Genes, environments, and sex: factors of importance in atopic diseases in 7-9-year-old Swedish twins

Increased loss-of-function filaggrin gene mutation prevalence in atopic dermatitis patients across northern latitudes indicates genetic fitness: A systematic review and meta-analysis

Loss-of-function (LoF) mutations in the filaggrin gene (FLG) constitute the strongest genetic risk for atopic dermatitis (AD). A latitude-dependent difference in the prevalence of LoF FLG mutations was systematically evaluated. A systematic review and meta-analysis were performed to estimate the prevalence of LoF FLG mutations in AD patients and the general population by geography and ethnicity. Risk of bias was assessed by Newcastle-Ottawa Scale and Jadad score. StatsDirect, version 3 software was used to calculate all outcomes. PubMed and EMBASE were searched until 9th December 2021. Studies were included if they contained data on the prevalence of LoF FLG mutations in AD patients or from the general population or associations between AD and LoF FLG mutations and were authored in English. Overall, 248 studies and 229 310 AD patients and individuals of the general population were included in the quantitative analysis. The prevalence of LoF FLG mutations was 19.1% (95% CI, 17.3-21.0) in AD patients and 5.8% (95% CI, 5.3-6.2) in the general population. There was a significant positive association between AD and LoF FLG mutations in all latitudes in the Northern hemisphere, but not in all ethnicities. The prevalence of LoF FLG mutations became gradually more prevalent in populations residing farther north of the Equator but was negligible in Middle Easterners and absent in most African populations. FLG LoF mutations are common and tend to increase with northern latitude, suggesting potential clinical implications for future AD management. The existence of possible genetic fitness from FLG LoF mutations remains unknown.

Genome-wide Association Study of Susceptibility Loci for Self-Reported Atopic Dermatitis and Allergic Rhinitis in the Korean Population

BACKGROUND

Allergic diseases include atopic dermatitis (AD) and allergic rhinitis (AR), which are chronic, relapsing inflammatory disorders of the skin or mucosa that usually accompany immunoglobulin E-mediated immune responses. They are complex, multifactorial diseases with an etiology involving interactions between genetic and environmental factors.

OBJECTIVE

We performed a genome-wide association study (GWAS) to identify single nucleotide polymorphisms (SNPs) associated with allergic diseases in the Korean population.

METHODS

A total of 8,840 samples were obtained from the Korean Association Resource Consortium dataset of the Korean Genome and Epidemiology Study Ansan-Anseong cohort. The allergic disease phenotype was determined based on self-reported physician diagnoses. After quality control, 8,823 subjects with 877,242 variants remained for the final analysis. The GWAS was performed using logistic regression analysis in an additive model adjusted for age and sex.

RESULTS

A total of 636 patients with allergic disease and 8,176 controls were analyzed. Three SNPs were associated with allergic disease at a level of genome-wide suggestive significance (p<1.0×10-5) in the Korean population: rs7275360, located in neural cell adhesion molecule 2; rs698195; and rs3750552, located in family with sequence similarity 189, member A2. These polymorphisms were on chromosomes 21q21.1, 7q31.1, and 9q21.12, respectively.

CONCLUSION

We identified 3 novel SNPs significantly associated with allergic diseases in the Korean population. Further research is required to confirm the association between these novel SNPs and allergic disease in the Korean population and in other ethnicities.

Genome-wide meta-analysis implicates variation affecting mast cell biology in urticaria

BACKGROUND

Urticaria is characterized by inappropriate mast cell degranulation leading to the development of wheals and/or angioedema. Twin and family studies indicate that there is a substantial heritable component to urticaria risk.

OBJECTIVE

Our aim was to identify genomic loci at which common genetic variation influences urticaria susceptibility.

METHODS

Genome-wide association studies of urticaria (including all subtypes) from 3 European cohorts (UK Biobank, FinnGen, and the Trøndelag Health Study [HUNT]) were combined through statistical meta-analysis (14,306 urticaria cases and 650,664 controls). Cases were identified via electronic health care records from primary and/or secondary care. To identify putative causal variants and genes, statistical fine-mapping, colocalization, and interrogation of publicly available single-cell transcriptome sequencing resources were performed.

RESULTS

Genome-wide significant associations (P < 5 × 10-8) were identified at 6 independent loci. These included 2 previously reported association signals at 1q44 and the human leucocyte antigen region on chromosome 6. Genes with expected or established roles in mast cell biology were associated with the 4 other genome-wide association signals (GCSAML, FCER1A, TPSAB1, and CBLB). Colocalization of association signals consistent with the presence of shared causal variants was observed between urticaria susceptibility and increased expression of GCSAML (posterior probability of colocalization [PPcoloc] = 0.89) and FCER1A (PPcoloc = 0.91) in skin.

CONCLUSION

Common genetic variation influencing the risk of developing urticaria was identified at 6 genomic loci. The relationship between genes with roles in mast cell biology and several association signals implicates genetic variability of specific components of mast cell function in the development of urticaria.

Maternal exposure to pyrethroid insecticides during pregnancy and respiratory allergy symptoms among children participating in the Venda Health Examination of Mothers, Babies and their Environment (VHEMBE)

BACKGROUND

Pyrethroid insecticides use for indoor residual spraying (IRS) in malaria-endemic areas results in high levels of exposure to local populations. Pyrethroids may cause asthma and respiratory allergies but no prior study has investigated this question in an IRS area.

METHODS

We measured maternal urinary concentrations of pyrethroid metabolites (cis-DBCA, cis-DCCA, trans-DCCA, 3-PBA) in samples collected at delivery from 751 mothers participating in the Venda Health Examination of Mothers, Babies, and their Environment (VHEMBE), a birth cohort study based in Limpopo, South Africa. At 3.5-year and 5-year follow-up visits, caregivers of 647 and 620 children, respectively, were queried about children's respiratory allergy symptoms based on validated instruments. We applied marginal structural models for repeated outcomes to estimate associations between biomarker concentrations and asthma diagnosis as well as respiratory allergy symptoms at ages 3.5 and 5 years.

RESULTS

We found that a10-fold increase in maternal urinary cis-DCCA, trans-DCCA and 3-PBA concentrations were associated with more than a doubling in the risk of doctor-diagnosed asthma (cis-DCCA: RR = 2.1, 95% CI = 1.3, 3.3; trans-DCCA: RR = 2.1, 95% CI = 1.1, 3.9; 3-PBA: RR = 2.4, 95% CI = 1.0, 5.8) and an about 80% increase in the risk of wheezing or whistling in the chest (cis-DCCA: RR = 1.8, 95% CI = 1.1, 3.0; trans-DCCA: RR = 1.7, 95% CI = 1.1, 2.6; 3-PBA: RR = 1.8, 95% CI = 1.0, 3.3) and suspected asthma (cis-DCCA: RR = 1.8, 95% CI = 1.1, 3.1; trans-DCCA: RR = 1.8, 95% CI = 1.1, 2.8). We also observed that higher concentrations of cis-DBCA and 3-PBA were related to increases in the risks of dry cough at night (RR = 3.5, 95% CI = 1.3, 9.5) and seasonal rhinoconjunctivitis (RR = 2.0, 95% CI = 1.1, 3.9), respectively.

CONCLUSION

Maternal exposure to pyrethroids may increase the risk of asthma and other respiratory allergy symptoms among preschool children from an IRS area.

Persistence of parental-reported asthma at early ages: A longitudinal twin study

BACKGROUND

Currently, we cannot predict whether a pre-school child with asthma-like symptoms will have asthma at school age. Whether genetic information can help in this prediction depends on the role of genetic factors in persistence of pre-school to school-age asthma. We examined to what extent genetic and environmental factors contribute to persistence of asthma-like symptoms at ages 3 to asthma at age 7 using a bivariate genetic model for longitudinal twin data.

METHODS

We performed a cohort study in monozygotic and dizygotic twins from the Netherlands Twin Register (NTR, n = 21,541 twin pairs). Bivariate genetic models were fitted to longitudinal data on asthma-like symptoms reported by parents at age 3 and 7 years to estimate the contribution of genetic and environmental factors.

