Histamine N-methyltransferase pharmacogenetics: association of a common functional polymorphism with asthma

Insights into S-adenosyl-l-methionine (SAM)-dependent methyltransferase related diseases and genetic polymorphisms

Enzymatic methylation catalyzed by methyltransferases has a significant impact on many human biochemical reactions. As the second most ubiquitous cofactor in humans, S-adenosyl-l-methionine (SAM or AdoMet) serves as a methyl donor for SAM-dependent methyltransferases (MTases), which transfer a methyl group to a nucleophilic acceptor such as O, As, N, S, or C as the byproduct. SAM-dependent methyltransferases can be grouped into different types based on the substrates. Here we systematically reviewed eight types of methyltransferases associated with human diseases. Catechol O-methyltransferase (COMT), As(III) S-adenosylmethionine methyltransferase (AS3MT), indolethylamine N-methyltransferase (INMT), phenylethanolamine N-methyltransferase (PNMT), histamine N-methyltransferase (HNMT), nicotinamide N-methyltransferase (NNMT), thiopurine S-methyltransferase (TPMT) and DNA methyltansferase (DNMT) are classic SAM-dependent MTases. Correlations between genotypes and disease susceptibility can be partially explained by genetic polymorphisms. The physiological function, substrate specificity, genetic variants and disease susceptibility associated with these eight SAM-dependent methyltransferases are discussed in this review.

Potential Metabolic Biomarkers in Adult Asthmatics

Asthma is the most common chronic airway inflammation, with multiple phenotypes caused by complicated interactions of genetic, epigenetic, and environmental factors. To date, various determinants have been suggested for asthma pathogenesis by a new technology termed omics, including genomics, transcriptomics, proteomics, and metabolomics. In particular, the systematic analysis of all metabolites in a biological system, such as carbohydrates, amino acids, and lipids, has helped identify a novel pathway related to complex diseases. These metabolites are involved in the regulation of hypermethylation, response to hypoxia, and immune reactions in the pathogenesis of asthma. Among them, lipid metabolism has been suggested to be related to lung dysfunction in mild-to-moderate asthma. Sphingolipid metabolites are an important mediator contributing to airway inflammation in obese asthma and aspirin-exacerbated respiratory disease. Although how these molecular variants impact the disease has not been completely determined, identification of new causative factors may possibly lead to more-personalized and precise pathway-specific approaches for better diagnosis and treatment of asthma. In this review, perspectives of metabolites related to asthma and clinical implications have been highlighted according to various phenotypes.

Computational analysis of multimorbidity between asthma, eczema and rhinitis

Background

The mechanisms explaining the co-existence of asthma, eczema and rhinitis (allergic multimorbidity) are largely unknown. We investigated the mechanisms underlying multimorbidity between three main allergic diseases at a molecular level by identifying the proteins and cellular processes that are common to them.

Methods

An in silico study based on computational analysis of the topology of the protein interaction network was performed in order to characterize the molecular mechanisms of multimorbidity of asthma, eczema and rhinitis. As a first step, proteins associated to either disease were identified using data mining approaches, and their overlap was calculated. Secondly, a functional interaction network was built, allowing to identify cellular pathways involved in allergic multimorbidity. Finally, a network-based algorithm generated a ranked list of newly predicted multimorbidity-associated proteins.

Results

Asthma, eczema and rhinitis shared a larger number of associated proteins than expected by chance, and their associated proteins exhibited a significant degree of interconnectedness in the interaction network. There were 15 pathways involved in the multimorbidity of asthma, eczema and rhinitis, including IL4 signaling and GATA3-related pathways. A number of proteins potentially associated to these multimorbidity processes were also obtained.

Conclusions

These results strongly support the existence of an allergic multimorbidity cluster between asthma, eczema and rhinitis, and suggest that type 2 signaling pathways represent a relevant multimorbidity mechanism of allergic diseases. Furthermore, we identified new candidates contributing to multimorbidity that may assist in identifying new targets for multimorbid allergic diseases.

Genetic Variation in the Histamine Production, Response, and Degradation Pathway Is Associated with Histamine Pharmacodynamic Response in Children with Asthma

Introduction: There is growing knowledge of the wide ranging effects of histamine throughout the body therefore it is important to better understand the effects of this amine in patients with asthma. We aimed to explore the association between histamine pharmacodynamic (PD) response and genetic variation in the histamine pathway in children with asthma.

Methods: Histamine Iontophoresis with Laser Doppler Monitoring (HILD) was performed in children with asthma and estimates for area under the effect curve (AUEC), maximal response over baseline (Emax), and time of Emax (Tmax) were calculated using non-compartmental analysis and non-linear mixed-effects model with a linked effect PK/PD model. DNA isolation and genotyping were performed among participants to detect known single nucleotide polymorphisms (SNPs) (n = 10) among genes (HDC, HNMT, ABP1, HRH1, HRH4) within the histamine pathway. General linear model was used to identify associations between histamine related genetic variants and measured histamine PD response parameters.

Results: Genotyping and HILD response profiles were completed for 163 children. ABP1 47 C/T, ABP1 4107, and HNMT-1639 C/Twere associated with Emax (ABP1 47 CC genotype mean Emax 167.21 vs. CT/TT genotype mean Emax 139.20, p = 0.04; ABP1 4107 CC genotype mean Emax 141.72 vs. CG/GG genotype mean Emax 156.09, p = 0.005; HNMT-1639 CC genotype mean Emax 132.62 vs. CT/TT genotype mean Emax 155.3, p = 0.02). In a stratified analysis among African American children only, ABP1 and HNMT SNPs were also associated with PD response; HRH4 413 CC genotype was associated with lower Emax, p = 0.009.

Conclusions: We show for the first time that histamine pathway genetic variation is associated with measureable changes in histamine response in children with asthma. The variability in histamine response and impact of histamine pathway genotype is important to further explore in patients with asthma so as to improve disease phenotyping leading to more personalized treatments.

Association between two polymorphisms of histamine-metabolising enzymes and the severity of allergic rhinitis in a group of Mexican children

BACKGROUND

It has been suggested that polymorphisms of histamine metabolising enzymes can be a risk factor for developing histamine-involving diseases. The aim of the present study is to research the possible association between two functional single nucleotide polymorphisms (SNPs): C314T in the Histamine-N-Methyl Transferase gene and C2029G in the Diamine Oxidase gene, with the severity of allergic rhinitis and the number of allergic diseases, in a group of allergic Mexican children.

METHODS

We studied 154 unrelated allergic children. SNPs were analysed by RT-PCR. The total serum IgE was measured by chemiluminescence and the serum histamine by ELISA. We used logistic regression analysis to determine OR.

RESULTS

Patients carrying the mutant allele for any SNP had more risk to develop higher rhinitis severity or a bigger number of allergic diseases. Haplotype analysis revealed that this effect is synergistic. In patients carrying one or two mutant alleles, serum histamine levels were higher than those of patients carrying only wild alleles. Serum IgE levels were not associated with the presence of mutant alleles.

