Linkage between severe atopy and chromosome 11q13 in Japanese families

Association of atopic dermatitis to the beta subunit of the high affinity immunoglobulin E receptor

IgE dysregulation is a major pathogenic feature of atopic dermatitis and other IgE-mediated allergic diseases such as asthma and rhinitis. Allergen complexed to IgE binds to the high affinity receptor for IgE (Fc epsilon RI) on the surface of epidermal Langerhans cells, mast cells and basophils, triggering the release of inflammatory mediators. The beta subunit of Fc epsilon RI has been localized to human chromosome 11q12-13, and variants within this gene have been shown to associate with asthma and measures of atopy. We have tested several polymorphisms within Fc epsilon RI-beta for association to atopic dermatitis in a panel of 60 families (panel A), recruited through a proband with atopic dermatitis. The findings were tested in a second panel of families (panel B). Significant sharing of maternal alleles was seen for atopic dermatitis and allele 2 of RsaI intron 2 (RsaIvin2*2) (P = 0.0022) and allele 1 of RsaI exon 7 (RsaIvex7*1) (P = 0.0036) Fc epsilon RI-beta gene polymorphisms. These findings were replicated in Panel B, confirming the association of Fc epsilon RI-beta RsaI polymorphisms with atopic dermatitis. The combined significance of the association of atopic dermatitis to RsaI polymorphisms was P = 0.0002 (RsaIvin2*2) and P = 0.00034 (RsaIvex7*1). The polymorphisms also showed association with asthma: P = 0.0068 (RsaIvin2*2) and P = 0.018 (RsaIvex7*1). Polymorphisms within the Fc epsilon RI-beta gene are strongly associated with atopic dermatitis.

Evidence for linkage between asthma/atopy in childhood and chromosome 5q31-q33 in a Japanese population

Susceptibility to the development of asthma and other atopic diseases is known to be associated with genetic components, and several candidate genes have been reported to be linked to atopy in Caucasian populations. We conducted a study of linkage between asthma and markers on chromosomes 5q31-q33 and 11q13 in 68 Japanese families (306 members) by affected sib-pair analysis. Families for the linkage study were ascertained through asthmatic children visiting the allergy clinic. The results provide supportive evidence for linkage between asthma and gene markers in or near the interleukin-4 (IL-4) gene, the IL-9 gene, and D5S393 on chromosome 5q31-q33 (p = 0.0013, p = 0.018, and p = 0.0077, respectively). Linkage between atopic phenotype and these genetic markers was also suggested (p = 0.006, p = 0.01, and p < 0.0001 for atopy, respectively). However, we failed to find evidence for linkage of asthma or atopy to the IgE high-affinity receptor gene on 11q13 (p > 0.1). These findings indicate that beyond ethnicity, there are specific loci that contribute to susceptibility to atopy on chromosome 5q31-q33. In addition, our findings suggest that loci on chromosome 5q31-q33 are linked to the development of asthma in childhood.

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.

Fc epsilon R1-beta polymorphism and total serum IgE levels in endemically parasitized Australian aborigines

Endemic helminthic infection is a major public-health problem and affects a large proportion of the world's population. In Australia, helminthic infection is endemic in Aboriginal communities living in tropical northern regions of the continent. Such infection is associated with nonspecific (polyclonal) stimulation of IgE synthesis and highly elevated total serum IgE levels. There is evidence that worm-infection variance (i.e., human capacity of resistance) and total serum IgE levels may be related to the presence of a major codominant gene. The beta chain of the high-affinity IgE receptor, Fc epsilon R1-beta, has been previously identified as a candidate for the close genetic linkage of the 11q13 region to IgE responses in several populations. We show a biallelic RsaI polymorphism in Fc epsilon R1-beta to be associated with total serum IgE levels (P = .0001) in a tropical population of endemically parasitized Australian Aborigines (n = 234 subjects). The polymorphism explained 12.4% of the total residual variation in serum total IgE and showed a significant (P = .0000) additive relationship with total serum IgE levels, across the three genotypes. These associations were independent of familial correlations, age, gender, racial admixture, or smoking status. Alleles of a microsatellite repeat in intron 5 of the same gene showed similar associations. The results suggest that variation in Fc epsilon R1-beta may regulate IgE-mediated immune responses in this population.

Genetic factors in lung disease: atopy and bronchial asthma

Atopy defined as high IgE responsiveness has now been subject to genetic studies at the molecular level owing to the development of a great number of DNA markers over the human genome. Either by linkage analysis or by association study strong candidate genes of atopy have been proposed to be located on chromosome 11q13 and 5q31 where high-affinity IgE Fc receptor beta subunit and allergy-associated cytokines, respectively, have been mapped. Meanwhile, we found a novel association between one of alleles of D11S97, an anonymous DNA marker on 11q13, and high total serum IgE in a large number of Japanese general population and atopic family members. However, failure to replicate linkage or association studies by different investigators suggest polygenic nature of atopy. In addition to the genes regulating IgE synthesis, the requirement of local (pulmonary) genetic factors in the development of bronchial asthma have been speculated. Linkage analysis suggested possible existence of gene(s) regulating susceptibility and/or clinical characteristics of bronchial asthma also on chromosome 5q. One of the candidate is beta 2-adrenergic receptor gene polymorphism. Mutated gene transfection studies suggested functional significance of some polymorphisms and clinical evaluations have revealed their contribution to airway responsiveness and severity of asthma.

Candidate gene loci in asthmatic and allergic inflammation

New techniques for scanning the human genome promise great advances in tracking the origins of disorders caused by multiple genes. However, it is clear from the studies presented in this overview that we are far from understanding the genetic basis of asthma and atopy and their interaction with the environment. It is also clear that agreement must be reached on definition of the phenotype and methods of ascertainment in order to carry out large multicentre collaborative studies. Positive findings need to be validated in different populations selected for the presence of the disease and then confirmed in a random population where the prevalence of asthma and atopy will also be expected to be significant.

Exclusion from proximal 11q of a common gene with megaphenic effect on atopy

We have typed three markers on proximal 11q in 131 random families with three or more children studied for atopy. A summary map that includes the FCER1B candidate was constructed. Using a 2-locus disease model, we performed combined segregation and linkage analysis of three models, none of which suggested linkage. Nine marker loci on other chromosomes were also negative. In the regions swept by these 12 markers we cannot rule out a rare gene, perhaps of large effect, nor a common gene of small effect. However, a common gene of large effect is excluded. These results and alternative strategies are discussed in the perspective of inconsistent evidence for a major atopy gene.