Familial risks for asthma among twins and other siblings based on hospitalizations in Sweden

Environmental exposures influence multigenerational epigenetic transmission

Epigenetic modifications control gene expression and are essential for turning genes on and off to regulate and maintain differentiated cell types. Epigenetics are also modified by a multitude of environmental exposures, including diet and pollutants, allowing an individual's environment to influence gene expression and resultant phenotypes and clinical outcomes. These epigenetic modifications due to gene-environment interactions can also be transmitted across generations, raising the possibility that environmental influences that occurred in one generation may be transmitted beyond the second generation, exerting a long-lasting effect. In this review, we cover the known mechanisms of epigenetic modification acquisition, reprogramming and persistence, animal models and human studies used to understand multigenerational epigenetic transmission, and examples of environmentally induced epigenetic change and its transmission across generations. We highlight the importance of environmental health not only on the current population but also on future generations that will experience health outcomes transmitted through epigenetic inheritance.

Large-scale health insurance study showed that antibiotic use in infancy was associated with an increase in atopic dermatitis

AIM

This retrospective large-scale study examined the association between prescribing antibiotics for infants and subsequent atopic dermatitis (AD).

METHODS

The data covered the period from 1 January 2005 to 31 December 2014 and were extracted from a Japanese health insurance claims database. The exposure was being prescribed antibiotics at less than 12 months of age and the outcome was a subsequent diagnosis of AD. The primary analysis method was multivariable Cox proportional hazard regression analysis. A sibling-matched analysis was also performed to adjust for shared familial and environmental confounders.

RESULTS

This study comprised 85 954 infants: 8654 (10.1%) who had received antibiotics and 77 300 who had not. AD was diagnosed in 1183 (13.7%) and 10 325 (13.4%) infants respectively. The exposed group was more likely to develop AD than the non-exposed group, but this association disappeared when we carried out the secondary, sibling-matched analysis of the two groups. Other risk factors for AD were macrolides, aminoglycosides, food allergies and histamine H1 receptor antagonists.

CONCLUSION

Antibiotic use in infancy was associated with a subsequent increase in the incidence of AD. This association should be considered when prescribing antibiotics, but antibiotic use may not be a critical factor for the development of AD.

Exploring the evidence for epigenetic regulation of environmental influences on child health across generations

Environmental exposures, psychosocial stressors and nutrition are all potentially important influences that may impact health outcomes directly or via interactions with the genome or epigenome over generations. While there have been clear successes in large-scale human genetic studies in recent decades, there is still a substantial amount of missing heritability to be elucidated for complex childhood disorders. Mounting evidence, primarily in animals, suggests environmental exposures may generate or perpetuate altered health outcomes across one or more generations. One putative mechanism for these environmental health effects is via altered epigenetic regulation. This review highlights the current epidemiologic literature and supporting animal studies that describe intergenerational and transgenerational health effects of environmental exposures. Both maternal and paternal exposures and transmission patterns are considered, with attention paid to the attendant ethical, legal and social implications.

Functional abdominal pain disorders and asthma: two disorders, but similar pathophysiology?

INTRODUCTION

Functional abdominal pain disorders (FAPDs) and asthma are common ailments affecting both children and adults worldwide. Multiple studies have demonstrated an association between these two disorders. However, the exact reason for this observed association is not apparent.

AREAS COVERED

The current review has explored available literature and outlined multiple underlying pathophysiological mechanisms, common to both asthma and FAPDs, as possible reasons for this association.

EXPERT OPINION

Smooth muscle dysfunction, hypersensitivity and hyper-responsiveness, mucosal inflammation, and barrier dysfunction involving gastrointestinal and respiratory tracts are the main underlying pathophysiological mechanisms described for the generation of symptoms in FAPDs and asthma. In addition, alterations in neuroendocrine regulatory functions, immunological dysfunction, and microbial dysbiosis have been described in both disorders. We believe that the pathophysiological processes that were explored in this article would be able to expand the mechanisms of the association. The in-depth knowledge is needed to be converted to therapeutic and preventive strategies to improve the quality of care of children suffering from FAPDs and asthma.

Familial associations between autoimmune hepatitis and primary biliary cholangitis and other autoimmune diseases

Autoimmune hepatitis (AH) and primary biliary cirrhosis (PBC) are autoimmune diseases (AIDs) targeting cellular components of the liver. Being rare diseases, limited data are available about familial risks among these AIDs (concordant) or between them and other AIDs (discordant). We aimed to carry out an unbiased study on these AIDs based on medically diagnosed patients. We collected data on patients diagnosed in Swedish hospitals with AH, PBC and other AIDs and calculated familial standardized incidence ratios (SIRs) for concordant and discordant familial relative risks. The number of AH patients was 6,269, of whom 43.0% were male; patient numbers for PBC were 4,269, with 17.8% males. AH accounted for 0.8% and 0.6% of all hospitalized AIDs in Sweden. For AH only the familial risk between siblings was significant (3.83). For PBC the risks for offspring of parents (9.05) and siblings (10.88) were high, but only risk for females was significant. Spousal risks were very high, 5.91 and 6.07 for AH. Risk for AH was 2.21 in families of PBC, and it was 2.47 for PBC in families of AH patients. Among other AIDs, 14 showed a significant association with AH, compared to 16 AIDs with PBC. The surprising finding in this nation-wide family study on medically diagnosed patients was the high risk for AH (6.0) between spouses, which exceed the risk between siblings, suggesting the existence of strong environmental risk factors. AH and PBC were associated with multiple other AIDs. The results call attention to environmental factors in AID etiology which should also be in focus in taking anamnestic data from patients.

