A major gene for allergy--fact or fancy?

Impact of parental asthma, prenatal maternal asthma control, and vitamin D status on risk of asthma and recurrent wheeze in 3-year-old children

BACKGROUND

While familial clustering of asthma is known, few studies have reported on the relative roles of paternal and maternal asthma and the role of maternal asthma control in pregnancy on the risk for asthma in the child.

OBJECTIVE

We aimed to investigate the relative roles of paternal asthma, maternal asthma, and maternal asthma control during pregnancy on the risk of asthma or recurrent wheeze in 3-year-old children and how prenatal and cord blood vitamin D status might affect this risk.

METHODS

Data from 806 women, their partners (biologic fathers of the infants), and their children participated in the Vitamin D Antenatal Asthma Reduction Trail (VDAART, clinicaltrials.gov identification number NCT00920621) were used for this cohort analysis. The parental report of physician-diagnosed asthma or recurrent wheeze in offspring was the main outcome. Weibull regression models for interval-censored event times were used to estimate the main variables of interests and additional covariates on the outcome.

RESULTS

The highest risk was observed among children with both parents being asthmatic relative to non-asthmatic parents (aHR = 2.30, 95% CI: 1.35-3.84), and less so if only the mother was asthmatic (aHR = 1.70, 95% CI: 1.17-2.40). In the subset of children born to asthmatic mothers, the risk for asthma was higher in those who were born to mothers whose asthma was uncontrolled (aHR = 1.60, 95% CI: 1.02-2.54). Children whose mothers had sufficient vitamin D status (25Hydroxyvitamin D ≥ 30 ng/mL) at early and late pregnancy and had cord blood vitamin D sufficiency demonstrated a lower risk of asthma/recurrent wheeze than children who had insufficient cord blood vitamin D status at birth (aHR = 0.47, 95% CI: 0.27-0.83).

CONCLUSION AND CLINICAL RELEVANCE

Careful attention to maternal asthma control, monitoring vitamin D status, and correcting insufficiency at early pregnancy and maintaining the sufficiency status throughout pregnancy have potential preventive roles in offspring asthma or recurrent wheeze.

Association of asthma with beta(2)-adrenergic receptor gene polymorphism and cigarette smoking

Recent studies have suggested that two polymorphisms of the beta(2)-adrenergic receptor (beta(2)AR) gene at codons 16 (arginine to glycine) and 27 (glutamine to glutamate) affect an individual's airway responsiveness, or response to acute or chronic beta(2)-agonist therapy but are not risk factors for asthma. We hypothesize that there is an interaction effect on asthma between the beta(2)AR gene polymorphisms and cigarette smoking. A case-control study was conducted in 128 asthma cases and 136 control individuals identified from 10,014 studied subjects in rural Anqing, China. Allele-specific polymerase chain reaction (PCR) was used to genotype beta(2)AR gene polymorphisms. Multiple logistic regression was used to adjust for potential confounding factors. We found a marginally significant interaction between cigarette smoking and beta(2)AR-16 genotype after adjusting for important confounding factors (p = 0.06). Specifically, we found that compared with never-smoking Gly-16 homozygotes, those ever-smokers who are Arg-16 homozygotes had a significantly increased risk of asthma (odds ratio [OR] = 7.81; 95% confidence interval [CI]: 2.07 to 29.5). This association showed a clear dose-response relationship with the number of cigarettes smoked. However, there was no significant association of asthma with polymorphisms of the beta(2)AR at position 27 (OR = 1.38; 95% CI: 0.69 to 2.73). Our study suggests a gene-environment interaction between the Arg-16 genotype and ever cigarette smoking with respect to the susceptibility of an individual to asthma.

Allergy-associated polymorphisms of the Fc epsilon RI beta subunit do not impact its two amplification functions

Two variants of the beta-chain of the high affinity IgE receptor Fc epsilon RI, I181L-V183L and E237G, have been found associated with allergy. We have previously shown that the beta-chain plays at least two distinct amplifier functions. It amplifies Fc epsilon RI surface expression and signaling, resulting in an estimated 12- to 30-fold amplification of downstream events. To test the hypothesis that the I181L-V183L and E237G beta variants may be functionally relevant and could directly contribute to an allergic phenotype, we have evaluated the functional impact of the beta variants on the two amplifier functions of beta. We found that these variants have no direct effect on the beta amplifier functions. However, the possibility remains that these variants are in linkage disequilibrium with other more relevant polymorphisms or are affecting unknown beta-chain functions.