CONCLUSION

The presence of these SNPs in patients with allergic rhinitis can lead to higher serum histamine, therefore to a higher risk of developing more severe symptoms or more associated allergic diseases, even if the serum IgE remains low.

Genetic Variation along the Histamine Pathway in Children with Allergic versus Nonallergic Asthma

Histamine is an important mediator in the pathogenesis of asthma. Variation in genes along the histamine production, response, and degradation pathway may be important in predicting response to antihistamines. We hypothesize that differences exist among single-nucleotide polymorphisms (SNPs) in genes of the histamine pathway between children with allergic versus nonallergic asthma. Children (7-18 yr of age; n = 202) with asthma were classified as allergic or nonallergic based on allergy skin testing. Genotyping was performed to detect known SNPs (n = 10) among genes (HDC, HNMT, ABP1, HRH1, and HRH4) within the histamine pathway. Chi square tests and Cochran-Armitage Trend were used to identify associations between genetic variants and allergic or nonallergic asthma. Significance was determined by P < 0.05 and false-positive report probability. After correction for race differences in genotype were observed, HRH1-17 TT (6% allergic versus 0% nonallergic; P = 0.04), HNMT-464 TT (41% allergic versus 29% nonallergic; P = 0.04), and HNMT-1639 TT (30% allergic versus 20% nonallergic; P = 0.04) were overrepresented among children with allergic asthma. Genotype differences specifically among the African-American children were also observed: HRH1-17 TT (13% allergic versus 0% nonallergic; P = 0.04) and HNMT-1639 TT (23% allergic versus 3% nonallergic; P = 0.03) genotypes were overrepresented among African-American children with allergic asthma. Our study suggests that genetic variation within the histamine pathway may be associated with an allergic versus nonallergic asthma phenotype. Further studies are needed to determine the functional significance of identified SNPs and their impact on antihistamine response in patients with asthma and allergic disease.

Mutations in the histamine N-methyltransferase gene, HNMT, are associated with nonsyndromic autosomal recessive intellectual disability

Histamine (HA) acts as a neurotransmitter in the brain, which participates in the regulation of many biological processes including inflammation, gastric acid secretion and neuromodulation. The enzyme histamine N-methyltransferase (HNMT) inactivates HA by transferring a methyl group from S-adenosyl-l-methionine to HA, and is the only well-known pathway for termination of neurotransmission actions of HA in mammalian central nervous system. We performed autozygosity mapping followed by targeted exome sequencing and identified two homozygous HNMT alterations, p.Gly60Asp and p.Leu208Pro, in patients affected with nonsyndromic autosomal recessive intellectual disability from two unrelated consanguineous families of Turkish and Kurdish ancestry, respectively. We verified the complete absence of a functional HNMT in patients using in vitro toxicology assay. Using mutant and wild-type DNA constructs as well as in silico protein modeling, we confirmed that p.Gly60Asp disrupts the enzymatic activity of the protein, and that p.Leu208Pro results in reduced protein stability, resulting in decreased HA inactivation. Our results highlight the importance of inclusion of HNMT for genetic testing of individuals presenting with intellectual disability.

Association of histamine N-methyltransferase Thr105Ile polymorphism with Parkinson's disease and schizophrenia in Han Chinese: a case-control study

Parkinson’s disease (PD) and schizophrenia (SCZ) are frequent central nervous disorders that have unclear etiologies but that show similarities in their pathogenesis. Since elevated histamine levels in the brain have been associated with PD and SCZ, we wanted to explore whether the Thr105Ile substitution in the histamine N-methyltransferase gene (HNMT-Thr105Ile), which impairs histamine degradation, is associated with either disease. We used the ligase detection reaction to genotype a case-control cohort of Han Chinese patients with PD or SCZ and healthy controls at the HNMT-Thr105Ile locus. The Ile allele was associated with reduced risk of PD (OR 0.516, 95%CI 0.318 to 0.838, p = 0.007) and of SCZ (OR 0.499, 95%CI 0.288 to 0.865, p = 0.011). Genotype frequencies and minor allele frequencies were similar between patients and controls when we compared males with females or early-onset patients with late-onset ones. Genotype and allele frequencies were not significantly different between PD patients with dyskinesia and PD patients without dyskinesia. Our results suggest that the heterozygous Thr/Ile genotype at the HNMT-Thr105Ile locus and the minor Ile105 allele protect against PD and SCZ in Han Chinese.

Genetic variation within the histamine pathway among patients with asthma--a pilot study

OBJECTIVE

Histamine is an important mediator in the pathophysiology of asthma. We have previously reported that HRH1 is differentially expressed among those with asthma compared to those without asthma. Single histamine-related genes have also been associated with asthma. We aimed to evaluate known single nucleotide polymorphisms (SNPs) in genes along the histamine biotransformation and response pathway, and determine their association with asthma and HRH1 mRNA expression.

METHODS

We enrolled children and adults (n = 93) with/without asthma who met inclusion/exclusion criteria. Genotyping was performed for nine known SNPs in the HDC, HRH1, HRH4, HNMT and ABP1 genes. HRH1 mRNA expression was determined on RNA from buccal tissue. General linear model, Fisher's exact test and Chi-square test were used to determine differences in allele, genotype and haplotype frequency between subjects with and without asthma and differential HRH1 mRNA expression relative to genotype. Statistical significance was determined by p < 0.05.

RESULTS

No difference was observed in genotype/allele frequency for the nine SNPs between subjects with and without asthma. The HNMT-1639C/-464C/314C/3'UTRA haplotype was more frequently observed in those without asthma than those with asthma (p = 0.03). We also observed genetic differences relative to race and gender. HNMT 314 genotype CT was more frequent in males with asthma compared to those without asthma (p = 0.04).

CONCLUSIONS

Histamine pathway haplotype was associated with a diagnosis of asthma in our cohort but allele and genotype were not. Subgroup evaluations may also be important. Further studies are needed to determine the potential biological/clinical significance of our findings.

Association of myasthenia gravis with polymorphisms in the gene of histamine N-methyltransferase

INTRODUCTION

Histamine N-methyltransferase (HNMT) is the main metabolizing enzyme of histamine. Histamine modulates immune responses and plays a role in the pathogenesis of autoimmune disorders.

METHODS

The non-synonymous HNMT C314T polymorphism and the A939G single-nucleotide polymorphism (SNP) influencing HNMT mRNA stability were genotyped in 213 patients with myasthenia gravis (MG) and 342 healthy controls.

RESULTS

The carrier frequency of the A allele of the A939G SNP was over-represented among patients with anti-AchR and anti-Titin antibodies (P = 0.05 and P = 0.004, respectively); the presence of the minor G allele was protective against anti-AchR and anti-Titin positive MG (OR = 0.67 and OR = 0.54, respectively). The combination of the G allele carrier status with wild-type C314C homozygosity was also protective against MG (OR = 0.55, P = 0.008) and against the development of anti-AchR antibodies (OR = 0.37, P = 0.01).

DISCUSSION

The A939G HNMT polymorphism is associated with autoimmune MG, while no association with C314T SNP was found.

