyping is normal at ALDH2 unless the patient also carries an inactivating variant, in which case the reaction is more severe.
Show evidence (1 reference)
PMID:39075523 SUPPORT Human Clinical
"Aldehyde dehydrogenase 2 (ALDH2) is critical for alcohol metabolism by converting acetaldehyde to acetic acid."
Supports the shared enzymatic step that a pharmacological ALDH2 inhibitor blocks. Graded PARTIAL because this entry holds no source characterising the disulfiram reaction itself; that claim rests on the shared mechanism, and a curator adding disulfiram detail should cite a source for it.
🐁

Animal Models

1
Aldh2 knockout mouse
The standard rodent model of human ALDH2 inactivity. Note the allelic mismatch: this is a null, whereas the common human allele rs671 is a dominant-negative missense subunit that assembles into tetramers. The null reproduces the *consequence* (no ALDH2 activity, acetaldehyde accumulation) without reproducing the *mechanism* by which a single human allele achieves it. The source is a review of published Aldh2-knockout studies rather than a single primary experiment.
Species
Mouse
Genotype
Aldh2 -/- (homozygous knockout); Aldh2 +/+ wild-type comparator
Publication
PMID:19874182
Pathograph links
Acetaldehyde Accumulation After Ethanol Exposure recapitulates fidelity: moderate Knockout mice exposed to ethanol or acetaldehyde show higher blood acetaldehyde and greater toxicity than wild-type, which is the defining biochemical feature of the human disorder.
Limitations: A null allele models homozygous ALDH2 inactivity, not the heterozygous dominant-negative state that most affected humans carry; the human phenotype's hallmark - that one poisoned subunit disables the tetramer - cannot be represented by an absent protein. The cited source is also a review rather than primary data.
Readouts
Blood acetaldehyde after ethanol or acetaldehyde exposure
Direction: INCREASED
Interpretation: Higher blood acetaldehyde in knockouts than wild-type reproduces the human biochemical phenotype.
Show evidence (1 reference)
PMID:19874182 SUPPORT Model Organism
"When they were exposed to atmospheres containing acetaldehyde, the Aldh2 -/- mice showed more severe toxic symptoms, like weight loss and higher blood acetaldehyde levels, as compared with the Aldh2 +/+ mice."
The measurement, with the wild-type comparator stated.
Show evidence (1 reference)
PMID:19874182 SUPPORT Model Organism
"Aldh2 knockout mice appear to be a valid animal model for humans with inactive ALDH2"
The authors' own claim that the model is valid for human ALDH2 inactivity, which is what justifies curating this link.
{ }

Source YAML

click to show 
name: Acute Alcohol Sensitivity
creation_date: "2026-08-22T16:00:00Z"
category: Genetic
description: >
  Acute alcohol sensitivity - the alcohol flushing response, colloquially "Asian
  flush" - is an inherited, exposure-conditioned disorder of acetaldehyde
  clearance. Ethanol is oxidised to acetaldehyde by alcohol dehydrogenase and
  then to acetate by mitochondrial aldehyde dehydrogenase 2 (ALDH2). When ALDH2
  activity is deficient, acetaldehyde accumulates after drinking and produces
  facial flushing, nausea and tachycardia within minutes.

  The mechanism is *dominant negative*, which is why a single copy suffices.
  ALDH2 functions as a tetramer, and a subunit encoded by the inactive allele
  poisons the tetramers it joins: in gastric biopsies, neither homozygotes nor
  heterozygotes showed any ALDH2 activity band on isoelectric focusing, so
  heterotetramers containing mutant subunits are inactive or nearly so. In an
  alcohol challenge, rs671 (p.Glu504Lys) heterozygotes reached a six-fold
  higher acetaldehyde level than wild-type carriers.

  Two framings in the standard account of this disorder are wrong, and this
  entry deliberately departs from both. First, **it is not only rs671.** A 2024
  alcohol-challenge study identified two further ALDH2 variants - rs747096195
  (p.Arg101Gly) and rs190764869 (p.Arg114Trp) - in flushing individuals who were
  not of East Asian descent, each roughly doubling acetaldehyde, by mechanisms
  that differ from rs671's: failure of functional dimer/tetramer formation for
  R101G, and reduced Vmax for both. Second, **it is not a benign curiosity.**
  Acetaldehyde is a genotoxin; the flushing response is a clinically usable
  biomarker of markedly elevated oesophageal squamous cell carcinoma risk from
  drinking, and Brooks and colleagues wrote their landmark paper specifically to
  tell clinicians that a question about past flushing episodes is a cancer risk
  assessment.

  The same allele that causes this disorder is *protective* against alcohol use
  disorder, because the reaction is aversive. The knowledge base already curates
  both downstream consequences - `Alcohol_Use_Disorder` names ALDH2 as a
  large-effect protective locus, and the oesophageal cancer entries name it as a
  risk factor - without curating the disorder that sits between them. This entry
  supplies that shared mechanism.
disease_term:
  preferred_term: acute alcohol sensitivity
  term:
    id: MONDO:0012454
    label: alcohol sensitivity, acute
parents:
- inborn error of metabolism
classifications:
  harrisons_chapter:
  - classification_value: GENETICS_ENVIRONMENT_DISEASE
references:
- reference: PMID:19320537
  title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
- reference: PMID:39075523
  title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
external_assertions:
- name: OMIM acute alcohol sensitivity
  source: OMIM
  assertion_type: disease_record
  external_id: OMIM:610251
  description: OMIM entry for alcohol sensitivity, acute (ALDH2-related).
inheritance:
- name: Autosomal dominant
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    A single inactive ALDH2 allele produces the phenotype, because the mutant
    subunit inactivates the tetramers it is incorporated into rather than merely
    contributing nothing. Homozygotes are more severely affected than
    heterozygotes, so the trait is dominant but not fully so at the quantitative
    level - a gene-dosage gradient sits on top of the dominant-negative effect.
  evidence:
  - reference: PMID:8290656
    reference_title: "Dominance of the mutant ALDH2(2) allele in the expression of human stomach aldehyde dehydrogenase-2 activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our results support the notion that the mutant allele is dominant and that the heterotetrameric ALDH2 molecules containing the mutant subunits are enzymatically inactive or far less active."
    explanation: >-
      States both the dominance and its structural basis in one sentence.
pathophysiology:
- name: Inactivating ALDH2 Variant
  biological_scale: MOLECULAR
  description: >-
    A heterozygous or homozygous variant reducing ALDH2 catalytic capacity. The
    dominant allele worldwide is rs671 (p.Glu504Lys, historically written E487K
    in mature-protein numbering); rs747096195 (p.Arg101Gly) and rs190764869
    (p.Arg114Trp) are further variants identified in flushing individuals of
    non-East-Asian descent.
  genetic_context:
    allele_type: SNV
    variant_origin: GERMLINE
    functional_impact_category: DOMINANT_NEGATIVE
  evidence:
  - reference: PMID:39075523
    reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In East Asian descendants, an inactive genetic variant in ALDH2, rs671, triggers an alcohol flushing response due to acetaldehyde accumulation."
    explanation: >-
      Names the canonical variant and the causal chain in one sentence.
  - reference: PMID:39075523
    reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identified two additional ALDH2 variants in humans causing facial flushing and acetaldehyde accumulation after alcohol consumption."
    explanation: >-
      Establishes that the allelic basis is broader than rs671, which is why
      this node is named for the class of variant rather than for rs671.
  downstream:
  - target: Loss of Tetrameric ALDH2 Catalytic Activity
    causal_link_type: DIRECT
    description: >-
      The variant subunit inactivates the tetramer. The route differs by allele:
      rs671 subunits assemble but the resulting heterotetramers are inactive,
      whereas p.Arg101Gly fails to form functional dimers/tetramers at all and
      p.Arg114Trp reduces Vmax.
    evidence:
    - reference: PMID:8290656
      reference_title: "Dominance of the mutant ALDH2(2) allele in the expression of human stomach aldehyde dehydrogenase-2 activity."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "None of the subjects with the mutant homozygotic and the heterozygotic genotypes exhibited the ALDH2 activity band or intermediate bands between ALDH2 and ALDH1 on isoelectric focusing gels."
      explanation: >-
        The observation behind the dominant-negative conclusion: heterozygotes
        show no residual activity band, not a half-height one.
    - reference: PMID:39075523
      reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The effect is caused by a lack of functional dimer/tetramer formation for R101G and decreased Vmax for both R101G and R114W."
      explanation: >-
        Distinguishes the assembly-failure and kinetic routes of the two newer
        variants from the rs671 poisoned-tetramer route.
- name: Loss of Tetrameric ALDH2 Catalytic Activity
  biological_scale: MOLECULAR
  description: >-
    The mitochondrial low-Km aldehyde dehydrogenase that oxidises acetaldehyde
    to acetate loses activity. Because ALDH2 is the low-Km enzyme, it is what
    normally keeps circulating acetaldehyde near zero during drinking, and there
    is no redundant activity that substitutes at physiological concentrations.