RESULTS

Bivariate genetic modeling showed a correlation on the liability scale between asthma-like symptoms at age 3 and asthma at age 7 of 0.746 and the contribution of genetics was estimated to be 0.917. The genetic analyses indicated a substantial influence of genetic factors on asthma-like symptoms at ages 3 and 7 (heritability 80% and 90%, respectively); hence, contribution of environmental factors was low. Persistence was explained by a high (rg = 0.807) genetic correlation.

CONCLUSION

Parental-reported asthma-like symptoms at age 3 and asthma at age 7 are highly heritably. The phenotype of asthma-like symptoms at age 3 and 7 was highly correlated and mainly due to heritable factors, indicating high persistence of asthma development over ages 3 and 7.

Role of selenium in IgE mediated soybean allergy development

Food allergy is a pathological immune reaction triggered by normal innocuous dietary proteins. Soybean is widely used in many food products and has long been recognized as a source of high-quality proteins. However, soybean is listed as one of the 8 most significant food allergens. The prevalence of soybean allergy is increasing worldwide and impacts the quality of life of patients. Currently, the only strategy to manage food allergy relies on strict avoidance of the offending food. Nutritional supplementation is a new prevention strategy which is currently under evaluation. Selenium (Se), as one of the essential micronutrients for humans and animals, carries out biological effects through its incorporation into selenoproteins. The use of interventions with micronutrients, like Se, might be an interesting new approach. In this review we describe the involvement of Se in a variety of processes, including maintaining immune homeostasis, preventing free radical damage, and modulating the gut microbiome, all of which may contribute to in both the prevention and treatment of food allergy. Se interventions could be an interesting new approach for future treatment strategies to manage soybean allergy, and food allergy in general, and could help to improve the quality of life for food allergic patients.

Analysis of the immunoglobin E molecular sensitization profile in children with allergic asthma and predictive factors for the efficacy of allergy immunotherapy

Background

As the incidence of allergic asthma in children increases, the immunoglobin E (IgE) molecular sensitization profile of allergic asthma remains underreported while the level of total IgE (tIgE) and sIgE/tIgE have not been studied as predictors of efficacy of allergen immunotherapy (AIT) for allergic asthma, specifically in children.

Methods

Starting from August 2018 to March 2019 in the Respiratory Department of the Children’s Hospital of Chongqing Medical University, asthmatic children, with positive skin prick tests to Der p or Der f, were enrolled in this study. Total IgE, allergen serum-specific IgE (sIgE) of Der p, Der f, Blomia tropicalis (Blo t), cat dander, dog dander, egg white, milk, cockroach, shrimp, and crab, along with Der p allergen components, Der p1 and Der p2, were measured by ImmunoCAP™ assay.

Results

A total of 142 children with allergic asthma were enrolled, all of whom showed positive IgE for Der p, Der p1, Der p2, and Der f; meanwhile, the positive rates of Blo t, cat dander, dog dander, egg white, milk, cockroach, shrimp, and crab were 91.84%, 10.96%, 7.32%, 9.15%, 11.58%, 17.03%, 18.90%, and 18.28% respectively. A significantly high correlation was found between total IgE and the sIgE of Der f, Der p, Der p 1, and Der p 2. Asthmatic children with a family history of allergy displayed higher total IgE and unknown IgE levels than those patients without a family history of allergy. The ratios of Der f sIgE/tIgE and Der p sIgE/tIgE were higher in the negative family history of allergy group than in the positive family history of allergy group. Furthermore, total IgE and unknown IgE were higher in the polysensitized group than in the in monosensitized group. The ratios of Der f sIgE/tIgE and Der p sIgE/tIgE were higher in the monosensitized group than in the polysensitized group.

Conclusions

From this study, we noticed that dust mites are the main cause of asthma in children investigated. Our findings indicate patients with no family history of allergy and monosensitized patients have a higher ratio of sIgE/tIgE, and those patients may benefit more from AIT.

Familial aggregation of atopic dermatitis and co-aggregation of allergic diseases in affected families in Taiwan

BACKGROUND

Atopic dermatitis (AD) is contributed from a result of genetic and environmental interaction. The evidence for familial aggregation in AD has been reported but population-based studies and co-aggregation with other allergic diseases are rarely reported.

OBJECTIVE

This study examined familial aggregation and heritability of atopic dermatitis (AD) and to estimate the relative risks (RRs) of other allergic diseases in individuals with relatives diagnosed with AD.

METHODS

We used Taiwan National Health Insurance Research Database to identify all registered beneficiaries (n = 26,525,074) in 2015; among them, 1,248,594 individuals had AD. We estimated familial risks of AD and other allergic diseases by using marginal Cox proportional models.

RESULTS

Prevalence of AD in individuals with relatives affected with atopic dermatitis was 3.1-fold higher than the general population (12.4 % vs. 4.0 %, respectively). The adjusted relative risks (RR) for individuals with an affected first-degree relative (FDR) was 2.25 (95 % CI, 2.25-2.26). The adjusted RRs for subjects with an affected parent, an affected offspring or an affected sibling was 2.39 (95 % CI, 2.37-2.41), 2.26 (95 % CI, 2.24-2.28) and 2.30 (95 % CI, 2.29-2.31) respectively. The RRs in individuals with an FDR with AD was 1.34 (95 %CI, 1.34 - 1.34) for asthma and 1.23 (95 %CI, 1.23-1.24) for allergic rhinitis.

CONCLUSION

This nationwide study ascertains that a family history of atopic dermatitis is a risk factor for atopic dermatitis. Individuals with relatives affected by atopic dermatitis have slightly higher risks of developing asthma and allergic rhinitis.

Estimated Prevalence of Asthma in US Children With Developmental Disabilities

IMPORTANCE

The prevalence of asthma in US children with various developmental disabilities and delays is unclear, including how estimates vary by ethnic group.

OBJECTIVE

To report asthma prevalence estimates by various disability categories and developmental delays in a diverse sample of the US pediatric population.

DESIGN, SETTING, AND PARTICIPANTS

This population-based cross-sectional study encompassed a total of 71 811 families with children or adolescents aged 0 to 17 years (hereinafter referred to as children) who participated in the 2016 and 2017 National Survey of Children's Health. Data were collected from June 10, 2016, to February 10, 2017, for the 2016 survey and from August 10, 2017, to February 10, 2018, for the 2017 survey. Data were analyzed from September 20, 2019, to April 5, 2020.

EXPOSURES

Developmental disability, including attention-deficit/hyperactivity disorder, autism spectrum disorder, cerebral palsy, seizure, intellectual and/or learning disability, and vision, hearing, and/or speech delay. Delay was defined as not meeting growth milestones with unknown cause.

MAIN OUTCOMES AND MEASURES

Weighted asthma prevalence estimates and 95% CIs were generated for children with and without disabilities.

RESULTS

A total of 71 811 participants (mean [SE] age, 8.6 [0.1] years; 36 800 boys [51.1%; 95% CI, 50.2%-52.0%]; 50 219 non-Hispanic white [51.4%; 95% CI, 50.6%-52.3%]) were included in our final analytical sample, of whom 5687 (7.9%; 95% CI, 7.5%-8.4%) had asthma and 11 426 (15.3%; 95% CI, 14.7%-16.0%) had at least 1 disability. Overall asthma prevalence estimates were 10 percentage points higher in children with a disability (16.1%; 95% CI, 14.3%-17.8%) vs children without a disability (6.5%; 95% CI, 6.0%-6.9%). The odds of asthma were significantly higher in children with a disability (odds ratio [OR], 2.77; 95% CI, 2.39-3.21) or delay (OR, 2.22; 95% CI, 1.78-2.77) vs typically growing children. Adjusted models remained significant for all disability categories (overall adjusted OR, 2.21; 95% CI, 1.87-2.62). Subgroup analyses showed ethnic minorities had a higher prevalence of concurrent asthma and developmental disabilities vs non-Hispanic whites (19.8% [95% CI, 16.6%-23.0%] vs 12.6% [95% CI, 11.1%-14.0%]; P < .001).

CONCLUSIONS AND RELEVANCE

These results suggest that US children with various developmental disabilities or delay may have higher odds for developing asthma vs their typically developing peers. These findings support asthma screening in pediatric health care settings among patients with developmental disabilities and delays, particularly among those from ethnic minority backgrounds. In addition, very young children with asthma should be screened for disabilities and delays, because temporality cannot be determined by the current data source and analytical approach.