Lack of association of plasma histamine with diamine oxidase in chronic idiopathic urticaria

BACKGROUND

Chronic idiopathic urticaria (CIU) is considered a complex and multifactorial disease. Excessive histamine intake may induce an attack of urticaria. The main enzyme for histamine metabolism is diamine oxidase (DAO).

OBJECTIVE

Plasma histamine concentrations and DAO activities were evaluated to determine whether there are abnormalities in the histamine metabolism of CIU patients.

METHODS

Seventy-five CIU patients and twenty-five healthy control subjects were included in the study. Blood was taken from all subjects to measure plasma levels of the histamine and DAO.

RESULTS

Mean plasma histamine levels were significantly higher in CIU patients (11.59±10.98 nM) than in the control subjects (8.75±2.55 nM) (p=0.04). Mean DAO activities were lower in patients of CIU (80.86±26.81 histamine degrading unit [HDU]/ml) than in the controls (81.60±9.67 HDU/ml), but without significant difference. In 15 CIU patients with gastrointestinal symptoms, the mean histamine concentration was higher (12.43±7.97 nM) and DAO activity was lower (77.93±27.53 HDU/ml) than in the remaining 60 CIU patients without gastrointestinal symptoms (11.38±11.67 nM and 81.58±26.82 HDU/ml), without significant difference. The relationship between DAO activity and plasma histamine concentrations showed a significant negative linear value (p=0.001). There were no significant relationships between plasma histamine concentrations and symptom severity score.

CONCLUSION

In CIU patients, a high plasma histamine concentration may not be explained by DAO activity. CIU patients with gastrointestinal (GI) symptoms showed no significantly lower DAO activity. Larger group studies are required to elucidate the relationship between plasma histamine concentrations and DAO activity, especially of CIU patients with GI symptomsto understand the difference in CIU patients with and without GI symptoms.

Defining risk factors for red man syndrome in children and adults

BACKGROUND

Red man syndrome (RMS) is a well-known adverse reaction that occurs in pediatric patients receiving vancomycin, yet reported prevalence is varied, and characteristics and risk factors are not well understood. Our objective was to determine the prevalence, characteristics and risk factors for RMS in pediatric patients receiving vancomycin, including contributing genetic factors.

METHODS

A multicenter retrospective study of 546 subjects (0.5-21 years) who received at least 1 dose of intravenous vancomycin was conducted. Demographic and symptom data were collected through chart review and parent/nurse report. Genotype analysis included 10 single nucleotide polymorphisms in the histamine pathway.

RESULTS

RMS was observed in 77 (14%) subjects receiving vancomycin. Forty percent of subjects with RMS symptoms developed rash, pruritis and flushing, without hypotension. Antecedent antihistamine use was identified as a risk factor for RMS (P < 0.001). Multivariate regression analysis identified age > 2 years (P = 0.008), previous RMS (P < 0.001), vancomycin dose (P = 0.02) and vancomycin concentration (P = 0.017) as RMS risk factors, whereas African American race was protective (P = 0.011). We observed an apparent association between RMS and a single nucleotide polymorphism in the diamine oxidasegene (P = 0.044); however, no associations were revealed by multifactor dimensionality reduction analysis.

CONCLUSIONS

RMS is a common adverse event in children receiving vancomycin. Identified risk factors are Caucasian ethnicity, age ≥ 2 years, previous RMS history, vancomycin dose ≥ 10 mg/kg, vancomycin concentration ≥ 5 mg/mL and antecedent antihistamine use. Known genetic variants in histamine metabolism or receptors do not appear to be substantial contributors to risk of RMS.

Involvement of human histamine N-methyltransferase gene polymorphisms in susceptibility to atopic dermatitis in korean children

Purpose

Histamine N-methyltransferase (HNMT) catalyzes one of two major histamine metabolic pathways. Histamine is a mediator of pruritus in atopic dermatitis (AD). The aim of this study was to evaluate the association between HNMT polymorphisms and AD in children.

Methods

We genotyped 763 Korean children for allelic determinants at four polymorphic sites in the HNMT gene: -465T>C, -413C>T, 314C>T, and 939A>G. Genotyping was performed using a TaqMan fluorogenic 5' nuclease assay. The functional effect of the 939A>G polymorphism was analyzed.

Results

Of the 763 children, 520 had eczema and 542 had atopy. Distributions of the genotype and allele frequencies of the HNMT 314C>T polymorphism were significantly associated with non-atopic eczema (P=0.004), and those of HNMT 939A>G were significantly associated with eczema in the atopy groups (P=0.048). Frequency distributions of HNMT -465T>C and -413C>T were not associated with eczema. Subjects who were AA homozygous or AG heterozygous for 939A>G showed significantly higher immunoglobulin E levels than subjects who were GG homozygous (P=0.009). In U937 cells, the variant genotype reporter construct had significantly higher mRNA stability (P<0.001) and HNMT enzyme activity (P<0.001) than the common genotype.

Conclusions

Polymorphisms in HNMT appear to confer susceptibility to AD in Korean children.

No association between histamine N-methyltransferase functional polymorphism Thr105Ile and Alzheimer's disease

Several abnormalities, including lower histamine levels in brain, elevated serum histamine and degeneration of histaminergic neurons in tuberomammillary nucleus, were described in the histaminergic system of patients with Alzheimer's disease (AD). Histamine is a central neurotransmitter with several functions in brain including regulation of memory, cognition, locomotion, and is degraded in part by histamine N-methyltransferase (HNMT). A common Thr105Ile polymorphism within HNMT gene results in decreased enzyme activity. The Thr105Ile polymorphism was associated with Parkinson's disease, essential tremor, attention-deficit hyperactivity disorder (ADHD), asthma and alcoholism, thus we tested possible association of HNMT functional polymorphism with AD. We have tested 256 AD cases and 1190 healthy controls of Croatian origin. Thr105Ile polymorphism was determined by TaqMan RT-PCR Genotyping Assay and EcoRV digestion. Prevalence of functional HNMT polymorphism among all tested groups was similar and frequency of less active Ile105 variant was 11.5% among AD patients and 13.4% for healthy controls (p=0.26, X(2)=1.25). Our results indicate lack of the association of HNMT Thr105Ile functional polymorphism with Alzheimer's disease.

Variability of the L-Histidine decarboxylase gene in allergic rhinitis

BACKGROUND

Nonsynonymous polymorphisms in genes coding for histamine-metabolizing enzymes, diamine oxidase and histamine N-methyltransferase are related to the risk of developing allergic diseases. The role of polymorphisms in the histidine decarboxylase gene remains unexplored. The objective of this study is to identify novel polymorphisms in the human histidine decarboxylase gene and to analyse the clinical association of nonsynonymous polymorphisms with rhinitis.

METHODS

We performed a single-strand conformational polymorphism analysis of the histidine decarboxylase gene sequence. The presence of two nonsynonymous polymorphisms Thr31Met (rs17740607) and Glu644Asp (rs2073440) was analysed in 442 unrelated patients with allergic rhinitis, 233 of whom also had asthma, and in 486 healthy subjects.