The high-affinity IgE receptor (Fc epsilon RI): from physiology to pathology

The high affinity receptor for immunoglobulin E (designated Fc epsilon RI) is the member of the antigen (Ag) receptor superfamily responsible for linking pathogen-or allergen-specific IgEs with cellular immunologic effector functions. This review provides background information on Fc epsilon RI function combined with more detailed summaries of recent progress in understanding specific aspects of Fc epsilon RI biology and biochemistry. Topics covered include the coordination and function of the large multiprotein signaling complexes that are assembled when Fc epsilon RI and other Ag receptors are engaged, new information on human receptor structures and tissue distribution, and the role of the FcR beta chain in signaling and its potential contribution to atopic phenotypes.

A genome-wide search for linkage to asthma. German Asthma Genetics Group

Asthma is among the most frequent chronic diseases in childhood. Although numerous environmental risk factors have already been identified, the basis for familial occurrence of asthma remains unclear. Previous genome screens for atopy in British/Australian families and for asthma in different American populations showed inconsistent results. We report a sib pair study of a sample of 97 families, including 415 persons and 156 sib pairs. Following an extensive clinical evaluation, all participants were genotyped for 351 polymorphic dinucleotide markers. Linkage analysis for asthma identified four chromosomal regions that could to be linked to asthma: chromosome 2 (at marker D2S2298, P = 0.007), chromosome 6 (around D6S291, lowest P = 0.008), chromosome 9 (proximal to D9S1784, P = 0.007), and chromosome 12 (D12S351, P = 0.010). These linkage regions could be reproduced for all loci by analysis of total or specific immunoglobulin E (minimum P values at these regions were 0. 003, 0.001, 0.010, and 0.015, respectively).

Linkage of chromosome 5q and 11q gene markers to asthma-associated quantitative traits in Australian children

Asthma is a genetically complex disease, and the investigation of putative linkages to candidate loci in independent populations is an important part of the gene discovery process. This study investigated the linkage of microsatellite markers in the 5q and 11q regions to asthma-associated quantitative traits in 121 Australian Caucasian nuclear families. The families were recruited on the basis of a child proband: a cohort of 95 randomly recruited families of unselected probands (n = 442 subjects) and a cohort of 26 families of probands selected on the basis of severe symptomatic asthma (n = 134 subjects). The quantitative traits assessed included serum levels of total IgE and specific IgE to house dust mite and mixed grass, blood eosinophil counts, and the dose-response slope (DRS) of FEV1 to histamine provocation. Multipoint linkage analysis using Haseman-Elston sib-pair methods provided evidence of significant linkage between the chromosome 5q markers and loge total serum IgE levels, specific serum IgE levels, and loge blood eosinophil counts. The chromosome 11q markers showed evidence of significant linkage to specific serum IgE levels. Neither region demonstrated significant linkage to the loge DRS to histamine. Phenotypes were residualized for age and sex. These data are consistent with the existence of loci regulating asthma-associated quantitative traits in both the 5q31-33 and 11q13 chromosomal regions.

High frequency of IgE receptor Fc epsilonRIbeta variant (Leu181/Leu183) in Kuwaiti Arabs and its association with asthma

The presence of IgE receptor Fc epsilonRIbeta polymorphism (181/183) was investigated in Kuwaiti asthmatic patients and controls using an allele refractory mutation screening (ARMS) test. The variant sequence (Leu181/Leu183) was detected in 72% (320/442) chromosomes analysed. Homozygous LL genotype was detected in 48% (46/96) asthmatic subjects compared to 31% (39/125) in non-asthmatics. In 11/52 families mothers of the asthmatic children were themselves asthmatic and 3/11 asthmatic mothers had homozygous LL genotype. 80% of the homozygous LL asthmatics showed a positive skin prick test (SPT) compared with 28% of non-asthmatics with the same genotype. In heterozygous NL asthmatics a positive SPT was found in 60% cases compared to 17% in non asthmatics with the same genotype. The incidence of hay fever (HF) and eczema (E) was also found to be higher in homozygous LL asthmatics compared with the non-asthmatics with the same genotype. This study reports a high prevalence of IgE receptor Fc epsilonRIbeta variants in Kuwaiti Arabs compared with British, Australian and Austrian populations studied before. The association of Leu181/Leu183 variant with asthma in Kuwaitis underlines its significance as a risk factor in manifesting the clinical phenotype in this population.