Atopic March: Collegium Internationale Allergologicum Update 2020

In recent decades, the worldwide prevalence of allergic disease has increased considerably. The atopic march is a model aimed at explaining the apparent progression of allergic diseases from atopic dermatitis (AD) to allergic asthma (AA) and to allergic rhinitis (AR). It hypothesizes that allergic disease begins, typically in children, with the development of AD, then AA, and finally progresses to AR. This theory has been widely studied in cross-sectional and long-term longitudinal studies and it has been found that as prevalence of AD declines, prevalence of AA increases. A similar relationship is reported between AA and AR. The legitimacy of the atopic march model is, however, currently debated. Epidemiological evidence and criticism of longitudinal studies point to an overstatement of the atopic march's prevalence and incorrect mechanisms, opening a discussion for alternative models to better explain the pathophysiological and epidemiological processes that promote this progression of allergic diseases. Albeit, risk factors for the development and progression of allergic disease, particularly AD, are critical in identifying disease progression. Investigating the role of age, severity, family history, phenotype, and genetic traits may give a better indication into the progression of allergic diseases. In addition, studies following patients from infancy into adulthood and a general increase in longitudinal studies would help broaden the knowledge of allergic disease progression and the atopic march.

The Genetics and Genomics of Asthma

Asthma is a common, clinically heterogeneous disease with strong evidence of heritability. Progress in defining the genetic underpinnings of asthma, however, has been slow and hampered by issues of inconsistency. Recent advances in the tools available for analysis-assaying transcription, sequence variation, and epigenetic marks on a genome-wide scale-have substantially altered this landscape. Applications of such approaches are consistent with heterogeneity at the level of causation and specify patterns of commonality with a wide range of alternative disease traits. Looking beyond the individual as the unit of study, advances in technology have also fostered comprehensive analysis of the human microbiome and its varied roles in health and disease. In this article, we consider the implications of these technological advances for our current understanding of the genetics and genomics of asthma.

Multi-Method Molecular Characterisation of Human Dust-Mite-associated Allergic Asthma

Asthma is a chronic inflammatory disorder of the airways. Disease presentation varies greatly in terms of cause, development, severity, and response to medication, and thus the condition has been subdivided into a number of asthma phenotypes. There is still an unmet need for the identification of phenotype-specific markers and accompanying molecular tools that facilitate the classification of asthma phenotype. To this end, we utilised a range of molecular tools to characterise a well-defined group of female adults with poorly controlled atopic asthma associated with house dust mite (HDM) allergy, relative to non-asthmatic control subjects. Circulating messenger RNA (mRNA) and microRNA (miRNA) were sequenced and quantified, and a differential expression analysis of the two RNA populations performed to determine how gene expression and regulation varied in the disease state. Further, a number of circulating proteins (IL-4, 5, 10, 13, 17 A, Eotaxin, GM-CSF, IFNy, MCP-1, TARC, TNFα, Total IgE, and Endotoxin) were quantified to determine whether the protein profiles differed significantly dependent on disease state. Finally, we utilised a previously published assessment of the circulating “blood microbiome” performed using 16S rRNA amplification and sequencing. Asthmatic subjects displayed a range of significant alterations to circulating gene expression and regulation, relative to healthy control subjects, that may influence systemic immune activity. Notably, several circulating mRNAs were detected in just the asthma group or just in the control group, and many more were observed to be expressed at significantly different levels in the asthma group compared to the control group. Proteomic analysis revealed increased levels of inflammatory proteins within the serum, and decreased levels of the bacterial endotoxin protein in the asthmatic state. Comparison of blood microbiome composition revealed a significant increase in the Firmicutes phylum with asthma that was associated with a concomitant reduction in the Proteobacteria phylum. This study provides a valuable insight into the systemic changes evident in the HDM-associated asthma, identifies a range of molecules that are present in the circulation in a condition-specific manner (with clear biomarker potential), and highlights a range of hypotheses for further study.

Gut Microbiome as Target for Innovative Strategies Against Food Allergy

The dramatic increase in food allergy prevalence and severity globally requires effective strategies. Food allergy derives from a defect in immune tolerance mechanisms. Immune tolerance is modulated by gut microbiota function and structure, and microbiome alterations (dysbiosis) have a pivotal role in the development of food allergy. Environmental factors, including a low-fiber/high-fat diet, cesarean delivery, antiseptic agents, lack of breastfeeding, and drugs can induce gut microbiome dysbiosis, and have been associated with food allergy. New experimental tools and technologies have provided information regarding the role of metabolites generated from dietary nutrients and selected probiotic strains that could act on immune tolerance mechanisms. The mechanisms are multiple and still not completely defined. Increasing evidence has provided useful information on optimal bacterial species/strains, dosage, and timing for intervention. The increased knowledge of the crucial role played by nutrients and gut microbiota-derived metabolites is opening the way to a post-biotic approach in the stimulation of immune tolerance through epigenetic regulation. This review focused on the potential role of gut microbiome as the target for innovative strategies against food allergy.

A curated collection of transcriptome datasets to investigate the molecular mechanisms of immunoglobulin E-mediated atopic diseases

Prevalence of allergies has reached ~20% of population in developed countries and sensitization rate to one or more allergens among school age children are approaching 50%. However, the combination of the complexity of atopic allergy susceptibility/development and environmental factors has made identification of gene biomarkers challenging. The amount of publicly accessible transcriptomic data presents an unprecedented opportunity for mechanistic discoveries and validation of complex disease signatures across studies. However, this necessitates structured methodologies and visual tools for the interpretation of results. Here, we present a curated collection of transcriptomic datasets relevant to immunoglobin E-mediated atopic diseases (ranging from allergies to primary immunodeficiencies). Thirty-three datasets from the Gene Expression Omnibus, encompassing 1860 transcriptome profiles, were made available on the Gene Expression Browser (GXB), an online and open-source web application that allows for the query, visualization and annotation of metadata. The thematic compositions, disease categories, sample number and platforms of the collection are described. Ranked gene lists and sample grouping are used to facilitate data visualization/interpretation and are available online via GXB (http://ige.gxbsidra.org/dm3/geneBrowser/list). Dataset validation using associated publications showed good concordance in GXB gene expression trend and fold-change.

Illicit Drug Use, Cigarette Smoking, and Eating Disorder Symptoms: Associations in an Adolescent Twin Sample

OBJECTIVE

Twin studies have shown that genetic factors in part explain the established relation between alcohol use (i.e., problematic use or abuse/dependence) and eating disorder symptoms in adolescent and adult females. However, studies have yet to elucidate if there are similar shared genetic factors between other aspects of substance involvement, such as illicit drug use and repeated cigarette smoking.

METHOD

For those sex-specific phenotypic correlations above our threshold of .20, we used a behavioral genetic design to examine potential shared genetic overlap between self-reported lifetime illicit drug use and repeated cigarette smoking and the eating disorder symptoms of drive for thinness (DT), bulimia (BU), and body dissatisfaction (BD), as assessed with the Eating Disorder Inventory-II, in 16- to 17-year-old female and male twin pairs.

RESULTS

Only phenotypic correlations with illicit drug use met our threshold for twin modeling. Small to moderate genetic correlations were observed between illicit drug use and BU in both girls and boys and between illicit drug use and DT in girls.

CONCLUSIONS

Similar etiological factors are at play in the overlap between illicit drug use and certain eating disorder symptoms in girls and boys during adolescence, such that genetic factors are important for covariance. Specifically, illicit drug use was associated with bulimia nervosa symptoms in girls and boys, which parallels previous substance use research finding a genetic overlap between alcohol use and bulimia nervosa symptoms. Future research should prospectively examine developmental trajectories to further understand the etiological overlap between substance involvement and eating disorder symptoms.

Associations Between Alcohol Involvement and Drive for Thinness and Body Dissatisfaction in Adolescent Twins: A Bivariate Twin Study

BACKGROUND

Alcohol involvement has familial associations with bulimic symptoms (i.e., binge eating, inappropriate compensatory behaviors), with several studies indicating a genetic overlap between the two. It is unclear whether overlapping familial risk with alcohol involvement extends to other eating disorder symptoms. Understanding the genetic overlap between alcohol involvement and other eating disorder symptoms may aid in more targeted interventions for comorbid alcohol use-eating disorder symptoms. Thus, we investigated associations between alcohol involvement and 2 core eating disorder symptoms: drive for thinness and body dissatisfaction in adolescent female and male twins.

