Adult-Type Hypolactasia

Metabolic Disorder MONDO:0006065 Pathograph 29 Show in embeddings browser Lactose Intolerance

Adult-type hypolactasia, or lactase non-persistence, is the common ancestral pattern of declining intestinal lactase activity after early childhood. Regulatory variation at the LCT-MCM6 locus contributes to whether lactase expression persists into adulthood, with different persistence-associated alleles in different populations. It is distinct from congenital LCT coding-variant deficiency and acquired mucosal injury. Reduced enzyme activity can allow ingested lactose to reach the colon, where osmotic effects and microbial fermentation may cause diarrhea, flatulence, bloating and pain. Lactase deficiency, lactose malabsorption and symptomatic lactose intolerance are related but distinct: many non-persistent individuals tolerate ordinary dietary amounts. Care is guided by symptoms, dietary tolerance and nutritional adequacy.

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1
Inheritance
10
Pathophys.
7
Phenotypes
2
Gaps
29
Pathograph
3
Genes
4
Medical Actions
4
Differentials
2
Trials
5
Models
17
References
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Inheritance

1
Autosomal recessive lactase non-persistence HP:0000007
Classical family studies describe recessive non-persistence, with dominant persistence. Enzyme activity is quantitative and symptoms additionally depend on diet and gastrointestinal physiology.
Autosomal recessive inheritance
Show evidence (1 reference)
PMID:11788828 SUPPORT DIRECT BACKGROUND Human Clinical
"Adult-type hypolactasia, also known as lactase non-persistence (lactose intolerance), is a common autosomal recessive condition"
Describes the classical inheritance of the enzyme phenotype, rather than fully penetrant symptomatic intolerance.
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Discussions and Knowledge Gaps

2
Which microbial, sensory and dietary factors determine symptoms at a given lactose load?
KNOWLEDGE GAP malabsorption_versus_intolerance
Attached to
pathophysiology#Colonic Microbial Fermentation of Lactose phenotypes#Abdominal Pain
Malabsorption and symptoms are not equivalent. Selected trials and guidelines show dose, meal context, visceral sensitivity and expectation effects. A single small milk trial cannot define a universal tolerated dose; absence of significant severity differences also does not erase its observed excess flatus count. No current source establishes one microbial mechanism for every symptomatic person.
Show evidence (2 references)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"only a proportion of carbohydrate malabsorbers develop symptoms"
The guideline distinguishes malabsorption from symptoms.
PMID:7776987 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"When the periods were compared, there were no statistically significant differences in the severity of these four gastrointestinal symptoms."
The crossover trial supports discordance between self-report and symptoms at a modest milk dose, within its small selected cohort.
Does changing regulatory DNA modification alter age-dependent LCT expression independently of genotype?
KNOWLEDGE GAP epigenetic_mediation
Attached to
pathophysiology#Genotype-Associated Regulatory DNA Modification pathophysiology#Reduced Enterocyte LCT Transcription
Adult and pediatric intestinal associations support a regulatory epigenetic model, but adult age trends are cross-sectional and pediatric enzyme-defined groups are not symptom cohorts. Deletion and RNAi experiments perturb DNA or RNA rather than methylation. Targeted epigenetic editing and appropriately sampled longitudinal studies are needed to resolve mediation.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT Other
"Future studies examining chromatin configuration35 at the LCT–MCM6 locus in aging individuals and targeted epigenetic editing with the CRISPR-Cas9 system41 will be necessary to fully understand genetic-epigenetic contributions to lactase persistence and non-persistence."
The authors explicitly identify epigenetic editing as future work.
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Pathophysiology

10
LCT-MCM6 Regulatory Haplotypes
The ancestral C-13910 haplotype is associated with lactase non-persistence in the populations studied; derived T-13910 and other regionally distributed alleles favor persistence. The relevant MCM6 intronic sequence regulates LCT rather than disrupting MCM6 protein. In one Caco-2 assay both C and T sequences enhanced a rat lactase promoter, with a stronger effect for T. Association, reporter and regulatory-deletion data support this locus, but do not imply that a single SNP explains all populations.
MCM6 hgnc:6949 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves MCM6 (hgnc:6949). hgnc:6949 is a gene from the HUGO Gene Nomenclature Committee.
Downstream
Reduced Enterocyte LCT Transcription Regulatory haplotypes influence LCT transcription; reporter assays and human association support the bridge, while the complete developmental mechanism remains unresolved.
Genotype-Associated Regulatory DNA Modification Genotype is associated with modification of regulatory DNA in intestinal tissue; causation and developmental timing are incompletely resolved.
Show evidence (2 references)
PMID:11788828 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"a DNA variant, C/T-13910, roughly 14 kb upstream from the LCT locus, completely associates with biochemically verified lactase non-persistence in Finnish families"
The original family study identifies an associated regulatory region; this is not a worldwide single-variant diagnostic rule.
PMID:12915462 SUPPORT DIRECT PRIMARY RESULT In Vitro
"The DNA region of the C/T_(13910) lactase persistence/non-persistence variant functions in vitro as a cis element capable of enhancing differential transcriptional activation of the lactase promoter."
Caco-2 reporter constructs with a rat lactase promoter support differential cis-regulation, not a completely inactive ancestral enhancer.
Genotype-Associated Regulatory DNA Modification
Adult surgical jejunal enterocytes show genotype-associated DNA modification and age associations at LCT-MCM6 regions. The assays measure modified cytosines without uniquely resolving 5mC from 5hmC. The 115 adults were sampled cross-sectionally at ages 21–72; proposed earlier-life trajectories are postdictions. A separate selected pediatric duodenal-biopsy study supports genotype-associated methylation and enzyme-activity correlations. Neither study proves a universal methylation-mediated route to symptoms. Regulatory DNA deletions establish element function, not the causal effect of changing its methylation.
Downstream
Reduced Enterocyte LCT Transcription Epigenetic repression is a proposed mediator of reduced LCT transcription, supported by intestinal associations but not targeted epigenetic editing.
Show evidence (2 references)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"In lactase non-persistent individuals (CC), DNA modifications consistently increased with age across LCT and MCM6 (Fig. 4)."
Cross-sectional adult jejunal enterocyte observations support genotype-associated epigenetic aging; no longitudinal childhood trajectory was measured.
PMID:29618745 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"These results suggest that most of the DNA methylation variation at the LCT enhancer is explained by the genotype at rs4988235 alone."
In the selected pediatric biopsy cohort, genotype accounted for most enhancer methylation variation; this does not establish methylation as an independent cause of symptoms.
Reduced Enterocyte LCT Transcription
LCT transcript abundance is lower with non-persistence-associated regulation. Cross-sectional adult CC carriers show decreasing LCT mRNA with age. Differentiated Caco-2 deletion models and mouse intronic deletions independently demonstrate the importance of regulatory elements, with species, intestinal-segment and differentiation-stage limits.
enterocyte CL:0000584 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves enterocyte (CL:0000584). CL:0000584 is a cell type from the Cell Ontology.
LCT hgnc:6530 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves LCT (hgnc:6530). hgnc:6530 is a gene from the HUGO Gene Nomenclature Committee.
LCT transcriptional regulation GO:0006357 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased LCT transcriptional regulation, annotated with regulation of transcription by RNA polymerase II (GO:0006357). GO:0006357 is a biological process from the Gene Ontology. ↓ DECREASED
Experimental models
Caco-2 human enhancer and rat promoter reporter CELL LINE Reporter transcription differs by enhancer allele.
Caco-2 East African persistence-haplotype reporter CELL LINE Reporter haplotypes alter transcriptional output.
Caco-2 regulatory-element deletion CELL LINE Differentiated cells show lower LCT mRNA after regulatory deletion.
Caco-2 LOC100507600 RNA interference CELL LINE lncRNA knockdown reduces LCT mRNA in the cell model.
Animal models
Mouse lactase regulatory-element deletions Mouse measures Regulatory deletions reduce intestinal Lct transcript abundance.
Downstream
Declining Intestinal Lactase Activity Reduced transcript production contributes to lower brush-border enzyme activity; transcript and enzyme abundance are not interchangeable assays.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"In our cohort of 21–72-year-old individuals, we detected that LCT mRNA was significantly decreasing with age in the lactase non-persistent (CC) individuals"
The age association is cross-sectional within adults, not a longitudinal measurement from weaning.
Declining Intestinal Lactase Activity
Post-weaning decline in brush-border lactase reduces the capacity to hydrolyze lactose to glucose and galactose. This can occur without intestinal mucosal injury. Residual activity and dietary load vary, and enzyme deficiency alone does not establish clinical intolerance.
enterocyte CL:0000584 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves enterocyte (CL:0000584). CL:0000584 is a cell type from the Cell Ontology.
lactase activity GO:0000016 Gene Ontology (GO) Relation: this pathophysiological event involves this molecular function This pathophysiological event involves decreased lactase activity (GO:0000016). GO:0000016 is a molecular function from the Gene Ontology. ↓ DECREASED
Downstream
Unhydrolysed Lactose Retained in the Intestinal Lumen Lactose exceeding digestive capacity remains incompletely absorbed and can reach the colon.
Show evidence (2 references)
PMID:11788828 SUPPORT DIRECT BACKGROUND Human Clinical
"resulting from the physiological decline in activity of the lactase-phlorizin hydrolase (LPH) in intestinal cells after weaning"
The paper describes the defining post-weaning enzyme decline.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Lactase deficient persons who are exposed to lactose may develop lactose malabsorption, depending on the amount of ingested lactose"
The guideline makes the enzyme-to-malabsorption relationship dose-dependent.
Unhydrolysed Lactose Retained in the Intestinal Lumen
Lactose that escapes small-intestinal hydrolysis remains in the lumen and is delivered distally. The quantity depends on ingested lactose, residual enzyme activity, meal composition and transit. This is the substrate for osmotic effects and colonic fermentation.
Downstream
Increased Intestinal Luminal Water Unabsorbed lactose increases luminal osmotic load and water retention.
Colonic Microbial Fermentation of Lactose Delivery of lactose to colonic microbes supplies fermentable substrate.
Nausea Nausea can accompany symptomatic lactose intolerance, but this general clinical association does not identify a specific sensory intermediate.
Vomiting Vomiting is a reported intolerance symptom; the precise pathway is not resolved by the clinical guideline.
Borborygmi Borborygmi can accompany the gastrointestinal response to lactose; the clinical descriptions do not isolate its mechanism.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"“Lactose malabsorption” refers to incomplete absorption of lactose in the small intestine with the consequence that ingested lactose reaches the colon."
The guideline distinguishes delivery of unabsorbed lactose to the colon from symptomatic intolerance.
Increased Intestinal Luminal Water
Luminal lactose and fermentation products can increase intestinal water content through osmotic movement and secretory processes. Stool output also depends on colonic salvage, transit and the absorbed fraction; watery diarrhea is not inevitable.
Downstream
Diarrhea An unhandled luminal water and osmotic load can produce diarrhea.
Intestinal Luminal Distension Increased fluid can contribute to intestinal distension; early symptoms need not wait for colonic fermentation.
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/ SUPPORT DIRECT REVIEW SYNTHESIS Other
"The accumulation of unabsorbed lactose increases intraluminal osmotic pressure, leading to fluid influx and osmotic diarrhea."
The clinical chapter describes osmotic water movement into the intestinal lumen.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"the production of short chain fatty acids increases passive movement (osmosis) and active secretion of water and sodium into the lumen that can result in diarrhea."
The guideline includes fermentation-product effects as well as the original carbohydrate load.
Colonic Microbial Fermentation of Lactose
Colonic microbes ferment malabsorbed lactose to organic acids and gases. Some fermentation products are absorbed and salvage energy; microbial composition and gas handling modify the response.
microbial lactose catabolism GO:0005990 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased microbial lactose catabolism, annotated with lactose catabolic process (GO:0005990). GO:0005990 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Increased Intestinal Gas Production Fermentation produces intestinal gases.
Increased Intestinal Luminal Water Fermentation products can add osmotic and secretory water effects, while absorption can also salvage the luminal load.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"The common end for all carbohydrates that are not fully absorbed in the small bowel is bacterial fermentation in the colon with production of short chain fatty acids and gases."
The guideline summarizes colonic fermentation of malabsorbed carbohydrate.
Increased Intestinal Gas Production
Microbial gas production includes hydrogen, carbon dioxide and methane. Methanogens consume hydrogen, so measured breath hydrogen is not a complete measure of fermentation or symptom severity.
Downstream
Intestinal Luminal Distension Gas retained within the bowel can distend the lumen.
Flatulence Expulsion of fermentation gases contributes to flatulence; production, retention and perception differ between people.
Show evidence (2 references)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"At the same time production of gases, such as CO2, H2, or CH4, may contribute to the sensation of abdominal bloating, pain and flatulence, related to perception of colonic distension."
Gas production and distension can contribute to symptoms; the relationship is not obligatory.
PMID:42434160 SUPPORT DIRECT REVIEW SYNTHESIS Other
"conversion of hydrogen to methane can reduce hydrogen concentrations and thereby produce false-negative hydrogen-only tests"
The national guideline explains a limitation of hydrogen-only testing.
Intestinal Luminal Distension
Accumulated gas and fluid may distend the intestinal lumen. Perceived bloating and observed abdominal distention overlap but are not identical; symptom intensity also depends on visceral sensitivity.
Downstream
Abdominal Distension Intraluminal expansion can contribute to abdominal distention or bloating.
Abdominal Pain Distension can produce pain, with variable sensory responsiveness.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Colorectal distension by gas remaining in the colon results in symptoms such as bloating or pain."
Retained gas and colorectal distension can produce bloating and pain, with individual sensitivity modifying the response.
Increased Visceral Sensitivity
Visceral sensitivity can amplify symptoms at a given carbohydrate load. This is a modifier, particularly relevant when disorders of gut-brain interaction coexist, rather than a proven downstream result of the lactase genotype.
Downstream
Abdominal Pain Heightened sensitivity can increase the painful response to intestinal distension without requiring greater malabsorption.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"The likelihood of reporting symptoms and the severity of symptoms depends on the degree of visceral sensitivity."
The guideline recognizes visceral sensitivity as a modifier of symptom expression.
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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 Adult-Type Hypolactasia 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