Genes for asthma? An analysis of the European Community Respiratory Health Survey

Besides environmental triggers, a family history of asthma is a strong risk factor for the development of asthma in offspring. The pooled data from 13,963 interviews of randomly selected, 20 to 48 yr-old participants from the 30 centers of the European Community Respiratory Health Survey (ECRHS) were analyzed with conventional logistic regression and a Class A regressive model adapted for the segregation of various transmission modes in families. The asthma prevalence in the interviewed index generation was 6.9% (95% confidence interval [CI]: 6.5 to 7.3), and in the parent generation was 6.1% (5.8 to 6.4). As with asthma prevalence, the risk of a subject having asthma if a parent had asthma also had a large geographic variation across the survey centers. The mean risk if a father had asthma was 2.9 (2.4 to 3.5), and If the mother had asthma was 3.2 (2.6 to 3.9). The risk increased to 7.0 (3.9 to 12.7) if both parents were affected. For developing extrinsic asthma, extrinsic asthma in any parent was a greater risk factor (4.9 [3.9 to 6.0]) than intrinsic asthma of the parent (1.5 [0.8 to 2.6]), and the risk for women was slightly higher than that for men (4.3 [3.3 to 5.5] versus 3.6 [2.6 to 5.0]). Applying different segregation models, only a model for a two-allele gene with a codominant inheritance could not be rejected, assuming a major gene with a population frequency of 24.2%. Further results make a multilocus/threshold model likely. In conclusion, a history of asthma in parents is a strong risk factor for asthma in the offspring. Under the assumptions of the applied segregation analysis, at least one major gene exists which could be a gene involved also in allergy. However, asthma is not fully described by a single-gene model. The risk for asthma varies within the European countries, and should be seen in the context of a complex genetic and environmental pathophysiology.

The candidate region approach to the genetics of asthma and allergy

To date, the strongest linkage claims for genes underlying asthma and atopy have been for chromosomes 5 and 11. Chromosome 5q contains the cytokine cluster and the beta2 adrenoceptor, and the beta chain of the high-affinity IgE receptor (FCepsilonRI-beta) is encoded on chromosome 11q13. We have attempted to replicate these findings in two distinct sample populations from the United Kingdom. Allelic associations were identified in both regions, but there was no significant evidence for linkage. Although we could not substantiate the existence of the nucleotide changes reported within exon 6 of the FCepsilonRI-beta gene, an amino acid substitution in exon 7 was strongly linked to asthma and atopy. We have also identified positive linkage and allelic associations to several markers on chromosome 12q in both our UK populations. Independent evidence from another study also supports linkage to 12q, so although our data could not confirm linkage to chromosomes 5 or 11, we have identified an additional region of the genome that could be important for the genetic predisposition to asthma and atopy.

Linkage analysis of bronchial hyperreactivity and atopy with chromosome 11q13

There are two key clinical features of asthma: allergy and bronchial hyperreactivity (BHR). Some pedigree studies of atopy have indicated linkage with the high affinity IgE receptor (Fc epsilon RI-beta) gene on chromosome 11q13, but others failed to confirm this linkage. We examined the genetic linkage of three polymorphic microsatellite markers to atopy and BHR in 120 affected sibling pairs recruited from the general community. We found no linkage to atopy at any of the three 11q13 loci studied. Our findings also do not favour linkage between BHR and loci approximately 8-9 cM either side of the Fc epsilon RI-beta gene.

Critical evaluation of food and mite allergy in the management of atopic dermatitis

The subject of allergic causation of atopic dermatitis (AD) has been a source of controversy for over sixty years. While there is general agreement of allergen-induced asthma and allergic rhinoconjunctivitis, AD lesions cannot be readily or consistently induced by foods and inhalants. The most consistent perturbators of atopic conditions are irritants, probably reflecting the consistent inflammatory cell hyper-reactivity due to elevated cyclic AMP-phosphodiesterase activity. The immunologic reactions are another manifestation of that general cellular dysregulation.