METHODS

We assessed 3 levels of alcohol involvement: alcohol use in the last month, having ever been intoxicated, and alcohol intoxication frequency via self-report. The Eating Disorder Inventory-II assessed drive for thinness and body dissatisfaction. Sex-specific biometrical twin modeling examined the genetic overlap between alcohol involvement and eating disorder symptoms.

RESULTS

Phenotypic associations between alcohol involvement, drive for thinness, and body dissatisfaction were significantly greater in girls compared with boys. A majority of the associations between alcohol involvement, drive for thinness, and body dissatisfaction in girls, but not boys, met our threshold for twin modeling (phenotypic r > 0.20). Moderate genetic correlations were observed between the 3 aspects of alcohol involvement and drive for thinness. Moderate genetic correlations were observed between alcohol use and intoxication frequency and body dissatisfaction.

CONCLUSIONS

Together with the literature on alcohol involvement and bulimic symptoms, these findings suggest a generalized association between alcohol involvement and eating disorder symptoms in girls, whereas this association may be symptom specific in boys. Genetic correlations indicate that the amount and direction of this genetic overlap differs across specific symptoms. When intervening on comorbid alcohol involvement and eating disorder symptoms, it may be important to target-specific eating disorder symptoms.

Shared familial risk between bulimic symptoms and alcohol involvement during adolescence

Twin studies show the established relation between bulimic symptoms and problematic alcohol involvement in adult females is partly due to shared familial factors, specifically shared genetic effects. However, it is unclear if similar shared etiological factors exist during adolescence or in males. We examined the familial overlap (i.e., genetic and common environmental correlations) between bulimic symptoms and various levels of alcohol involvement in 16- to 17-year-old female and male same-sex twin pairs using sex-specific biometrical twin modeling. Bulimic symptoms were assessed with the Eating Disorder Inventory-2. Alcohol involvement included alcohol use in the last month, having ever been intoxicated, and alcohol intoxication frequency. Results revealed 3 distinct patterns. First, in general, phenotypic correlations indicated statistically similar associations between bulimic symptoms and alcohol involvement in girls and boys. Second, common environmental overlap was significant for the bivariate associations including having ever been intoxicated. Third, moderate genetic correlations were observed between all bulimic symptoms and alcohol involvement in girls and moderate common environmental correlations were observed in boys for the more risky/deviant levels of involvement. Similar to adults, there is familial overlap between bulimic symptoms and alcohol involvement in adolescent girls and boys. These results could inform symptom- and sex-specific, developmentally targeted prevention and intervention programs for the comorbidity between bulimic symptoms and alcohol involvement. (PsycINFO Database Record

Is the atopic march related to confounding by genetics and early-life environment? A systematic review of sibship and twin data

A popular hypothesis known as the atopic march proposes a set of sequential allergy and respiratory disorders in early childhood contributes enormously to the burden of disease in developed countries. Although the concept of the atopic march has been refined and strengthened by many cross-sectional and longitudinal studies linking eczema as the initial manifestation with progression to hay fever and then asthma, there is yet no definitive proof that the atopic march is the primary causal factor in childhood allergic disease. This debate is mainly related to the controversy around potential confounding of these associations by genetic and environmental factors. Family studies are ideally suited to unravelling the role of these factors. While multiple reviews have synthesized evidence from studies investigating this question, no review to date has explored specific evidence generated by twin and sibling studies to understand the aetiology of atopic march diseases. Our aim was to conduct a systematic review of twin and sibling studies that examine the allergic phenotypes that form the atopic march, to determine whether such analyses of data from these studies attempt to control for the effect confounding by shared factors, and to report estimates of the magnitude of associations between multiple phenotypes. Our review suggests that (1) genetics play a bigger role predisposing eczema to hay fever and eczema to asthma than environmental factors, and (2) the link between eczema and asthma and hay fever is independent of shared early-life environmental factors.

Sex-specific lung functional changes in adult mice exposed only to second-hand smoke in utero

Background

An increasing number of epidemiological and experimental studies have associated exposure to second-hand smoke (SHS) during pregnancy with adverse outcomes in newborns. As we have previously shown in mice, in utero exposure to SHS at critical stages of fetal development, results in altered lung responses and increased disease susceptibility upon re-exposure to irritants (SHS or ovalbumin) in adulthood. In this study, we asked whether the in utero SHS exposure alone is sufficient to alter lung structure and function in adult mice.

Methods

Pregnant BALB/c mice were exposed from days 6 to 19 of pregnancy to 10 mg/m³ of SHS or HEPA-filtered air. Male and female offspring (n = 13–15/group) were sacrificed at 15 weeks of age. We measured lung function with non-invasive and invasive methods, performed lung morphometric analysis on trichrome-stained lung tissue samples, and assessed lung gene expression via RNA sequencing and protein assays.

Results

In utero SHS exposure significantly increased mean linear intercept and decreased the surface area per unit volume of the lungs in both males and females, indicating perturbation in alveolar developmental processes. Tidal volume, minute volume and inspiratory capacity were significantly decreased compared with the controls only in male mice exposed in utero to SHS, suggesting that males are more sensitive than females to an SHS insult during lung development. This also suggests that in our model, lung structure changes may be necessary but are not sufficient to impair lung function. SERPINA1A, the mouse ortholog of human α1-antitrypsin, deficiency of which is a known genetic risk factor for emphysema, was down-regulated at the protein level in the in utero SHS-exposed mice. Additionally, DNMT3A protein expression was dysregulated, indicating that DNA methylation occurred in the lungs.

Conclusions

Our results indicate that in utero SHS exposure alone alters both lung function and structure well into adulthood (15 weeks) in male mice. Furthermore, lung function alterations in this model are sex-specific, with males being more susceptible to in utero SHS effects. Overall, our data suggest that in utero SHS exposure alone can predispose to adult lung diseases.

Severe Asthma: Have We Made Progress?

Tremendous efforts have been invested in research to (1) discover risk factors, biomarkers, and clinical characteristics; (2) understand the pathophysiology and treatment response variability in severe asthma; and (3) design new therapies. However, to combat severe asthma, many questions concerning the pathogenesis of severe asthma, including its natural history, genetic and environmental risk factors, and disease mechanisms, must be answered. In this article we highlight some of the major discoveries concerning the pathogenesis of severe asthma and its therapeutic development. We conclude that discoveries on numerous fronts of severe asthma, from disease heterogeneity, features of airway remodeling, cytokine mediators and signaling pathways underlying disease pathogenesis, disease mechanisms, potential biomarkers, to new therapeutic targets, demonstrate that progress has been made in understanding and developing more effective treatments for this difficult-to-treat disease.

Prevention of food allergy

The past few decades have witnessed an increase in the prevalence of IgE-mediated food allergy (FA). For prevention strategies to be effective, we need to understand the causative factors underpinning this rise. Genetic factors are clearly important in the development of FA, but given the dramatic increase in prevalence over a short period of human evolution, it is unlikely that FA arises through germline genetic changes alone. A plausible hypothesis is that 1 or more environmental exposures, or lack thereof, induce epigenetic changes that result in interruption of the default immunologic state of tolerance. Strategies for the prevention of FA might include primary prevention, which seeks to prevent the onset of IgE sensitization; secondary prevention, which seeks to interrupt the development of FA in IgE-sensitized children; and tertiary prevention, which seeks to reduce the expression of end-organ allergic disease in children with established FA. This review emphasizes the prevention of IgE-mediated FA through dietary manipulation, among other strategies; in particular, we focus on recent interventional studies in this field.

Genetic Disposition for Global Maturity: An Explanation for Genetic Effects on Parental Report on ADHD

Attention deficit hyperactivity disorder (ADHD) has been shown to be substantially influenced by genetic factors. However it is still not known how these effects are mediated. The aim of this study is to evaluate whether genetic disposition for global maturity could be a mediator of the well-known findings of genetic factors for ADHD symptoms. A total of 1480 pairs of twins aged 8-9 years were identified through the population-based Swedish Twin Registry. A mailed questionnaire with items from DSM-III-R for ADHD and items concerning global maturity were completed by the parents. The results showed that global maturity mediated part of genetic effects for ADHD for both boys and girls. There were also genetic, shared environmental, as well as nonshared environmental effects unique to ADHD not in common with global maturity. Thus, there are at least two pathways through which genetic effects can influence ADHD: one through predisposition for maturational lag and one unique to ADHD, possibly mediated by personality. The results indicate that maturational lag could be of importance for treatment and prognosis of ADHD.