7
Digestive 6
Diarrhea HP:0002014 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Diarrhea (HP:0002014). HP:0002014 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea."
These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
Flatulence HP:0033589 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Flatulence (HP:0033589). HP:0033589 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea."
These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
Abdominal Distension Abdominal distention HP:0003270 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abdominal distention (HP:0003270). HP:0003270 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Established indications for carbohydrate breath tests and symptom assessment include intermittent diarrhea, abdominal pain, bloating, distension, nausea and flatulence"
The guideline separately names bloating and distension in the symptomatic assessment context.
Nausea HP:0002018 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Nausea (HP:0002018). HP:0002018 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea."
These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
Vomiting HP:0002013 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Vomiting (HP:0002013). HP:0002013 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea."
These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
Borborygmi Hyperactive bowel sounds HP:0030143 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Hyperactive bowel sounds (HP:0030143). HP:0030143 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/ SUPPORT DIRECT REVIEW SYNTHESIS Other
"Lactose intolerance is a clinical syndrome characterized by gastrointestinal symptoms, such as bloating, abdominal pain, flatulence, nausea, borborygmi, and diarrhea, following the ingestion of lactose-containing food."
Borborygmi is listed in the clinical symptom description.
Constitutional 1
Abdominal Pain HP:0002027 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Abdominal pain (HP:0002027). HP:0002027 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea."
These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
🧬

Genetic Associations

3
MCM6 intronic regulatory haplotypes
Gene: MCM6 hgnc:6949 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is MCM6 (hgnc:6949). hgnc:6949 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE
Show evidence (2 references)
PMID:11788828 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"a DNA variant, C/T-13910, roughly 14 kb upstream from the LCT locus, completely associates with biochemically verified lactase non-persistence in Finnish families"
The original family study identifies an associated regulatory region; this is not a worldwide single-variant diagnostic rule.
PMID:11788828 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"A second variant, G/A-22018, 8 kb telomeric to C/T-13910, is also associated with the trait in 229 of 236 cases."
Records the linked marker association without asserting independent enhancer causality.
Regionally distributed lactase-persistence variants
Gene: MCM6 hgnc:6949 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is MCM6 (hgnc:6949). hgnc:6949 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: PROTECTIVE
Show evidence (3 references)
PMID:17159977 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"These SNPs originated on different haplotype backgrounds from the European C/T-13910 SNP and from each other."
The study supports multiple regulatory backgrounds for persistence.
PMID:17159977 SUPPORT DIRECT PRIMARY RESULT In Vitro
"have derived alleles that significantly enhance transcription from the LCT promoter in vitro"
Reporter haplotypes support transcriptional enhancement, with construct and linkage limits.
PMID:17159977 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Although C/G-13907 and T/G-13915 are associated with the phenotype, this association was not statistically significant after Bonferroni correction in either the individual populations or in the meta-analysis"
The full results qualify the abstract association claim for these two candidate variants.
LCT, the regulated lactase gene
Gene: LCT hgnc:6530 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is LCT (hgnc:6530). hgnc:6530 is a gene from the HUGO Gene Nomenclature Committee.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT Model Organism
"In adult and infant mice, deletion in Lct intron 1 as well as in Lct intron 2 caused widespread downregulation of Lct throughout the duodenum and jejunum"
Mouse regulatory deletions demonstrate contributions from intragenic elements, distinct from human congenital coding deficiency.
💊

Medical Actions

4
Individualized lactose reduction
Action: Dietary InterventionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Dietary Intervention (NCIT:C15447). NCIT:C15447 is a clinical intervention from the NCI Thesaurus. NCIT:C15447
Platform: Behavioral / lifestyle
For documented symptomatic intolerance, reduce lactose to an individually tolerated amount, use lactose-free equivalents and consider smaller portions with meals. Complete dairy avoidance is usually unnecessary. Do not prescribe restriction solely for a non-persistence genotype or asymptomatic malabsorption.
Mechanism Target:
INHIBITS Unhydrolysed Lactose Retained in the Intestinal Lumen — Reduces delivery of undigested lactose without restoring endogenous enzyme expression.
Show evidence (1 reference)
PMID:33887513 SUPPORT DIRECT REVIEW SYNTHESIS Other
"An appropriate intervention concerns the dietetic style, such as the consumption of lactose-free foods, but with nutritional characteristics comparable to dairy products."
The review recommends nutritionally comparable low-lactose alternatives.
Show evidence (2 references)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"should be limited to cases in which the relationship between ingestion of the carbohydrate and development of symptoms has been documented."
The guideline reserves elimination or enzyme use for a documented relationship between intake and symptoms.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"The severity of symptoms depends on whether the carbohydrate is administered in a single or split dose or together with other nutrients."
Meal context and split intake affect tolerance.
Exogenous lactase supplementation
Action: PharmacotherapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Pharmacotherapy (NCIT:C15986). NCIT:C15986 is a clinical intervention from the NCI Thesaurus. NCIT:C15986
Platform: Protein replacement
Oral lactase tablets or drops can improve luminal lactose digestion without changing endogenous LCT expression. Timing and formulation matter, and gas and symptom responses vary. In an uncontrolled paired study of 96 symptomatic C/C-13910 malabsorbers, enzyme given one hour before a 25-g aqueous challenge made 21 breath tests negative, reduced 17 and left 58 similar; this is not a placebo-controlled efficacy estimate or a universal failure rate.
Mechanism Target:
BYPASSES Declining Intestinal Lactase Activity — Supplies luminal hydrolytic activity to compensate for low endogenous enzyme.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/ SUPPORT DIRECT REVIEW SYNTHESIS Other
"Lactase enzyme supplements extracted from yeasts and molds are available as tablets or drops."
The chapter describes exogenous digestive enzyme preparations.
Show evidence (3 references)
PMID:24967391 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"The response to oral administration of Beta-Galactosidase in patients with symptoms of lactose malabsorption presents a significant variability."
The paired study reports heterogeneous breath and symptom responses; symptom benefit was not shown to track hydrogen reduction.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/ SUPPORT DIRECT REVIEW SYNTHESIS Other
"In most cases, these supplements should be taken just before eating a high-lactose product or with the first bite."
General clinical administration advice differs from the one-hour prechallenge research protocol.
PMID:36149331 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"The likelihood of experiencing higher-severity abdominal pain (based on the participant-wise maximum severity that was experienced during each challenge) with lactase treatment was 0.32 times that with Bi-07 (P = 0.033) and placebo (P = 0.036)"
Lactase improved selected symptoms in the randomized milk challenge; the result is not generalized to every formulation or substrate.
Dietetic and nutritional support
Action: Dietary InterventionNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is Dietary Intervention (NCIT:C15447). NCIT:C15447 is a clinical intervention from the NCI Thesaurus. NCIT:C15447
Platform: Behavioral / lifestyle
Provide individualized dietary counseling and maintain adequate calcium, vitamin D, protein and energy intake when dairy is reduced. Assess nutritional adequacy and supplement where appropriate. Restriction-related deficiency is a care concern, not an inevitable intrinsic phenotype of lactase non-persistence.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/ SUPPORT DIRECT REVIEW SYNTHESIS Other
"Dietitians play a central role in formulating personalized, well-balanced low-lactose or lactose-free diets while ensuring adequate intake of calcium, vitamin D, and other key nutrients."
The chapter recommends dietetic support to prevent nutritional consequences of restriction.
Investigational strain-specific probiotic supplementation
Platform: Other
Bi-07 was tested as a high-dose, acute co-ingested preparation in two small randomized crossover trials. Breath-hydrogen exposure decreased relative to placebo, but a consistent symptom benefit was not demonstrated; nausea increased in the aqueous-lactose trial. These findings do not establish routine probiotic therapy, long-term benefit, a class effect or equivalence to lactase across food matrices.
Mechanism Target:
INHIBITS Unhydrolysed Lactose Retained in the Intestinal Lumen — The preparation hydrolyzes lactose in milk in vitro; the clinical breath-gas outcome is consistent with improved digestion but does not directly measure the anatomical site of hydrolysis.
Show evidence (1 reference)
PMID:36149331 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Bi-07 effected a decrease in the amount of lactose comparable with those of the commercial lactase and laboratory-grade β-galactosidase"
Direct in-vitro milk measurements support lactose hydrolysis by this specific preparation.
Show evidence (2 references)
PMID:36149331 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"In Booster Alpha, there were no significant differences in any GI symptom between Bi-07 and placebo."
A reduction in the primary gas outcome did not establish symptom benefit in the milk trial.
PMID:36149331 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"In Booster Omega, except for symptoms of nausea, there were no differences between the 3 treatments."
The aqueous-lactose trial showed no broad symptom advantage and more nausea with Bi-07.
🌍

Environmental Factors

1
Dietary lactose ingestion
dietary lactose ingestion ECTO:9000240 Environmental Conditions, Treatments and Exposures Ontology (ECTO) Relation: this environmental factor is this exposure This environmental factor is dietary lactose ingestion, annotated with exposure to disaccharide (ECTO:9000240). ECTO:9000240 is an exposure from the Environmental Conditions, Treatments and Exposures Ontology.
Lactose supplies the substrate for malabsorption and intolerance after lactase declines. Symptom likelihood varies with dose, distribution across meals and individual physiology; ingestion does not itself establish primary enzyme deficiency.
Show evidence (1 reference)
PMID:7776987 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"When the periods were compared, there were no statistically significant differences in the severity of these four gastrointestinal symptoms."
In 30 self-described severely intolerant adults, including 21 malabsorbers, a one-week 240-mL milk crossover produced minimal symptom severity. A small excess flatus count remained among malabsorbers; this is not a universal tolerance threshold.
Mechanism Target:
TRIGGERS Unhydrolysed Lactose Retained in the Intestinal Lumen — The ingested load supplies lactose that may exceed hydrolytic capacity.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"The likelihood of reporting symptoms and the severity of symptoms in individuals with lactose malabsorption depends on the dose of lactose."
Dose modifies the clinical response.
🔬

Biochemical Markers

2
Breath hydrogen after lactose challenge (INCREASED)
Context: An increase reflects microbial fermentation of unabsorbed substrate, with false-positive and false-negative causes. It is not a direct lactase measurement or a symptom-severity score. The study reporting an AUC of 1.00 enrolled 40 healthy women aged 18–30, enriched for self-reported milk symptoms (30/40), with 14 genotype-defined non-persistent participants and 26 persistent participants. Cutoffs were optimized in the same cohort without external validation; the standard 20-ppm cutoff after 50 g lactose had 100% sensitivity and 96.2% specificity. Both 750-mL milk arms contained 37.5 g lactose and involved these same participants. No superiority of one milk for clinical symptoms or universal test accuracy follows.
Pathograph Readouts
Readout Of Increased Intestinal Gas Production Positive Diagnostic
Exhaled hydrogen is an indirect gas-production readout, affected by hydrogen-consuming organisms and transit.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"increased H2 production is readily detectable as an increase in H2 excretion in the breath."
Breath hydrogen reflects intestinal microbial production.
Show evidence (1 reference)
PMID:32600320 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Genetic testing identified 14 out of 40 subjects as having LNP (C/C13910 and G/G22018)."
The diagnostic marker study uses a small genotype-defined reference group.
Intestinal regulatory-region DNA modification (INCREASED)
Context: Research finding in defined intestinal tissues and genotypes, not a validated blood test or routine clinical diagnostic. The pediatric methylation classifier underwent internal leave-one-out validation, not independent external validation. Associations with lactase activity do not prove methylation causally mediates symptoms.
Show evidence (2 references)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"In lactase non-persistent individuals (CC), DNA modifications consistently increased with age across LCT and MCM6 (Fig. 4)."
Cross-sectional adult jejunal enterocyte observations support genotype-associated epigenetic aging; no longitudinal childhood trajectory was measured.
PMID:29618745 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"These results suggest that most of the DNA methylation variation at the LCT enhancer is explained by the genotype at rs4988235 alone."
In the selected pediatric biopsy cohort, genotype accounted for most enhancer methylation variation; this does not establish methylation as an independent cause of symptoms.
🔬