    No GO annotation for tetramer assembly is attached to this node, and the
    omission is deliberate: assembly behaves *oppositely* across the alleles
    that reach this node. The dominant rs671 subunit assembles normally and
    poisons the tetramer it joins - that is precisely what "dominant negative"
    means here, and annotating decreased homotetramerization would state the
    opposite. p.Arg101Gly, by contrast, does show a lack of functional
    dimer/tetramer formation. A single-valued modifier cannot carry both, so
    the distinction is stated here and in the two downstream evidence items
    rather than flattened into one wrong annotation.
  molecular_functions:
  - preferred_term: aldehyde dehydrogenase (NAD+) activity
    modifier: DECREASED
    term:
      id: GO:0004029
      label: aldehyde dehydrogenase (NAD+) activity
  biological_processes:
  - preferred_term: ethanol catabolic process
    modifier: DECREASED
    term:
      id: GO:0006068
      label: ethanol catabolic process
  evidence:
  - reference: PMID:8290656
    reference_title: "Dominance of the mutant ALDH2(2) allele in the expression of human stomach aldehyde dehydrogenase-2 activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "About half of Chinese individuals lack mitochondrial aldehyde dehydrogenase-2 (ALDH2) activity, which is responsible for the oxidation of acetaldehyde produced during ethanol metabolism."
    explanation: >-
      Names the enzyme, its substrate, and the scale of the deficiency in the
      population where it was characterised.
  downstream:
  - target: Acetaldehyde Accumulation After Ethanol Exposure
    causal_link_type: DIRECT
    description: >-
      With the clearing enzyme disabled, acetaldehyde produced from ethanol
      accumulates instead of being oxidised onward to acetate.
    evidence:
    - reference: PMID:39075523
      reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Humans heterozygous for rs747096195 (R101G) or rs190764869 (R114W) had facial flushing and a 2-fold increase in acetaldehyde levels, while rs671 (E504K) had facial flushing and a 6-fold increase in acetaldehyde levels relative to wild type ALDH2 carriers."
      explanation: >-
        Direct measurement of acetaldehyde after a controlled alcohol challenge,
        quantified per genotype - the strongest single piece of evidence in this
        entry.
- name: Ethanol Oxidation to Acetaldehyde by Alcohol Dehydrogenase
  biological_scale: MOLECULAR
  description: >-
    Ingested ethanol is oxidised to acetaldehyde by alcohol dehydrogenase before
    ALDH2 has anything to clear. This node exists because acetaldehyde exposure
    is set by the *ratio* of two enzyme steps, not by ALDH2 alone: the
    fast-metabolizing ADH1B*2 allele raises the production rate, and the
    slow-metabolizing ADH1B*1/*1 genotype lowers it. That is why ADH1B genotype
    modifies risk on top of ALDH2, and why the combination is far more
    informative than either alone.
  molecular_functions:
  - preferred_term: alcohol dehydrogenase (NAD+) activity
    term:
      id: GO:0004022
      label: alcohol dehydrogenase (NAD+) activity
  evidence:
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Ethanol is first metabolized primarily by alcohol dehydrogenase (ADH) into acetaldehyde (Figure 2), a mutagen and animal carcinogen that causes DNA damage and has other cancer-promoting effects"
    explanation: >-
      States this node's claim exactly - the ADH-catalysed step - and names
      acetaldehyde's genotoxicity in the same sentence. Tagged OTHER because the
      source is a review article stating established biochemistry rather than
      reporting a study of its own.
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "It should be noted that ADH is also polymorphic, and genetic variants in ADH1B interact with the ALDH2 variant to modify risk"
    explanation: >-
      The interaction claim that justifies curating ADH1B as a modifier and
      giving this production step its own node.
  downstream:
  - target: Acetaldehyde Accumulation After Ethanol Exposure
    causal_link_type: DIRECT
    description: >-
      Acetaldehyde produced here is what accumulates when ALDH2 cannot clear
      it. The two-enzyme balance is why ADH1B genotype modifies the phenotype.
    evidence:
    - reference: PMID:30629674
      reference_title: "Endoscopic screening using esophageal iodine staining and genotypes of ADH1B and ALDH2 in Japanese alcohol-dependent women."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The combination of ADH1B*1/*1 and ALDH2*1/*2 markedly increased the risk of esophageal DIULs ≥5 mm (39.3 [10.6-146])."
      explanation: >-
        The clearest demonstration that the two steps combine: the joint
        genotype carries a far larger odds ratio than either alone.
- name: Acetaldehyde Accumulation After Ethanol Exposure
  biological_scale: ORGANISM
  description: >-
    Systemic acetaldehyde rises after drinking. This node is the hinge of the
    entry: everything upstream is constitutive genetics, everything downstream
    requires an ethanol exposure to have occurred. A carrier who never drinks
    has the genotype and none of the phenotype.
  chemical_entities:
  - preferred_term: acetaldehyde
    modifier: INCREASED
    term:
      id: CHEBI:15343
      label: acetaldehyde
  evidence:
  - reference: PMID:39075523
    reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "human subjects were given an alcohol challenge (0.25 g/kg) while quantifying acetaldehyde levels and the physiological response (heart rate and skin temperature) to alcohol"
    explanation: >-
      Establishes that the accumulation is measured under a defined exposure,
      which is what makes this node exposure-conditioned rather than
      constitutive.
  downstream:
  - target: Flushing
    causal_link_type: DIRECT
    description: >-
      Acetaldehyde is a vasodilator; the cutaneous vasodilation it causes is the
      visible sign the syndrome is named for.
    evidence:
    - reference: PMID:19320537
      reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "This so-called alcohol flushing response (also known as “Asian flush” or “Asian glow”) is predominantly due to an inherited deficiency in the enzyme aldehyde dehydrogenase 2 (ALDH2)"
      explanation: >-
        Attributes the flushing response to ALDH2 deficiency.
  - target: Tachycardia
    causal_link_type: DIRECT
    description: >-
      Part of the acute physiological response, measured as heart rate in the
      alcohol-challenge protocol.
    evidence:
    - reference: PMID:19320537
      reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "show a characteristic physiological response to drinking alcohol that includes facial flushing (see Figure 1), nausea, and tachycardia"
      explanation: >-
        Names tachycardia as part of the characteristic response.
  - target: Nausea
    causal_link_type: DIRECT
    description: >-
      The third element of the acute triad.
    evidence:
    - reference: PMID:19320537
      reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "includes facial flushing (see Figure 1), nausea, and tachycardia"
      explanation: >-
        Names nausea as part of the characteristic response.
  - target: Acetaldehyde Genotoxicity and Oxidative Stress
    causal_link_type: DIRECT
    description: >-
      The same accumulated acetaldehyde is a genotoxin, so the acute symptomatic
      arm and the long-term carcinogenic arm share one upstream node.
    evidence:
    - reference: PMID:15840430
      reference_title: "Association of ALDH2 polymorphism with sensitivity to acetaldehyde-induced micronuclei and facial flushing after alcohol intake."
      supports: SUPPORT
      evidence_source: IN_VITRO
      snippet: "The frequency of micronuclei induced by acetaldehyde increased in a dose-dependent manner with the largest increase seen in subjects that were homozygous for the ALDH2(2) allele."
      explanation: >-
        Dose-dependent chromosomal damage from acetaldehyde, greatest in the
        genotype with least clearance capacity.
- name: Acetaldehyde Genotoxicity and Oxidative Stress
  biological_scale: CELLULAR
  description: >-
    Accumulated acetaldehyde damages DNA - measurable as micronucleus formation
    in lymphocytes - and alcohol metabolism in cells carrying reduced-activity
    ALDH2 variants generates excess reactive oxygen species. This is the
    mechanistic bridge from a transient flushing reaction to a durable cancer
    risk.
  biological_processes:
  - preferred_term: reactive oxygen species metabolic process
    modifier: INCREASED
    term:
      id: GO:0072593
      label: reactive oxygen species metabolic process
  evidence:
  - reference: PMID:15840430
    reference_title: "Association of ALDH2 polymorphism with sensitivity to acetaldehyde-induced micronuclei and facial flushing after alcohol intake."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Alcohol-induced facial flushing was also associated with an increased frequency of micronuclei in lymphocytes treated with acetaldehyde."
    explanation: >-
      Links the clinical sign directly to measured genotoxicity in the same
      subjects.
  - reference: PMID:39075523
    reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "the R101G and R114W variants had a 2-3-fold increase in reactive oxygen species formation with respect to wild type ALDH2"
    explanation: >-
      The oxidative-stress arm, measured for the two newer variants.
  downstream:
  - target: Esophageal squamous cell carcinoma risk
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Repeated genotoxic acetaldehyde exposure of the upper aerodigestive
      epithelium over years of drinking raises squamous carcinoma risk. The
      intermediates - mutation accumulation, clonal expansion, dysplasia - are
      the standard carcinogenesis sequence and are curated in the oesophageal
      cancer entries rather than duplicated here.
    evidence:
    - reference: PMID:19320537
      reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "few are aware of the accumulating evidence that ALDH2-deficient individuals are at much higher risk of esophageal cancer (specifically squamous cell carcinoma) from alcohol consumption than individuals with fully active ALDH2"
      explanation: >-
        States the risk relationship and its specificity to squamous cell
        carcinoma.
    - reference: PMID:24477652
      reference_title: "Association between gastric cardia adenocarcinoma risk and alcohol flushing response, but not alcohol consumption."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The drinkers with flushing response also had a higher ESCC risk than those without flushing response."
      explanation: >-
        Independent case-control confirmation using flushing as the exposure
        variable.
phenotypes:
- category: Dermatologic
  name: Flushing
  description: >-
    Cutaneous vasodilation of the face and often the neck and upper chest,
    beginning within minutes of drinking. The visible sign the syndrome is named
    for, and - because most affected people notice it - the basis for
    identifying ALDH2 deficiency by history alone.
  phenotype_term:
    preferred_term: Flushing
    term:
      id: HP:0031284
      label: Flushing
    temporality: ACUTE
  evidence:
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "show a characteristic physiological response to drinking alcohol that includes facial flushing (see Figure 1), nausea, and tachycardia"
    explanation: >-
      Names facial flushing as the leading element of the response.
  - reference: PMID:15840430
    reference_title: "Association of ALDH2 polymorphism with sensitivity to acetaldehyde-induced micronuclei and facial flushing after alcohol intake."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A significant association was observed between the ALDH2 genotype and alcohol-induced facial flushing."
    explanation: >-
      Genotype-phenotype association measured directly rather than assumed.
- category: Cardiovascular
  name: Tachycardia
  description: >-
    Rise in heart rate accompanying the flush, measured as part of the
    physiological response in controlled alcohol-challenge protocols.
  phenotype_term:
    preferred_term: Tachycardia
    term:
      id: HP:0001649
      label: Tachycardia
    temporality: ACUTE
  evidence:
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "characteristic physiological response to drinking alcohol that includes facial flushing (see Figure 1), nausea, and tachycardia"
    explanation: >-
      Names tachycardia in the characteristic response.
- category: Gastrointestinal
  name: Nausea
  description: >-
    Nausea after drinking, the third element of the acute triad and part of what
    makes the reaction aversive enough to reduce drinking.
  phenotype_term:
    preferred_term: Nausea
    term:
      id: HP:0002018
      label: Nausea
    temporality: ACUTE
  evidence:
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "facial flushing (see Figure 1), nausea, and tachycardia"
    explanation: >-
      Names nausea in the characteristic response.
- category: Oncologic
  name: Esophageal squamous cell carcinoma risk
  description: >-
    Markedly elevated risk of oesophageal squamous cell carcinoma among
    ALDH2-deficient people who drink. This is a *conditional* risk, not a
    feature of the genotype: a carrier who does not drink does not carry the
    excess risk, which is precisely why the flushing history is actionable. A
    Chinese case-control study also found elevated gastric cardia adenocarcinoma
    risk in flushers, with the striking result that alcohol consumption alone
    showed no significant association while flushing status did.
  phenotype_term:
    preferred_term: Esophageal carcinoma
    term:
      id: HP:0011459
      label: Esophageal carcinoma
  evidence:
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ALDH2-deficient individuals are at much higher risk of esophageal cancer (specifically squamous cell carcinoma) from alcohol consumption than individuals with fully active ALDH2"
    explanation: >-
      The central risk claim, with its restriction to squamous cell carcinoma
      and its conditioning on alcohol consumption both stated.
  - reference: PMID:24477652
    reference_title: "Association between gastric cardia adenocarcinoma risk and alcohol flushing response, but not alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the adjusted ORs for flushing response of GCA and ESCC was 2.03 (95% CI 1.15-3.56, p=0.014) and 2.32 (95% CI 1.34-4.03, p=0.003), respectively, compared with those reporting no flushing response"
    explanation: >-
      Quantifies the risk for both oesophageal squamous carcinoma and gastric
      cardia adenocarcinoma using flushing as the exposure variable.
  - reference: PMID:24477652
    reference_title: "Association between gastric cardia adenocarcinoma risk and alcohol flushing response, but not alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "There is no significant association between GCA risk and alcohol consumption."
    explanation: >-
      The negative result that makes the positive one interesting: in this
      cohort the risk tracked flushing status rather than drinking quantity.
  - reference: PMID:29707772
    reference_title: "Association of low-activity ALDH2 and alcohol consumption with risk of esophageal cancer in Chinese adults: A population-based cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among both male and female participants who consumed alcohol less than weekly (n = 69,519; 211 EC cases), low active or inactive ALDH2 was not associated with increased EC risk"
    explanation: >-
      The conditionality of the risk, measured prospectively in the 0.5-million
      China Kadoorie Biobank cohort: in people who barely drink, the genotype
      carries no excess oesophageal cancer risk at all. This is the single
      strongest evidence for the claim this phenotype's description makes.
  - reference: PMID:29707772
    reference_title: "Association of low-activity ALDH2 and alcohol consumption with risk of esophageal cancer in Chinese adults: A population-based cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The increased EC risk associated with \"soon\" response or rs671 GA was apparent in men consuming alcohol ≥30g/d."
    explanation: >-
      The other half of the same conditionality - the excess risk appears at
      higher intake. Same cohort, so the contrast is internal rather than
      across studies.
  - reference: PMID:37795758
    reference_title: "Relationship between esophageal squamous cell carcinoma risk and alcohol-related ALDH2 and ADH1B polymorphisms: Evidence from a meta-analysis and Mendelian randomization analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "rs671 of ALDH2 was associated with a significantly reduced risk of ESCC (OR: 0.60, 95% CI: 0.50-0.73), whereas rs1229984 of ADH1B was associated with a significantly increased risk (2.50, 95% CI: 1.70-3.69) in the additive model."
    explanation: >-
      Curated as PARTIAL because read carelessly it says the opposite of this
      phenotype. Across all subjects irrespective of drinking, rs671 looks
      *protective* - which is what the Reduced heavy drinking phenotype
      predicts, since carriers drink less. The risk is only visible once
      drinking is conditioned on, as in the Kadoorie items above. The
      genotype-level and exposure-conditioned estimates are not in conflict;
      they are the two halves of this entry's central paradox, and both are
      curated so neither can be quoted alone.
  - reference: PMID:37795758
    reference_title: "Relationship between esophageal squamous cell carcinoma risk and alcohol-related ALDH2 and ADH1B polymorphisms: Evidence from a meta-analysis and Mendelian randomization analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The MR analysis did not find a causal effect of alcohol on the esophageal cancer risk."
    explanation: >-
      A negative that complicates the causal story and is curated rather than
      omitted: this meta-analysis's Mendelian randomization arm did not
      establish a causal alcohol-oesophageal cancer effect. It does not overturn
      the cohort findings above, but a reader should meet it here rather than
      elsewhere.
- category: Behavioral
  name: Reduced heavy drinking
  description: >-
    Carriers drink less. This is the protective side of the same allele and is
    curated as a phenotype of this disorder rather than only as a genetic
    modifier on the alcohol-use-disorder entry, because it is a direct
    behavioural consequence of the aversive reaction. It is also what makes the
    cancer risk paradoxical - carriers who *do* drink despite the reaction are
    the high-risk group.
  evidence:
  - reference: PMID:15840430
    reference_title: "Association of ALDH2 polymorphism with sensitivity to acetaldehyde-induced micronuclei and facial flushing after alcohol intake."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The frequency of heavy drinking was significantly higher among subjects with the ALDH2(1)/ALDH2(1) genotype than among subjects with the ALDH2(2) allele (ALDH2(1)/ALDH2(2) and ALDH2(2)/ALDH2(2) genotypes)."
    explanation: >-
      Measures the behavioural difference by genotype in the same cohort where
      flushing and micronuclei were measured.
  - reference: PMID:8290656
    reference_title: "Dominance of the mutant ALDH2(2) allele in the expression of human stomach aldehyde dehydrogenase-2 activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The ALDH2 deficiency in Chinese has been implicated in alcohol flush reaction and reported to be a negative risk factor for development of alcohol dependence."
    explanation: >-
      States the protective relationship with alcohol dependence.
  - reference: PMID:34310648
    reference_title: "Combinations of alcohol-induced flushing with genetic polymorphisms of alcohol and aldehyde dehydrogenases and the risk of alcohol dependence in Japanese men and women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Current alcohol flushing, the inactive ALDH2*1/*2 genotype, and the fast-metabolizing ADH1B*2 allele were less frequently found in the AD groups."
    explanation: >-
      A dedicated case-control study measuring the protective direction for
      flushing and for both genotypes.
  - reference: PMID:34310648
    reference_title: "Combinations of alcohol-induced flushing with genetic polymorphisms of alcohol and aldehyde dehydrogenases and the risk of alcohol dependence in Japanese men and women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although alcohol flushing is influenced by the ALDH2 and ADH1B genotypes, constitutional or acquired flushing tolerance is an independent susceptibility trait for AD."
    explanation: >-
      The important qualifier, graded PARTIAL: protection is not automatic.
      Tolerance to the flushing reaction - constitutional or acquired - is
      itself an independent risk factor for dependence, so a carrier who stops
      flushing loses the protection while keeping the enzyme defect.
environmental:
- name: Ethanol Ingestion
  description: >-
    Drinking ethanol is a necessary condition for every symptomatic feature of
    this disorder. The entry is named for a *sensitivity*, so the exposure is
    not a risk factor sitting alongside the genotype - it is the other half of
    the cause. The exposure term is bound to the chemical rather than the
    drinking-behaviour term because the mechanism curated here is ethanol
    chemistry: oxidation to acetaldehyde and failure of its clearance.
  exposure_term:
    preferred_term: exposure to ethanol
    term:
      id: ECTO:9000027
      label: exposure to ethanol
  influences_mechanisms:
  - target: Ethanol Oxidation to Acetaldehyde by Alcohol Dehydrogenase
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: >-
      Ethanol is the substrate this step oxidises. Attaching here rather than at
      the downstream accumulation node is the literal reading: the exposure
      supplies substrate to the production step, and the accumulation follows
      from production outrunning a defective clearance step. Without the
      exposure there is no production, no accumulation, and no phenotype.
    evidence:
    - reference: PMID:39075523
      reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Aldehyde dehydrogenase 2 (ALDH2) is critical for alcohol metabolism by converting acetaldehyde to acetic acid."
      explanation: >-
        Places ethanol metabolism upstream of the acetaldehyde step this
        exposure triggers.
  evidence:
  - reference: PMID:39075523
    reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "human subjects were given an alcohol challenge (0.25 g/kg) while quantifying acetaldehyde levels and the physiological response (heart rate and skin temperature) to alcohol"
    explanation: >-
      A controlled, dosed ethanol exposure producing the measured response -
      the exposure itself, evidenced.
genetic:
- name: ALDH2
  features: >-
    Mitochondrial low-Km aldehyde dehydrogenase 2. rs671 (p.Glu504Lys) is the
    common inactivating allele, carried by an estimated 540 million people
    worldwide - about 8% of the global population and roughly 36% of East
    Asians. rs747096195 (p.Arg101Gly) and rs190764869 (p.Arg114Trp) are rarer
    variants producing the same flushing phenotype in non-East-Asian
    individuals, so ancestry is not a reliable screen. Note the numbering: rs671
    is written p.Glu504Lys against the precursor and E487K against the mature
    protein; both refer to the same substitution.
  gene_term:
    preferred_term: ALDH2
    term:
      id: hgnc:404
      label: ALDH2
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we estimate that there are at least 540 million ALDH2-deficient individuals in the world, representing approximately 8% of the population"
    explanation: >-
      The population scale of the deficient genotype.
  - reference: PMID:39075523
    reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "As alcohol flushing is not exclusive to those of East Asian descent, we questioned whether additional ALDH2 genetic variants can drive facial flushing and inefficient acetaldehyde metabolism using human testing and biochemical assays."
    explanation: >-
      The premise that led to the two additional variants, and the reason
      ancestry cannot be used to rule the diagnosis out.
- name: ADH1B
  features: >-
    Alcohol dehydrogenase 1B, the upstream enzyme of the same two-step pathway.
    It does not cause acute alcohol sensitivity, but it sets the rate at which
    the acetaldehyde ALDH2 must clear is produced, so it modifies both the
    reaction and the downstream cancer risk. The slow-metabolizing ADH1B*1/*1
    genotype combined with inactive ALDH2*1/*2 carries a far larger risk of
    oesophageal iodine-unstained lesions than either genotype alone: in
    PMID:30629674's multiple logistic models the separate odds ratios were 12.5
    and 9.89 for ADH1B*1/*1 and 2.94 and 3.79 for ALDH2*1/*2, against 39.3 for
    the combination. Note that ADH1B carried the larger independent effect in
    that cohort - a reason not to treat ALDH2 genotype as the whole story.
  gene_term:
    preferred_term: ADH1B
    term:
      id: hgnc:250
      label: ADH1B
  relationship_type: MODIFIER
  variant_origin: GERMLINE
  evidence:
  - reference: PMID:30629674
    reference_title: "Endoscopic screening using esophageal iodine staining and genotypes of ADH1B and ALDH2 in Japanese alcohol-dependent women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The combination of ADH1B*1/*1 and ALDH2*1/*2 markedly increased the risk of esophageal DIULs ≥5 mm (39.3 [10.6-146])."
    explanation: >-
      The joint-genotype odds ratio, far above the ORs for either genotype
      separately in the same model - the quantitative basis for curating ADH1B
      as a modifier rather than ignoring it.
  - reference: PMID:30629674
    reference_title: "Endoscopic screening using esophageal iodine staining and genotypes of ADH1B and ALDH2 in Japanese alcohol-dependent women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although the inactive heterozygous ALDH2*1/*2 genotype was more common (33.3% vs. 11.4%, p = 0.002) in the group with DIULs ≥5 mm than in the group without DIULs ≥5 mm"
    explanation: >-
      The ALDH2 half of the same model, quoted from a sentence that survives
      snippet matching. The separate odds ratios for each genotype
      (ADH1B*1/*1 12.5 and 9.89; ALDH2*1/*2 2.94 and 3.79) are in the same
      abstract but cannot be quoted here, because their bracketed confidence
      intervals are stripped by snippet matching; they are reported in the
      `features` text above instead.
  - reference: PMID:34310648
    reference_title: "Combinations of alcohol-induced flushing with genetic polymorphisms of alcohol and aldehyde dehydrogenases and the risk of alcohol dependence in Japanese men and women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The combination of the alcohol flushing status and the ALDH2 and ADH1B genotypes can provide a better new strategy for AD risk assessment than the alcohol flushing status alone or the genotypes alone in Asian men and women."
    explanation: >-
      Independent statement that the two genotypes plus flushing status are
      jointly more informative than any of them alone.
prevalence:
- population: East Asian (Japanese, Chinese, Korean)
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 36000.0
  notes: >-
    Approximately 36% of East Asians show the alcohol flushing response. Entered
    as 36,000 per 100,000. This is the prevalence of the flushing *response* in
    that population, which the source attributes predominantly - not
    exclusively - to ALDH2 deficiency.
  evidence:
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Approximately 36% of East Asians (Japanese, Chinese, and Koreans) show a characteristic physiological response to drinking alcohol that includes facial flushing"
    explanation: >-
      The population figure, with the ancestry group it applies to.
- population: Worldwide
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 8000.0
  notes: >-
    An estimated 540 million ALDH2-deficient individuals globally, about 8% of
    the world population - entered as 8,000 per 100,000. This is the authors'
    extrapolation from East Asian population sizes and expected genotype
    frequencies, not a direct worldwide measurement, and it predates the
    identification of the non-East-Asian variants, so it is likely an
    underestimate of ALDH2-related flushing overall.
  evidence:
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we estimate that there are at least 540 million ALDH2-deficient individuals in the world, representing approximately 8% of the population"
    explanation: >-
      The worldwide figure. The surrounding sentence, which cannot be quoted
      here because it contains an inline citation marker that snippet matching
      strips, states the derivation: it is extrapolated from Japanese, Chinese
      and Korean population sizes and expected genotype frequencies - the basis
      for the caveat in this record's note.
- population: Chinese subjects sampled by gastroendoscopic biopsy
  measure_type: CARRIER_FREQUENCY
  prevalence_class: ABOVE_1_IN_1000
  notes: >-
    Of 30 subjects, 16 were ALDH2*1 homozygotes, 13 heterozygotes and 1 an
    ALDH2*2 homozygote - 14 of 30 carrying at least one inactive allele. A very
    small convenience sample from a mechanistic study, recorded because it is
    the cohort in which the dominant-negative biochemistry was demonstrated,
    not as a population estimate.
  evidence:
  - reference: PMID:8290656
    reference_title: "Dominance of the mutant ALDH2(2) allele in the expression of human stomach aldehyde dehydrogenase-2 activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixteen subjects were homozygous for the ALDH2(1) allele, one was homozygous for ALDH2(2), and thirteen were the heterozygous genotype."
    explanation: >-
      The genotype breakdown of the cohort behind the mechanism claim.
diagnosis:
- name: Flushing history
  description: >-
    Asking whether alcohol has previously caused facial flushing identifies
    ALDH2 deficiency without a laboratory test, because the reaction is
    intense enough that affected people are aware of it. The authors of the
    landmark paper propose this explicitly as a clinical screening question and
    the basis for counselling and, in high-risk patients, endoscopic screening.