RESULTS

We observed three novel polymorphisms designated as ss50402829, ss50402830 and ss50402831-(rs17740607) with allele frequencies = 0.005, 0.208 and 0.073, respectively. Statistically significant differences were observed for the histidine decarboxylase Glu644Asp (rs2073440) polymorphism, with OR (95% CI) values for homozygous carriers of the Glu644 allele equal to 3.12 (1.75-5.56, P < 0.00005) for all patients, 3.38 (1.54-7.44, P = 0.002) for patients with rhinitis alone, and 2.92 (1.43-5.95), P = 0.003 for patients with rhinitis + asthma, when compared with healthy controls. A significant Glu644 gene-dose effect was observed for overall patients (P = 0.0001), for patients with rhinitis alone (P = 0.005) and for patients with rhinitis + asthma (P = 0.010).

CONCLUSIONS

The HDC allele Glu644 in homozygosity increases the risk of developing rhinitis in the studied population. This adds to increasing evidence supporting a prominent role of genetic variations related to histamine homeostasis in the risk to develop allergic diseases.

Polymorphisms of two histamine-metabolizing enzymes genes and childhood allergic asthma: a case control study

Background

Histamine-metabolizing enzymes (N-methyltransferase and amiloride binding protein 1) are responsible for histamine degradation, a biogenic amine involved in allergic inflammation. Genetic variants of HNMT and ABP1 genes were found to be associated with altered enzyme activity. We hypothesized that alleles leading to decreased enzyme activity and, therefore, decreased inactivation of histamine may be responsible for altered susceptibility to asthma.

Methods

The aim of this study was to analyze polymorphisms within the HNMT and ABP1 genes in the group of 149 asthmatic children and in the group of 156 healthy children. The genetic analysis involved four polymorphisms of the HNMT gene: rs2071048 (-1637T/C), rs11569723 (-411C/T), rs1801105 (Thr105Ile = 314C/T) and rs1050891 (1097A/T) and rs1049793 (His645Asp) polymorphism for ABP1 gene. Genotyping was performed with use of PCR-RFLP. Statistical analysis was performed using Statistica software; linkage disequilibrium analysis was done with use of Haploview software.

Results

We found an association of TT genotype and T allele of Thr105Ile polymorphism of HNMT gene with asthma. For other polymorphisms for HNMT and ABP1 genes, we have not observed relationship with asthma although the statistical power for some SNPs might not have been sufficient to detect an association. In linkage disequilibrium analysis, moderate linkage was found between -1637C/T and -411C/T polymorphisms of HNMT gene. However, no significant differences in haplotype frequencies were found between the group of the patients and the control group.

Conclusions

Our results indicate modifying influence of histamine N-methyltransferase functional polymorphism on the risk of asthma. The other HNMT polymorphisms and ABP1 functional polymorphism seem unlikely to affect the risk of asthma.

Histamine pharmacogenomics

Genetic polymorphisms for histamine-metabolizing enzymes are responsible for interindividual variation in histamine metabolism and are associated with diverse diseases. Initial reports on polymorphisms of histamine-related genes including those coding for the enzymes histidine decarboxylase (HDC), diamine oxidase (ABP1) and histamine N-methyltransferase (HNMT), as well as histamine receptor genes, often have pointed to polymorphisms that occur with extremely low frequencies or that could not be verified by later studies. In contrast, common and functionally significant polymorphisms recently described have been omitted in many association studies. In this review we analyze allele frequencies, functional and clinical impact and interethnic variability on histamine-related polymorphisms. The most relevant nonsynonymous polymorphisms for the HDC gene are rs17740607 Met31Thr, rs16963486 Leu553Phe and rs2073440 Asp644Glu. For ABP1 the most relevant polymorphisms are rs10156191 Thr16Met, rs1049742 Ser332Phe, and particularly because of its functional effect, rs1049793 His645Asp. In addition the ABP1 polymorphisms rs45558339 Ile479Met and rs35070995 His659Asn are relevant to Asian and African subjects, respectively. For HNMT the only nonsynonymous polymorphism present with a relevant frequency is rs1801105 Thr105Ile. For HRH1 the polymorphism rs7651620 Glu270Gly is relevant to African subjects only. The HRH2 rs2067474 polymorphism, located in an enhancer element of the gene promoter, is common in all populations. No common nonsynonymous SNPs were observed in the HRH3 gene and two SNPs were observed with a significant frequency in the HRH4 gene: rs11665084 Ala138Val and rs11662595 His206Arg. This review summarizes relevant polymorphisms, discusses controversial findings on association of histamine-related polymorphisms and allergies and other diseases, and identifies topics requiring further investigation.

Association of the histamine N-methyltransferase C314T (Thr105Ile) polymorphism with atopic dermatitis in Caucasian children

STUDY OBJECTIVE

To investigate potential associations between the histamine N-methyltransferase (HNMT) gene, HNMT, C314T (Thr105Ile) polymorphism and atopic dermatitis in a cohort of Caucasian children.

DESIGN

Prospective, multicenter, genotype-association study.

SETTING

Four academic, tertiary care medical centers within the Pediatric Pharmacology Research Unit network.

PARTICIPANTS

Two hundred forty-nine Caucasian children aged 6 months-5 years with atopic dermatitis (127 patients) or without (122 control subjects).

INTERVENTION

Buccal swabs (one swab/cheek) were performed to obtain epithelial cells for extraction of genomic DNA.

MEASUREMENTS AND MAIN RESULTS

Data were collected on severity of atopic dermatitis, oral antihistamine treatment, and treatment response through parental report. The HNMT genotypes were successfully obtained in 116 control subjects and 122 patients with atopic dermatitis. Frequencies of the T314 variant allele (0.12 vs 0.06, p=0.04) and combined CT/TT genotype (0.24 vs 0.12, p=0.02) were significantly higher in children with atopic dermatitis compared with control subjects. Children with genotypes conferring reduced HNMT activity were 2 times more likely to have atopic dermatitis than those who were homozygous for the C314 reference allele.

CONCLUSION

Increased histamine levels in patients with atopic dermatitis may result, at least in part, from reduced enzymatic inactivation via HNMT. Genetically associated reduction in histamine biotransformation may therefore contribute to the pathogenesis, persistence, and progression of atopic dermatitis. If confirmed, these data indicate that HNMT genotype might represent a common risk factor for development of atopic dermatitis, asthma, and allergic rhinitis and may be useful in identifying individuals who are candidates for early preventive pharmacotherapeutic intervention. Additional longitudinal studies will be required to assess the relationship between genotype, disease severity, and antihistamine response.

Histamine N-methyltransferase 939A>G polymorphism affects mRNA stability in patients with acetylsalicylic acid-intolerant chronic urticaria

BACKGROUND

Histamine plays an important role in allergic inflammation. Histamine levels are regulated by histamine N-methyltransferase (HNMT).

OBJECTIVE

To investigate the functional variability of HNMT gene in relation to genetic polymorphisms in patients with aspirin intolerant chronic urticaria (AICU).