Diagnosis

5
Clinical assessment and lactose withdrawal-rechallenge
Establish a reproducible relationship between lactose intake and symptoms. Improvement on a supervised reduction and recurrence with reintroduction supports intolerance; asymptomatic non-persistence needs no symptom-directed treatment. Evaluate alarm signs and alternative diagnoses before attributing symptoms to lactose.
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/ SUPPORT DIRECT REVIEW SYNTHESIS Other
"Symptom resolution following lactose elimination and recurrence upon reintroduction supports the diagnosis of lactose intolerance."
The chapter describes clinical confirmation through withdrawal and reintroduction.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Patients with alarm symptoms and/or signs should be investigated by biochemical, endoscopic and imaging investigations prior to performance of breath tests."
The guideline prioritizes investigation of alarm findings.
Hydrogen breath test with concurrent symptom assessment
The 2022 European guideline recommends 25–50 g lactose for adult malabsorption testing and 25 g when assessing intolerance, with an H2 rise of at least 20 ppm above baseline. Record symptoms concurrently and report malabsorption and intolerance separately. Preparation, low hydrogen excretion, methane production, SIBO, rapid transit and slow substrate arrival can alter results. The 2026 Israeli consensus recommends simultaneous H2/CH4 measurements; the European guideline is more cautious about the added clinical utility of methane. Neither gas response establishes congenital versus primary versus secondary deficiency.
lactose hydrogen breath test NCIT:C116515 NCI Thesaurus (NCIT)
Show evidence (4 references)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"The dose of test substance in adults for diagnosis of lactose intolerance should be 25 g lactose."
The adult intolerance protocol uses a physiologically more relevant load than older 50-g challenges.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"A H2 cut‐off ≥20 parts per million increase above baseline at a single time point during the test shall indicate maldigestion or malabsorption."
The guideline threshold concerns malabsorption.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"The recording of symptoms manifesting after carbohydrate ingestion is an integral part of a carbohydrate challenge test."
Symptom recording is needed to assess intolerance.
+ 1 more reference
Lactase-persistence genotyping
Genotyping provides evidence of inherited persistence/non-persistence predisposition in the relevant population. A C/T-13910-only test misses other persistence-associated alleles and does not diagnose current symptom intolerance or secondary mucosal deficiency. Quantitative enzyme activity can vary among heterozygotes and occasional genotype-phenotype discordance occurs.
Genetic Testing NCIT:C15709 NCI Thesaurus (NCIT)
Show evidence (2 references)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Lactase deficiency can be diagnosed directly by measurement of enzyme activity in mucosal biopsies, and indirectly either by genetic testing or by measurement of serum glucose concentration after ingestion of lactose."
These methods assess different components of digestion and do not substitute for clinical symptom assessment.
PMID:29618745 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"We are not aware of any clinical feature that might be responsible for the lactase non-persistence phenotype of the three TT individuals"
The selected pediatric cohort included genotype-phenotype discordance, limiting universal single-SNP prediction.
Lactose tolerance test
Serial blood glucose after lactose indirectly assesses hydrolysis and absorption. The 40-person comparison study found weaker genotype discrimination than breath H2 after lactose and poor performance after milk. This small study does not establish universal comparative accuracy, and blood glucose is affected by factors other than lactase.
post-lactose blood glucose response
Show evidence (1 reference)
PMID:32600320 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Plasma glucose and urinary galactose/creatinine were unreliable (AUC < 0.70) after milk ingestion."
The milk-challenge result is limited to this study and genotype reference standard.
Duodenal biopsy enzyme assay when otherwise indicated
Mucosal enzyme assays directly assess lactase activity. Endoscopy is invasive and is generally reserved for investigation of secondary causes or other indications; a low activity result alone does not establish symptomatic intolerance.
Biopsy Procedure NCIT:C15189 NCI Thesaurus (NCIT)
Show evidence (2 references)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/ SUPPORT DIRECT REVIEW SYNTHESIS Other
"Small bowel biopsy: This test is invasive and rarely used; reserved for excluding secondary causes such as celiac disease."
The chapter limits routine use of biopsy.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Lactase deficiency can be diagnosed directly by measurement of enzyme activity in mucosal biopsies"
The guideline identifies the direct enzyme measurement.
📈

Progression

2
Age-dependent enzyme decline
Primary non-persistence develops after early childhood with population and individual variation. It is not a lifelong enzyme absence from birth. Adult cross-sectional associations suggest that regulatory changes may continue after childhood, without establishing an individual longitudinal rate.
Show evidence (2 references)
PMID:11788828 SUPPORT DIRECT BACKGROUND Human Clinical
"resulting from the physiological decline in activity of the lactase-phlorizin hydrolase (LPH) in intestinal cells after weaning"
The paper describes the defining post-weaning enzyme decline.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"usually presents after 3 years of life in more than half of the world population, depending on the geographical origin and ethnicity."
The guideline places primary malabsorption after early childhood; adult-type does not mean exclusively adult onset.
Exposure-dependent symptoms
Intolerance episodes depend on dose, meal composition, transit and sensitivity. Pain or bloating may precede diarrhea; symptoms need not all begin or end within one fixed time window. Persistent or alarm symptoms require evaluation for other or coexisting disease.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"In patients with intolerance, symptoms such as pain, bloating, and flatulence may precede onset of diarrhea by several hours after carbohydrate ingestion."
The guideline describes different symptom time courses.
📊

Prevalence

1
Worldwide, with substantial population variation
Common
Lactase non-persistence is common, but available genotype and enzyme-phenotype surveys are heterogeneous and do not estimate the prevalence of symptomatic intolerance. Geographic interpolation and reciprocal persistence frequencies are not converted into a global rate.
Show evidence (2 references)
PMID:12915462 SUPPORT DIRECT BACKGROUND Human Clinical
"The majority of the world's human population experiences a decline in production of the digestive enzyme lactase-phlorizin hydrolase during maturation."
This background statement supports common non-persistence, without giving a symptom-prevalence estimate.
PMID:20144208 SUPPORT DIRECT PRIMARY RESULT Computational
"We accept that surface interpolation can give misleading results when data are sparse and so urge caution in interpreting our results for such regions."
The global mapping study cautions against interpreting sparse geographic estimates as representative population rates.
🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Adult-Type Hypolactasia:

Irritable bowel syndrome MONDO:0005052
Overlapping Features IBS and lactose intolerance may coexist. A positive lactose breath test does not establish that a prior IBS diagnosis was wrong, and lactose-related symptoms can be amplified by visceral sensitivity.
Distinguishing Features
  • Assess reproducible lactose-related symptoms as well as the independent clinical criteria for IBS.
  • Persistent symptoms despite appropriate lactose management require evaluation for coexisting disease.
Show evidence (2 references)
PMID:32623873 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"At the HBT, 79.9% (N.=207) of patients with IBS were positive, while in the control group were positive 25.0% (N.=27) of subjects (P<0.001)."
This selected monocentric cohort documents breath-test overlap, not the fraction of all IBS diagnoses that are erroneous.
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"The likelihood of reporting symptoms and the severity of symptoms depends on the degree of visceral sensitivity."
The guideline recognizes visceral sensitivity as a modifier of symptom expression.
Secondary lactase deficiency
Overlapping Features Acquired small-intestinal mucosal injury can lower lactase at any age. Celiac disease, infection including giardiasis and rotavirus, Crohn disease and malnutrition are possible causes; activity may improve when the underlying process resolves.
Distinguishing Features
  • Look for underlying intestinal disease, alarm signs, acquired timing or other evidence of malabsorption.
  • Lactase-persistence genotype does not rule out secondary deficiency.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"Secondary lactase deficiency, due to damage to the small intestinal mucosa, may occur at any age and may be caused by infectious enteritis (i.e., Rotavirus, particularly in infancy), enteropathy (i.e., celiac disease, Giardiasis, and Crohn's disease), or severe malnutrition and may, thus, be..."
The guideline distinguishes secondary mucosal deficiency from primary non-persistence.
Congenital lactase deficiency
Overlapping Features Rare congenital lactase deficiency causes severe neonatal milk-related diarrhea rather than the age-dependent primary decline addressed here.
Distinguishing Features
  • Onset in the first days of life with severe watery diarrhea and nutritional consequences.
  • Congenital LCT deficiency requires a different diagnostic and dietary approach.
Show evidence (1 reference)
PMID:34431620 SUPPORT DIRECT REVIEW SYNTHESIS Other
"manifests with severe symptoms (intractable watery osmotic diarrhea associated with metabolic acidosis, dehydration and weight loss) in the first days of life"
The guideline describes the neonatal congenital presentation.
Milk protein allergy
Overlapping Features Immune-mediated reactions to milk proteins differ from lactose maldigestion. Lactose-free dairy still contains milk protein and does not by itself address milk allergy.
Distinguishing Features
  • Assess an allergic phenotype and refer for allergy evaluation when indicated.
  • A response to avoiding whole dairy does not identify which component caused symptoms.
Show evidence (1 reference)
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/ SUPPORT DIRECT REVIEW SYNTHESIS Other
"Referral to an allergist is important if a milk allergy&#x02014;an immune-mediated reaction to milk proteins&#x02014;is suspected, as this condition is often confused with lactose intolerance."
The clinical chapter separates milk-protein allergy from lactose intolerance.
🔬

Clinical Trials

2
clinicaltrials:NCT03659747 NOT_APPLICABLE COMPLETED
Booster Alpha randomized 34 adults aged 25–60 with a positive screening lactose breath test in a blinded three-period crossover. Each 25-g lactose challenge used fat-free milk and Bi-07, 4662 FCC units lactase or placebo. The primary six-hour breath-H2 iAUC was lower with Bi-07 than placebo, but higher than with lactase; noninferiority to lactase was not established. No Bi-07 symptom advantage over placebo was demonstrated. The primary per-protocol population was 33 after one smoking exclusion.
Show evidence (2 references)
PMID:36149331 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"The noninferiority of Bi-07 compared with lactase was not shown"
The milk trial failed its lactase noninferiority hypothesis.
PMID:36149331 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"In Booster Alpha, there were no significant differences in any GI symptom between Bi-07 and placebo."
The symptom endpoint does not establish clinical superiority despite improved breath hydrogen.
clinicaltrials:NCT03814668 NOT_APPLICABLE COMPLETED
Booster Omega randomized 34 adults in the analogous three-period crossover protocol using 25 g aqueous lactose. Bi-07 lowered breath-H2 iAUC relative to placebo and met the prespecified noninferiority margin against lactase for that gas endpoint. Lactase did not significantly outperform placebo on the primary iAUC measure. No broad symptom advantage was shown; Bi-07 increased nausea. All 34 were in the per-protocol population, but two Bi-07 visits with vomiting were excluded from that outcome analysis (32 Bi-07 versus 34 comparator observations).
Show evidence (2 references)
PMID:36149331 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"Bi-07 was superior to placebo and noninferior to lactase, based on BHC iAUC values."
Noninferiority applies specifically to this gas endpoint and aqueous challenge.
PMID:36149331 SUPPORT DIRECT PRIMARY RESULT Human Clinical
"With regard to nausea, participants experienced symptoms with greater frequency and severity during Bi-07 treatment than for placebo and lactase."
The clinical adverse symptom qualifies the favorable gas result.
🧫