Heritability and confirmation of genetic association studies for childhood asthma in twins

BACKGROUND

Although the genetics of asthma has been extensively studied using both quantitative and molecular genetic analysis methods, both approaches lack studies specific to the childhood phenotype and including other allergic diseases. This study aimed to give specific estimates for the heritability of childhood asthma and other allergic diseases, to attempt to replicate findings from genomewide association studies (GWAS) for childhood asthma and to test the same variants against other allergic diseases.

METHODS

In a cohort of 25 306 Swedish twins aged 9 or 12 years, data on asthma were available from parental interviews and population-based registers. The interviews also inquired about wheeze, hay fever, eczema, and food allergy. Through structural equation modeling, the heritability of all phenotypes was calculated. A subset of 10 075 twins was genotyped for 16 single nucleotide polymorphisms (SNPs) selected from previous GWAS; these were first tested for association with asthma and significant findings also against the other allergic diseases.

RESULTS

The heritability of any childhood asthma was 0.82 (95% CI 0.79-0.85). For the other allergic diseases, the range was approximately 0.60-0.80. Associations for six SNPs with asthma were replicated, including rs2305480 in the GSDMB gene (OR 0.80, 95% CI 0.74-0.86, P = 1.5*10(-8) ; other significant associations all below P = 3.5*10(-4) ). Of these, only rs3771180 in IL1RL1 was associated with any other allergic disease (for hay fever, OR 0.64, 95% CI 0.53-0.77, P = 2.5*10(-6) ).

CONCLUSION

Asthma and allergic diseases of childhood are highly heritable, and these high-risk genetic variants associated specifically with childhood asthma, except for one SNP shared with hay fever.

Impact of asthma medication and familial factors on the association between childhood asthma and attention-deficit/hyperactivity disorder: a combined twin- and register-based study: Epidemiology of Allergic Disease

BACKGROUND

Asthma and attention-deficit/hyperactivity disorder (ADHD) are prevalent in childhood and may cause functional impairment and stress in families. Previous research supports an association between asthma and ADHD in children, but several aspects of this relationship are unclear.

OBJECTIVE

Our aim was to study whether the association between asthma and ADHD is restricted to either the inattentive or the hyperactive/impulsive symptoms of ADHD, to explore the impact of asthma severity and asthma medication and the contribution of shared genetic and environmental risk factors on the asthma-ADHD relationship.

METHODS

Data on asthma, ADHD, zygosity and possible confounders were collected from parental questionnaires at 9 or 12 years on 20 072 twins through the Swedish Twin Register, linked to the Swedish Medical Birth Register, the National Patient Register and the Prescribed Drug Register. The association between asthma and ADHD, the impact of asthma severity and medication, was assessed by generalized estimating equations. Cross-twin-cross-trait correlations (CTCT) were estimated to explore the relative importance of genes and environment for the association.

RESULTS

Asthmatic children had a higher risk of also having ADHD [odds ratio (OR) 1.53, 95% confidence interval (CI): 1.16-2.02]. The association was not restricted to either of the two dimensions of ADHD. The magnitude of the association increased with asthma severity (OR 2.84, 95% CI: 1.86-4.35) for ≥ 4 asthma attacks in the last 12 months and was not affected by asthma treatment. The CTCTs possibly indicate that the genetic component in overlap of the disorders is weak.

CONCLUSIONS AND CLINICAL RELEVANCE

Childhood asthma, especially severe asthma, is associated with ADHD. Asthma medication seems not to increase the risk of ADHD. Clinicians should be aware of the potential of ADHD in asthma. Optimal asthma care needs to be integrated with effective evaluation and treatment of ADHD in children with co-existing disorders.

The contribution of twin studies to the understanding of the aetiology of asthma and atopic diseases

The prevalence of asthma and other atopic diseases has increased markedly during the past decades and the reasons for this are not fully understood. Asthma is still increasing in many parts of the world, notably in developing countries, and this emphasizes the importance of continuing research aimed at studying the aetiological factors of the disease and the causes of its increase in prevalence. Twin studies enable investigations into the genetic and environmental causes of individual variation in multifactorial diseases such as asthma. Thorough insight into these causes is important as this will ultimately guide the development of preventive strategies and targeted therapies. This review explores the contribution of twin studies to the understanding of the aetiology of asthma and atopic diseases.

Twin Studies of Atopic Dermatitis: Interpretations and Applications in the Filaggrin Era

Aim. The aim of this study was to conduct a systematic review of population-based twin studies of (a) the concordance and heritability of AD and (b) the relationship between AD and asthma and, furthermore, to reinterpret findings from previous twin studies in the light of the emerging knowledge about filaggrin and its role in the atopic march and provide suggestions for future research in this area. Methods. We identified all twin studies (published after 1970) that have calculated the concordance rate and/or the heritability of AD, or the genetic and environmental correlations between AD and asthma. Results. Reported concordance rates for AD ranged, respectively. From 0.15 to 0.86 for MZ and from 0.05 to 0.41 for DZ twins, with an overall ratio of MZ : DZ twins of approximately three. The heritability of AD was estimated to be approximately 75%, and the association between AD and asthma was around 85% explained by genetic pleiotropy. Conclusions. Genetic factors account for most of the variability in AD susceptibility and for the association between AD and asthma. Controversy remains as to whether the atopic diseases are causally related or whether they are diverse clinical manifestations of a common, underlying (genetic) disease trait. Future twin studies may help solve this enigma.

Genome-wide association study of recalcitrant atopic dermatitis in Korean children

BACKGROUND

Atopic dermatitis (AD) is a heterogeneous chronic inflammatory skin disease. Most AD during infancy resolves during childhood, but moderate-to-severe AD with allergic sensitization is more likely to persist into adulthood and more often occurs with other allergic diseases.

OBJECTIVE

We sought to find susceptibility loci by performing the first genome-wide association study (GWAS) of AD in Korean children with recalcitrant AD, which was defined as moderate-to-severe AD with allergic sensitization.

METHODS

Our study included 246 children with recalcitrant AD and 551 adult control subjects with a negative history of both allergic disease and allergic sensitization. DNA from these subjects was genotyped; sets of common single nucleotide polymorphisms (SNPs) were imputed and used in the GWAS after quality control checks.

RESULTS

SNPs at a region on 13q21.31 were associated with recalcitrant AD at a genome-wide threshold of significance (P < 2.0 × 10(-8)). These associated SNPs are more than 1 Mb from the closest gene, protocadherin (PCDH)9. SNPs at 4 additional loci had P values of less than 1 × 10(-6), including SNPs at or near the neuroblastoma amplified sequence (NBAS; 2p24.3), thymus-expressed molecule involved in selection (THEMIS; 6q22.33), GATA3 (10p14), and S-phase cyclin A-associated protein in the ER (SCAPER; 15q24.3) genes. Further analysis of total serum IgE levels suggested 13q21.31 might be primarily an IgE locus, and analyses of published data demonstrated that SNPs at the 15q24.3 region are expression quantitative trait loci for 2 nearby genes, ISL2 and proline-serine-threonine phosphatase interacting protein 1 (PSTPIP1), in immune cells.

CONCLUSION

Our GWAS of recalcitrant AD identified new susceptibility regions containing genes involved in epithelial cell function and immune dysregulation, 2 key features of AD, and potentially extend our understanding of their role in pathogenesis.