Linkage of high-affinity IgE receptor gene with bronchial hyperreactivity, even in absence of atopy

Asthma is a manifestation of bronchial hyperreactivity (BHR) and forms part of the spectrum of atopic disease. Some pedigree studies of atopy have suggested linkage with the high-affinity IgE receptor (Fc epsilon RI beta) gene on chromosome 11q13, but others find no linkage. The molecular genetics of asthma and BHR have not been studied in the general population. We examined the genetic linkage of the Fc epsilon RI beta gene with clinical asthma and the underlying phenotypes of BHR (to methacholine) and atopy (defined by skinprick testing) in 123 affected sibling-pairs recruited from the general population. We found evidence of significant linkage of a highly polymorphic microsatellite marker in the fifth intron of the Fc epsilon RI beta gene to a diagnosis of asthma (18.0% excess of shared alleles, p = 0.002) and to BHR (21.7% excess of shared alleles, p = 0.001). Significant linkage was also observed in siblings sharing BHR when those with atopy were excluded (32.8% excess of shared alleles, p = 0.004). Atopy in the absence of BHR did not show significant linkage to the Fc epsilon RI beta gene (7.2% excess of shared alleles, p = 0.124). These findings suggest that mutations in the Fc epsilon RI beta gene or a closely linked gene influence the BHR underlying asthma, even in the absence of atopy.

HLA genetics and allergic disease

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Linkage of the angiotensinogen gene locus to human essential hypertension in African Caribbeans

The renin-angiotensin system regulates blood pressure and sodium balance. The angiotensinogen gene which encodes the key substrate within this system has been linked to essential hypertension in White Europeans. It has been suggested that people of West African ancestry may have a different genetic basis for hypertension. In this study we have tested whether there is linkage of the angiotensinogen gene to essential hypertension in African Caribbeans from St. Vincent and the Grenadines. DNA from 63 affected sibling pairs with hypertension was tested for linkage by analyzing whether there was excess allele sharing among siblings genotyped using an angiotensinogen dinucleotide repeat sequence. There was significant support for linkage (T = 3.07, P = 0.001) and association of this locus to hypertension (chi 2 = 50.2, 12 degrees of freedom, P << 0.001). A DNA polymorphism which alters methionine to threonine at position 235 (M235T) within the angiotensinogen peptide has been associated previously with hypertension. However, we found no association of this variant with hypertension in this study. These findings provide support for linkage and association of the angiotensinogen locus to hypertension in African Caribbeans and suggest some similarities in the genetic basis of essential hypertension in populations of different ethnicity.

Association between high serum total IgE levels and D11S97 on chromosome 11q13 in Japanese subjects

The genetic linkage of atopy to chromosome 11q13 through maternally derived alleles has been previously reported. Linkage analysis in Japanese families did not confirm the existence of a major gene for atopy at this locus under the model of autosomal dominant inheritance. However, we observed a significant association between serum total IgE levels and genetic markers at this locus both in 14 Japanese atopic families and in 120 unrelated Japanese subjects. We detected eight alleles at the D11S97 locus and eight alleles in the CA/GT repeat region in the fifth intron of the Fc epsilon RI beta gene. A significantly increased frequency of the D11S97/PstI 0.96 kb allele was observed in the chromosomes of the subjects with high serum total IgE levels both in the family study (p < 0.001) and in the population study (p < 0.05). However, multipoint linkage analysis again did not show any evidence for the existence of a major gene regulating atopy on chromosome 11q13 with location scores to -35 under the model of maternal inheritance. Evidence against linkage was confirmed by the non-parametric linkage analysis, using the affected pedigree member method. Also, there was no substitution of isoleucine for leucine in the fourth transmembrane domain of Fc epsilon RI beta (Leu181), which was reported to be responsible for a subset of atopy in the British population. Therefore, the association of serum total IgE levels with chromosome 11q13 indicates that a gene or genes at this locus may contribute to the expression of high IgE levels in the Japanese population as well as in the British population, but the heterogeneity of the genetic regulation of serum total IgE levels is evident between the two populations.

Prognosis of asthma in children: a cohort study into adulthood

Fifty-six children with asthma, randomly selected from a hospital clinic, were followed prospectively for 15 years from a median age of 9-24 years of age. Four follow-ups were performed and included scoring of the frequency of wheezing, the need for medication, admissions to hospital, spirometry, skin prick tests and RAST to common inhaled allergens, and evaluation of living conditions. One patient died of asthma. The remaining 55 reported for all follow-ups. After the second follow-up at a median age of 13 years, all parameters of severity of asthma showed improvement, which was significant at the last follow-up when all subjects were more than 20 years of age. Only 16% of the subjects had been free from wheezing and medication the year prior to the last follow-up. Approximately 90% of the children had clinical allergies and positive allergy tests to pollens and danders and the majority of children retained both the allergies and the reactivity into adulthood. Reactivity to moulds and mites was less frequent (40% and 31%, respectively) and seemed to decrease in adulthood. Approximately 10% of the subjects developed neither clinical allergies nor reactivity in allergy tests. Children with atopic eczema usually retained their eczema as adults. Frequent wheezing and abnormal spirometry in childhood and early onset of asthma were associated with poorer outcome. The social prognosis was excellent.