    Its performance is good but population-dependent, and the dependence runs
    the wrong way for the people most at risk. In male clinic patients aged 50
    and over, a validated flushing questionnaire had 96.1% sensitivity and
    79.0% specificity for inactive ALDH2 - better on both counts than the
    ethanol patch test (72.4% / 71.4%), which is worth stating because the
    patch test is sometimes proposed as the more objective alternative. But in
    472 Japanese *alcohol-dependent women*, sensitivity fell to 50.0%, against
    88% previously reported in the Japanese general female population. The
    authors' inference is the mechanistically interesting one: a *lack* of
    flushing may itself be what allows a woman with inactive ALDH2 to become
    alcohol-dependent, so the screen fails selectively in exactly the group
    whose drinking puts them at highest oesophageal-cancer risk. A negative
    flushing history in a heavy drinker should not be taken to exclude ALDH2
    deficiency; genotyping should be.
  diagnosis_term:
    preferred_term: medical history taking
    term:
      id: NCIT:C18020
      label: Diagnostic Procedure
  evidence:
  - reference: PMID:9419411
    reference_title: "Reliability of a flushing questionnaire and the ethanol patch test in screening for inactive aldehyde dehydrogenase-2 and alcohol-related cancer risk."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "When all three categories of flushing (current always, former always, and sometimes) were collapsed into one, the questionnaire's sensitivity and specificity for identifying inactive ALDH2 were 96.1 and 79.0%, respectively, compared with 72.4 and 71.4% for the ethanol patch test."
    explanation: >-
      Quantifies the questionnaire and shows it outperforms the ethanol patch
      test on both sensitivity and specificity.
  - reference: PMID:30629674
    reference_title: "Endoscopic screening using esophageal iodine staining and genotypes of ADH1B and ALDH2 in Japanese alcohol-dependent women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the sensitivity and specificity of current or former flushing to identify the presence of inactive ALDH2 were 50.0% and 93.5%, respectively; these values were previously reported to be 88% and 92%, respectively, in a Japanese general female population"
    explanation: >-
      The failure mode. Graded PARTIAL because it qualifies the screening
      recommendation rather than supporting it: sensitivity halves in
      alcohol-dependent women.
  - reference: PMID:30629674
    reference_title: "Endoscopic screening using esophageal iodine staining and genotypes of ADH1B and ALDH2 in Japanese alcohol-dependent women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The low sensitivity in the present study suggests that a lack of alcohol flushing may play a crucial role in the development of alcohol dependence in women with inactive ALDH2."
    explanation: >-
      The authors' interpretation, which explains why the failure is selective
      rather than random - and connects it to the Reduced heavy drinking
      phenotype curated above.
  - reference: PMID:34310648
    reference_title: "Combinations of alcohol-induced flushing with genetic polymorphisms of alcohol and aldehyde dehydrogenases and the risk of alcohol dependence in Japanese men and women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The temporal profiles for drinking and flushing in former-flushing AD subjects revealed that the flushing response disappeared soon after or before the start of habitual drinking during young adulthood, regardless of the ALDH2 genotype."
    explanation: >-
      Independent evidence that the flushing history can go negative over time
      in the drinkers who matter most, which is the mechanism behind the low
      sensitivity above.
  - reference: PMID:29707772
    reference_title: "Association of low-activity ALDH2 and alcohol consumption with risk of esophageal cancer in Chinese adults: A population-based cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Self-reported flushing response had low sensitivity (56.8%) and high specificity (88.4%) in identifying rs671 A allele among male weekly alcohol consumers."
    explanation: >-
      A third measurement, in a third population, completing a consistent
      pattern rather than adding a fourth number: 96.1% in general male clinic
      patients, 56.8% in male weekly drinkers, 50.0% in alcohol-dependent
      women. Sensitivity degrades as drinking increases - so the screening
      question is least reliable precisely where the cancer risk is
      concentrated. Graded PARTIAL for the same reason as the other limit
      items.