Experimental Models

4
Caco-2 human enhancer and rat promoter reporter CELL_LINE
A 200-bp human C-13910 region increased the 3-kb rat promoter reporter 2.2-fold and the T-containing region 2.8-fold. Both enhanced basal activity. EMSA showed different nuclear binding without identifying a unique causal factor. Only the published abstract was recovered.
Cell source
Human Caco-2 cells transfected with human variant regions upstream of a rat lactase promoter
Publication
PMID:12915462
Pathograph links
Reduced Enterocyte LCT Transcription measures fidelity: moderate Reporter transcription differs by enhancer allele.
Limitations: Artificial constructs with a rat promoter do not directly measure childhood human LCT decline.
Show evidence (1 reference)
PMID:12915462 SUPPORT DIRECT PRIMARY RESULT In Vitro
"The DNA region of the C/T_(13910) lactase persistence/non-persistence variant functions in vitro as a cis element capable of enhancing differential transcriptional activation of the lactase promoter."
Caco-2 reporter constructs with a rat lactase promoter support differential cis-regulation, not a completely inactive ancestral enhancer.
Show evidence (1 reference)
PMID:12915462 SUPPORT DIRECT PRIMARY RESULT In Vitro
"The DNA region of the C/T_(13910) lactase persistence/non-persistence variant functions in vitro as a cis element capable of enhancing differential transcriptional activation of the lactase promoter."
Caco-2 reporter constructs with a rat lactase promoter support differential cis-regulation, not a completely inactive ancestral enhancer.
Caco-2 East African persistence-haplotype reporter CELL_LINE
Derived haplotype reporters increased transcription relative to ancestral constructs. The G-13907 haplotype also carried T-13495, so that comparison does not isolate one variant. These experiments complement population association rather than validating every single-allele clinical prediction.
Cell source
Human Caco-2 cells with MCM6 intronic haplotype constructs and a human LCT promoter
Publication
PMID:17159977
Pathograph links
Reduced Enterocyte LCT Transcription measures fidelity: moderate Reporter haplotypes alter transcriptional output.
Limitations: In-vitro reporter effects do not resolve all linked variants or population-level predictive accuracy.
Show evidence (1 reference)
PMID:17159977 SUPPORT DIRECT PRIMARY RESULT In Vitro
"have derived alleles that significantly enhance transcription from the LCT promoter in vitro"
The experimental readout is promoter-reporter activity.
Caco-2 regulatory-element deletion CELL_LINE
MCM6 intron-13 or LCT intron-2 deletion reduced LCT mRNA after differentiation at day 15, but not before confluence at day 6. A nonregulatory LCT intron-1 deletion served as a negative control. Removing DNA establishes regulatory-element importance, not a causal methylation effect.
Cell source
Engineered Caco-2 cells with CRISPR-Cas9n deletions
Publication
PMID:27159559
Pathograph links
Reduced Enterocyte LCT Transcription measures fidelity: moderate Differentiated cells show lower LCT mRNA after regulatory deletion.
Limitations: Cell differentiation and regulatory-sequence loss are distinct from natural aging and targeted epigenetic modification.
Readouts
LCT mRNA in differentiated cells
Direction: DECREASED
Interpretation: Differentiated cells show lower LCT mRNA after regulatory deletion.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT In Vitro
"However, in the differentiated, epithelial-like cell state the deletion in MCM6 intron 13 or LCT intron 2 resulted in a significant decrease in LCT mRNA levels"
CRISPR regulatory-DNA deletions reduce LCT in differentiated Caco-2 cells; this is not targeted methylation manipulation.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT In Vitro
"However, in the differentiated, epithelial-like cell state the deletion in MCM6 intron 13 or LCT intron 2 resulted in a significant decrease in LCT mRNA levels"
CRISPR regulatory-DNA deletions reduce LCT in differentiated Caco-2 cells; this is not targeted methylation manipulation.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT In Vitro
"However, in the differentiated, epithelial-like cell state the deletion in MCM6 intron 13 or LCT intron 2 resulted in a significant decrease in LCT mRNA levels"
CRISPR regulatory-DNA deletions reduce LCT in differentiated Caco-2 cells; this is not targeted methylation manipulation.
Caco-2 LOC100507600 RNA interference CELL_LINE
Partial lncRNA knockdown coincided with reduced LCT mRNA while MCM6 mRNA was unchanged. The proposed CTCF and chromatin-loop mechanism was not directly established.
Cell source
T/T-13910 Caco-2 cells with antisense-transcript siRNA or scrambled control
Publication
PMID:27159559
Pathograph links
Reduced Enterocyte LCT Transcription measures fidelity: moderate lncRNA knockdown reduces LCT mRNA in the cell model.
Limitations: This does not establish LOC100507600 deficiency as a measured cause of clinical non-persistence.
Readouts
LCT mRNA after lncRNA knockdown
Direction: DECREASED
Interpretation: lncRNA knockdown reduces LCT mRNA in the cell model.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Transfection with small-interfering RNAs directed to LOC100507600 reduced its expression by 20%, and resulted in concomitant 25% reduction in LCT mRNA"
RNA interference supports a role for the antisense transcript in the cell model, without establishing a human disease mediator.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Transfection with small-interfering RNAs directed to LOC100507600 reduced its expression by 20%, and resulted in concomitant 25% reduction in LCT mRNA"
RNA interference supports a role for the antisense transcript in the cell model, without establishing a human disease mediator.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT In Vitro
"Transfection with small-interfering RNAs directed to LOC100507600 reduced its expression by 20%, and resulted in concomitant 25% reduction in LCT mRNA"
RNA interference supports a role for the antisense transcript in the cell model, without establishing a human disease mediator.
🐁

Animal Models

1
Mouse lactase regulatory-element deletions
Infant day-6 and adult day-60 intestinal segments were examined after intronic deletions. Lct intron-1/2 deletions reduced mRNA broadly by 3–8-fold; Mcm6 intron-13 effects were smaller and segment-specific. Lct intron-2 dependence was greater in adults. Deletions avoided exons and splice sites; these are sequence perturbations, not epigenetic editing or human persistence-allele models.
Species
Mouse
Genotype
Separate CRISPR deletions of Lct intron 1, Lct intron 2 or Mcm6 intron 13
Background
C57BL/6N
Publication
PMID:27159559
Pathograph links
Reduced Enterocyte LCT Transcription measures fidelity: moderate Regulatory deletions reduce intestinal Lct transcript abundance.
Limitations: Does not establish methylation causality, human symptom thresholds or diarrhea frequency.
Readouts
Intestinal Lct mRNA
Direction: DECREASED
Interpretation: Regulatory deletions reduce intestinal Lct transcript abundance.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT Model Organism
"In adult and infant mice, deletion in Lct intron 1 as well as in Lct intron 2 caused widespread downregulation of Lct throughout the duodenum and jejunum"
Mouse regulatory deletions reduce Lct mRNA; clinical intolerance was not the measured endpoint.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT Model Organism
"In adult and infant mice, deletion in Lct intron 1 as well as in Lct intron 2 caused widespread downregulation of Lct throughout the duodenum and jejunum"
Mouse regulatory deletions reduce Lct mRNA; clinical intolerance was not the measured endpoint.
Show evidence (1 reference)
PMID:27159559 SUPPORT DIRECT PRIMARY RESULT Model Organism
"In adult and infant mice, deletion in Lct intron 1 as well as in Lct intron 2 caused widespread downregulation of Lct throughout the duodenum and jejunum"
Mouse regulatory deletions reduce Lct mRNA; clinical intolerance was not the measured endpoint.
{ }