Linkage of the angiotensinogen gene to essential hypertension

BACKGROUND

The renin-angiotensin system is a powerful pressor system with a major influence on salt and water homeostasis. Angiotensinogen (also called renin substrate) is a key component of this system; it is cleaved by renin to yield angiotensin I, which is then cleaved by angiotensin-converting enzyme to yield angiotensin II. The observation that plasma angiotensinogen levels correlate with blood pressure and track through families suggests that angiotensinogen may have a role in essential hypertension. We therefore investigated whether there is linkage between the angiotensinogen gene on chromosome 1q42-43 and essential hypertension.

METHODS

Samples of DNA from 63 white European families in which two or more members had essential hypertension were tested for linkage of the angiotensinogen gene to this disorder. Affected cousins, nephews, nieces, and half-siblings were included when possible. To test for linkage, we used as a marker a dinucleotide-repeat sequence flanking this gene, and we employed the affected-pedigree-member method of linkage analysis. Two molecular variants of the angiotensinogen gene, one encoding threonine instead of methionine at position 235 (M235T) and the other encoding methionine rather than threonine at position 174 (T174M), were also tested for possible association with essential hypertension.

RESULTS

We found significant linkage (t = 5.00, P < 0.001) and association (chi-square = 53.3, P < 0.001) of the angiotensinogen-gene locus to essential hypertension in the 63 multiplex families. This linkage was consistently maintained in the subgroup of subjects with diastolic pressure above 100 mm Hg and in the subgroups classified according to sex. It has been proposed previously that T174M and M235T are associated with essential hypertension. However, we found no association in our population between either polymorphism and this disorder.

CONCLUSIONS

This study provides strong and consistent support for the linkage to essential hypertension of regions within or close to the angiotensinogen gene. Precisely how mutations in this region may result in hypertension remains to be determined.

Linkage analysis of IL4 and other chromosome 5q31.1 markers and total serum immunoglobulin E concentrations

Sib-pair analysis of 170 individuals from 11 Amish families revealed evidence for linkage of five markers in chromosome 5q31.1 with a gene controlling total serum immunoglobulin E (IgE) concentration. No linkage was found between these markers and specific IgE antibody concentrations. Analysis of total IgE within a subset of 128 IgE antibody-negative sib pairs confirmed evidence for linkage to 5q31.1, especially to the interleukin-4 gene (IL4). A combination of segregation and maximum likelihood analyses provided further evidence for this linkage. These analyses suggest that IL4 or a nearby gene in 5q31.1 regulates IgE production in a nonantigen-specific (noncognate) fashion.

Genetic approaches to common diseases

Combined molecular and epidemiological studies are advancing our understanding of the genetic basis of multifactorial diseases. Several of the results obtained during the past year highlight methodological issues associated with these approaches. For example, the affected sib-pair method has been applied successfully to detect linkage between the angiotensinogen gene and susceptibility to hypertension, and a large multi-centre epidemiological study has demonstrated association of a polymorphism of the angiotensin-converting enzyme gene with increased risk of myocardial infarction. The study of Mendelian forms of multifactorial diseases has also led to many new results. These include the characterization of mutations in the glucokinase gene in maturity onset diabetes of the young, localization to chromosome 2 of a gene involved in familial colon cancer, and localization to chromosome 19 of a gene responsible for hemiplegic migraine. New insights have been provided into the genetics of multifactorial disorders such as diabetes and hypertension through the study of animal models. Localization of susceptibility loci in such models has recently led to the identification of new candidate genes that may be implicated in disease.

Polygenic disease

Considerable success is now being achieved in defining genetic susceptibility loci in polygenic disease. In particular, new susceptibility loci have been identified in hypertension, type I and type II diabetes, asthma and malaria infection. The approaches and tools for mapping such susceptibility determinants are becoming more clearly defined and the identification of further susceptibility genes is likely to be in demand in the near future.