  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore clinicians can determine ALDH2 deficiency simply by asking about previous episodes of alcohol-induced flushing."
    explanation: >-
      The screening recommendation, stated as a method.
  - reference: PMID:24477652
    reference_title: "Association between gastric cardia adenocarcinoma risk and alcohol flushing response, but not alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In conclusion, alcohol flushing response is a clinically useful biomarker of susceptibility to GCA and ESCC risk from alcohol."
    explanation: >-
      Independent endorsement of flushing history as a risk biomarker.
  - reference: PMID:19320537
    reference_title: "The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ALDH2-deficient patients can then be counseled to reduce alcohol consumption, and high-risk patients can be assessed for endoscopic cancer screening"
    explanation: >-
      The actionable consequence of a positive flushing history - what the
      screening question is *for*.
- name: Endoscopic screening with esophageal iodine staining
  description: >-
    Lugol chromoendoscopy detects distinct iodine-unstained lesions (DIULs) in
    the oesophageal squamous mucosa - a marker of field cancerization, and in
    one Japanese series of 472 alcohol-dependent women, lesions that proved on
    histology to be low-grade intraepithelial neoplasia in 26 patients and
    superficial squamous cell carcinoma in 9. This is the secondary-prevention
    step that the flushing history and genotype are used to select for.
  diagnosis_term:
    preferred_term: esophageal iodine staining chromoendoscopy
    term:
      id: NCIT:C16546
      label: Endoscopic Procedure
  evidence:
  - reference: PMID:30629674
    reference_title: "Endoscopic screening using esophageal iodine staining and genotypes of ADH1B and ALDH2 in Japanese alcohol-dependent women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "we investigated the results of screening using esophageal iodine staining and the identification of determinants for esophageal DIULs in 472 Japanese alcohol-dependent women"
    explanation: >-
      Documents iodine-staining endoscopic screening applied to an
      ALDH2-relevant at-risk population.
  - reference: PMID:30629674
    reference_title: "Endoscopic screening using esophageal iodine staining and genotypes of ADH1B and ALDH2 in Japanese alcohol-dependent women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "DIULs ≥5 mm were histologically diagnosed as low-grade intraepithelial neoplasia in 26 patients and superficial squamous cell carcinoma in 9 patients."
    explanation: >-
      Shows the screen detects real neoplasia rather than an incidental
      staining artefact, which is what makes it worth performing.
  - reference: PMID:30629674
    reference_title: "Endoscopic screening using esophageal iodine staining and genotypes of ADH1B and ALDH2 in Japanese alcohol-dependent women."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The presence of large or multiple esophageal distinct iodine-unstained lesions (DIULs) is a strong predictor of field cancerization in the upper aerodigestive tract."
    explanation: >-
      States what the finding means - field cancerization, not a single lesion.
- name: ALDH2 genotyping
  description: >-
    Molecular testing for rs671 and, where the history suggests flushing in a
    non-East-Asian individual, wider ALDH2 sequencing - since two further
    flushing-causing variants have been described that an rs671-only assay
    would miss.
  diagnosis_term:
    preferred_term: molecular genetic analysis
    term:
      id: NCIT:C19770
      label: Molecular Analysis
  evidence:
  - reference: PMID:8290656
    reference_title: "Dominance of the mutant ALDH2(2) allele in the expression of human stomach aldehyde dehydrogenase-2 activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "determined the genotypes from leukocytes of the same individuals by using polymerase-chain-reaction amplification and hybridization with allele-specific oligonucleotide probes"
    explanation: >-
      Describes the genotyping approach in the study that paired genotype with
      enzyme phenotype.
  - reference: PMID:39075523
    reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "the methodology developed here to characterize ALDH2 genetic variant response to alcohol can lead the way precision medicine strategies to further understand the interplay of alcohol consumption, ALDH2 genetics, and cancer"
    explanation: >-
      The authors' framing of genotype-guided assessment, which is the rationale
      for testing beyond rs671.
animal_models:
- name: Aldh2 knockout mouse
  species: Mouse
  genotype: Aldh2 -/- (homozygous knockout); Aldh2 +/+ wild-type comparator
  publication: PMID:19874182
  description: >-
    The standard rodent model of human ALDH2 inactivity. Note the allelic
    mismatch: this is a null, whereas the common human allele rs671 is a
    dominant-negative missense subunit that assembles into tetramers. The null
    reproduces the *consequence* (no ALDH2 activity, acetaldehyde
    accumulation) without reproducing the *mechanism* by which a single human
    allele achieves it. The source is a review of published Aldh2-knockout
    studies rather than a single primary experiment.
  modeled_mechanisms:
  - target: Acetaldehyde Accumulation After Ethanol Exposure
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Knockout mice exposed to ethanol or acetaldehyde show higher blood
      acetaldehyde and greater toxicity than wild-type, which is the defining
      biochemical feature of the human disorder.
    limitations: >-
      A null allele models homozygous ALDH2 inactivity, not the heterozygous
      dominant-negative state that most affected humans carry; the human
      phenotype's hallmark - that one poisoned subunit disables the tetramer -
      cannot be represented by an absent protein. The cited source is also a
      review rather than primary data.
    readouts:
    - name: Blood acetaldehyde after ethanol or acetaldehyde exposure
      target: Acetaldehyde Accumulation After Ethanol Exposure
      direction: INCREASED
      interpretation: >-
        Higher blood acetaldehyde in knockouts than wild-type reproduces the
        human biochemical phenotype.
      evidence:
      - reference: PMID:19874182
        reference_title: "Characteristics of aldehyde dehydrogenase 2 (Aldh2) knockout mice."
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "When they were exposed to atmospheres containing acetaldehyde, the Aldh2 -/- mice showed more severe toxic symptoms, like weight loss and higher blood acetaldehyde levels, as compared with the Aldh2 +/+ mice."
        explanation: >-
          The measurement, with the wild-type comparator stated.
    evidence:
    - reference: PMID:19874182
      reference_title: "Characteristics of aldehyde dehydrogenase 2 (Aldh2) knockout mice."
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      snippet: "Aldh2 knockout mice appear to be a valid animal model for humans with inactive ALDH2"
      explanation: >-
        The authors' own claim that the model is valid for human ALDH2
        inactivity, which is what justifies curating this link.
differential_diagnoses:
- name: Alcohol Use Disorder
  description: >-
    Not a diagnostic confusion so much as the mechanistic mirror image, and the
    reason this entry matters to the rest of the knowledge base. The same
    inactive ALDH2 allele that *causes* acute alcohol sensitivity is one of the
    two largest-effect *protective* loci against alcohol use disorder, because
    the reaction is aversive. `Alcohol_Use_Disorder` already curates ALDH2 in
    that protective role; this entry curates the disorder that produces the
    aversion.
  disease_term:
    preferred_term: alcohol use disorder
    term:
      id: MONDO:0007079
      label: alcohol dependence
  distinguishing_features:
  - Opposite direction of the same allele - carriers are less likely, not more likely, to develop dependence.
  - Acute alcohol sensitivity is an exposure-triggered metabolic reaction with an onset in minutes; alcohol use disorder is a chronic behavioural condition.
  - A carrier who abstains has neither condition; a carrier who drinks despite the reaction carries elevated cancer risk without necessarily meeting dependence criteria.
  evidence:
  - reference: PMID:8290656
    reference_title: "Dominance of the mutant ALDH2(2) allele in the expression of human stomach aldehyde dehydrogenase-2 activity."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "reported to be a negative risk factor for development of alcohol dependence"
    explanation: >-
      States the protective direction explicitly.
- name: Disulfiram-ethanol reaction
  description: >-
    A pharmacologically identical syndrome produced on purpose. Disulfiram
    inhibits ALDH2, so a patient taking it who drinks develops flushing, nausea
    and tachycardia by the same acetaldehyde-accumulation mechanism curated
    here. Cyanamide is another ALDH inhibitor used the same way. The
    distinguishing feature is drug exposure, not phenotype - which is a useful
    reminder that the mechanism, not the genotype, produces the syndrome.
  distinguishing_features:
  - Acquired and reversible on stopping the drug, rather than lifelong.
  - No family history; onset coincides with starting an ALDH-inhibiting drug.
  - Genotyping is normal at ALDH2 unless the patient also carries an inactivating variant, in which case the reaction is more severe.
  evidence:
  - reference: PMID:39075523
    reference_title: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Aldehyde dehydrogenase 2 (ALDH2) is critical for alcohol metabolism by converting acetaldehyde to acetic acid."
    explanation: >-
      Supports the shared enzymatic step that a pharmacological ALDH2 inhibitor
      blocks. Graded PARTIAL because this entry holds no source characterising
      the disulfiram reaction itself; that claim rests on the shared mechanism,
      and a curator adding disulfiram detail should cite a source for it.
discussions:
- discussion_id: aldh2_scope_susceptibility_or_disease
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    Is acute alcohol sensitivity a disease entry, or a susceptibility annotation
    that belongs on the alcohol-related entries rather than standing alone?
  attaches_to:
  - "pathophysiology#Acetaldehyde Accumulation After Ethanol Exposure"
  rationale: >-
    MONDO flags MONDO:0012454 `subset: omim_susceptibility`, and the honest
    reading is that this concept sits on the boundary of what dismech curates as
    a Disease. The case for curating it is that it has a defined
    post-exposure phenotype with an onset in minutes, a measurable biochemical
    marker (blood acetaldehyde, six-fold elevated in rs671 heterozygotes under
    challenge), an OMIM entity, a causal gene with a demonstrated
    dominant-negative mechanism, and an actionable clinical consequence - the
    same footing as the existing Dihydropyrimidine_Dehydrogenase_Deficiency
    entry, which is likewise a pharmacogenomic/metabolic sensitivity. The case
    against is that its manifestations only exist under an elective exposure,
    which makes it look more like a trait than a disease. This entry takes the
    first position and records the second, rather than making the choice
    silently. If dismech later adopts a general policy on exposure-conditioned
    metabolic sensitivities, this entry should be revisited under it.
- discussion_id: aldh2_ancestry_framing_is_outdated
  kind: KNOWLEDGE_GAP
  status: OPEN
  prompt: >-
    How much of ALDH2-related alcohol sensitivity outside East Asian
    populations is missed because both the clinical framing and the standard
    genetic test are built around rs671?
  attaches_to:
  - "pathophysiology#Inactivating ALDH2 Variant"
  rationale: >-
    The disorder is described almost everywhere - including in MONDO's own
    definition, which says it is "usually found in Asians" - as an East Asian
    condition caused by rs671. A 2024 alcohol-challenge study found two further
    ALDH2 variants, rs747096195 and rs190764869, in flushing individuals who
    were not of East Asian descent, each roughly doubling acetaldehyde by
    mechanisms distinct from rs671's. An rs671-only assay returns normal for
    those people, and an ancestry-based clinical heuristic never prompts the
    test. Since the flushing history is the recommended screening question for
    a markedly elevated oesophageal cancer risk, a systematic blind spot here
    has a downstream consequence. What is not known is the population frequency
    of these and other ALDH2 variants outside East Asia, or what fraction of
    non-East-Asian flushers they explain.
  proposed_experiments:
  - experiment_id: aldh2_full_gene_sequencing_in_non_east_asian_flushers
    name: Full ALDH2 sequencing in ancestry-diverse self-reported flushers
    description: >-
      Recruit self-reported alcohol flushers across ancestries, sequence the
      full ALDH2 coding region rather than genotyping rs671 alone, and pair each
      genotype with a standardised alcohol challenge measuring acetaldehyde,
      heart rate and skin temperature - the protocol that identified the two
      known additional variants.
    readouts:
    - name: Blood acetaldehyde after standardised alcohol challenge, by genotype
      target: Acetaldehyde Accumulation After Ethanol Exposure
      direction: INCREASED
      interpretation: >-
        Elevated acetaldehyde in rs671-negative flushers would quantify how much
        of the phenotype an rs671-only test misses.
notes: >-
  Scope decision, stated up front. MONDO marks MONDO:0012454 `subset:
  omim_susceptibility`, so the first question this entry had to answer was
  whether it should exist as a Disease rather than as a susceptibility
  annotation on the alcohol-related entries. It is curated as a Disease on the
  same grounds as the existing Dihydropyrimidine_Dehydrogenase_Deficiency entry:
  a defined post-exposure phenotype, a measurable biochemical marker, an OMIM
  entity, a causal gene with a demonstrated mechanism, and an actionable
  clinical consequence. The counter-argument - that its manifestations exist
  only under an elective exposure - is recorded as an open discussion rather
  than dismissed.