Cohort Profile: Swedish Twin Study on Prediction and Prevention of Asthma (STOPPA)

Asthma is a common childhood disease and several risk factors have been identified; however, the impact of genes and environment is not fully understood. The aim of the Swedish Twin study On Prediction and Prevention of Asthma (STOPPA) is to identify environmental (birth characteristics and early life) and genetic (including epigenetic) factors as determinants for asthmatic disease. Based on the Child and Adolescent Twin Study in Sweden (CATSS) (parental interview at 9 or 12 years, N ~23,900) and an asthma and/or wheezing algorithm, we identified a sample of monozygotic (MZ) and dizygotic (DZ) same-sexed twin pairs. The twin pairs were classified as asthma concordant (ACC), asthma discordant (ADC) and healthy concordant (HCC). A sample of 9- to 14-year-old twins and their parents were invited to participate in a clinical examination. Background characteristics were collected in questionnaires and obtained from the National Health Registers. A clinical examination was performed to test lung function and capacity (spirometry with reversibility test and exhaled nitric oxide) and collect blood (serology and DNA), urine (metabolites), feces (microbiota), and saliva (cortisol). In total, 376 twin pairs (752 individual twins) completed the study, response rate 52%. All participating twins answered the questionnaire and >90% participated in lung function testing, blood-, and saliva sampling. This article describes the design, recruitment, data collection, measures, and background characteristics, as well as ongoing and planned analyses in STOPPA. Potential gains of the study include the identification of biomarkers, the emergence of candidates for drug development, and new leads for prevention of asthma and allergic disease.

Natural progression of childhood asthma symptoms and strong influence of sex and puberty

RATIONALE

Asthma prevalence, onset, remission and relapse, and healthcare use have been intensively studied. However, asthma symptom progression through childhood and adolescence has not been well studied, in part due to the challenges in obtaining consistent and robust long-term follow-up data on a large series of subjects with asthma.

OBJECTIVES

To use the asthma diary symptom data of the Childhood Asthma Management Program placebo group (5 yr, 418 subjects, and total 564,518 records) to establish sex-specific high-resolution time courses of the natural progression of asthma symptoms through childhood and adolescence.

METHODS

We used the asthma diary symptom code as a measure of daily disease severity. Annual records of Tanner stage were used to determine the influence of puberty on severity. A data alignment technique was used to derive 13-year time courses of mean symptoms and mean Tanner stage.

MEASUREMENTS AND MAIN RESULTS

Data analyses showed three age- and sex-related phases of asthma symptom progression: Phase 1 (ages 5 and 6 yr)-greater severity in boys; Phase 2 (ages 7 to 9 yr)-no sex difference in severity; and Phase 3 (age 10-17 yr)-greater severity in girls. The continuous decline of symptoms in both sexes stops abruptly at the onset of puberty.

CONCLUSIONS

The severity of asthma symptoms varies through childhood and adolescence, and patterns differ by sex. Puberty has a strong influence on symptom progression in both sexes. Progression of symptoms is a distinct aspect of asthma epidemiology.

Oral allergy syndrome in children

Oral allergy syndrome (OAS) is an allergic reaction that occurs after consumption of fresh fruits and vegetables in patients with allergy to pollen. It is mediated by immunoglobulin E (IgE) antibodies and symptoms arise as a result of cross-reactivity between pollen and plant-derived food. OAS is rarely seen in young children, but the prevalence increases with age. The objectives of the study were to identify the prevalence of OAS and probable risk factors in children and adolescents with seasonal allergic rhinitis (AR). One-hundred and twenty patients with seasonal AR were included. Patients were diagnosed based on their clinical history, skin prick test outcome and specific IgE. In patients describing OAS, prick-by-prick tests with fresh fruit or vegetables were carried out. Thirty-two patients had OAS and it was more frequent in female patients than in male patients. OAS was more frequent in adolescents than in small children and in patients with higher total IgE. OAS was significantly more prevalent in patients with AR and asthma (P=0.0016), as was the case in patients with AR and atopic dermatitis (P=0.0004). OAS is rarely diagnosed in small children, partly because of an inadequate clinical history. Patients with OAS may have some risk factors in addition to pollen allergy, and those with more severe atopy are more likely to develop OAS.

Asthma and height in twins: a cohort and within-pair analyses study

In singletons, asthma may be associated with shorter height and delayed growth during adolescence. Yet, these studies do not account for heritability of asthma, puberty/menarche, and height. We aimed to study the association between asthma and puberty in boys and menarche in girls, and height, in a cohort of twins and subsequently in same-sex twin pairs discordant for asthma. From a Swedish twin cohort, parent- and self-reported data on asthma, puberty/menarche, and height were collected. Pubertal staging was established via the Petersen index. Logistic and linear regression was used to estimate associations between asthma and puberty/menarche and height, respectively. For within-pair analyses in twins discordant for asthma, conditional logistic and linear regression were used. Data on 2,658 (49.1% boys) twins were included. Among boys, asthma prevalence was 8.2% at 8-9 years and 10.2% at 13-14 years. Corresponding numbers for girls were 4.2% and 4.9%, respectively. In the entire cohort, no statistically significant associations were found between current asthma and puberty/menarche. Boys with asthma were shorter than boys without asthma at 8-9 years (on average, 1.86 [0.17-3.56] cm, p = .03) and at 13-14 years (on average, 2.94 [0.98-4.91] cm, p = .003) but not at 19-20 years. No such associations were found for girls. Within same-sex twin pairs discordant for asthma, no statistically significant associations were found for either sex. Twin boys, but not girls, with asthma were shorter than those without asthma. Non-statistically significant estimates from within-pair analyses suggest the association is partly confounded by genetic or familial environmental factors.

Exploring the origins of asthma: Lessons from twin studies

This thesis explores the contribution of twin studies, particularly those studies originating from the Danish Twin Registry, to the understanding of the aetiology of asthma. First, it is explored how twin studies have established the contribution of genetic and environmental factors to the variation in the susceptibility to asthma, and to the variation in several aspects of the clinical expression of the disease such as its age at onset, its symptomatology, its intermediate phenotypes, and its relationship with other atopic diseases. Next, it is explored how twin studies have corroborated theories explaining asthma's recent increase in prevalence, and last, how these fit with the explanations of the epidemiological trends in other common chronic diseases of modernity.

Gene-environment interaction in atopic diseases: a population-based twin study of early-life exposures

INTRODUCTION

The development of atopic diseases early in life suggests an important role of perinatal risk factors.

OBJECTIVES

To study whether early-life exposures modify the genetic influence on atopic diseases in a twin population.

METHODS

Questionnaire data on atopic diseases from 850 monozygotic and 2279 like-sex dizygotic twin pairs, 3-9 years of age, from the Danish Twin Registry were cross-linked with data on prematurity, Cesarean section, maternal age at birth, parental cohabitation, season of birth and maternal smoking during pregnancy, from the Danish National Birth Registry. Significant predictors of atopic diseases were identified with logistic regression and subsequently tested for genetic effect modification using variance components analysis.

RESULTS

After multivariable adjustment, prematurity (gestational age below 32 weeks) [odds ratio (OR) = 1.93, confidence interval (CI) = 1.45-2.56], Cesarean section (OR = 1.25, CI = 1.05-1.49) and maternal smoking during pregnancy (OR = 1.70, CI = 1.42-2.04) significantly influenced the risk of asthma, whereas none of the factors were significantly associated with atopic dermatitis and hay fever. Variance components analysis stratified by exposure status showed no significant change in the heritability of asthma according to the identified risk factors.

CONCLUSION

In this population-based study of children, there was no evidence of genetic effect modification of atopic diseases by several identified early-life risk factors. The causal relationship between these risk factors and atopic diseases may therefore be mediated via mechanisms different from gene-environment interaction.

A genome-wide association study of atopic dermatitis identifies loci with overlapping effects on asthma and psoriasis

Atopic dermatitis (AD) is the most common dermatological disease of childhood. Many children with AD have asthma and AD shares regions of genetic linkage with psoriasis, another chronic inflammatory skin disease. We present here a genome-wide association study (GWAS) of childhood-onset AD in 1563 European cases with known asthma status and 4054 European controls. Using Illumina genotyping followed by imputation, we generated 268 034 consensus genotypes and in excess of 2 million single nucleotide polymorphisms (SNPs) for analysis. Association signals were assessed for replication in a second panel of 2286 European cases and 3160 European controls. Four loci achieved genome-wide significance for AD and replicated consistently across all cohorts. These included the epidermal differentiation complex (EDC) on chromosome 1, the genomic region proximal to LRRC32 on chromosome 11, the RAD50/IL13 locus on chromosome 5 and the major histocompatibility complex (MHC) on chromosome 6; reflecting action of classical HLA alleles. We observed variation in the contribution towards co-morbid asthma for these regions of association. We further explored the genetic relationship between AD, asthma and psoriasis by examining previously identified susceptibility SNPs for these diseases. We found considerable overlap between AD and psoriasis together with variable coincidence between allergic rhinitis (AR) and asthma. Our results indicate that the pathogenesis of AD incorporates immune and epidermal barrier defects with combinations of specific and overlapping effects at individual loci.