METHODS

Two single-nucleotide polymorphisms of the HNMT gene (314C>T, 939A>G) were genotyped in chronic urticaria patients. The functional variability of 3'-untranslated region polymorphism (3'-UTR) was assessed using the pEGFP-HNMT 3'-UTR reporter construct to examine mRNA stability and fluorescence-tagged protein expression. The HNMT enzymatic activities related to the 939A>G polymorphism were examined both in the human mast cells (HMC-1) transfected with the pHNMT CDS-3'-UTR construct and in the patients' red blood cells (RBCs). Histamine release from the basophils of AICU patients was examined.

RESULTS

The 939A>G polymorphism was significantly associated with the AICU phenotype, while no association was found with the 314C>T polymorphism. An in vitro functional study using HMC-1 cells demonstrated that the 939A allele gave lower levels of HNMT mRNA stability, HNMT protein expression, and HNMT enzymatic activity and higher histamine release than the 939G allele. The in vivo functional study demonstrated that the AICU patients with the 939A allele had lower HNMT activity in RBC lysates and higher histamine release from their basophils.

CONCLUSION

The HNMT 939A>G polymorphism lowers HNMT enzymatic activity by decreasing HNMT mRNA stability, which leads to an increase in the histamine level and contributes to the development of AICU.

The histamine N-methyltransferase T105I polymorphism affects active site structure and dynamics

Histamine N-methyltransferase (HNMT) is the primary enzyme responsible for inactivating histamine in the mammalian brain. The human HNMT gene contains a common threonine-isoleucine polymorphism at residue 105, distal from the active site. The 105I variant has decreased activity and lower protein levels than the 105T protein. Crystal structures of both variants have been determined but reveal little regarding how the T105I polymorphism affects activity. We performed molecular dynamics simulations for both 105T and 105I at 37 degrees C to explore the structural and dynamic consequences of the polymorphism. The simulations indicate that replacing Thr with the larger Ile residue leads to greater burial of residue 105 and heightened intramolecular interactions between residue 105 and residues within helix alpha3 and strand beta3. This altered, tighter packing is translated to the active site, resulting in the reorientation of several cosubstrate-binding residues. The simulations also show that the hydrophobic histamine-binding domain in both proteins undergoes a large-scale breathing motion that exposes key catalytic residues and lowers the hydrophobicity of the substrate-binding site.

C314T polymorphism in histamine N-methyltransferase gene and susceptibility to duodenal ulcer in Chinese population

BACKGROUND

Histamine is a regulator of gastric acid secretion, which is involved in the development of duodenal ulcer (DU). Histamine is metabolized by both histamine N-methyltransferase (HNMT) and diamine oxidase, and its local action is terminated primarily by methylation which is catalyzed by HNMT.

METHODS

Polymerase chain reaction-restriction fragment length polymorphism assay was used to identify the polymorphism of the point mutation C314T of HNMT gene of 498 Chinese patients with DU and 151 healthy individuals.

RESULTS

In normal controls, the allele frequency of HNMT T314 was 3.3%, which was significantly lower than American Caucasians. The HNMT T314 allele was detected in 3.5% of the DU patients. In cases and controls, the frequency of C/C genotypes were 93.0% and 93.4%, respectively. The HNMT T/T genotype was not found in this population. No significant differences were seen in both genotype frequencies and allele frequencies between DU groups and controls. After stratified by H. pylori infection, they also could not reach significant differences in our current study.

CONCLUSION

The HNMT T314 allele frequency is lower in Chinese population than in American Caucasians. No association can be found in the involvement of HNMT C314T polymorphism in the susceptibility to duodenal ulcer.

Gene expression programs of human smooth muscle cells: tissue-specific differentiation and prognostic significance in breast cancers

Smooth muscle is present in a wide variety of anatomical locations, such as blood vessels, various visceral organs, and hair follicles. Contraction of smooth muscle is central to functions as diverse as peristalsis, urination, respiration, and the maintenance of vascular tone. Despite the varied physiological roles of smooth muscle cells (SMCs), we possess only a limited knowledge of the heterogeneity underlying their functional and anatomic specializations. As a step toward understanding the intrinsic differences between SMCs from different anatomical locations, we used DNA microarrays to profile global gene expression patterns in 36 SMC samples from various tissues after propagation under defined conditions in cell culture. Significant variations were found between the cells isolated from blood vessels, bronchi, and visceral organs. Furthermore, pervasive differences were noted within the visceral organ subgroups that appear to reflect the distinct molecular pathways essential for organogenesis as well as those involved in organ-specific contractile and physiological properties. Finally, we sought to understand how this diversity may contribute to SMC-involving pathology. We found that a gene expression signature of the responses of vascular SMCs to serum exposure is associated with a significantly poorer prognosis in human cancers, potentially linking vascular injury response to tumor progression.

Polymorphisms of histamine-metabolizing enzymes and clinical manifestations of asthma and allergic rhinitis

BACKGROUND

Polymorphisms of enzymes involved in histamine biodisposition may affect clinical symptoms in diseases related to histamine, such as asthma or allergic rhinitis (AR).

OBJECTIVE

This study aims to analyse two common polymorphisms in genes coding for histamine-metabolizing enzymes in patients with allergic diseases.

METHODS

Five-hundred and sixty-five individuals participated in the study, including 270 unrelated patients with asthma and/or AR recruited from a single centre and 295 healthy volunteers. Participants were analysed for the presence of Thr105Ile and His645Asp amino acid substitutions at histamine N-methyltransferase (HNMT) and diamine oxidase (amiloride binding protein 1) enzymes, respectively, by amplification-restriction procedures.

RESULTS

The variant HNMT allele frequencies were slightly higher among patients with asthma [16.0%, 95% confidence interval (CI) 12.0-20.0] and among patients with rhinitis (13.2, 95% CI 10.3-16.1) as compared with healthy subjects (11.5 95% CI 8.9-14.1). The variant ABP1 allele frequencies were similar among patients with asthma (30.8%, 95% CI 25.7-35.9), rhinitis (28.7, 95% CI 24.8-32.6) and healthy subjects (26.8 95% CI 23.2-30.3). Individuals carrying mutated ABP1 alleles presented allergy symptoms with significantly lower IgE levels as compared with individuals without mutated genes, with a significant gene-dose effect (P<0.001). In addition, the percentage of individuals presenting symptoms without eosinophilia was significantly higher among homozygous carriers of ABP1 variant alleles (P<0.020) as compared with the rest of the atopic patients.

CONCLUSION

There is a lack of association between the allelic variants studied and the risk of developing allergic asthma and rhinitis. However, patients carrying the His645Asp polymorphism of ABP1 are more prone to developing symptoms with lower IgE levels.