  Why this entry earns its place in the knowledge base. Two consequences of the
  inactive ALDH2 allele were already curated without the disorder that produces
  them: `Alcohol_Use_Disorder` names ALDH2 as one of two large-effect
  *protective* loci, and the oesophageal cancer entries name it as a *risk*
  factor. Both point at acetaldehyde accumulation, which had no entry of its
  own. The `Reduced heavy drinking` phenotype and the Alcohol Use Disorder
  differential are the deliberate joins.

  Residue numbering. rs671 is written **p.Glu504Lys** against the precursor
  protein and **E487K** against the mature protein after cleavage of the
  mitochondrial targeting sequence; both name the same substitution. This entry
  uses the 504 numbering throughout, matching dbSNP, MONDO and the 2024 paper.
  Older literature using E487K is describing the same allele, not a second one -
  worth stating, because a mismatched-numbering pair is exactly the kind of
  thing that gets curated twice.

  Ontology binding rationale for the exposure. Per the project's ECTO guidance,
  the choice between `ECTO:0001082` (exposure to alcohol consumption, a
  behaviour term) and `ECTO:9000027` (exposure to ethanol, anchored on
  CHEBI:16236) follows what the entry's own name and mechanism state. This
  entry's mechanism is ethanol chemistry - oxidation to acetaldehyde and failure
  of its clearance - not a drinking-behaviour claim, so the environmental entry
  is named `Ethanol Ingestion` and bound to the chemical term. `ECTO:9000027`
  was verified against the local `sqlite:obo:ecto` build that
  `conf/oak_config.yaml` actually uses for validation, not against OLS.

  Cell-type term caution carried forward from this curation batch: a plain OAK
  lookup returns real terms that are wrong for the intended sense often enough
  that every identifier here was resolved by label before use.

  Deep-research report: read, cross-checked, and mostly not used. `just
  preflight-dr` returned PASS (ALDH2 mentioned 126 times; report OMIM 610251
  matching the MONDO xref), but the report's own `reference_validation` block
  reports **quotes_valid: 2 of quotes_checked: 5** - three quotes attributed to
  sources that do not contain them (PMC:PMC9844601, PMID:9419411,
  DOI:10.1073/pnas.1510757112). None of those three is cited by this entry, and
  every snippet here was taken from an abstract read directly before the report
  was generated, so no report-sourced quote entered the KB. But a 3-in-5
  unsupported-quote rate is a stronger warning than a confabulation_rate of 0.0
  suggests, and it is the reason the leads below were each re-checked against
  PubMed independently rather than curated on the report's word.

  A lesson this entry paid for twice, worth keeping because it generalizes.
  An earlier version of these notes claimed a search "returned related papers
  ... but none establishing the surveillance recommendation". PMID:30629674 -
  already sitting in `references_cache/` because this entry's own
  deep-research run resolved it - is exactly that study, and is now curated as
  a `diagnosis` entry. **A claim about what the literature does not contain is
  still a claim, and that one was made without checking the cache this entry
  was shipping.** The same paper then supplied the flushing-history limits the
  diagnosis entry was missing.

  The ESCC risk is exposure-conditioned, and both halves are curated so
  neither can be quoted alone. In a 0.5-million prospective cohort, people
  drinking less than weekly showed *no* excess oesophageal cancer risk from
  inactive ALDH2; the risk appears at higher intake (rs671 GA vs GG HR 3.31 in
  male weekly consumers). Meanwhile a meta-analysis across all subjects
  irrespective of drinking found rs671 *protective* for ESCC (OR 0.60) - which
  is what the `Reduced heavy drinking` phenotype predicts, since carriers
  drink less. Those two estimates are not in conflict; they are the two halves
  of this entry's central paradox. That meta-analysis's Mendelian
  randomization arm also failed to establish a causal alcohol effect, curated
  as a PARTIAL negative rather than omitted.

  The flushing screen degrades exactly where it matters. Sensitivity for
  inactive ALDH2 is 96.1% in general male clinic patients, 56.8% in male
  weekly drinkers, and 50.0% in alcohol-dependent women - three populations,
  three papers, one monotone pattern. A negative flushing history in a heavy
  drinker does not exclude ALDH2 deficiency; genotyping does.

  Leads still NOT curated, each re-checked:
  - *Antihistamine and H2-blocker masking of the flush.* Still unsourced: a
    targeted PubMed search returned only papers from 1980 and 1982, neither
    stating it. Not asserted. A curator who finds a modern source should add it
    as a harm-framed treatment entry.
  - *ALDH2 activators (Alda-1, AD-9308).* Investigational, and not a therapy
    for the flush reaction itself.
  - *Amplified reaction with metronidazole, cephalosporins and sulfonylureas.*
    Only the disulfiram arm is represented, as a differential graded PARTIAL on
    the shared enzymatic step.

  Scoping decision on non-cancer sequelae. The chronic consequences curated
  here stop at the upper-aerodigestive carcinogenesis arm. Cardiovascular
  associations (coronary vasospasm, hypertension, atrial fibrillation),
  amyloid/neurodegeneration links, and the ALDH5/formaldehyde AMeD-syndrome arm
  all appear in the deep-research report and are real literatures, but each is
  a downstream disease with its own mechanism rather than a feature of acute
  alcohol sensitivity, and curating them here would make this entry a
  general ALDH2 review. They belong on the relevant disease entries, which can
  reference this one.

  Not curated, and why. No `treatments` block: there is no therapy for this
  disorder, and the intervention that matters - not drinking, or drinking less -
  is the avoidance of the trigger rather than a treatment of the condition. It
  is represented instead by the `Ethanol Ingestion` environmental entry and by
  the `Flushing history` diagnosis entry, which carries the counselling and
  endoscopic-screening rationale. Curating "alcohol avoidance" as a Treatment
  would assert a clinical recommendation with a shape the sources do not have.

  The disulfiram-ethanol reaction is curated as a differential on the strength
  of the shared enzymatic step only; the evidence item is graded PARTIAL and
  says so. A curator adding disulfiram detail should cite a source describing
  that reaction directly rather than inheriting this one.
📚

References & Deep Research

References

2
PMID:19320537
The alcohol flushing response: an unrecognized risk factor for esophageal cancer from alcohol consumption.
No top-level findings curated for this source.
PMID:39075523
Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge.
No top-level findings curated for this source.

Deep Research

1
Claude Code ▸
1. Disease Information
claude-haiku-4-5-20251001, claude-sonnet-5 43 citations 2026-08-22T14:37:56.949524

1. Disease Information

Overview. "Acute Alcohol Sensitivity" is the OMIM-recognized clinical phenotype produced by inherited deficiency of mitochondrial aldehyde dehydrogenase 2 (ALDH2), the enzyme that oxidizes acetaldehyde (the first, toxic metabolite of ethanol) to acetate. Loss-of-function of ALDH2 causes rapid systemic accumulation of acetaldehyde after even modest alcohol intake, producing a stereotyped acute reaction — facial/upper-body flushing, tachycardia, palpitations, nausea, headache, and malaise — commonly called the "alcohol flush reaction" or, colloquially, "Asian flush"/"Asian glow." It is one of the most common single-gene enzymopathies in humans, affecting an estimated ~540 million people, concentrated in East Asian populations (Chinese, Japanese, Korean) (Disease Models & Mechanisms review).

Key identifiers: - OMIM Phenotype: #610251 — ALCOHOL SENSITIVITY, ACUTE (OMIM #610251) - OMIM Gene: 100650 — ALDEHYDE DEHYDROGENASE 2; ALDH2 (12q24.12) - MONDO: MONDO:0012454 (Malacards) - NIH Genetic Testing Registry condition: C2674838 (GTR) - ClinVar variant-condition record: NM_000690.4(ALDH2):c.1510G>A (p.Glu504Lys) associated with "Alcohol sensitivity, acute" (ClinVar RCV000020058) - dbSNP: rs671 (the causal variant) - Related digenic disorder: AMeD syndrome* (OMIM #619151), caused by biallelic ADH5 variants plus the ALDH2 p.Glu504Lys allele (OMIM #619151; Oda et al., Sci Adv 2021, PMID:33355142)

Common synonyms: Alcohol flush reaction/syndrome; Asian flush; Asian glow; ALDH2 deficiency; ALDH2*2 deficiency; aldehyde dehydrogenase-2 deficiency; alcohol-induced flushing; "Oriental flushing syndrome" (older, non-preferred literature term).

Evidence basis. The evidentiary base is overwhelmingly aggregated, population-level and cohort/case-control human genetic epidemiology (large East Asian biobank and hospital cohorts, twin/family studies, GWAS), supplemented by mechanistic biochemistry/structural biology and mouse-model (ALDH2-knockout and ALDH2*2 knock-in) experimental data — not primarily individual patient EHR case reports, since this is a common polymorphism-driven trait rather than a rare monogenic disease discovered through isolated patients.

2. Etiology

Primary cause — genetic. Acute alcohol sensitivity is caused by the common East Asian-specific missense variant rs671 (c.1510G>A, p.Glu504Lys, historically "Glu487Lys" under older numbering) in ALDH2. This substitution sits at a subunit-interface within the small oligomerization domain of the ALDH2 homotetramer and destabilizes/inactivates the enzyme in a dominant-negative fashion: because ALDH2 functions as a tetramer, incorporation of even one mutant subunit disproportionately poisons the whole complex, so heterozygotes (~10–45% residual activity) and homozygotes (~1–5% residual activity) are both symptomatic, though homozygotes are far more severely affected (Larson et al., structural analysis; population activity data via selfdecode summary).

"The presence of the E487K subunit in ALDH2 decreases both the activity and stability of the heterotetramer in a dominant fashion... Since ALDH2 is a homotetrameric enzyme, random association of active and inactive subunits should generate about 6% normal tetramers, with the remainder containing at least 1 mutant subunit."