A twin study of early-childhood asthma in Puerto Ricans

BACKGROUND

The relative contributions of genetics and environment to asthma in Hispanics or to asthma in children younger than 3 years are not well understood.

OBJECTIVE

To examine the relative contributions of genetics and environment to early-childhood asthma by performing a longitudinal twin study of asthma in Puerto Rican children ≤ 3 years old.

METHODS

678 twin infants from the Puerto Rico Neo-Natal Twin Registry were assessed for asthma at age 1 year, with follow-up data obtained for 624 twins at age 3 years. Zygosity was determined by DNA microsatellite profiling. Structural equation modeling was performed for three phenotypes at ages 1 and 3 years: physician-diagnosed asthma, asthma medication use in the past year, and ≥ 1 hospitalization for asthma in the past year. Models were additionally adjusted for early-life environmental tobacco smoke exposure, sex, and age.

RESULTS

The prevalences of physician-diagnosed asthma, asthma medication use, and hospitalization for asthma were 11.6%, 10.8%, 4.9% at age 1 year, and 34.1%, 40.1%, and 8.5% at 3 years, respectively. Shared environmental effects contributed to the majority of variance in susceptibility to physician-diagnosed asthma and asthma medication use in the first year of life (84%-86%), while genetic effects drove variance in all phenotypes (45%-65%) at age 3 years. Early-life environmental tobacco smoke, sex, and age contributed to variance in susceptibility.

CONCLUSION

Our longitudinal study in Puerto Rican twins demonstrates a changing contribution of shared environmental effects to liability for physician-diagnosed asthma and asthma medication use between ages 1 and 3 years. Early-life environmental tobacco smoke reduction could markedly reduce asthma morbidity in young Puerto Rican children.

Urticaria in monozygotic and dizygotic twins

Aim. To identify risk factors for urticaria, to determine the relative proportion of the susceptibility to urticaria that is due to genetic factors in an adult clinical twin sample, and to further determine whether the genetic susceptibility to urticaria overlaps with the genetic susceptibility to atopic diseases. Methods. A total of 256 complete twin pairs and 63 single twins, who were selected from sibships with self-reported asthma via a questionnaire survey of 21,162 adult twins from the Danish Twin Registry, were clinically interviewed about a history of urticaria and examined for atopic diseases. Data were analysed with Cox proportional hazards regression and variance components models. Results. A total of 151 individuals (26%) had a history of urticaria, whereas 24 (4%) had had symptoms within the past year. Female sex, HR = 2.09 (1.46–2.99), P = 0.000; hay fever, HR = 1.92 (1.36–2.72), P = 0.000; and atopic dermatitis, HR = 1.44 (1.02–2.06), P = 0.041 were significant risk factors for urticaria. After adjustment for sex and age at onset of urticaria in the index twin, the risk of urticaria was increased in MZ cotwins relative to DZ cotwins, HR = 1.42 (0.63–3.18), P = 0.394. Genetic factors explained 45% (16–74%), P = 0.005, of the variation in susceptibility to urticaria. The genetic correlation between urticaria and hay fever was 0.45 (0.01–0.89), P = 0.040. Conclusions. Susceptibility to urticaria is partly determined by genetic factors. Urticaria is more common in women, and in subjects with hay fever and atopic dermatitis, and shares genetic variance with hay fever.

Does eczema in infancy cause hay fever, asthma, or both in childhood? Insights from a novel regression model of sibling data

BACKGROUND

The atopic march hypothesis proposes that eczema precedes the development of asthma and allergic rhinitis.

OBJECTIVE

We sought to assess the evidence for a causal effect of infantile eczema on childhood hay fever, asthma, or both.

METHODS

We used parental reports on infantile eczema and childhood asthma and hay fever for 3778 pairs of 7-year-olds matched to their sibling closest in age within 2 years from the Tasmanian Longitudinal Health Study. We analyzed paired sibling data using a logistic regression model that allowed inference about a causal effect of a familial predictor on a child's outcome by examining the change in association with their cosibling's predictor after adjusting for their own predictor status.

RESULTS

Siblings were concordant for infantile eczema (tetrachoric correlation, 0.40). For having both hay fever and asthma by age 7 years, the association with cosibling's eczema was an odds ratio (OR) of 1.98 (95% CI, 1.37-2.86), which reduced after adjusting for own eczema to an OR of 1.65 (95% CI, 1.17-2.34). For having hay fever only, the association with cosibling's eczema was an OR of 1.68 (95% CI, 1.22-2.31) before and an OR of 1.59 (95% CI, 1.19-2.14) after adjusting for own eczema. There was no association between having asthma only and cosibling's eczema (OR, 1.00; 95% CI, 0.77-1.30).

CONCLUSIONS

Eczema in infancy might have a causal effect on hay fever in children with and perhaps without asthma. The association of infantile eczema on asthma in children without hay fever, which might be early transient wheeze, is unlikely to be causal or familial. These findings have implications for hay fever prevention.

Association between childhood asthma and ADHD symptoms in adolescence--a prospective population-based twin study

BACKGROUND

Cross-sectional studies report a relationship between childhood asthma and attention-deficit hyperactivity disorder (ADHD) symptoms, but the mechanisms are yet unclear. Our objective was to investigate the longitudinal link between childhood asthma and the two dimensions of ADHD (hyperactivity-impulsivity, HI, and inattention, IN) in adolescence. We also aimed to explore the genetic and environmental contributions and the impact of asthma medication.

METHODS

Data on asthma, HI and IN, birth weight, socioeconomic status, zygosity, and medication were collected from the Swedish Medical Birth Register and through parental questionnaires at ages 8-9 and 13-14 years on 1480 Swedish twin pairs born 1985-1986. The association between asthma at age 8-9 and ADHD symptoms at age 13-14 was assessed with generalized estimating equations, and twin analyses to assess the genetic or environmental determinants were performed.

RESULTS

Children with asthma at age 8-9 had an almost twofold increased risk of having one or more symptom of HI (OR 1.88, 95% CI 1.18-3.00) and a more than twofold increased risk to have three symptoms or more of HI (OR 2.73, 95% CI 1.49-5.00) at age 13-14, independent of asthma medication. For IN, no significant relationship was seen. Results from twin modeling indicate that 68% of the phenotypic correlation between asthma and HI (r=0.23, 0.04-0.37) was because of genetic influences.

CONCLUSIONS

Our findings suggest that childhood asthma is associated with subsequent development of HI in early adolescence, which could be partly explained by genetic influences. Early strategies to identify children at risk may reduce burden of the disease in adolescence.

Sex differences and developmental stability in genetic and environmental influences on psychoactive substance consumption from early adolescence to young adulthood

BACKGROUND

Genetic and environmental factors are important in the etiology of substance use. However, little is known about the stability of these factors across development. We aimed to answer three crucial questions about this etiology that have never been addressed in a single study: (1) Is there a general vulnerability to substance consumption from early adolescence to young adulthood? (2) If so, do the genetic and environmental influences on this vulnerability change across development? (3) Do these developmental processes differ in males and females?

METHOD

Subjects included 1480 twin pairs from the Swedish Twin Study of Child and Adolescent Development who have been followed since 1994. Prospective, self-reported regular smoking, alcohol intoxication and illicit drug use were assessed at ages 13-14, 16-17 and 19-20 years. Structural modeling was performed with the program Mx.

RESULTS

An underlying common factor accounted for the association between smoking, alcohol and illicit drug consumption for the three age groups. Common genetic and shared environmental effects showed substantial continuity. In general, as participants aged, the influence of the shared environment decreased, and genetic effects became more substance specific in their effect.

CONCLUSIONS

The current report answers three important questions in the etiology of substance use. The genetic and environmental risk for substance consumption is partly mediated through a common factor and is partly substance specific. Developmentally, evidence was strongest for stability of common genetic effects, with less evidence for genetic innovation. These processes seem to be the same in males and females.