Molecular mechanisms of primary and secondary mucosal immunity using avian infectious bronchitis virus as a model system

Although mucosal immune responses are critical for protection of hosts from clinical illness and even mortality caused by mucosal pathogens, the molecular mechanism of mucosal immunity, which is independent of systemic immunity, remains elusive. To explore the mechanistic basis of mucosal protective immunity, gene transcriptional profiling in mucosal tissues was evaluated after the primary and secondary immunization of animals with an attenuated avian infectious bronchitis virus (IBV), a prototype of Coronavirus and a well-characterized mucosal pathogen. Results showed that a number of innate immune factors including toll-like receptors (TLRs), retinoic-acid-inducible gene-1 (RIG-1), type I interferons (IFNs), complements, and interleukin-1 beta (IL-1β) were activated locally after the primary immunization. This was accompanied or immediately followed by a potent Th1 adaptive immunity as evidenced by the activation of T-cell signaling molecules, surface markers, and effector molecules. A strong humoral immune response as supported by the significantly up-regulated immunoglobulin (Ig) gamma chain was observed in the absence of innate, Th1 adaptive immunity, or IgA up-regulation after the secondary immunization, indicating that the local memory response is dominated by IgG. Overall, the results provided the first detailed kinetics on the molecular basis underlying the development of primary and secondary mucosal immunity. The key molecular signatures identified may provide new opportunities for improved prophylactic and therapeutic strategies to combat mucosal infections.

Histamine in food: is there anything to worry about?

Biogenic mono-, di- and poly-amines are widely distributed among living organisms. The amines fulfil many important functions in the human body both in the periphery and brain. Some authors suggest that foods rich in biogenic amines, especially histamine, present high health hazards for consumers. However, this is conditional on a range of other factors. The alimentary tract is well equipped with enzymes that inactivate amines and the blood-brain barrier prevents them entering the brain from the circulation. Oxidative deamination, methylation, acetylation and transglutamylation are the degradation pathways which operate efficiently in the stomach, intestines and liver. Particularly important is oxidative deamination. Food histamine poisoning or cheese reaction, manifested itself in patients treated with drugs that inhibit amine oxidases or in patients showing an enterocytic diamine oxidase deficit. It is rather food allergy, which should worry us more, as endogenous histamine release from mast cells is more dangerous. Preventive measures should be undertaken against increases in food allergies.

[Asthma genetic factors]

Asthma is a chronic inflammatory airways disease, with a rising prevalence, particularly in childhood, and is considered an important public health problem. Its familial transmission is recognised, while the description and identification of the genes implicated in this disease are a challenge. In this revision paper the authors give a comprehensive explanation of the associated genes as well as the laboratorial methods that allow their identification.

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.

Association of THR105Ile, a functional polymorphism of histamine N-methyltransferase (HNMT), with alcoholism in German Caucasians

BACKGROUND

CNS histamine has been shown to have an inhibitory effect on reward and it is implicated in the etiology of addiction and stress. Histamine N-methyltransferase (HNMT) is believed to be the sole pathway for termination of the neurotransmitter action of histamine in mammalian brain. A common, functional polymorphism, a C314T transition in the HNMT gene, results in a Thr105Ile substitution of the protein encoded. A recent study has shown that the frequency of the Ile105 allele was significantly lower in alcoholics compared to that in non-alcoholics in Finns and Plains American Indians. Following up these results, we tested whether the Thr105Ile polymorphism was associated with alcoholism in German Caucasians.

METHODS

Thr105Ile was genotyped in n=366 psychiatrically interviewed German Caucasian ICD-10 lifetime alcoholics, along with n=200 ethnically matched controls.

RESULTS

No significant difference was found in the frequency of the Ile105 allele between alcoholics (0.11) and controls (0.10) (chi(2)=0.21, d.f.=1, p=0.647). Likewise, genotype distributions did not differ significantly. However, the frequency of the Ile105 allele was significantly lower in male alcoholics with a family history of alcoholism compared to that in male alcoholics without a family history of alcoholism (chi(2)=4.07, d.f.=1, p=0.044).

CONCLUSIONS

In German Caucasians the association of the HNMT Thr105Ile polymorphism with alcoholism was not replicated per se, but a congruent association was found between the Ile105 allele and family history of alcoholism supporting the protective role of the Ile105 allele against alcoholism.

Altered methylprednisolone pharmacodynamics in healthy subjects with histamine N-methyltransferase C314T genetic polymorphism

This study investigated the potential differences in methylprednisolone pharmacodynamics between healthy subjects with different histamine N-methyltransferase (HNMT) C314T genotypes. Six individuals with C/C genotype and 4 with C/T genotype were administered a single intravenous dose of methylprednisolone 0.6 mg/kg ideal body weight in a randomized 2-period manner. Methylprednisolone plasma concentrations were fitted with a 1-compartment model. Cortisol and whole blood histamine suppression were assessed by indirect response models, with circadian baseline cortisol analyzed by Fourier analysis. The area between the baseline and effect curve and the area under the effect versus time curve suppression ratio were used to characterize plasma histamine suppression. Methylprednisolone pharmacokinetics and plasma and whole blood histamine suppression were similar between the 2 genotype groups. Median nadir of cortisol and the 50% inhibitory concentration for cortisol were significantly higher in subjects with C/T genotype than those with C/C genotype (P=.031 and .033, respectively, Wilcoxon rank sum test). Subjects who are heterozygous for the T314 variant allele thus appeared less sensitive to the suppressive effects of methylprednisolone on cortisol secretion.

Endogenous histamine and cortisol levels in subjects with different histamine N-methyltransferase C314T genotypes : a pilot study

BACKGROUND

Histamine N-methyltransferase (HNMT) catalyzes the methylation of histamine and plays an important role in histamine biotransformation in bronchial epithelium. Enzymatic activity of HNMT has been shown to be regulated by genetic factors, including polymorphisms in the HNMT gene. In this pilot study we determined endogenous levels of histamine and cortisol in plasma and whole blood samples from subjects with different genotypes for the HNMT C314T polymorphism, and investigated whether these parameters differed between individuals with the HNMT CC genotype and those with the CT genotype.

METHODS

Blood samples were collected from 48 unrelated volunteers (36 males, 12 females), aged 21-40 years, who participated in the study. PCR-restriction fragment length polymorphism analysis was used to determine HNMT C314T genotypes. Erythrocyte HNMT activity was determined as well as plasma and whole blood levels of histamine and cortisol. Two-group comparisons of the various parameters were analyzed by Blocked Wilcoxon test and Wilcoxon Rank Sum test as appropriate.

RESULTS

Thirty-seven subjects (24 Caucasians, three African Americans, one Middle Eastern, five Indians, three Chinese, and one Filipino) were found to have the homozygous CC genotype. Ten subjects (eight Caucasians, one Middle Eastern, and one Chinese) were heterozygous and one individual (Pakistani) was homozygous for the variant 314T allele. The frequency of HNMT CT heterozygotes in the small Caucasian cohort was 0.125. Median enzyme activity was significantly lower in subjects with the heterozygous CT genotype than in those with the homozygous CC genotype (485 vs 631 U/mL of red blood cells; p=0.023). A broad range of histamine levels in plasma and whole blood was observed for all subjects. Whereas the median plasma histamine level was found to be higher in heterozygotes for the wild-type 314C allele than homozygotes (3.32 vs 2.30 nmol/L; p=0.021), there was no difference between the two groups in histamine levels in whole blood. Cortisol levels were similar between individuals with the homozygous CC genotype and those with the heterozygous CT genotype.

CONCLUSION

Wide variability of plasma and whole-blood histamine levels was observed in subjects with different HNMT C314T genotypes. Endogenous levels of histamine are likely to be affected by various genes and polymorphisms.