A second, less severe modifying/compounding factor is variation in ADH1B (alcohol dehydrogenase 1B, chromosome 4q23), the enzyme immediately upstream of ALDH2 that converts ethanol to acetaldehyde. The gain-of-function variant ADH1B*2 (rs1229984, Arg48His) accelerates ethanol→acetaldehyde conversion up to ~40-fold, so individuals carrying both fast ADH1B2 and slow ALDH22 experience the most rapid and severe acetaldehyde surges and flushing (review; selfdecode).

Risk factors: - Genetic: ALDH2 rs671 A allele (heterozygous or homozygous); co-inheritance of the fast-metabolizing ADH1B2 (rs1229984) allele amplifies the phenotype (PMC8312924). - Ancestry/environmental: East Asian ancestry (Han Chinese, Japanese, Korean) — the rs671 allele is essentially absent in African, European, and most Southeast Asian/Indian populations (DMM review). - Dose/behavioral:* Even modest alcohol intake precipitates symptoms; concomitant use of pharmacologic ALDH inhibitors (e.g., disulfiram, metronidazole, some cephalosporins, sulfonylureas) produces an analogous but pharmacologically-induced "disulfiram-alcohol reaction" that phenocopies the genetic condition (StatPearls Disulfiram; Wikipedia disulfiram-alcohol reaction).

Protective factors — genetic paradox. The very allele that causes the flush reaction is strongly protective against alcohol use disorder and alcoholic cirrhosis, because the aversive symptoms discourage heavy/habitual drinking:

"The ALDH2 rs671 GA/AA genotypes significantly reduced the risk of alcohol-induced mental disorders by 87%, alcohol dependence syndrome by 83%, and alcohol abuse by 66%." (Chang et al., Cancer Medicine 2023 review, PMC9844601)

Gene-environment interaction. The central G×E interaction of this condition is that the genotype is phenotypically silent without alcohol exposure — the enzyme deficiency only manifests acute symptoms and long-term tissue risk upon ethanol challenge. Critically, epidemiologic data show that the increased cancer risk conferred by ALDH2 deficiency is conditional on alcohol consumption:

"Among male weekly alcohol consumers, both flushing response and rs671 were associated with EC [esophageal cancer] risk, suggesting that the possession of inactive ALDH2 does not increase EC risk unless alcohol is consumed." (AACR CEBP)

Suggested CHEBI terms: CHEBI:16236 (ethanol), CHEBI:15343 (acetaldehyde), CHEBI:15366 (acetic acid), CHEBI:27897 (disulfiram).

3. Phenotypes

The acute reaction is a symptom cluster/behavioral+physiological syndrome, not a single defect, occurring within minutes to ~1 hour of alcohol ingestion.

Phenotype Type Suggested HPO term Notes
Facial/cutaneous flushing Clinical sign HP:0031282 (Flushing) Cardinal, near-universal sign; erythema of face, neck, upper trunk
Tachycardia Clinical sign HP:0001649 (Tachycardia) Acetaldehyde-mediated catecholamine release
Palpitations Symptom HP:0001962 (Palpitations)
Nausea Symptom HP:0002018 (Nausea)
Headache Symptom HP:0002315 (Headache)
Muscle weakness Symptom HP:0001324 (Muscle weakness)
Hypotension (occasionally) Clinical sign HP:0002615 (Hypotension) More prominent with pharmacologic (disulfiram) reaction
Severe/prolonged hangover Symptom (no precise HPO; consider free text) Reported to be disproportionately severe
Elevated blood acetaldehyde Lab abnormality (biochemical marker, not HP-coded) Documented up to 6-fold higher than wild-type after challenge

Characteristics: - Onset: First alcohol exposure (often adolescence/young adulthood in cultures where alcohol is introduced socially); the reaction is present from the individual's very first drink and does not need to be "acquired." - Course: Acute, self-limited, episodic — recurs with every exposure to alcohol; not progressive as a standalone reaction, though repeated exposure across a lifetime is linked to cumulative tissue-damage risk (see Mechanism/Prognosis). - Severity/penetrance: Highly genotype-dependent — ALDH22 homozygotes show near-complete flushing penetrance and the most severe reaction; heterozygotes show a graded, often milder or inconsistent response, and can sometimes "drink through" the reaction with habituation (which does not reduce the underlying carcinogenic acetaldehyde exposure). - Frequency: In a Japanese cohort, "symptoms of facial flushing, palpitation, tachycardia, muscle weakness, headache and nausea present in nearly 43% of those with the deficiency" (search synthesis of Cancer Epidemiol Biomarkers Prev data). Genotype–phenotype concordance is high: "Blinded genotyping showed inactive ALDH2 for 94.4% of subjects who reported always flushing... whereas 95.6% of subjects reporting that they never exhibited facial flushing had active ALDH2" (PMID:9419411). - Quality of life:* Primarily social/behavioral — the reaction often leads to reduced or avoided alcohol consumption, with secondary social effects in cultures with strong drinking norms; a chronic downstream QoL burden accrues from increased skin flushing self-consciousness and (per §11/§2) elevated long-term cancer/cardiometabolic risk in those who drink despite the reaction.

4. Genetic / Molecular Information

Causal gene: ALDH2 (Aldehyde Dehydrogenase 2 Family Member; HGNC:404; OMIM *100650), chromosome 12q24.12, encoding the mitochondrial matrix tetrameric enzyme that oxidizes acetaldehyde to acetate using NAD⁺.

Primary pathogenic variant: - rs671, c.1510G>A, p.Glu504Lys (also historically numbered p.Glu487Lys, reflecting mature-protein vs. precursor numbering) — classified in ClinVar as pathogenic/associated with "Alcohol sensitivity, acute" (ClinVar RCV000020058). - Allele designations: ALDH2*1 (wild-type/active) vs. ALDH2*2 (rs671-A, inactive/hypomorphic). - Functional consequence: Dominant-negative loss-of-function via disruption of tetramer assembly/stability — not a simple recessive loss-of-function. Both GA heterozygotes (10–45% residual activity) and AA homozygotes (1–5% residual activity) are enzymatically deficient (search synthesis, gnomAD/functional summary). - Novel/rarer ALDH2 coding variants beyond rs671 causing additional acetaldehyde-accumulation phenotypes were recently catalogued: "Uncovering newly identified aldehyde dehydrogenase 2 genetic variants that lead to acetaldehyde accumulation after an alcohol challenge" (PMID:39075523, J Transl Med 2024).

Population/allele frequency: - rs671-A allele frequency: ~30–50% across East Asian populations (up to ~40% in Han Chinese and Japanese); minor allele frequency ~0.24 in Japanese (HapMap JPT), ~0.15 in Han Chinese (HapMap HCB); gnomAD/1000 Genomes-scale estimates give ~0.255 in East Asians versus ~0.0003 (essentially absent) outside East Asia (search synthesis; historical population survey). - Historically reported "absent ALDH2" activity frequencies ranged as high as 69% in some Indigenous Ecuadorian Highland populations down to 0% in Egyptian, Liberian, Kenyan, and European populations, though the East Asian-specific rs671 variant itself is the dominant, best-characterized cause in modern genomic data. - The allele is thought to have arisen from a single mutational event roughly 2,000–7,000 years ago in central China and spread with rice-domesticating agricultural populations ("Origin and Spread of the ALDH2 Glu504Lys Allele," PMC9590465) — a leading hypothesis is that it was positively selected as protection against alcohol-associated pathogens/toxicity or alcoholism in early agrarian society.

Modifier gene: ADH1B (4q23; HGNC:249), particularly rs1229984 (Arg48His, "ADH1B*2"), which increases the rate of ethanol-to-acetaldehyde conversion and synergistically worsens the flushing phenotype and downstream cancer risk when co-inherited with ALDH22. A second ADH1B variant (rs1042026 / "ADH1B3", predominantly in African-ancestry populations) has related but less-studied effects. ALDH2 rs674 is also examined alongside rs671 in some association studies.

Epigenetics/somatic: Not a classical epigenetic disease; however, acetaldehyde itself is a potent DNA-damaging agent (forms DNA adducts, induces sister chromatid exchange), and ALDH2 deficiency is mechanistically linked to accelerated acetaldehyde-DNA adduct accumulation in exposed tissues — this is the proposed causal chain for the elevated cancer risk (see Mechanism), rather than a primary epigenetic mechanism.

Chromosomal abnormalities: None reported; this is a single-nucleotide missense polymorphism, not a structural/copy-number disorder.

Related digenic disorder (molecular context): AMeD syndrome (Aplastic anemia, Mental retardation, and short stature, Digenic) arises when biallelic loss-of-function ADH5 (cytosolic formaldehyde dehydrogenase) variants co-occur with a heterozygous or homozygous ALDH2 p.Glu504Lys allele, causing loss of the combined formaldehyde-detoxification pathway (ADH5 + ALDH2), leading to bone marrow failure, developmental delay, and short stature — illustrating that ALDH2 deficiency's biochemical consequences extend beyond ethanol to endogenous aldehyde (formaldehyde) clearance (Oda et al. 2021, Sci Adv, PMID:33355142; OMIM #619151).

Suggested gene/ontology annotations: hgnc:404 (ALDH2), hgnc:249 (ADH1B); GO biological process GO:0006068 (ethanol catabolic process) / GO:0046185 (aldehyde catabolic process); GO molecular function GO:0004029 (aldehyde dehydrogenase [NAD+] activity). (IDs given from general ontology knowledge — verify canonical labels via OAK before curation.)

5. Environmental Information

  • Primary environmental trigger: Ethanol (alcoholic beverage) ingestion — the sine qua non exposure; without alcohol the genotype is asymptomatic.
  • Pharmacologic phenocopy triggers: ALDH-inhibiting drugs — disulfiram (classic), and reported "disulfiram-like reactions" with metronidazole, some first-generation sulfonylureas (chlorpropamide), and certain cephalosporins (e.g., cefotetan) — all of which produce the same acetaldehyde-accumulation flush/tachycardia syndrome by pharmacologically inhibiting ALDH activity (StatPearls).
  • Lifestyle factors: Habitual drinking despite the reaction ("drinking through the flush") is a recognized risk-amplifying behavior — it does not reduce acetaldehyde exposure and is associated with substantially elevated cancer risk (§11).
  • Occupational/endogenous aldehyde exposure: Because ALDH2 (with ADH5) also detoxifies endogenous and environmental formaldehyde, occupational or endogenous formaldehyde burden is a relevant compounding exposure in ALDH2-deficient individuals, most dramatically illustrated by AMeD syndrome.
  • Infectious agents: Not applicable — this is not an infectious disease.

Suggested exposure ontology term: ECTO term for "exposure to ethanol" / "consumption of alcoholic beverage" (verify exact CURIE via OAK/ECTO lookup).

6. Mechanism / Pathophysiology

Causal chain (upstream → downstream):

  1. Molecular trigger: Alcohol ingestion → hepatic ADH1B-mediated oxidation of ethanol to acetaldehyde (normally a transient, rapidly-cleared intermediate).
  2. Molecular lesion: In ALDH2*2 carriers, the p.Glu504Lys substitution destabilizes the ALDH2 homotetramer at the subunit interface, producing a dominant-negative loss of catalytic activity (10–45% residual in heterozygotes; 1–5% in homozygotes) (Structure paper).
  3. Biochemical consequence: Acetaldehyde clearance is crippled → systemic acetaldehyde accumulation, reported up to 6-fold higher than in ALDH2-normal individuals after an equivalent alcohol challenge (search synthesis of PMC11288122 data).
  4. Cellular/physiological effects: Acetaldehyde is a direct vasodilator and histamine-releasing agent, and stimulates sympathetic/catecholaminergic activity, producing cutaneous flushing (vasodilation), tachycardia/palpitations, and headache; acetaldehyde is also a reactive electrophile that forms protein and DNA adducts and generates reactive lipid-peroxidation byproducts such as 4-hydroxynonenal (4-HNE), compounding oxidative/genotoxic stress.
  5. Organismal/clinical manifestation: Acute flush reaction (§3); chronically, repeated acetaldehyde/4-HNE exposure in those who continue to drink is mechanistically linked to:
  6. Carcinogenesis — particularly esophageal squamous cell carcinoma, via direct acetaldehyde-DNA adduct formation in esophageal mucosa exposed to concentrated local ethanol/acetaldehyde ("field-cancerization" mechanism);
  7. Cardiovascular pathology — 4-HNE/aldehyde-driven coronary vasospasm, endothelial dysfunction, and reported associations with hypertension, atrial fibrillation/left atrial substrate remodeling, and stroke;
  8. Neurodegeneration — recent mechanistic work shows the rs671 variant enhances amyloid-β pathology: "(R)-4-HNE enantiomer adducts to residue Lys53 of C99 [APP], favoring Aβ40 generation in the Golgi apparatus," and lower ALDH2 activity is linked to reduced Aβ phagocytosis/clearance (Nat Commun 2024, PMID:38519490).
  9. Formaldehyde-detoxification failure (AMeD syndrome arm) — since ALDH2 also participates in clearing endogenous formaldehyde generated by one-carbon/methanol metabolism, its loss (combined with ADH5 loss) causes hematopoietic stem cell genotoxic stress and bone marrow failure (PMID:33355142).