Source YAML

click to show 
name: Adult-Type Hypolactasia
creation_date: '2026-09-04T02:40:00Z'
category: Metabolic Disorder
disease_term:
  preferred_term: lactose intolerance adult type
  term:
    id: MONDO:0006065
    label: lactose intolerance adult type
parents:
- Lactose Intolerance
description: 'Adult-type hypolactasia, or lactase non-persistence, is the common ancestral pattern of declining intestinal lactase activity after early childhood. Regulatory variation at the LCT-MCM6 locus contributes to whether lactase expression persists into adulthood, with different persistence-associated alleles in different populations. It is distinct from congenital LCT coding-variant deficiency and acquired mucosal injury. Reduced enzyme activity can allow ingested lactose to reach the colon, where osmotic effects and microbial fermentation may cause diarrhea, flatulence, bloating and pain. Lactase deficiency, lactose malabsorption and symptomatic lactose intolerance are related but distinct: many non-persistent individuals tolerate ordinary dietary amounts. Care is guided by symptoms, dietary tolerance and nutritional adequacy.'
synonyms:
- lactase non-persistence
- adult lactase deficiency
- hypolactasia, adult type
- disaccharide intolerance 3
- lactose intolerance, adult type
notes: This entry covers primary lactase non-persistence and its possible dietary intolerance, not congenital alactasia or secondary lactase deficiency. The MCM6 intronic annotations locate cis-regulatory DNA; they do not imply loss of MCM6 protein function. The familial recessive non-persistence versus dominant persistence shorthand does not make symptom expression a fully penetrant Mendelian trait. No worldwide percentage or disease-level symptom frequency is inferred from heterogeneous studies that conflate deficiency, malabsorption and intolerance. The retracted global meta-analysis PMID:28690131 is not used. The 2021 review's loosely labelled 57–65% intolerance range is neither relabelled as malabsorption nor converted to an invented midpoint. The broader Lactose Intolerance StatPearls chapter was reviewed despite the exact-disease lookup returning NO_CHAPTER; its imprecise prevalence and genotype generalizations are not imported. No matching deep-research report was found.
inheritance:
- name: Autosomal recessive lactase non-persistence
  description: Classical family studies describe recessive non-persistence, with dominant persistence. Enzyme activity is quantitative and symptoms additionally depend on diet and gastrointestinal physiology.
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  evidence:
  - reference: PMID:11788828
    reference_title: Identification of a variant associated with adult-type hypolactasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: Adult-type hypolactasia, also known as lactase non-persistence (lactose intolerance), is a common autosomal recessive condition
    explanation: Describes the classical inheritance of the enzyme phenotype, rather than fully penetrant symptomatic intolerance.
pathophysiology:
- name: LCT-MCM6 Regulatory Haplotypes
  biological_scale: MOLECULAR
  description: The ancestral C-13910 haplotype is associated with lactase non-persistence in the populations studied; derived T-13910 and other regionally distributed alleles favor persistence. The relevant MCM6 intronic sequence regulates LCT rather than disrupting MCM6 protein. In one Caco-2 assay both C and T sequences enhanced a rat lactase promoter, with a stronger effect for T. Association, reporter and regulatory-deletion data support this locus, but do not imply that a single SNP explains all populations.
  evidence:
  - &id006
    reference: PMID:11788828
    reference_title: Identification of a variant associated with adult-type hypolactasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: a DNA variant, C/T-13910, roughly 14 kb upstream from the LCT locus, completely associates with biochemically verified lactase non-persistence in Finnish families
    explanation: The original family study identifies an associated regulatory region; this is not a worldwide single-variant diagnostic rule.
  - &id012
    reference: PMID:12915462
    reference_title: 'Lactase persistence DNA variant enhances lactase promoter activity in vitro: functional role as a cis regulatory element.'
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The DNA region of the C/T_(13910) lactase persistence/non-persistence variant functions in vitro as a cis element capable of enhancing differential transcriptional activation of the lactase promoter.
    explanation: Caco-2 reporter constructs with a rat lactase promoter support differential cis-regulation, not a completely inactive ancestral enhancer.
  downstream:
  - target: Reduced Enterocyte LCT Transcription
    description: Regulatory haplotypes influence LCT transcription; reporter assays and human association support the bridge, while the complete developmental mechanism remains unresolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:12915462
      reference_title: 'Lactase persistence DNA variant enhances lactase promoter activity in vitro: functional role as a cis regulatory element.'
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: The DNA region of the C/T_(13910) lactase persistence/non-persistence variant functions in vitro as a cis element capable of enhancing differential transcriptional activation of the lactase promoter.
      explanation: Caco-2 reporter constructs with a rat lactase promoter support differential cis-regulation, not a completely inactive ancestral enhancer.
  - target: Genotype-Associated Regulatory DNA Modification
    description: Genotype is associated with modification of regulatory DNA in intestinal tissue; causation and developmental timing are incompletely resolved.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:27159559
      reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: In lactase non-persistent individuals (CC), DNA modifications consistently increased with age across LCT and MCM6 (Fig. 4).
      explanation: Cross-sectional adult jejunal enterocyte observations support genotype-associated epigenetic aging; no longitudinal childhood trajectory was measured.
    - reference: PMID:29618745
      reference_title: Differences in DNA Methylation and Functional Expression in Lactase Persistent and Non-persistent Individuals.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: These results suggest that most of the DNA methylation variation at the LCT enhancer is explained by the genotype at rs4988235 alone.
      explanation: In the selected pediatric biopsy cohort, genotype accounted for most enhancer methylation variation; this does not establish methylation as an independent cause of symptoms.
  gene:
    preferred_term: MCM6
    term:
      id: hgnc:6949
      label: MCM6
- name: Genotype-Associated Regulatory DNA Modification
  biological_scale: MOLECULAR
  description: Adult surgical jejunal enterocytes show genotype-associated DNA modification and age associations at LCT-MCM6 regions. The assays measure modified cytosines without uniquely resolving 5mC from 5hmC. The 115 adults were sampled cross-sectionally at ages 21–72; proposed earlier-life trajectories are postdictions. A separate selected pediatric duodenal-biopsy study supports genotype-associated methylation and enzyme-activity correlations. Neither study proves a universal methylation-mediated route to symptoms. Regulatory DNA deletions establish element function, not the causal effect of changing its methylation.
  evidence:
  - &id008
    reference: PMID:27159559
    reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: In lactase non-persistent individuals (CC), DNA modifications consistently increased with age across LCT and MCM6 (Fig. 4).
    explanation: Cross-sectional adult jejunal enterocyte observations support genotype-associated epigenetic aging; no longitudinal childhood trajectory was measured.
  - &id009
    reference: PMID:29618745
    reference_title: Differences in DNA Methylation and Functional Expression in Lactase Persistent and Non-persistent Individuals.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: These results suggest that most of the DNA methylation variation at the LCT enhancer is explained by the genotype at rs4988235 alone.
    explanation: In the selected pediatric biopsy cohort, genotype accounted for most enhancer methylation variation; this does not establish methylation as an independent cause of symptoms.
  downstream:
  - target: Reduced Enterocyte LCT Transcription
    description: Epigenetic repression is a proposed mediator of reduced LCT transcription, supported by intestinal associations but not targeted epigenetic editing.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:27159559
      reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: PRIMARY_RESULT
      directness: INDIRECT
      snippet: Overall, our findings suggest that lactase non-persistence may be mediated by an age-related increase in DNA modifications at regulatory elements in MCM6 and LCT, while such elements are protected from epigenetic inactivation in lactase persistent individuals.
      explanation: The authors propose mediation; their human observations and DNA deletions do not directly test methylation causality.
- name: Reduced Enterocyte LCT Transcription
  biological_scale: MOLECULAR
  description: LCT transcript abundance is lower with non-persistence-associated regulation. Cross-sectional adult CC carriers show decreasing LCT mRNA with age. Differentiated Caco-2 deletion models and mouse intronic deletions independently demonstrate the importance of regulatory elements, with species, intestinal-segment and differentiation-stage limits.
  evidence:
  - reference: PMID:27159559
    reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: In our cohort of 21–72-year-old individuals, we detected that LCT mRNA was significantly decreasing with age in the lactase non-persistent (CC) individuals
    explanation: The age association is cross-sectional within adults, not a longitudinal measurement from weaning.
  downstream:
  - target: Declining Intestinal Lactase Activity
    description: Reduced transcript production contributes to lower brush-border enzyme activity; transcript and enzyme abundance are not interchangeable assays.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:11788828
      reference_title: Identification of a variant associated with adult-type hypolactasia.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      quote_role: BACKGROUND
      directness: INDIRECT
      snippet: resulting from the physiological decline in activity of the lactase-phlorizin hydrolase (LPH) in intestinal cells after weaning
      explanation: The paper describes the defining post-weaning enzyme decline.
  gene:
    preferred_term: LCT
    term:
      id: hgnc:6530
      label: LCT
  cell_types:
  - preferred_term: enterocyte
    term:
      id: CL:0000584
      label: enterocyte
  biological_processes:
  - preferred_term: LCT transcriptional regulation
    term:
      id: GO:0006357
      label: regulation of transcription by RNA polymerase II
    modifier: DECREASED
- name: Declining Intestinal Lactase Activity
  biological_scale: MOLECULAR
  description: Post-weaning decline in brush-border lactase reduces the capacity to hydrolyze lactose to glucose and galactose. This can occur without intestinal mucosal injury. Residual activity and dietary load vary, and enzyme deficiency alone does not establish clinical intolerance.
  evidence:
  - &id007
    reference: PMID:11788828
    reference_title: Identification of a variant associated with adult-type hypolactasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: resulting from the physiological decline in activity of the lactase-phlorizin hydrolase (LPH) in intestinal cells after weaning
    explanation: The paper describes the defining post-weaning enzyme decline.
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Lactase deficient persons who are exposed to lactose may develop lactose malabsorption, depending on the amount of ingested lactose
    explanation: The guideline makes the enzyme-to-malabsorption relationship dose-dependent.
  downstream:
  - target: Unhydrolysed Lactose Retained in the Intestinal Lumen
    description: Lactose exceeding digestive capacity remains incompletely absorbed and can reach the colon.
    causal_link_type: DIRECT
    evidence:
    - &id001
      reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: “Lactose malabsorption” refers to incomplete absorption of lactose in the small intestine with the consequence that ingested lactose reaches the colon.
      explanation: The guideline distinguishes delivery of unabsorbed lactose to the colon from symptomatic intolerance.
  cell_types:
  - preferred_term: enterocyte
    term:
      id: CL:0000584
      label: enterocyte
  molecular_functions:
  - preferred_term: lactase activity
    term:
      id: GO:0000016
      label: lactase activity
    modifier: DECREASED
- name: Unhydrolysed Lactose Retained in the Intestinal Lumen
  biological_scale: TISSUE
  description: Lactose that escapes small-intestinal hydrolysis remains in the lumen and is delivered distally. The quantity depends on ingested lactose, residual enzyme activity, meal composition and transit. This is the substrate for osmotic effects and colonic fermentation.
  evidence:
  - *id001
  downstream:
  - target: Increased Intestinal Luminal Water
    description: Unabsorbed lactose increases luminal osmotic load and water retention.
    causal_link_type: DIRECT
    evidence:
    - &id002
      reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
      reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: The accumulation of unabsorbed lactose increases intraluminal osmotic pressure, leading to fluid influx and osmotic diarrhea.
      explanation: The clinical chapter describes osmotic water movement into the intestinal lumen.
  - target: Colonic Microbial Fermentation of Lactose
    description: Delivery of lactose to colonic microbes supplies fermentable substrate.
    causal_link_type: DIRECT
    evidence:
    - &id003
      reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: The common end for all carbohydrates that are not fully absorbed in the small bowel is bacterial fermentation in the colon with production of short chain fatty acids and gases.
      explanation: The guideline summarizes colonic fermentation of malabsorbed carbohydrate.
  - target: Nausea
    description: Nausea can accompany symptomatic lactose intolerance, but this general clinical association does not identify a specific sensory intermediate.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: INDIRECT
      snippet: Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea.
      explanation: These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
  - target: Vomiting
    description: Vomiting is a reported intolerance symptom; the precise pathway is not resolved by the clinical guideline.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: INDIRECT
      snippet: Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea.
      explanation: These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
  - target: Borborygmi
    description: Borborygmi can accompany the gastrointestinal response to lactose; the clinical descriptions do not isolate its mechanism.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
      reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: INDIRECT
      snippet: Lactose intolerance is a clinical syndrome characterized by gastrointestinal symptoms, such as bloating, abdominal pain, flatulence, nausea, borborygmi, and diarrhea, following the ingestion of lactose-containing food.
      explanation: The chapter lists borborygmi among potential symptoms.
  conforms_to: diet_induced_osmotic_diarrhea#Unabsorbed Dietary Solute Retention in the Intestinal Lumen
- name: Increased Intestinal Luminal Water
  biological_scale: TISSUE
  description: Luminal lactose and fermentation products can increase intestinal water content through osmotic movement and secretory processes. Stool output also depends on colonic salvage, transit and the absorbed fraction; watery diarrhea is not inevitable.
  evidence:
  - *id002
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: the production of short chain fatty acids increases passive movement (osmosis) and active secretion of water and sodium into the lumen that can result in diarrhea.
    explanation: The guideline includes fermentation-product effects as well as the original carbohydrate load.
  downstream:
  - target: Diarrhea
    description: An unhandled luminal water and osmotic load can produce diarrhea.
    causal_link_type: DIRECT
    evidence:
    - *id002
  - target: Intestinal Luminal Distension
    description: Increased fluid can contribute to intestinal distension; early symptoms need not wait for colonic fermentation.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: INDIRECT
      snippet: This may suggest that distension of the small intestine by fluids
      explanation: The guideline presents small-intestinal fluid distension as one possible contributor to early symptoms.
- name: Colonic Microbial Fermentation of Lactose
  biological_scale: TISSUE
  description: Colonic microbes ferment malabsorbed lactose to organic acids and gases. Some fermentation products are absorbed and salvage energy; microbial composition and gas handling modify the response.
  evidence:
  - *id003
  downstream:
  - target: Increased Intestinal Gas Production
    description: Fermentation produces intestinal gases.
    causal_link_type: DIRECT
    evidence:
    - *id003
  - target: Increased Intestinal Luminal Water
    description: Fermentation products can add osmotic and secretory water effects, while absorption can also salvage the luminal load.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: INDIRECT
      snippet: the production of short chain fatty acids increases passive movement (osmosis) and active secretion of water and sodium into the lumen that can result in diarrhea.
      explanation: Fermentation products may contribute to water accumulation.
  conforms_to: diet_induced_osmotic_diarrhea#Colonic Microbial Fermentation of the Malabsorbed Substrate
  biological_processes:
  - preferred_term: microbial lactose catabolism
    term:
      id: GO:0005990
      label: lactose catabolic process
    modifier: INCREASED
- name: Increased Intestinal Gas Production
  biological_scale: TISSUE
  description: Microbial gas production includes hydrogen, carbon dioxide and methane. Methanogens consume hydrogen, so measured breath hydrogen is not a complete measure of fermentation or symptom severity.
  evidence:
  - &id004
    reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: At the same time production of gases, such as CO2, H2, or CH4, may contribute to the sensation of abdominal bloating, pain and flatulence, related to perception of colonic distension.
    explanation: Gas production and distension can contribute to symptoms; the relationship is not obligatory.
  - reference: PMID:42434160
    reference_title: A national consensus guideline on the performance and interpretation of hydrogen- and methane-based breath tests for carbohydrate malabsorption, small intestinal bacterial overgrowth, and intestinal methanogen overgrowth.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: conversion of hydrogen to methane can reduce hydrogen concentrations and thereby produce false-negative hydrogen-only tests
    explanation: The national guideline explains a limitation of hydrogen-only testing.
  downstream:
  - target: Intestinal Luminal Distension
    description: Gas retained within the bowel can distend the lumen.
    causal_link_type: DIRECT
    evidence:
    - &id005
      reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: Colorectal distension by gas remaining in the colon results in symptoms such as bloating or pain.
      explanation: Retained gas and colorectal distension can produce bloating and pain, with individual sensitivity modifying the response.
  - target: Flatulence
    description: Expulsion of fermentation gases contributes to flatulence; production, retention and perception differ between people.
    causal_link_type: DIRECT
    evidence:
    - *id004
- name: Intestinal Luminal Distension
  biological_scale: TISSUE
  description: Accumulated gas and fluid may distend the intestinal lumen. Perceived bloating and observed abdominal distention overlap but are not identical; symptom intensity also depends on visceral sensitivity.
  evidence:
  - *id005
  downstream:
  - target: Abdominal Distension
    description: Intraluminal expansion can contribute to abdominal distention or bloating.
    causal_link_type: DIRECT
    evidence:
    - *id004
  - target: Abdominal Pain
    description: Distension can produce pain, with variable sensory responsiveness.
    causal_link_type: DIRECT
    evidence:
    - *id005
- name: Increased Visceral Sensitivity
  biological_scale: ORGANISM
  description: Visceral sensitivity can amplify symptoms at a given carbohydrate load. This is a modifier, particularly relevant when disorders of gut-brain interaction coexist, rather than a proven downstream result of the lactase genotype.
  evidence:
  - &id010
    reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: The likelihood of reporting symptoms and the severity of symptoms depends on the degree of visceral sensitivity.
    explanation: The guideline recognizes visceral sensitivity as a modifier of symptom expression.
  downstream:
  - target: Abdominal Pain
    description: Heightened sensitivity can increase the painful response to intestinal distension without requiring greater malabsorption.
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    evidence:
    - reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: INDIRECT
      snippet: The likelihood of reporting symptoms and the severity of symptoms depends on the degree of visceral sensitivity.
      explanation: The guideline recognizes visceral sensitivity as a modifier of symptom expression.
phenotypes:
- name: Diarrhea
  category: Gastrointestinal
  description: Loose or watery stools may follow a symptomatic lactose load; not every non-persistent or malabsorbing individual develops diarrhea.
  phenotype_term:
    preferred_term: Diarrhea
    term:
      id: HP:0002014
      label: Diarrhea
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea.
    explanation: These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
- name: Flatulence
  category: Gastrointestinal
  description: Excess passage of gas can occur after lactose ingestion. Gas production is not a direct measure of perceived severity.
  phenotype_term:
    preferred_term: Flatulence
    term:
      id: HP:0033589
      label: Flatulence
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea.
    explanation: These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
- name: Abdominal Pain
  category: Gastrointestinal
  description: Abdominal pain or cramping can accompany intolerance and may be modified by visceral sensitivity.
  phenotype_term:
    preferred_term: Abdominal pain
    term:
      id: HP:0002027
      label: Abdominal pain
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea.
    explanation: These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