Pharmacogenomics: catechol O-methyltransferase to thiopurine S-methyltransferase

1. Pharmacogenomics is the study of the role of inheritance in variation in the drug response phenotype-a phenotype that can vary from adverse drug reactions at one end of the spectrum to lack of therapeutic efficacy at the other. 2. The thiopurine S-methyltransferase (TPMT) genetic polymorphism represents one of the best characterized and most clinically relevant examples of pharmacogenomics. This polymorphism has also served as a valuable "model system" for studies of the ways in which variation in DNA sequence might influence function. 3. The discovery and characterization of the TPMT polymorphism grew directly out of pharmacogenomic studies of catechol O-methyltransferase (COMT), an enzyme discovered by Julius (Julie) Axelrod and his coworkers. 4. This review will outline the process by which common, functionally significant genetic polymorphisms for both COMT and TPMT were discovered and will use these two methyltransferase enzymes to illustrate general principles of pharmacogenomic research-both basic mechanistic and clinical translational research-principles that have been applied to a series of genes encoding methyltransferase enzymes.

Evidence for a reduced histamine degradation capacity in a subgroup of patients with atopic eczema

BACKGROUND

A diminished histamine degradation based on a reduced diaminoxidase activity is suspected as a reason for non-IgE-mediated food intolerance caused by histamine. Atopic eczema (AE) is often complicated by relapses triggered by IgE-mediated allergy to different kinds of food. However, in a subgroup of patients with AE, allergy testing proves negative, although these patients report a coherence of food intake and worsening of AE and describe symptoms that are very similar to histamine intolerance (HIT).

OBJECTIVES

It was the aim of our study to evaluate symptoms of HIT in combination with diaminoxidase levels in a total of 360 individuals consisting of patients with AE (n = 162) in comparison with patients with HIT (n = 124) without AE and healthy control volunteers (n = 85).

METHODS

Histamine plasma level was determined with an ELISA and diaminoxidase serum activity with the help of radio extraction assays using [3H]-labeled putrescine-dihydrochloride as a substrate. Detailed clinical evaluations of characteristic features of AE and HIT were performed.

RESULTS

Reduced diaminoxidase serum levels leading to occurrence of HIT symptoms like chronic headache, dysmenorrhea, flushing, gastrointestinal symptoms, and intolerance of histamine-rich food and alcohol were significantly more common in patients with AE than in controls. Reduction of both symptoms of HIT and Severity Scoring of Atopic Dermatitis could be achieved by a histamine-free diet in the subgroup of patients with AE and low diaminoxidase serum levels.

CONCLUSION

Higher histamine plasma levels combined with a reduced histamine degradation capacity might influence the clinical course of a subgroup of patients with AE.

CLINICAL IMPLICATIONS

As HIT emerges in a subgroup of patients with AE, a detailed anamnestic evaluation of food intolerance and HIT symptoms complemented by an allergological screening for food allergy, a diet diary, and, in confirmed suspicion of HIT, measurement of diaminoxidase activity and a histamine-free diet should be undertaken.

In-Silico Pharmacodynamics

Adverse effects are exhibited by most drugs in current clinical practice, the causes for which are often not known. In this post genomic era, bioinformatics has the potential to address several issues in understanding the mechanism of drug action and in designing improved drugs. This study describes the analysis of the possible pharmacodynamic behaviour of antihistamines blocking the histamine H(2) receptor (H(2)-antihistamines), by adopting the basic tenets of a systems biology approach. The different components that could form an appropriate sub-system are identified, thus providing a system landscape. Docking and analysis of the chosen antihistamines into each of these components resulted in identifying histamine N-methyl transferase (HNMT) as a potential unintended target for H(2)-antihistamines. Correlation with experimental data available from the literature indicates the inhibition of HNMT to be a possible cause for the adverse effects exhibited by these drugs. Implications for design of safer H(2)-antihistamines are discussed. The method reported here has the potential for application as a general strategy in understanding drug effects.

Lack of association of histamine-N-methyltransferase (HNMT) polymorphisms with asthma in the Indian population

Histamine plays a major role in allergic disorders, including asthma. A major pathway of histamine biotransformation in the lungs is mediated by histamine N-methyltransferase (HNMT). We investigated the association of a functional SNP C314T; a SNP A929G, a (CA)n repeat in intron 5, and a novel (CA)n repeat (BV677277), 7.5 kb downstream of the HNMT gene with asthma and its associated traits such as total serum IgE levels in a case-control as well as in a family-based study design. In contrast to a previous study, no association was observed for the polymorphisms investigated with asthma (P>0.05). When haplotypes were constructed for these loci and compared, no significant difference was observed in the distribution between cases and controls. In the family-based design, no biased transmission was observed for any of the polymorphisms and haplotypes with asthma using the additive model of inheritance in family-based association test (FBAT). Thus, consistent with the case-control findings, the polymorphisms and haplotypes in the HNMT gene are not associated with asthma in the Indian population.

Comparison of serum tryptase and urine N-methylhistamine in patients with suspected mastocytosis

BACKGROUND

The disease extent of mastocytosis can be assessed by measurement of mediators or their metabolites, secreted from mast cells. In the present study, we compared results of urinary N-methylhistamine measurements with analysis of total tryptase in serum from patients with suspected mastocytosis.

METHODS

Tryptase in serum was determined with the UniCAP tryptase fluor-enzyme-immunoassay, according to the manufacturers' instructions (Pharmacia, Woerden, Netherlands). N-methylhistamine in urine was determined by competitive radioimmunoassay, according to the manufacturers' instructions (Pharmacia).

RESULTS

A significant correlation between serum tryptase and urine N-methylhistamine was found both for 138 patients aged 14 or older (Spearman Rank r(s)=0.43, p<0.0001) and for 23 younger patients (Spearman Rank r(s)=0.46, p=0.0267). The between-run coefficient of variation of the tryptase assay was half (6.7%) of the one (13%) found with the urinary N-methylhistamine assay. Both for urine N-methylhistamine and serum tryptase, a significant difference was found between corresponding biopsies with an increased number of mast cell aggregates and biopsies without such an increase. The difference between tryptase levels however was stronger (Mann-Whitney: p=0.0012) than the difference between N-methylhistamine levels (Mann-Whitney: p=0.0140).

CONCLUSION

Serum tryptase discriminates better than urinary N-methylhistamine between patients with an increased number of mast cell aggregates and persons without such an increase.

Bronchodilator response in relation to beta2-adrenoceptor haplotype in patients with asthma

RATIONALE

Genetic variation of the beta2-adrenoceptor (ADRB2) influences receptor function in vitro. There are reports that, in vivo, bronchodilator response is related to ADRB2 genotype, and that clinical outcomes during chronic therapy with beta2-agonist drugs are also influenced by genotype. Whether these features are related to single nucleotide polymorphisms or to combinations (haplotypes) is unclear.

OBJECTIVES

Our aim was to measure bronchodilator response in patients with asthma stratified by ADRB2 haplotype. This was done after eliminating the confounding effect of prior drug treatment with inhaled beta2-agonists and corticosteroids.