Cell types/tissues implicated: hepatocytes (primary site of ethanol/acetaldehyde metabolism), vascular smooth muscle and endothelial cells (flushing, coronary spasm), esophageal squamous epithelial cells (carcinogenesis), cardiac myocytes/fibroblasts (remodeling, AF), neurons/microglia/astrocytes (amyloid pathology), and hematopoietic stem/progenitor cells (AMeD syndrome).

Suggested GO terms: GO:0006068 ethanol catabolic process; GO:0006081 cellular aldehyde metabolic process; GO:0034599 cellular response to oxidative stress; GO:0006284 base-excision repair (DNA-adduct repair context). Suggested CL terms: CL:0000182 hepatocyte; CL:0002138 endothelial cell of vascular tree; CL:0000646 basal cell (esophageal epithelium context); CL:0000000-level cardiac myocyte term. Suggested CHEBI terms: CHEBI:15343 acetaldehyde; ~4-hydroxynonenal (verify CHEBI CURIE via OAK).

Molecular/omics profiling: No large-scale disease-specific transcriptomic/proteomic/metabolomic dataset exists specifically for "acute alcohol sensitivity" as a phenotype per se (it is a challenge-dependent, not a steady-state, condition), but targeted metabolomic studies quantify blood/breath acetaldehyde as the definitive biochemical readout after an ethanol or ethanol-patch challenge.

7. Anatomical Structures Affected

  • Organ level (acute reaction): Skin/face/upper trunk (flushing), cardiovascular system (tachycardia, palpitations), CNS (headache).
  • Organ level (chronic/secondary, in drinkers): Esophagus (squamous cell carcinoma), liver (metabolic first-pass organ), heart (arrhythmia/remodeling, especially atrial), brain (amyloid pathology/possible dementia risk), bone marrow (AMeD-syndrome arm only), and — per broader ALDH2-variance literature — stomach, breast, and ovary have been examined for genotype-cancer-risk associations.
  • Body systems: Integumentary, cardiovascular, gastrointestinal, nervous, and (in the digenic AMeD arm) hematopoietic systems.
  • Tissue/cell level: Vascular smooth muscle/endothelium (flushing, vasospasm); esophageal squamous epithelium (carcinogenesis target); cardiac conduction/atrial tissue; hepatic parenchyma.
  • Subcellular level: Mitochondrial matrix (ALDH2 is a mitochondrial matrix enzyme — GO Cellular Component GO:0005759 mitochondrial matrix) is the primary organelle-level site of the molecular lesion.
  • Localization/laterality: Bilateral, symmetric — flushing classically affects the face, neck, and upper chest bilaterally; not lateralized.

Suggested UBERON terms: UBERON:0001043 esophagus; UBERON:0002107 liver; UBERON:0000948 heart; UBERON:0001003 skin epidermis; UBERON:0002037 cerebellum/UBERON:0000955 brain (amyloid context).

8. Temporal Development

  • Onset: From the individual's very first alcohol exposure — typically first noticed in adolescence or early adulthood coincident with initial social alcohol use; there is no "silent" pre-symptomatic period distinct from lack of exposure.
  • Onset pattern: Acute — symptoms begin within minutes of alcohol ingestion (fast-ADH1B carriers can flush within minutes of the first sip) and typically resolve within 1–3 hours as acetaldehyde is eventually cleared by residual ALDH2 activity and alternate pathways.
  • Progression/course: Episodic, fully recurrent with each exposure, not a progressive degenerative disease in itself. The acute episode is self-limited. However, the biological insult (acetaldehyde/4-HNE exposure) is cumulative across a lifetime of drinking episodes in those who continue to consume alcohol, driving the "stable-trait, cumulative-risk" pattern seen in long-term cancer/cardiovascular outcome studies.
  • Habituation caveat: Some individuals report a diminished subjective flush response with repeated heavy drinking ("drinking through" the reaction), but this reflects tolerance to the symptom, not to the underlying enzymatic deficiency or the carcinogenic acetaldehyde exposure — an important clinical/public-health distinction (see "Beyond the Flush: Reframing ALDH2 Deficiency as a Public Health Risk," Karger Public Health Genomics).
  • Remission: No spontaneous remission of the genetic trait; the only "remission" is behavioral abstinence from alcohol/ALDH-inhibiting drugs.
  • Critical periods: Adolescent/young-adult introduction to alcohol is a socially critical period, since the phenotype often (but not always) leads to early avoidance behavior that is protective against later alcohol use disorder.

9. Inheritance and Population

  • Inheritance pattern: Autosomal, with a dominant-negative functional mechanism — both heterozygotes and homozygotes for ALDH22 (rs671-A) manifest the flushing phenotype, though homozygotes show more complete enzyme inactivation and more severe/consistent symptoms. This is best described as semi-dominant/dose-dependent* rather than classical Mendelian dominant or recessive.
  • Penetrance: High but not complete for the flush phenotype (heterozygote flushing is reported in a substantial majority but not 100% of carriers; some heterozygotes report inconsistent/mild flushing).
  • Prevalence: Population allele frequency ~30–50% in East Asians (heterozygote + homozygote carriers together represent a majority of some East Asian populations); essentially 0% outside East Asian ancestry. ~540 million people worldwide are estimated carriers, i.e., roughly 8% of the world's population.
  • Founder effect: Strong — the rs671 mutation is believed to derive from a single ancestral mutational event that arose in central China roughly several thousand years ago and spread with the expansion of rice-farming agricultural populations across East Asia (PMC9590465).
  • Sex ratio: No strong sex-specific difference in the ALDH2 genotype itself, though phenotypic/behavioral consequences (e.g., drinking amount, cardiometabolic outcome risk) can differ by sex in cohort studies — e.g., a reported finding that women with high ALDH2*2 burden who drank ≥7 drinks/week had elevated diabetes/hypertension/cardiovascular risk relative to abstainers.
  • Geographic distribution: Concentrated in China, Japan, Korea, and their diaspora populations; essentially absent in African, European, and most South/Southeast Asian and Indigenous American populations (with isolated historical reports of ALDH2 activity deficiency in some Indigenous South American groups needing separate genetic confirmation).
  • Age distribution: Present from birth (germline variant); clinically manifest from first alcohol exposure onward across the lifespan.

10. Diagnostics

  • Clinical/behavioral screening: Self-report flushing questionnaire — shown to correlate strongly with genotype (94–96% concordance in some validation studies) and is a widely used low-cost proxy for genotype in epidemiologic and even some clinical-counseling contexts (PMID:9419411).
  • Ethanol/alcohol patch test: A validated cutaneous provocation test — a small ethanol-soaked patch is applied to the skin, and the resulting local flush is scored (including quantitative hue-saturation-value colorimetric analysis in newer studies) to predict ALDH2 genotype, particularly useful in adolescents/young people with little drinking history:

"Blinded genotyping showed inactive ALDH2 for 94.4% of subjects who reported always flushing... Genotype distribution... in subjects with positive ethanol patch test results was 5.9% for normal homozygote (NN), 82.4% for mutant heterozygote (NM), and 11.8% for mutant homozygote (MM)." (synthesis of patch-test validation literature)

  • Genetic testing: Direct genotyping of ALDH2 rs671 (and optionally ADH1B rs1229984) via targeted SNP assay, PCR-RFLP, or as part of broader pharmacogenomic/consumer genomic panels — this is a single-variant test, not a gene panel or WES/WGS indication, since the causal variant is essentially the single well-characterized common polymorphism; the condition is listed in the NIH Genetic Testing Registry (C2674838) (GTR).
  • Laboratory/biomarker confirmation: Direct or breath-based measurement of blood acetaldehyde concentration following a standardized alcohol challenge is the most direct biochemical confirmation, though it is primarily a research tool rather than routine clinical practice.
  • Differential diagnosis: True IgE-mediated alcohol/ingredient allergy (e.g., to sulfites, histamines in wine/beer, or grape/grain proteins); carcinoid syndrome flushing; mast cell activation syndrome; rosacea exacerbation; pharmacologic disulfiram-like reactions from concurrent medications (metronidazole, certain cephalosporins, chlorpropamide); niacin flush. Genetic testing and the characteristic alcohol-dose-dependent, immediate-onset, tachycardia-associated presentation distinguish ALDH2-deficiency flush from these mimics.
  • Screening applications: Endoscopic screening (esophageal iodine/Lugol staining) combined with ADH1B/ALDH2 genotyping has been used as a targeted esophageal-cancer surveillance strategy in high-risk (heavy-drinking, ALDH2-deficient) Japanese cohorts (PMC6328133).

11. Outcome / Prognosis

The acute reaction itself is not life-threatening in typical social-drinking doses and resolves spontaneously; however, ALDH2 deficiency carries substantial long-term morbidity risk conditional on continued alcohol exposure:

  • Esophageal squamous cell carcinoma (ESCC): Strongest and best-replicated cancer association. A 2023 meta-analysis (23 studies) found rs671 was associated with altered ESCC risk (reported OR 0.60, 95% CI 0.50–0.73 for the variant in the additive/allelic model reported in that analysis), and multiple cohort studies confirm that low-activity ALDH2 combined with continued alcohol consumption substantially elevates ESCC risk relative to non-carriers or abstaining carriers (Zhang et al. 2023, Cancer Medicine, PMID:37795758; population cohort study, PMID:29707772).
  • Other cancers: Associations reported with gastric cancer (PMC5731965), and studied (with more heterogeneous findings) in breast and ovarian cancer in East Asian women.
  • Cardiovascular disease: Associations with hypertension, coronary vasospasm/myocardial infarction risk, atrial substrate remodeling and atrial fibrillation with modest alcohol consumption, and broader cardiometabolic risk factors in East Asian cohorts (PMC10986734 updated meta-analysis; PMC8615757 AF study; PMC4693762 hypertension case-control).
  • Neurodegenerative disease: Emerging evidence that rs671 enhances amyloid-β pathology and may modulate Alzheimer's disease risk/cortical thickness patterns, though it is "not an independent risk factor for Alzheimer's disease" on its own (PMID:38519490).
  • All-cause mortality: A Japanese population study found ADH1B and ALDH2 functional variants non-additively associated with all-cause mortality, implying complex interaction effects rather than simple linear dose-risk (PMC7028931).
  • Protective/net-population effect: Because the reaction discourages heavy drinking in many carriers, ALDH2 deficiency is associated with substantially reduced rates of alcohol use disorder and alcoholic liver disease/cirrhosis at the population level — creating a genuine risk/benefit duality that a 2025 review frames explicitly:

"Beyond the Flush: Reframing ALDH2 Deficiency as a Public Health Risk" (Karger Public Health Genomics, 2025) — arguing the trait should be understood as a modifiable cancer/cardiovascular risk factor specifically in the (growing, per a 2025 AACR commentary) subset of carriers who drink despite the reaction, including in U.S./diaspora populations unfamiliar with the risk (AACR CEBP 2025, "ALDH2 Deficiency and Alcohol Intake in the United States: Opportunity for Precision Cancer Prevention").

  • Notable emerging/exploratory association: A recent hypothesis-generating paper proposes the East Asian-specific rs671 polymorphism may partly explain the comparatively low incidence of Sudden Infant Death Syndrome (SIDS) in Asian infant populations, via an aldehyde-metabolism-related mechanism — this is a preliminary/associative hypothesis requiring further validation, not an established causal claim (ScienceDirect 2025).

12. Treatment

There is no approved disease-modifying or curative treatment; management is centered on avoidance, symptomatic care, and risk counseling.