- name: Abdominal Distension
  category: Gastrointestinal
  description: Bloating or abdominal distention can follow lactose ingestion. The cited clinical sources use overlapping symptom language without always measuring visible expansion.
  phenotype_term:
    preferred_term: Abdominal distention
    term:
      id: HP:0003270
      label: Abdominal distention
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Established indications for carbohydrate breath tests and symptom assessment include intermittent diarrhea, abdominal pain, bloating, distension, nausea and flatulence
    explanation: The guideline separately names bloating and distension in the symptomatic assessment context.
- name: Nausea
  category: Gastrointestinal
  description: Nausea is a recognized possible symptom of lactose intolerance.
  phenotype_term:
    preferred_term: Nausea
    term:
      id: HP:0002018
      label: Nausea
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea.
    explanation: These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
- name: Vomiting
  category: Gastrointestinal
  description: Vomiting is reported among intolerance symptoms; no population frequency is established here.
  phenotype_term:
    preferred_term: Vomiting
    term:
      id: HP:0002013
      label: Vomiting
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Symptoms of lactose intolerance are diarrhea, abdominal pain, bloating, flatulence, vomiting, and nausea.
    explanation: These are potential symptoms of intolerance after exposure, not universal findings in lactase non-persistence.
- name: Borborygmi
  category: Gastrointestinal
  description: Audible bowel rumbling can accompany intolerance; the HPO term includes borborygmi as a synonym.
  phenotype_term:
    preferred_term: Hyperactive bowel sounds
    term:
      id: HP:0030143
      label: Hyperactive bowel sounds
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
    reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Lactose intolerance is a clinical syndrome characterized by gastrointestinal symptoms, such as bloating, abdominal pain, flatulence, nausea, borborygmi, and diarrhea, following the ingestion of lactose-containing food.
    explanation: Borborygmi is listed in the clinical symptom description.
prevalence:
- population: Worldwide, with substantial population variation
  prevalence_class: COMMON
  notes: Lactase non-persistence is common, but available genotype and enzyme-phenotype surveys are heterogeneous and do not estimate the prevalence of symptomatic intolerance. Geographic interpolation and reciprocal persistence frequencies are not converted into a global rate.
  evidence:
  - reference: PMID:12915462
    reference_title: 'Lactase persistence DNA variant enhances lactase promoter activity in vitro: functional role as a cis regulatory element.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: BACKGROUND
    directness: DIRECT
    snippet: The majority of the world's human population experiences a decline in production of the digestive enzyme lactase-phlorizin hydrolase during maturation.
    explanation: This background statement supports common non-persistence, without giving a symptom-prevalence estimate.
  - reference: PMID:20144208
    reference_title: A worldwide correlation of lactase persistence phenotype and genotypes.
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: We accept that surface interpolation can give misleading results when data are sparse and so urge caution in interpreting our results for such regions.
    explanation: The global mapping study cautions against interpreting sparse geographic estimates as representative population rates.
genetic:
- name: MCM6 intronic regulatory haplotypes
  gene_term:
    preferred_term: MCM6
    term:
      id: hgnc:6949
      label: MCM6
  relationship_type: CAUSATIVE
  notes: The term locates cis-regulatory DNA affecting LCT, not a defect in MCM6 protein. C-13910-containing ancestral haplotypes are associated with non-persistence in studied populations; derived T-13910 supports persistence. The original linkage study used nine extended Finnish families and examined additional populations. The linked G/A-22018 marker is associated but is not automatically an independent functional variant. Rare congenital LCT coding variants cause a different condition.
  evidence:
  - *id006
  - reference: PMID:11788828
    reference_title: Identification of a variant associated with adult-type hypolactasia.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: A second variant, G/A-22018, 8 kb telomeric to C/T-13910, is also associated with the trait in 229 of 236 cases.
    explanation: Records the linked marker association without asserting independent enhancer causality.
- name: Regionally distributed lactase-persistence variants
  gene_term:
    preferred_term: MCM6
    term:
      id: hgnc:6949
      label: MCM6
  relationship_type: PROTECTIVE
  notes: The 2007 East African study analyzed 470 reliable lactose-tolerance phenotypes. C-14010 had robust corrected association; G-13915 and G-13907 were candidate associations that did not remain significant after multiple-testing correction in that study. Derived reporter haplotypes enhanced transcription relative to ancestral constructs, but the G-13907 construct also contained linked T-13495. These variants favor persistence; they are not non-persistence alleles. A C/T-13910-only assay has incomplete population coverage, rather than being uniformly invalid in every non-European individual.
  evidence:
  - reference: PMID:17159977
    reference_title: Convergent adaptation of human lactase persistence in Africa and Europe.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: These SNPs originated on different haplotype backgrounds from the European C/T-13910 SNP and from each other.
    explanation: The study supports multiple regulatory backgrounds for persistence.
  - reference: PMID:17159977
    reference_title: Convergent adaptation of human lactase persistence in Africa and Europe.
    supports: SUPPORT
    evidence_source: IN_VITRO
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: have derived alleles that significantly enhance transcription from the LCT promoter in vitro
    explanation: Reporter haplotypes support transcriptional enhancement, with construct and linkage limits.
  - reference: PMID:17159977
    reference_title: Convergent adaptation of human lactase persistence in Africa and Europe.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Although C/G-13907 and T/G-13915 are associated with the phenotype, this association was not statistically significant after Bonferroni correction in either the individual populations or in the meta-analysis
    explanation: The full results qualify the abstract association claim for these two candidate variants.
- name: LCT, the regulated lactase gene
  gene_term:
    preferred_term: LCT
    term:
      id: hgnc:6530
      label: LCT
  notes: LCT encodes the intestinal enzyme whose expression declines. Both intragenic and upstream regulatory elements contribute to expression. The early study's absence of coding/promoter association does not refute every possible LCT regulatory contribution or imply that LCT is mechanistically irrelevant.
  evidence:
  - reference: PMID:27159559
    reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: In adult and infant mice, deletion in Lct intron 1 as well as in Lct intron 2 caused widespread downregulation of Lct throughout the duodenum and jejunum
    explanation: Mouse regulatory deletions demonstrate contributions from intragenic elements, distinct from human congenital coding deficiency.
progression:
- phase: Age-dependent enzyme decline
  notes: Primary non-persistence develops after early childhood with population and individual variation. It is not a lifelong enzyme absence from birth. Adult cross-sectional associations suggest that regulatory changes may continue after childhood, without establishing an individual longitudinal rate.
  evidence:
  - *id007
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: usually presents after 3 years of life in more than half of the world population, depending on the geographical origin and ethnicity.
    explanation: The guideline places primary malabsorption after early childhood; adult-type does not mean exclusively adult onset.
- phase: Exposure-dependent symptoms
  notes: Intolerance episodes depend on dose, meal composition, transit and sensitivity. Pain or bloating may precede diarrhea; symptoms need not all begin or end within one fixed time window. Persistent or alarm symptoms require evaluation for other or coexisting disease.
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: In patients with intolerance, symptoms such as pain, bloating, and flatulence may precede onset of diarrhea by several hours after carbohydrate ingestion.
    explanation: The guideline describes different symptom time courses.
diagnosis:
- name: Clinical assessment and lactose withdrawal-rechallenge
  description: Establish a reproducible relationship between lactose intake and symptoms. Improvement on a supervised reduction and recurrence with reintroduction supports intolerance; asymptomatic non-persistence needs no symptom-directed treatment. Evaluate alarm signs and alternative diagnoses before attributing symptoms to lactose.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
    reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Symptom resolution following lactose elimination and recurrence upon reintroduction supports the diagnosis of lactose intolerance.
    explanation: The chapter describes clinical confirmation through withdrawal and reintroduction.
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Patients with alarm symptoms and/or signs should be investigated by biochemical, endoscopic and imaging investigations prior to performance of breath tests.
    explanation: The guideline prioritizes investigation of alarm findings.
- name: Hydrogen breath test with concurrent symptom assessment
  diagnosis_term:
    preferred_term: lactose hydrogen breath test
    term:
      id: NCIT:C116515
      label: Breath Test
  description: The 2022 European guideline recommends 25–50 g lactose for adult malabsorption testing and 25 g when assessing intolerance, with an H2 rise of at least 20 ppm above baseline. Record symptoms concurrently and report malabsorption and intolerance separately. Preparation, low hydrogen excretion, methane production, SIBO, rapid transit and slow substrate arrival can alter results. The 2026 Israeli consensus recommends simultaneous H2/CH4 measurements; the European guideline is more cautious about the added clinical utility of methane. Neither gas response establishes congenital versus primary versus secondary deficiency.
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: The dose of test substance in adults for diagnosis of lactose intolerance should be 25 g lactose.
    explanation: The adult intolerance protocol uses a physiologically more relevant load than older 50-g challenges.
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: A H2 cut‐off ≥20 parts per million increase above baseline at a single time point during the test shall indicate maldigestion or malabsorption.
    explanation: The guideline threshold concerns malabsorption.
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: The recording of symptoms manifesting after carbohydrate ingestion is an integral part of a carbohydrate challenge test.
    explanation: Symptom recording is needed to assess intolerance.
  - reference: PMID:42434160
    reference_title: A national consensus guideline on the performance and interpretation of hydrogen- and methane-based breath tests for carbohydrate malabsorption, small intestinal bacterial overgrowth, and intestinal methanogen overgrowth.
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: The panel recommends that laboratories use devices that measure hydrogen and methane simultaneously
    explanation: The newer national consensus supports combined gas measurement; this is a local expert recommendation.
- name: Lactase-persistence genotyping
  diagnosis_term:
    preferred_term: Genetic Testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  description: Genotyping provides evidence of inherited persistence/non-persistence predisposition in the relevant population. A C/T-13910-only test misses other persistence-associated alleles and does not diagnose current symptom intolerance or secondary mucosal deficiency. Quantitative enzyme activity can vary among heterozygotes and occasional genotype-phenotype discordance occurs.
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Lactase deficiency can be diagnosed directly by measurement of enzyme activity in mucosal biopsies, and indirectly either by genetic testing or by measurement of serum glucose concentration after ingestion of lactose.
    explanation: These methods assess different components of digestion and do not substitute for clinical symptom assessment.
  - reference: PMID:29618745
    reference_title: Differences in DNA Methylation and Functional Expression in Lactase Persistent and Non-persistent Individuals.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: We are not aware of any clinical feature that might be responsible for the lactase non-persistence phenotype of the three TT individuals
    explanation: The selected pediatric cohort included genotype-phenotype discordance, limiting universal single-SNP prediction.
- name: Lactose tolerance test
  diagnosis_term:
    preferred_term: post-lactose blood glucose response
  description: Serial blood glucose after lactose indirectly assesses hydrolysis and absorption. The 40-person comparison study found weaker genotype discrimination than breath H2 after lactose and poor performance after milk. This small study does not establish universal comparative accuracy, and blood glucose is affected by factors other than lactase.
  evidence:
  - reference: PMID:32600320
    reference_title: Evaluation of breath, plasma, and urinary markers of lactose malabsorption to diagnose lactase non-persistence following lactose or milk ingestion.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Plasma glucose and urinary galactose/creatinine were unreliable (AUC < 0.70) after milk ingestion.
    explanation: The milk-challenge result is limited to this study and genotype reference standard.
- name: Duodenal biopsy enzyme assay when otherwise indicated
  diagnosis_term:
    preferred_term: Biopsy Procedure
    term:
      id: NCIT:C15189
      label: Biopsy Procedure
  description: Mucosal enzyme assays directly assess lactase activity. Endoscopy is invasive and is generally reserved for investigation of secondary causes or other indications; a low activity result alone does not establish symptomatic intolerance.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
    reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: 'Small bowel biopsy: This test is invasive and rarely used; reserved for excluding secondary causes such as celiac disease.'
    explanation: The chapter limits routine use of biopsy.
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Lactase deficiency can be diagnosed directly by measurement of enzyme activity in mucosal biopsies
    explanation: The guideline identifies the direct enzyme measurement.
biochemical:
- name: Breath hydrogen after lactose challenge
  presence: INCREASED
  context: An increase reflects microbial fermentation of unabsorbed substrate, with false-positive and false-negative causes. It is not a direct lactase measurement or a symptom-severity score. The study reporting an AUC of 1.00 enrolled 40 healthy women aged 18–30, enriched for self-reported milk symptoms (30/40), with 14 genotype-defined non-persistent participants and 26 persistent participants. Cutoffs were optimized in the same cohort without external validation; the standard 20-ppm cutoff after 50 g lactose had 100% sensitivity and 96.2% specificity. Both 750-mL milk arms contained 37.5 g lactose and involved these same participants. No superiority of one milk for clinical symptoms or universal test accuracy follows.
  readouts:
  - target: Increased Intestinal Gas Production
    relationship: READOUT_OF
    direction: POSITIVE
    endpoint_context: DIAGNOSTIC
    interpretation: Exhaled hydrogen is an indirect gas-production readout, affected by hydrogen-consuming organisms and transit.
    evidence:
    - reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: increased H2 production is readily detectable as an increase in H2 excretion in the breath.
      explanation: Breath hydrogen reflects intestinal microbial production.
  evidence:
  - reference: PMID:32600320
    reference_title: Evaluation of breath, plasma, and urinary markers of lactose malabsorption to diagnose lactase non-persistence following lactose or milk ingestion.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Genetic testing identified 14 out of 40 subjects as having LNP (C/C13910 and G/G22018).
    explanation: The diagnostic marker study uses a small genotype-defined reference group.
- name: Intestinal regulatory-region DNA modification
  presence: INCREASED
  context: Research finding in defined intestinal tissues and genotypes, not a validated blood test or routine clinical diagnostic. The pediatric methylation classifier underwent internal leave-one-out validation, not independent external validation. Associations with lactase activity do not prove methylation causally mediates symptoms.
  evidence:
  - *id008
  - *id009
environmental:
- name: Dietary lactose ingestion
  exposure_term:
    preferred_term: dietary lactose ingestion
    term:
      id: ECTO:9000240
      label: exposure to disaccharide
  chemicals:
  - lactose
  description: Lactose supplies the substrate for malabsorption and intolerance after lactase declines. Symptom likelihood varies with dose, distribution across meals and individual physiology; ingestion does not itself establish primary enzyme deficiency.
  influences_mechanisms:
  - target: Unhydrolysed Lactose Retained in the Intestinal Lumen
    environmental_effect: TRIGGERS
    causal_link_type: DIRECT
    description: The ingested load supplies lactose that may exceed hydrolytic capacity.
    evidence:
    - reference: PMID:34431620
      reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: The likelihood of reporting symptoms and the severity of symptoms in individuals with lactose malabsorption depends on the dose of lactose.
      explanation: Dose modifies the clinical response.
  evidence:
  - reference: PMID:7776987
    reference_title: A comparison of symptoms after the consumption of milk or lactose-hydrolyzed milk by people with self-reported severe lactose intolerance.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: When the periods were compared, there were no statistically significant differences in the severity of these four gastrointestinal symptoms.
    explanation: In 30 self-described severely intolerant adults, including 21 malabsorbers, a one-week 240-mL milk crossover produced minimal symptom severity. A small excess flatus count remained among malabsorbers; this is not a universal tolerance threshold.
differential_diagnoses:
- name: Irritable bowel syndrome
  disease_term:
    preferred_term: irritable bowel syndrome
    term:
      id: MONDO:0005052
      label: irritable bowel syndrome
  description: IBS and lactose intolerance may coexist. A positive lactose breath test does not establish that a prior IBS diagnosis was wrong, and lactose-related symptoms can be amplified by visceral sensitivity.
  distinguishing_features:
  - Assess reproducible lactose-related symptoms as well as the independent clinical criteria for IBS.
  - Persistent symptoms despite appropriate lactose management require evaluation for coexisting disease.
  evidence:
  - reference: PMID:32623873
    reference_title: 'Irritable bowel syndrome and lactose intolerance: the importance of differential diagnosis. A monocentric study.'
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: At the HBT, 79.9% (N.=207) of patients with IBS were positive, while in the control group were positive 25.0% (N.=27) of subjects (P<0.001).
    explanation: This selected monocentric cohort documents breath-test overlap, not the fraction of all IBS diagnoses that are erroneous.
  - *id010
- name: Secondary lactase deficiency
  description: Acquired small-intestinal mucosal injury can lower lactase at any age. Celiac disease, infection including giardiasis and rotavirus, Crohn disease and malnutrition are possible causes; activity may improve when the underlying process resolves.
  distinguishing_features:
  - Look for underlying intestinal disease, alarm signs, acquired timing or other evidence of malabsorption.
  - Lactase-persistence genotype does not rule out secondary deficiency.
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Secondary lactase deficiency, due to damage to the small intestinal mucosa, may occur at any age and may be caused by infectious enteritis (i.e., Rotavirus, particularly in infancy), enteropathy (i.e., celiac disease, Giardiasis, and Crohn's disease), or severe malnutrition and may, thus, be transient and related to the underlying condition.
    explanation: The guideline distinguishes secondary mucosal deficiency from primary non-persistence.
- name: Congenital lactase deficiency
  description: Rare congenital lactase deficiency causes severe neonatal milk-related diarrhea rather than the age-dependent primary decline addressed here.
  distinguishing_features:
  - Onset in the first days of life with severe watery diarrhea and nutritional consequences.
  - Congenital LCT deficiency requires a different diagnostic and dietary approach.
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: manifests with severe symptoms (intractable watery osmotic diarrhea associated with metabolic acidosis, dehydration and weight loss) in the first days of life
    explanation: The guideline describes the neonatal congenital presentation.
- name: Milk protein allergy
  description: Immune-mediated reactions to milk proteins differ from lactose maldigestion. Lactose-free dairy still contains milk protein and does not by itself address milk allergy.
  distinguishing_features:
  - Assess an allergic phenotype and refer for allergy evaluation when indicated.
  - A response to avoiding whole dairy does not identify which component caused symptoms.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
    reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Referral to an allergist is important if a milk allergy&#x02014;an immune-mediated reaction to milk proteins&#x02014;is suspected, as this condition is often confused with lactose intolerance.
    explanation: The clinical chapter separates milk-protein allergy from lactose intolerance.
treatments:
- name: Individualized lactose reduction
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Dietary Intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  description: For documented symptomatic intolerance, reduce lactose to an individually tolerated amount, use lactose-free equivalents and consider smaller portions with meals. Complete dairy avoidance is usually unnecessary. Do not prescribe restriction solely for a non-persistence genotype or asymptomatic malabsorption.
  target_mechanisms:
  - target: Unhydrolysed Lactose Retained in the Intestinal Lumen
    treatment_effect: INHIBITS
    description: Reduces delivery of undigested lactose without restoring endogenous enzyme expression.
    evidence:
    - reference: PMID:33887513
      reference_title: 'Lactose intolerance: An update on its pathogenesis, diagnosis, and treatment.'
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: An appropriate intervention concerns the dietetic style, such as the consumption of lactose-free foods, but with nutritional characteristics comparable to dairy products.
      explanation: The review recommends nutritionally comparable low-lactose alternatives.
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: should be limited to cases in which the relationship between ingestion of the carbohydrate and development of symptoms has been documented.
    explanation: The guideline reserves elimination or enzyme use for a documented relationship between intake and symptoms.
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: The severity of symptoms depends on whether the carbohydrate is administered in a single or split dose or together with other nutrients.
    explanation: Meal context and split intake affect tolerance.
- name: Exogenous lactase supplementation
  therapeutic_modality: PROTEIN_REPLACEMENT
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
  description: Oral lactase tablets or drops can improve luminal lactose digestion without changing endogenous LCT expression. Timing and formulation matter, and gas and symptom responses vary. In an uncontrolled paired study of 96 symptomatic C/C-13910 malabsorbers, enzyme given one hour before a 25-g aqueous challenge made 21 breath tests negative, reduced 17 and left 58 similar; this is not a placebo-controlled efficacy estimate or a universal failure rate.
  target_mechanisms:
  - target: Declining Intestinal Lactase Activity
    treatment_effect: BYPASSES
    description: Supplies luminal hydrolytic activity to compensate for low endogenous enzyme.
    evidence:
    - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
      reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
      supports: SUPPORT
      evidence_source: OTHER
      quote_role: REVIEW_SYNTHESIS
      directness: DIRECT
      snippet: Lactase enzyme supplements extracted from yeasts and molds are available as tablets or drops.
      explanation: The chapter describes exogenous digestive enzyme preparations.
  evidence:
  - reference: PMID:24967391
    reference_title: Effects of exogenous lactase administration on hydrogen breath excretion and intestinal symptoms in patients presenting lactose malabsorption and intolerance.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The response to oral administration of Beta-Galactosidase in patients with symptoms of lactose malabsorption presents a significant variability.
    explanation: The paired study reports heterogeneous breath and symptom responses; symptom benefit was not shown to track hydrogen reduction.
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
    reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: In most cases, these supplements should be taken just before eating a high-lactose product or with the first bite.
    explanation: General clinical administration advice differs from the one-hour prechallenge research protocol.
  - reference: PMID:36149331
    reference_title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The likelihood of experiencing higher-severity abdominal pain (based on the participant-wise maximum severity that was experienced during each challenge) with lactase treatment was 0.32 times that with Bi-07 (P = 0.033) and placebo (P = 0.036)
    explanation: Lactase improved selected symptoms in the randomized milk challenge; the result is not generalized to every formulation or substrate.
- name: Dietetic and nutritional support
  therapeutic_modality: BEHAVIORAL
  treatment_term:
    preferred_term: Dietary Intervention
    term:
      id: NCIT:C15447
      label: Dietary Intervention
  description: Provide individualized dietary counseling and maintain adequate calcium, vitamin D, protein and energy intake when dairy is reduced. Assess nutritional adequacy and supplement where appropriate. Restriction-related deficiency is a care concern, not an inevitable intrinsic phenotype of lactase non-persistence.
  evidence:
  - reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
    reference_title: Lactose Intolerance - StatPearls - NCBI Bookshelf
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: Dietitians play a central role in formulating personalized, well-balanced low-lactose or lactose-free diets while ensuring adequate intake of calcium, vitamin D, and other key nutrients.
    explanation: The chapter recommends dietetic support to prevent nutritional consequences of restriction.
- name: Investigational strain-specific probiotic supplementation
  therapeutic_modality: OTHER
  description: Bi-07 was tested as a high-dose, acute co-ingested preparation in two small randomized crossover trials. Breath-hydrogen exposure decreased relative to placebo, but a consistent symptom benefit was not demonstrated; nausea increased in the aqueous-lactose trial. These findings do not establish routine probiotic therapy, long-term benefit, a class effect or equivalence to lactase across food matrices.
  target_mechanisms:
  - target: Unhydrolysed Lactose Retained in the Intestinal Lumen
    treatment_effect: INHIBITS
    description: The preparation hydrolyzes lactose in milk in vitro; the clinical breath-gas outcome is consistent with improved digestion but does not directly measure the anatomical site of hydrolysis.
    evidence:
    - reference: PMID:36149331
      reference_title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Bi-07 effected a decrease in the amount of lactose comparable with those of the commercial lactase and laboratory-grade β-galactosidase
      explanation: Direct in-vitro milk measurements support lactose hydrolysis by this specific preparation.
  evidence:
  - reference: PMID:36149331
    reference_title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: In Booster Alpha, there were no significant differences in any GI symptom between Bi-07 and placebo.
    explanation: A reduction in the primary gas outcome did not establish symptom benefit in the milk trial.
  - reference: PMID:36149331
    reference_title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: In Booster Omega, except for symptoms of nausea, there were no differences between the 3 treatments.
    explanation: The aqueous-lactose trial showed no broad symptom advantage and more nausea with Bi-07.
animal_models:
- name: Mouse lactase regulatory-element deletions
  species: Mouse
  genotype: Separate CRISPR deletions of Lct intron 1, Lct intron 2 or Mcm6 intron 13
  background: C57BL/6N
  publication: PMID:27159559
  description: Infant day-6 and adult day-60 intestinal segments were examined after intronic deletions. Lct intron-1/2 deletions reduced mRNA broadly by 3–8-fold; Mcm6 intron-13 effects were smaller and segment-specific. Lct intron-2 dependence was greater in adults. Deletions avoided exons and splice sites; these are sequence perturbations, not epigenetic editing or human persistence-allele models.
  modeled_mechanisms:
  - target: Reduced Enterocyte LCT Transcription
    relationship: MEASURES
    fidelity: MODERATE
    description: Regulatory deletions reduce intestinal Lct transcript abundance.
    limitations: Does not establish methylation causality, human symptom thresholds or diarrhea frequency.
    evidence:
    - &id011
      reference: PMID:27159559
      reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
      supports: SUPPORT
      evidence_source: MODEL_ORGANISM
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: In adult and infant mice, deletion in Lct intron 1 as well as in Lct intron 2 caused widespread downregulation of Lct throughout the duodenum and jejunum
      explanation: Mouse regulatory deletions reduce Lct mRNA; clinical intolerance was not the measured endpoint.
    readouts:
    - name: Intestinal Lct mRNA
      target: Reduced Enterocyte LCT Transcription
      direction: DECREASED
      interpretation: Regulatory deletions reduce intestinal Lct transcript abundance.
      evidence:
      - reference: PMID:27159559
        reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        quote_role: PRIMARY_RESULT
        directness: DIRECT
        snippet: In adult and infant mice, deletion in Lct intron 1 as well as in Lct intron 2 caused widespread downregulation of Lct throughout the duodenum and jejunum
        explanation: Mouse regulatory deletions reduce Lct mRNA; clinical intolerance was not the measured endpoint.
  evidence:
  - *id011
experimental_models:
- name: Caco-2 human enhancer and rat promoter reporter
  experimental_model_type: CELL_LINE
  cell_source: Human Caco-2 cells transfected with human variant regions upstream of a rat lactase promoter
  publication: PMID:12915462
  description: A 200-bp human C-13910 region increased the 3-kb rat promoter reporter 2.2-fold and the T-containing region 2.8-fold. Both enhanced basal activity. EMSA showed different nuclear binding without identifying a unique causal factor. Only the published abstract was recovered.
  modeled_mechanisms:
  - target: Reduced Enterocyte LCT Transcription
    relationship: MEASURES
    fidelity: MODERATE
    description: Reporter transcription differs by enhancer allele.
    limitations: Artificial constructs with a rat promoter do not directly measure childhood human LCT decline.
    evidence:
    - *id012
  evidence:
  - *id012
- name: Caco-2 East African persistence-haplotype reporter
  experimental_model_type: CELL_LINE
  cell_source: Human Caco-2 cells with MCM6 intronic haplotype constructs and a human LCT promoter
  publication: PMID:17159977
  description: Derived haplotype reporters increased transcription relative to ancestral constructs. The G-13907 haplotype also carried T-13495, so that comparison does not isolate one variant. These experiments complement population association rather than validating every single-allele clinical prediction.
  modeled_mechanisms:
  - target: Reduced Enterocyte LCT Transcription
    relationship: MEASURES
    fidelity: MODERATE
    description: Reporter haplotypes alter transcriptional output.
    limitations: In-vitro reporter effects do not resolve all linked variants or population-level predictive accuracy.
    evidence:
    - reference: PMID:17159977
      reference_title: Convergent adaptation of human lactase persistence in Africa and Europe.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: have derived alleles that significantly enhance transcription from the LCT promoter in vitro
      explanation: The experimental readout is promoter-reporter activity.
- name: Caco-2 regulatory-element deletion
  experimental_model_type: CELL_LINE
  cell_source: Engineered Caco-2 cells with CRISPR-Cas9n deletions
  publication: PMID:27159559
  description: MCM6 intron-13 or LCT intron-2 deletion reduced LCT mRNA after differentiation at day 15, but not before confluence at day 6. A nonregulatory LCT intron-1 deletion served as a negative control. Removing DNA establishes regulatory-element importance, not a causal methylation effect.
  modeled_mechanisms:
  - target: Reduced Enterocyte LCT Transcription
    relationship: MEASURES
    fidelity: MODERATE
    description: Differentiated cells show lower LCT mRNA after regulatory deletion.
    limitations: Cell differentiation and regulatory-sequence loss are distinct from natural aging and targeted epigenetic modification.
    evidence:
    - &id013
      reference: PMID:27159559
      reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: However, in the differentiated, epithelial-like cell state the deletion in MCM6 intron 13 or LCT intron 2 resulted in a significant decrease in LCT mRNA levels
      explanation: CRISPR regulatory-DNA deletions reduce LCT in differentiated Caco-2 cells; this is not targeted methylation manipulation.
    readouts:
    - name: LCT mRNA in differentiated cells
      target: Reduced Enterocyte LCT Transcription
      direction: DECREASED
      interpretation: Differentiated cells show lower LCT mRNA after regulatory deletion.
      evidence:
      - reference: PMID:27159559
        reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        directness: DIRECT
        snippet: However, in the differentiated, epithelial-like cell state the deletion in MCM6 intron 13 or LCT intron 2 resulted in a significant decrease in LCT mRNA levels
        explanation: CRISPR regulatory-DNA deletions reduce LCT in differentiated Caco-2 cells; this is not targeted methylation manipulation.
  evidence:
  - *id013
- name: Caco-2 LOC100507600 RNA interference
  experimental_model_type: CELL_LINE
  cell_source: T/T-13910 Caco-2 cells with antisense-transcript siRNA or scrambled control
  publication: PMID:27159559
  description: Partial lncRNA knockdown coincided with reduced LCT mRNA while MCM6 mRNA was unchanged. The proposed CTCF and chromatin-loop mechanism was not directly established.
  modeled_mechanisms:
  - target: Reduced Enterocyte LCT Transcription
    relationship: MEASURES
    fidelity: MODERATE
    description: lncRNA knockdown reduces LCT mRNA in the cell model.
    limitations: This does not establish LOC100507600 deficiency as a measured cause of clinical non-persistence.
    evidence:
    - &id014
      reference: PMID:27159559
      reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
      supports: SUPPORT
      evidence_source: IN_VITRO
      quote_role: PRIMARY_RESULT
      directness: DIRECT
      snippet: Transfection with small-interfering RNAs directed to LOC100507600 reduced its expression by 20%, and resulted in concomitant 25% reduction in LCT mRNA
      explanation: RNA interference supports a role for the antisense transcript in the cell model, without establishing a human disease mediator.
    readouts:
    - name: LCT mRNA after lncRNA knockdown
      target: Reduced Enterocyte LCT Transcription
      direction: DECREASED
      interpretation: lncRNA knockdown reduces LCT mRNA in the cell model.
      evidence:
      - reference: PMID:27159559
        reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
        supports: SUPPORT
        evidence_source: IN_VITRO
        quote_role: PRIMARY_RESULT
        directness: DIRECT
        snippet: Transfection with small-interfering RNAs directed to LOC100507600 reduced its expression by 20%, and resulted in concomitant 25% reduction in LCT mRNA
        explanation: RNA interference supports a role for the antisense transcript in the cell model, without establishing a human disease mediator.
  evidence:
  - *id014
discussions:
- discussion_id: malabsorption_versus_intolerance
  kind: KNOWLEDGE_GAP
  prompt: Which microbial, sensory and dietary factors determine symptoms at a given lactose load?
  attaches_to:
  - pathophysiology#Colonic Microbial Fermentation of Lactose
  - phenotypes#Abdominal Pain
  rationale: Malabsorption and symptoms are not equivalent. Selected trials and guidelines show dose, meal context, visceral sensitivity and expectation effects. A single small milk trial cannot define a universal tolerated dose; absence of significant severity differences also does not erase its observed excess flatus count. No current source establishes one microbial mechanism for every symptomatic person.
  evidence:
  - reference: PMID:34431620
    reference_title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
    supports: SUPPORT
    evidence_source: OTHER
    quote_role: REVIEW_SYNTHESIS
    directness: DIRECT
    snippet: only a proportion of carbohydrate malabsorbers develop symptoms
    explanation: The guideline distinguishes malabsorption from symptoms.
  - reference: PMID:7776987
    reference_title: A comparison of symptoms after the consumption of milk or lactose-hydrolyzed milk by people with self-reported severe lactose intolerance.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: When the periods were compared, there were no statistically significant differences in the severity of these four gastrointestinal symptoms.
    explanation: The crossover trial supports discordance between self-report and symptoms at a modest milk dose, within its small selected cohort.
- discussion_id: epigenetic_mediation
  kind: KNOWLEDGE_GAP
  prompt: Does changing regulatory DNA modification alter age-dependent LCT expression independently of genotype?
  attaches_to:
  - pathophysiology#Genotype-Associated Regulatory DNA Modification
  - pathophysiology#Reduced Enterocyte LCT Transcription
  rationale: Adult and pediatric intestinal associations support a regulatory epigenetic model, but adult age trends are cross-sectional and pediatric enzyme-defined groups are not symptom cohorts. Deletion and RNAi experiments perturb DNA or RNA rather than methylation. Targeted epigenetic editing and appropriately sampled longitudinal studies are needed to resolve mediation.
  evidence:
  - reference: PMID:27159559
    reference_title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
    supports: SUPPORT
    evidence_source: OTHER
    directness: DIRECT
    snippet: Future studies examining chromatin configuration35 at the LCT–MCM6 locus in aging individuals and targeted epigenetic editing with the CRISPR-Cas9 system41 will be necessary to fully understand genetic-epigenetic contributions to lactase persistence and non-persistence.
    explanation: The authors explicitly identify epigenetic editing as future work.
clinical_trials:
- name: clinicaltrials:NCT03659747
  status: COMPLETED
  phase: NOT_APPLICABLE
  description: Booster Alpha randomized 34 adults aged 25–60 with a positive screening lactose breath test in a blinded three-period crossover. Each 25-g lactose challenge used fat-free milk and Bi-07, 4662 FCC units lactase or placebo. The primary six-hour breath-H2 iAUC was lower with Bi-07 than placebo, but higher than with lactase; noninferiority to lactase was not established. No Bi-07 symptom advantage over placebo was demonstrated. The primary per-protocol population was 33 after one smoking exclusion.
  notes: Registry status, phase and actual enrollment checked against the live ClinicalTrials.gov API on 2026-09-21. One-week washouts, significant carryover and sequence effects, an unvalidated symptom questionnaire and industry involvement limit inference. These were acute challenges, not chronic symptom-control trials.
  evidence:
  - reference: PMID:36149331
    reference_title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: The noninferiority of Bi-07 compared with lactase was not shown
    explanation: The milk trial failed its lactase noninferiority hypothesis.
  - reference: PMID:36149331
    reference_title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: In Booster Alpha, there were no significant differences in any GI symptom between Bi-07 and placebo.
    explanation: The symptom endpoint does not establish clinical superiority despite improved breath hydrogen.
- name: clinicaltrials:NCT03814668
  status: COMPLETED
  phase: NOT_APPLICABLE
  description: Booster Omega randomized 34 adults in the analogous three-period crossover protocol using 25 g aqueous lactose. Bi-07 lowered breath-H2 iAUC relative to placebo and met the prespecified noninferiority margin against lactase for that gas endpoint. Lactase did not significantly outperform placebo on the primary iAUC measure. No broad symptom advantage was shown; Bi-07 increased nausea. All 34 were in the per-protocol population, but two Bi-07 visits with vomiting were excluded from that outcome analysis (32 Bi-07 versus 34 comparator observations).
  notes: Registry status, phase and actual enrollment checked against the live ClinicalTrials.gov API on 2026-09-21. Sequence effects, possible taste-related unblinding, an unvalidated symptom questionnaire and industry involvement limit translation. The gas noninferiority result does not show symptomatic equivalence or long-term efficacy.
  evidence:
  - reference: PMID:36149331
    reference_title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: Bi-07 was superior to placebo and noninferior to lactase, based on BHC iAUC values.
    explanation: Noninferiority applies specifically to this gas endpoint and aqueous challenge.
  - reference: PMID:36149331
    reference_title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    quote_role: PRIMARY_RESULT
    directness: DIRECT
    snippet: With regard to nausea, participants experienced symptoms with greater frequency and severity during Bi-07 treatment than for placebo and lactase.
    explanation: The clinical adverse symptom qualifies the favorable gas result.
references:
- reference: PMID:11788828
  title: Identification of a variant associated with adult-type hypolactasia.
- reference: PMID:12915462
  title: 'Lactase persistence DNA variant enhances lactase promoter activity in vitro: functional role as a cis regulatory element.'
- reference: PMID:17159977
  title: Convergent adaptation of human lactase persistence in Africa and Europe.
- reference: PMID:20144208
  title: A worldwide correlation of lactase persistence phenotype and genotypes.
- reference: PMID:24967391
  title: Effects of exogenous lactase administration on hydrogen breath excretion and intestinal symptoms in patients presenting lactose malabsorption and intolerance.
- reference: PMID:27159559
  title: Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
- reference: PMID:29618745
  title: Differences in DNA Methylation and Functional Expression in Lactase Persistent and Non-persistent Individuals.
- reference: PMID:32600320
  title: Evaluation of breath, plasma, and urinary markers of lactose malabsorption to diagnose lactase non-persistence following lactose or milk ingestion.
- reference: PMID:32623873
  title: 'Irritable bowel syndrome and lactose intolerance: the importance of differential diagnosis. A monocentric study.'
- reference: PMID:33887513
  title: 'Lactose intolerance: An update on its pathogenesis, diagnosis, and treatment.'
- reference: PMID:34431620
  title: 'European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.'
- reference: PMID:36149331
  title: Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
- reference: PMID:42434160
  title: A national consensus guideline on the performance and interpretation of hydrogen- and methane-based breath tests for carbohydrate malabsorption, small intestinal bacterial overgrowth, and intestinal methanogen overgrowth.
- reference: PMID:7776987
  title: A comparison of symptoms after the consumption of milk or lactose-hydrolyzed milk by people with self-reported severe lactose intolerance.
- reference: clinicaltrials:NCT03659747
  title: 'Effect of Probiotic Supplementation on Lactose Maldigestion Induced by Fat-free Milk: Randomized, Double-blind, Placebo-controlled, Crossover, Acute Lactose Challenge'
- reference: clinicaltrials:NCT03814668
  title: 'Effect of Probiotic Supplementation on Lactose Maldigestion Induced by Lactose Solution: Randomized, Double-blind, Placebo-controlled, Positive-controlled, Three-way Crossover, Acute Lactose Challenge'
- reference: url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
  title: Lactose Intolerance - StatPearls - NCBI Bookshelf
📚