METHODS

ADRB2 haplotype was determined in 176 patients with asthma, of whom 161 harbored the six most common combinations. Treatment with inhaled beta2-agonists and inhaled corticosteroids was withheld for appropriate intervals. Spirometric changes 20 minutes after a single dose of albuterol (2.5 mg by nebulizer) were then recorded.

RESULTS

There were no significant differences in bronchodilator response (% improvement in FEV(1)) with respect to any of the major ADRB2 haplotypes or genotypes.

CONCLUSIONS

Genetic variation of the ADRB2 does not influence the immediate response to inhaled beta2-agonist. The confounding effect of tolerance resulting from regular beta2-agonist use must be controlled when assessing the pharmacogenetic influences on clinical outcomes with beta2-agonists.

Polymorphisms of high-affinity IgE receptor and histamine-related genes in patients with ASA-induced urticaria/angioedema

The pathogenic mechanism of ASA-induced urticaria/angioedema (AIU) is still poorly understood, but it has been known that histamine releasing by cutaneous mast cell activation is considered to be an important role. Considering the importance of histamine in AIU, we speculated that a genetic abnormality of histamine-related genes such as a high-affinity IgE receptor, a metabolic enzyme of histamines and histamine receptors, may be involved in the development of AIU. Enrolled in the study were 110 patients with AIU, 53 patients without ASA hypersensitivity who had various drug allergies presenting as exanthematous skin symptoms, and 99 normal healthy controls (NC). Eleven single nucleotide polymorphisms (SNPs) of the beta chain of the high-affinity IgE receptor (FCER1B) and three histamine-related genes-histamine N-methyltransferase (HNMT), histamine H1 receptor (HRH1), histamine H2 receptor (HRH2)-were screened using the SNP-IT assay based on a single base extension method. No significant differences were observed in allele and genotype frequencies, and haplotype frequencies of all the SNPs of FCER1B, HNMT, HRH1, and HRH2 among the three groups (p>0.05, respectively). These results suggest that the polymorphisms of FCER1B and the three histamine-related genes may not contribute to the development of AIU phenotype in the Korean population.

Thr105Ile, a Functional Polymorphism of Histamine N-Methyltransferase, Is Associated with Alcoholism in Two Independent Populations

BACKGROUND

Histamine is expressed in cortical and limbic areas that are involved in emotion and cognition and modulates these behaviors. H1 receptor antagonists are sedative. Histamine N-methyltransferase (HNMT) catalyzes the Ntau methylation of histamine, the sole pathway for termination of the neurotransmitter action of histamine in mammalian brain. A common and functionally significant polymorphism, a C314T transition in exon 4 of the HNMT gene results in a Thr105Ile substitution of the protein encoded. The Thr105 allele is associated with approximately 2-fold higher enzyme activity, leading to the prediction that it might be associated with diminished histamine levels, resulting in differences in anxiety, cognition, and sedation that play important roles in alcoholism. In two ethnically distinct populations, we tested whether the Thr105Ile polymorphism was associated with alcoholism and with harm avoidance, a dimensional measure of anxious personality.

METHODS

A 5' exonuclease assay (TaqMan) was used to genotype Thr105Ile in psychiatrically interviewed Finnish Caucasian (n = 218) and Plains American Indian (n = 186) alcoholics, along with ethnically matched, psychiatrically interviewed, controls (Finns: n = 313, Plains Indian: n = 140).

RESULTS

Ile105 allele frequencies were significantly lower in alcoholics compared with nonalcoholics in both populations (Finns: 0.12 vs. 0.17, chi(2) = 6, p = 0.015; Plains Indians: 0.03 vs. 0.08, chi(2) = 5, p = 0.023). Genotype distributions also differed significantly. In Finns, Ile105 showed borderline significance for an association with lower harm avoidance (p = 0.070) after correcting for alcoholism diagnosis.

CONCLUSIONS

Decreased levels of brain histamine consequent to the Thr105 allele may result in higher levels of anxiety and, as a consequence, vulnerability to alcoholism.

No association of histamine- N-methyltransferase polymorphism with asthma or bronchial hyperresponsiveness in two German pediatric populations

Histamine plays an important role in the allergic inflammation. Histamin N-Methyltransferase (HNMT) catalyses the major pathway of histamine metabolism in the human lung. A common functional single nucleotide polymorphism (SNP) within the HNMT gene (C314T) was recently related to asthma. We tested this SNP for associations with asthma and asthma associated traits in two German pediatric populations (1. MAS-cohort, n=888, 85 children with asthma; 2. asthmatic children from Freiburg, n=176). Non-asthmatic (n=515) and non-atopic (n=211) children from the MAS-cohort were used as controls. For genotyping melting curve analyses (Light Cycler System) were applied. In contrast to a previous study, no association of the HNMT 314T allele with asthma, bronchial hyperresponsiveness (BHR) or other asthma related phenotypes could be observed in either study population. We conclude that this SNP might not play a major role in the pathogenesis of asthma or BHR in German children.

Protective role of glutathione S-transferase P1 (GSTP1) Val105Val genotype in patients with bronchial asthma

BACKGROUND

Glutathione S-transferase P1 (GSTP1), the abundant isoform of glutathione S-transferases (GSTs) in lung epithelium, plays an important role in cellular protection against oxidative stress and toxic foreign chemicals. It has been suggested that polymorphisms in the GSTP1 gene are associated with asthma and related phenotypes. As significant interindividual and interethnic differences exist in the distribution of xenobiotic-metabolizing enzymes, we have studied the GSTP1 Ile105Val polymorphism in patients with asthma in a Turkish sample.

METHODS

GSTP1 Ile105Val polymorphism in exon 5 was determined in 210 patients with asthma (112 extrinsic and 108 intrinsic) and 265 control individuals without lung diseases and without history of allergy or atopy, using polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) techniques.

RESULTS

The proportion of GSTP1 Val105 homozygotes was significantly lower in the patients with asthma than in the control individuals (3.8% vs 12.1%). The odds ratio for GSTP1 Val105 homozygotes vs all other genotypes was 0.29 (95%CL 0.13-0.64, p = 0.01) for asthmatics. The distribution of GSTP1 Ile105Val genotypes and the frequency of GSTP1 Val105Val homozygotes (3.7% vs 3.9%) was not significantly different between extrinsic and intrinsic asthmatics.

CONCLUSION

These results suggest a significant association between GSTP1 Ile105Val polymorphism and susceptibility to asthma and that the GSTP1 Val105Val genotype may be protective against developing this disease.

Association studies for asthma and atopic diseases: a comprehensive review of the literature

Hundreds of genetic association studies on asthma-related phenotypes have been conducted in different populations. To date, variants in 64 genes have been reported to be associated with asthma or related traits in at least one study. Of these, 33 associations were replicated in a second study, 9 associations were not replicated either in a second study or a second sample in the same study, and 22 associations were reported in just a single published study. These results suggest the potential for a great amount of heterogeneity underlying asthma. However, many of these studies are methodologically limited and their interpretation hampered by small sample sizes.