  • Primary management — behavioral/avoidance: Counseling to reduce or abstain from alcohol consumption is the mainstay, given the direct, dose-dependent link between continued drinking and cancer/cardiovascular risk in ALDH2-deficient individuals.
  • Symptomatic pharmacotherapy: H2-receptor antagonists (e.g., famotidine) and H1-antihistamines have been used off-label/empirically by some individuals to blunt flushing (via effects on gastric ADH activity and vasodilation, respectively), though this is not recommended as a routine clinical strategy, since suppressing the aversive warning symptom while continuing to drink increases silent acetaldehyde exposure and associated cancer/cardiovascular risk — a point emphasized in the public-health-reframing literature above.
  • Investigational/experimental — ALDH2 pharmacological activators: A major active research area involves small-molecule ALDH2 activators, most notably Alda-1 and newer analogs (e.g., AD-9308), which partially restore catalytic activity of the ALDH2*2 mutant enzyme:

"Alda-1 increases activity of wild-type ALDH21 and variant ALDH22 (by ~2-fold and 11-fold respectively), and is capable of partly restoring mutant ALDH2*2 activity, providing protection against cardiac ischemia." (search synthesis of pharmacology literature)

These compounds are being explored preclinically/clinically for indications including ischemic stroke/cardioprotection, alcohol use disorder (reducing acquisition/relapse of drinking in animal models), diabetic cardiomyopathy, and protection of hematopoietic stem cells in Fanconi anemia models exposed to aldehyde stress — not yet as an approved therapy for the flush reaction itself. A related ANS-6637 clinical protocol for alcohol use disorder targeting ALDH2 pharmacology has been registered (NCT03970109) (ClinicalTrials.gov protocol PDF). - Pharmacogenomic caution: Because the same enzyme system is pharmacologically inhibited by disulfiram, metronidazole, and certain cephalosporins/sulfonylureas, ALDH2-deficient individuals should be counseled that these drugs will produce an amplified, potentially more severe flush/tachycardia/hypotension reaction if alcohol is consumed concurrently. - Genetic counseling: Recommended in the context of pre-conception/family counseling primarily to inform risk communication about alcohol-related cancer risk rather than reproductive risk, since this is a common polymorphism rather than a rare severe Mendelian disorder.

Suggested NCIT terms: NCIT:C15240 (Genetic Counseling); NCIT:C15986 (Pharmacotherapy) with therapeutic_agent bound to a CHEBI/NCIT term for disulfiram or an investigational ALDH2-activator compound class; NCIT:C49236 (Therapeutic Procedure) for behavioral alcohol-avoidance counseling.

13. Prevention

  • Primary prevention: Genetic/behavioral risk education — informing ALDH2-deficient individuals (identifiable via self-reported flushing history, patch test, or genotyping) that continued heavy alcohol consumption carries substantially elevated esophageal cancer and cardiovascular risk, and counseling toward abstinence or minimal intake. This is explicitly framed as an actionable precision-prevention opportunity in East Asian and diaspora populations unaware of their genetic status (AACR CEBP 2025).
  • Secondary prevention/screening: Endoscopic surveillance with iodine (Lugol) chromoendoscopy in known ALDH2-deficient heavy drinkers, used clinically in Japan to detect early esophageal squamous neoplasia/dysplasia (PMC6328133).
  • Population/public-health screening: Health education campaigns in Japan using the ethanol patch test in youth, specifically to identify ALDH2-deficient individuals before they establish drinking habits.
  • Genetic screening: Not typically part of newborn or prenatal screening programs (this is a common, non-severe polymorphism rather than a serious early-onset Mendelian disorder), but is increasingly offered through consumer/direct-to-consumer genomics and can be incorporated into personalized alcohol-risk counseling.
  • Public health/policy: Advocacy for greater clinician and public awareness of ALDH2 deficiency as a modifiable cancer risk factor, given its high prevalence and low current recognition outside East Asia (the 2025 AACR commentary specifically calls out the U.S. as an "opportunity for precision cancer prevention" given growing East Asian-American populations).
  • Prophylaxis: No pharmacologic prophylaxis is currently recommended; suppressing symptoms with antihistamines/H2-blockers while continuing to drink is discouraged as a "false safety" strategy given the risk of masking, not eliminating, the underlying acetaldehyde exposure.

14. Other Species / Natural Disease

  • Taxonomic scope: ALDH2 and the ethanol/acetaldehyde oxidation pathway are broadly conserved across mammals; however, the specific rs671/Glu504Lys inactivating polymorphism causing "acute alcohol sensitivity" is, per current evidence, specific to Homo sapiens (NCBITaxon:9606) and, within humans, largely restricted to East Asian ancestry populations.
  • Naturally occurring analogous phenotype in other species: Search of the primate literature did not identify a well-characterized naturally occurring ALDH2-inactivating polymorphism in cynomolgus or rhesus macaques analogous to human rs671; primate alcohol-metabolism polymorphism research in these species has instead focused on CYP2E1 repeat-length variation, which does not recapitulate the human ALDH2-deficiency phenotype (PMID:11505041). This represents a genuine gap/negative finding rather than an established comparative model.
  • Veterinary relevance: No established veterinary disease entity corresponding to this condition; not currently listed as a naturally occurring disorder in the veterinary/OMIA literature to the extent surfaced by this search.
  • Comparative biology: The ALDH2 enzyme and its catalytic mechanism are highly conserved across vertebrates (used as the basis for cross-species structural/biochemical studies), supporting strong evolutionary conservation of the underlying detoxification pathway even though the specific human-deficiency allele is not shared with other species.
  • Zoonotic potential: Not applicable — this is a non-infectious, purely genetic/metabolic condition.

15. Model Organisms

  • Mouse (Mus musculus) — gene-targeted models:
  • ALDH2 global/conditional knockout mice (Aldh2⁻/⁻): Show markedly higher blood acetaldehyde concentrations than wild-type after ethanol gavage or inhalational acetaldehyde exposure, with more severe toxic symptoms including weight loss; dramatically dampened energy expenditure/motility after ethanol; and near-complete voluntary alcohol avoidance in two-bottle-choice and drinking-in-the-dark paradigms — directly recapitulating the human aversive/protective-against-alcoholism phenotype (characterization paper, PMID:19874182; PMC4323349 review). Floxed conditional-knockout mice develop normally with no baseline phenotype absent alcohol/acetaldehyde challenge, confirming the trait is exposure-dependent, as in humans.
  • ALDH2 E487K "humanized" knock-in mice (modeling the human dominant-negative Glu487Lys/Glu504Lys mutation): Used to study both acute acetaldehyde sensitivity and chronic consequences — e.g., the mutation "increases protein turnover and promotes murine hepatocarcinogenesis" (PNAS, PMID unlisted directly but described in search results), and human ALDH2*2 knock-in mice have been used to demonstrate that the ALDH2 activator Alda-1 protects against alcohol-derived esophageal DNA damage (Carcinogenesis, Oxford Academic).
  • Applications: These models are used to study acute intoxication/toxicity thresholds, alcohol-avoidance behavior genetics, alcohol-related liver/gut-barrier injury (gut-liver axis endotoxemia models), esophageal/hepatic carcinogenesis, cardioprotection pharmacology (Alda-1/AD-9308 testing), and — via the digenic Aldh2/Adh5 double-knockout — hematopoietic stem cell genotoxic stress modeling relevant to AMeD syndrome.
  • Model limitations: Mouse ALDH2 biology recapitulates the core biochemical lesion (acetaldehyde accumulation, aversive behavior) and several downstream consequences (hepatic, esophageal, cardiac), but species differences in ethanol pharmacokinetics, esophageal anatomy/carcinogen susceptibility, and social/behavioral drinking patterns mean the models do not fully capture the human socio-behavioral dimension of "drinking through the flush," nor the human population-genetic context of the rs671 founder allele.
  • Other model systems: No major zebrafish, Drosophila, or C. elegans disease-model literature specific to this human-variant phenotype was identified in this search; cell-based/biochemical (recombinant ALDH2*2 enzyme kinetics) and structural-biology (X-ray crystallography of the tetramer) systems have been extensively used to define the dominant-negative mechanism at the protein level.

Suggested resources: MGI (Aldh2 knockout/knock-in mouse strain records); IMPC for systematic Aldh2 phenotyping data, if available.

Summary of Key Ontology Term Suggestions (verify exact CURIEs/labels via OAK/OLS before curation)

  • MONDO: MONDO:0012454 (Alcohol Sensitivity, Acute)
  • Genes (HGNC): hgnc:404 (ALDH2), hgnc:249 (ADH1B)
  • HPO: HP:0031282 (Flushing), HP:0001649 (Tachycardia), HP:0001962 (Palpitations), HP:0002018 (Nausea), HP:0002315 (Headache), HP:0001324 (Muscle weakness)
  • CHEBI: CHEBI:16236 (ethanol), CHEBI:15343 (acetaldehyde), CHEBI:15366 (acetic acid), CHEBI:27897 (disulfiram)
  • UBERON: UBERON:0001043 (esophagus), UBERON:0002107 (liver), UBERON:0000948 (heart), UBERON:0001003 (skin epidermis)
  • GO: GO:0006068 (ethanol catabolic process), GO:0004029 (aldehyde dehydrogenase [NAD+] activity), GO:0005759 (mitochondrial matrix)
  • NCIT (treatment/procedure): NCIT:C15240 (Genetic Counseling), NCIT:C15986 (Pharmacotherapy), NCIT:C49236 (Therapeutic Procedure)

Notable Gaps / Areas Not Fully Resolved in Current Literature

  • No approved pharmacotherapy that safely restores ALDH2 function in humans; Alda-1/AD-9308-class activators remain preclinical-to-early-clinical.
  • No confirmed naturally occurring non-human animal model carrying an rs671-equivalent polymorphism (only engineered knock-in/knockout mice).
  • The SIDS-protective hypothesis is preliminary and needs independent replication.
  • Quantitative, standardized reference ranges for "diagnostic" blood acetaldehyde thresholds post-challenge are not well standardized across labs/populations.
  • Long-term outcome data (cancer/cardiovascular/neurodegenerative risk) are drawn overwhelmingly from East Asian cohorts; risk quantification in diaspora/mixed-ancestry populations (e.g., US East Asian-American cohorts) is comparatively sparse, which the 2025 AACR commentary explicitly flags as a research and precision-prevention gap.

Sources

Reference Validation

Checked with linkml-reference-validator 0.2.1.

Outcome Count
References checked 22
Resolved 22
Unresolved (possible confabulation) 0
Unverifiable 0
Quoted claims checked 5
Quoted claims found in source 2
Quoted claims not found in source 3
References weighed for topical relevance 22
On topic 20
Off topic 0

Quotes not found in the cited source

Searched the abstract, any retrieved full text, and the title. A quote drawn from a part of the paper that was not retrieved will appear here too, so check before treating one as invented:

Every one of these was searched against an abstract alone, with no full text retrieved - marked abstract only below. Where full text can be fetched, re-running with it will settle them; where the source publishes only a summary to PubMed, as GeneReviews chapters do, it will not, and the quote has to be checked by hand against the chapter itself.

  • PMC:PMC9844601 (abstract only): "The ALDH2 rs671 GA/AA genotypes significantly reduced the risk of alcohol-induced mental disorders by 87%, alcohol dependence syndrome by 83%, and alcohol abuse by 66%."
  • closest text in source: "The results suggested that are reduction in alcohol consumption should be advised as a preventive measure for high-risk patients carrying ADH1B rs1229984 C or the ALDH2 rs671 A allele."
  • PMID:9419411 (abstract only): "Blinded genotyping showed inactive ALDH2 for 94.4% of subjects who reported always flushing... whereas 95.6% of subjects reporting that they never exhibited facial flushing had active ALDH2"
  • closest text in source: "Blinded genotyping showed inactive ALDH2 for 94.4% (102 of 108) of subjects who reported always flushing (early in their drinking history or currently) and for 47.7% (21 of 44) of those who reported sometimes flushing, whereas 95.6% (109 of 114) of subjects reporting that they never exhibited facial flushing had active ALDH2"
  • DOI:10.1073/pnas.1510757112 (abstract only): "increases protein turnover and promotes murine hepatocarcinogenesis"
  • closest text in source: "With this model, we show that murine ALDH2*2 increases ALDH2 protein turnover and promotes chemical-induced liver tumor development"