References & Deep Research

References

17
PMID:11788828
Identification of a variant associated with adult-type hypolactasia.
No top-level findings curated for this source.
PMID:12915462
Lactase persistence DNA variant enhances lactase promoter activity in vitro: functional role as a cis regulatory element.
No top-level findings curated for this source.
PMID:17159977
Convergent adaptation of human lactase persistence in Africa and Europe.
No top-level findings curated for this source.
PMID:20144208
A worldwide correlation of lactase persistence phenotype and genotypes.
No top-level findings curated for this source.
PMID:24967391
Effects of exogenous lactase administration on hydrogen breath excretion and intestinal symptoms in patients presenting lactose malabsorption and intolerance.
No top-level findings curated for this source.
PMID:27159559
Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.
No top-level findings curated for this source.
PMID:29618745
Differences in DNA Methylation and Functional Expression in Lactase Persistent and Non-persistent Individuals.
No top-level findings curated for this source.
PMID:32600320
Evaluation of breath, plasma, and urinary markers of lactose malabsorption to diagnose lactase non-persistence following lactose or milk ingestion.
No top-level findings curated for this source.
PMID:32623873
Irritable bowel syndrome and lactose intolerance: the importance of differential diagnosis. A monocentric study.
No top-level findings curated for this source.
PMID:33887513
Lactose intolerance: An update on its pathogenesis, diagnosis, and treatment.
No top-level findings curated for this source.
PMID:34431620
European guideline on indications, performance, and clinical impact of hydrogen and methane breath tests in adult and pediatric patients: European Association for Gastroenterology, Endoscopy and Nutrition, European Society of Neurogastroenterology and Motility, and European Society for Paediatric Gastroenterology Hepatology and Nutrition consensus.
No top-level findings curated for this source.
PMID:36149331
Bifidobacterium animalis subsp. lactis Bi-07 supports lactose digestion in vitro and in randomized, placebo- and lactase-controlled clinical trials.
No top-level findings curated for this source.
PMID:42434160
A national consensus guideline on the performance and interpretation of hydrogen- and methane-based breath tests for carbohydrate malabsorption, small intestinal bacterial overgrowth, and intestinal methanogen overgrowth.
No top-level findings curated for this source.
PMID:7776987
A comparison of symptoms after the consumption of milk or lactose-hydrolyzed milk by people with self-reported severe lactose intolerance.
No top-level findings curated for this source.
clinicaltrials:NCT03659747
Effect of Probiotic Supplementation on Lactose Maldigestion Induced by Fat-free Milk: Randomized, Double-blind, Placebo-controlled, Crossover, Acute Lactose Challenge
No top-level findings curated for this source.
clinicaltrials:NCT03814668
Effect of Probiotic Supplementation on Lactose Maldigestion Induced by Lactose Solution: Randomized, Double-blind, Placebo-controlled, Positive-controlled, Three-way Crossover, Acute Lactose Challenge
No top-level findings curated for this source.
url:https://www.ncbi.nlm.nih.gov/sites/books/NBK532285/
Lactose Intolerance - StatPearls - NCBI Bookshelf
No top-level findings curated for this source.