Genetic polymorphisms of histamine degrading enzymes: from small-scale screening to high-throughput routine testing

Histamine Intolerance-A Kind of Pseudoallergic Reaction

Histamine intolerance (HIT) is a common disorder associated with impaired histamine metabolism. Notwithstanding, it is often misdiagnosed as other diseases because of its lack of specific clinical manifestations. HIT did not gain traction until the early 21st century. In this review, we will focus on the latest research and elaborate on the clinical manifestations of HIT, including its manifestations in special populations such as atopic dermatitis (AD) and chronic urticaria (CU), as well as the latest understanding of its etiology and pathogenesis. In addition, we will explore the latest treatment strategies for HIT and the treatment of specific cases.

Dietary Renaissance in IBS: Has Food Replaced Medications as a Primary Treatment Strategy?

OPINION STATEMENT

The medical community has only recently started to focus attention on the role of food in the pathogenesis of irritable bowel syndrome (IBS), though the association between food and gastrointestinal (GI) symptoms has been recognized by patients for decades. Health care providers receive little formal training in the dietary management of IBS and have traditionally viewed dietary interventions with skepticism. There is mounting evidence that links food to changes in motility, visceral sensation, microbiome, permeability, immune activation, and brain-gut interactions-all key elements in the pathogenesis of IBS. The role of specific dietary modification in the management of IBS has not been rigorously investigated until recently. There is now credible evidence suggesting that targeted dietary carbohydrate exclusion provides clinical benefits to IBS patients. There is emerging evidence to suggest that proteins such as gluten, as well as food chemicals, may play a role in IBS.

Association of single nucleotide polymorphisms in the diamine oxidase gene with diamine oxidase serum activities

BACKGROUND

Histamine intolerance (HIT) is associated with an excess of histamine because of an impaired function of the histamine-degrading enzyme diamine oxidase (DAO). The genetic background of HIT is unknown yet.

METHODS

Case-control association study of all haplotype tagging and four previously reported DAO SNPs and one HNMT Single nucleotide polymorphism with symptoms of HIT and DAO serum activity in 484 German individuals including 285 patients with clinical symptoms of HIT and 199 controls.

RESULTS

Diamine oxidase serum activity was significantly associated with seven SNPs within the DAO gene. The minor allele at rs2052129, rs2268999, rs10156191 and rs1049742 increased the risk for a reduced DAO activity whereas showing a moderate protective effect at rs2071514, rs1049748 and rs2071517 in the genotypic (P = 2.1 × 10(-8) , 7.6 × 10(-10) , 8.3 × 10(-10) , 0.009, 0.005, 0.00001, 0.006, respectively) and allelic genetic model (P = 2.5 × 10(-11) , 5.4 × 10(-13) , 8.9 × 10(-13) , 0.00002, 0.006, 0.0003, 0.005, respectively). Reporter gene assays at rs2052129 revealed a lower promoter activity (P = 0.016) of the minor allele. DAO mRNA expression in peripheral blood mononuclear cells of homozygous carriers of the minor allele at rs2052129, rs2268999, rs10156191 was lower (P = 0.002) than homozygous carriers of the major allele. Diamine oxidase variants were not associated with the HIT phenotype per se, only with DAO activity alone and the subgroup of HIT patients displaying a reduced DAO activity.

CONCLUSIONS

DAO gene variants strongly influence DAO expression and activity but alone are not sufficient to fully effectuate the potentially associated disease state of HIT, suggesting an interplay of genetic and environmental factors.

Histamine intolerance: a metabolic disease?

OBJECTIVE

To evaluate the evidence regarding the disease concept of histamine intolerance as a state of inadequate histamine inactivation.

METHODS

Keyword-based systematic screening of the scientific literature and of public websites focusing on diagnostic and therapeutic procedures.

RESULTS

Histamine intolerance is commonly diagnosed based solely on subjective reporting of symptoms instead of following systematic diagnostic procedures based on objective laboratory and physical parameters. The only effective long-term therapy is avoidance of histamine-containing food.

CONCLUSIONS

The concept of histamine intolerance as a metabolic disease is in need of more experimental and clinical evidence and affected patients will benefit from a clear, evidence-based diagnostic and therapeutic regime.

Histamine and histamine intolerance

Histamine intolerance results from a disequilibrium of accumulated histamine and the capacity for histamine degradation. Histamine is a biogenic amine that occurs to various degrees in many foods. In healthy persons, dietary histamine can be rapidly detoxified by amine oxidases, whereas persons with low amine oxidase activity are at risk of histamine toxicity. Diamine oxidase (DAO) is the main enzyme for the metabolism of ingested histamine. It has been proposed that DAO, when functioning as a secretory protein, may be responsible for scavenging extracellular histamine after mediator release. Conversely, histamine N-methyltransferase, the other important enzyme inactivating histamine, is a cytosolic protein that can convert histamine only in the intracellular space of cells. An impaired histamine degradation based on reduced DAO activity and the resulting histamine excess may cause numerous symptoms mimicking an allergic reaction. The ingestion of histamine-rich food or of alcohol or drugs that release histamine or block DAO may provoke diarrhea, headache, rhinoconjunctival symptoms, asthma, hypotension, arrhythmia, urticaria, pruritus, flushing, and other conditions in patients with histamine intolerance. Symptoms can be reduced by a histamine-free diet or be eliminated by antihistamines. However, because of the multifaceted nature of the symptoms, the existence of histamine intolerance has been underestimated, and further studies based on double-blind, placebo-controlled provocations are needed. In patients in whom the abovementioned symptoms are triggered by the corresponding substances and who have a negative diagnosis of allergy or internal disorders, histamine intolerance should be considered as an underlying pathomechanism.