The genetics of asthma and allergic disease: a 21st century perspective

Asthma and allergy are common conditions with complex etiologies involving both genetic and environmental contributions. Recent genome-wide association studies (GWAS) and meta-analyses of GWAS have begun to shed light on both common and distinct pathways that contribute to asthma and allergic diseases. Associations with variation in genes encoding the epithelial cell-derived cytokines, interleukin-33 (IL-33) and thymic stromal lymphopoietin (TSLP), and the IL1RL1 gene encoding the IL-33 receptor, ST2, highlight the central roles for innate immune response pathways that promote the activation and differentiation of T-helper 2 cells in the pathogenesis of both asthma and allergic diseases. In contrast, variation at the 17q21 asthma locus, encoding the ORMDL3 and GSDML genes, is specifically associated with risk for childhood onset asthma. These and other genetic findings are providing a list of well-validated asthma and allergy susceptibility genes that are expanding our understanding of the common and unique biological pathways that are dysregulated in these related conditions. Ongoing studies will continue to broaden our understanding of asthma and allergy and unravel the mechanisms for the development of these complex traits.

Association screening in the Epidermal Differentiation Complex (EDC) identifies an SPRR3 repeat number variant as a risk factor for eczema

The genetically determined impairment of the skin barrier is a primary cause of eczema. As numerous genes essential for an intact epidermis reside within the epidermal differentiation complex (EDC), we screened the National Center for Biotechnology Information (NCBI) database for putatively functional polymorphisms in the EDC genes and tested them for association with eczema. We identified 20 polymorphisms with predicted major impact on protein function. Of these, 4 were validated in 94 eczema patients: a nonsense mutation in FLG2 (rs12568784), a stop codon mutation in LCE1D (rs41268500), a 24-bp deletion in SPRR3 (rs28989168), and a frameshift mutation in S100A3 (rs11390146). The minor allele frequencies were 15.1, 6.1, 47.2, and 0.4%, respectively. Association testing of the validated polymorphisms in 555 eczema patients and 375 controls identified a significant effect of rs28989168 (SPRR3) on eczema. The association was replicated in another 1,314 cases and 1,322 controls, yielding an overall odds ratio of 1.30 (95% confidence interval 1.12-1.51; P=0.00067) for a dominant mode of inheritance. Small proline-rich proteins (SPRRs) are crossbridging proteins in the cornified cell envelope (CE), which provides the main barrier function of stratified squamous epithelia. The SPRR3 variant associated with eczema carried an extra 24-bp repeat in the central domain, which may alter the physical properties of the CE.

Immunological and genetic aspects of asthma and allergy

Prevalence of allergy and allergic asthma are increasing worldwide. More than half of the US population has a positive skin prick test and approximately 10% are asthmatics. Many studies have been conducted to define immunological pathways underlying allergy and asthma development and to identify the main genetic determinants. In the effort to find missing pieces of the puzzle, new genomic approaches and more standardized ones, such as the candidate gene approach, have been used collectively. This article proposes an overview of the actual knowledge about immunological and genetic aspects of allergy and asthma. Special attention has been drawn to the challenges linked to genetic research in complex traits such as asthma and to the contribution of new genomic approaches.

Genetic risk factors for disordered eating in adolescent males and females

The etiologic role of genetic and environmental factors on disordered eating was examined in a sample of 15- to 17-year-old female-female, male-male, and opposite-sex twin pairs. Also assessed was whether a single factor is underlying 3 facets (body dissatisfaction, drive for thinness, bulimia) of disordered eating, including the possible importance of sex differences. Univariate model-fitting analyses indicated that genetic factors are more important for girls and environment more important for boys for body dissatisfaction and drive for thinness. A multivariate common factor analysis indicated that a single factor accounted for the association among these 3 facets of disordered eating in both sexes. However, only 50% of the genetic risk for this factor is shared between the sexes.

Genome-wide association studies in the genetics of asthma

The field of asthma genetics has progressed rapidly over the past decade, implicating many genes and variants in the etiology of this complex disease. However, many of these factors have failed to replicate consistently, indicating a high false-positive rate and/or insufficient power for the detection of small effects. Technological limitations also have restricted the potential to detect novel mechanisms, fostering a dependence on existing knowledge. Since its inception almost 4 years ago, genome-wide association (GWA) has transformed genetic studies of multifactorial traits and yielded unprecedented insights into mechanisms of causation. Asthma is at the forefront of this revolution, as it uses GWA to map not only genetic determinants of clinical status but also transcript and protein abundance and structural (copy number) variants that may underlie disease susceptibility. In this review, we consider the applications of GWA data to asthma and describe the factors likely to influence the procedure's success.

Messages from the Aalst Allergy Study

BACKGROUND

The prevalence of sensitization and allergic disease has increased significantly worldwide. The aim of the "Aalst Allergy Study" was to document prevalences of sensitization and allergic symptoms, and to evaluate the effect of personal and environmental influences on these prevalences in an unbiased Belgian pediatric population.

METHODS

A cross-sectional study was performed in an unbiased population of 2021 Belgian schoolchildren (3.4-14.8 years). Skin prick testing with the most common aeroallergens was performed. Allergic symptoms as well as potential risk factors for sensitization and allergic disease were documented by a parental questionnaire.

RESULTS

The prevalence of sensitization to the most common aeroallergens and the prevalence of allergic diseases (eczema, asthma and rhinoconjunctivitis) were in line with the data in the literature. The association of current allergic symptoms with sensitization was only significant in the children aged > or =6 years. Age, gender, body mass index, bedroom environment and exposure to pets were the factors significantly associated with sensitization and allergic symptoms.

CONCLUSIONS

Our study corroborates the reported prevalences of sensitization and allergic diseases. Moreover the study illustrates the complexity of the search for factors involved in the process of sensitization and allergic disease. The impact of different potential causative factors is not only influenced by mutual interactions of these factors, but also by the existence of distinct subtypes of disease.

Twins studies as a model for studies on the interaction between smoking and genetic factors in the development of chronic bronchitis

Smoking is the main risk factor for COPD (chronic obstructive pulmonary disease) but genetic factors are of importance, since only a subset of smokers develops the disease. Sex differences have been suggested both in disease prevalence and response to environmental exposures. Furthermore, it has been shown that acquisition of ‘addiction’ to smoking is partly genetically mediated. Disease cases and smoking habits were identified in 44919 twins aged >40 years from the Swedish Twin Registry. Disease was defined as self-reported chronic bronchitis or emphysema, or recurrent cough with phlegm. The results showed that chronic bronchitis seems to be more prevalent among females, and that the heritability estimate for chronic bronchitis was a moderate 40% and only 14% of the genetic influences were shared by smoking. In addition, 392 twins have been invited to a clinical investigation to evaluate: (i) to what extent genetic factors contribute to individual differences (variation) in FEV1 (forced expiratory volume in 1 s), vital capacity and DLCO (diffusion capacity), taking sex into consideration, and (ii) whether smoking behaviour and respiratory symptoms influence these estimates.

Intrauterine testosterone exposure and risk for disordered eating

Previous research has suggested that prenatal testosterone exposure masculinises disordered eating by comparing opposite- and same-gender twins. The objective of the current study is to replicate this finding using a sample of 439 identical and 213 fraternal females, 461 identical and 344 fraternal males, and 361 males and 371 females from opposite-gender twin pairs. Disordered eating was compared across twin types using the Eating Disorder Inventory-2. Inconsistent with previous findings, a main effect of co-twin gender was not found. Our results raise questions about the validity of prior evidence of the impact of prenatal testosterone exposure on patterns of disordered eating.

Etiological relationships in atopy: a review of twin studies

The genetics of asthma and atopy has been studied frequently in twin populations from various parts of the world. However, emphasis has been put on univariate analysis of questionnaire data, whereas clinical and intermediate traits only sporadically have been studied, especially in multivariate settings. This review focuses on multivariate twin studies of atopy and related traits. We conclude that the genetic liability to most atopic traits is significantly correlated but that trait-specific genes also play a role. Previous studies have estimated the genetic correlation between upper and lower respiratory allergic symptoms, that is, asthma and hay fever, to be between .47 and .95. Furthermore, atopic traits share a portion of their genetic determinants with other complex disorders like obesity and behavioral traits. A correlation of about .3 and .34 has been reported between genes associated with asthma and obesity, and between genes associated with asthma and depression, respectively. We emphasize that multivariate methods applied to twin studies, especially when genetic marker information is available, provide a valuable framework within which complex etiological mechanisms underlying atopy can be disentangled.