Prenatal and early-life antibiotic use and risk of childhood asthma: A retrospective cohort study

BACKGROUND

Although associations between antibiotic exposure in infants and asthma development are reported, few studies have examined the effects of prenatal exposure to antibiotics. We evaluated this association considering the antibiotic types using a large-scale claim database in Japan.

METHODS

This retrospective study using health insurance administrative claim data in Japan included children born between January 2005 and September 2014. We constructed 2 cohorts: initial cohort, with information on children's mothers, and sibling cohort, with at least one sibling. Cox proportional hazard regression and sibling-matched cohort analyses were performed to determine the association between exposure to antibiotics in utero or the first year of life and asthma development until age 6.

RESULTS

In the initial cohort, antibiotic exposure during the foetal period was associated with early asthma development (until age 3; HR: 1.18, 95% CI: 1.08-1.30). However, this association disappeared after 3 years. The association between antibiotic exposure in the first year of life and asthma was stronger in early (HR: 2.43, 95% CI: 2.20-2.69) than later (HR: 1.23, 95% CI: 1.11-1.36) life. In the sibling cohort, we observed positive associations between foetal exposure and asthma by adjusting for familial factors (HR: 1.34, 95% CI: 1.05-1.72), which remained during the first year of life (HR: 1.62, 95% CI: 1.27-2.07).

CONCLUSIONS

Exposure to antibiotics during the first year of life was associated with childhood asthma even after adjusting for familial factors. However, a weak association was observed between prenatal antibiotic exposure and asthma development.

Depression or anxiety in adult twins is associated with asthma diagnosis but not with offspring asthma

BACKGROUND

Asthma is common in both children and adults in the Western world, just like anxiety and depression. While some research has revealed that these diseases might share important environmental and pathophysiological aspects, the exact mechanisms still remain unclear.

OBJECTIVE

To study the correlation firstly between depression or anxiety and asthma diagnosis in adult twins and secondly the association between parental depression or anxiety and offspring asthma in children of twins.

METHODS

In total, 24 685 adult twins aged 20-47 years were interviewed or completed a Web-based questionnaire and their children were identified through the Multi-Generation Register. Asthma diagnosis was obtained from the Patient Register and the Prescribed Drug Register. Assessment of depression and anxiety was obtained from questionnaires using Center for Epidemiologic Studies Depression Scale (CES-D), major depression and generalized anxiety disorder (GAD) from DSM-IV. The association between depression or anxiety and asthma was analyzed with logistic regression adjusting for confounders in twins and offspring. To address genetic and familial environmental confounding, we performed a cotwin analysis using disease-discordant twin pairs.

RESULTS

We found an association between asthma and CES-D, major depression and GAD, for example adjusted OR for major depression and register-based asthma 1.56 (1.36-1.79). Most of the point estimates remained in the co-twin control analysis, indicating that the association was likely not due to genetic or familial environmental factors. There was no association between parental depression and/or anxiety and asthma diagnosis in the offspring which implies lack of genetic confounding.

CONCLUSIONS

We found an association between own asthma diagnosis and anxiety or depression, but not with offspring asthma. Our results indicate that the associations were not due to confounding from genes or environment shared by the twins.

Polymorphisms of TGFB1, TLE4 and MUC22 are associated with childhood asthma in Chinese population

OBJECTIVE

To investigate whether the genetic variants of TGFB1, TLE4, MUC22 and IKZF3 are associated with the development of asthma in Chinese children.

METHODS

572 adolescent asthma patients and 590 age-matched healthy controls were included in this study. A total of four SNPs were genotyped, including rs2241715 of TGFB1, rs2378383 of TLE4, rs2523924 of MUC22, and rs907092 of IKZF3. Allele frequencies of the patients and the control group were compared by the Chi-square test. The Student t test was used to analyse the relationship between genotypes and clinical feature of the patients.

RESULTS

Patients were found to have significantly different frequencies of allele A of rs2241715, allele G of rs2378383 and allele A of rs2523924 as compared with the controls (40.4% vs. 45.9%, p=0.01 for rs2241715; 17.2% vs. 13.4%, p=0.01 for rs2378383; 15.3% vs. 11.9%, p=0.02 for rs2523924). For patients with severe asthma, those with genotype AA/AG of rs2241715 had remarkably higher FEV1% as compared with those with genotype GG (59.1±4.3% vs. 55.4±3.7%, p<0.001). Moreover, those with genotype GG/GA of rs2378383 had remarkably lower FEV1% as compared with those with genotype AA (54.6±2.9% vs. 58.6±4.1%, p<0.001).

CONCLUSIONS

Genes TGFB1, TLE4 and MUC22 are associated with the risk of childhood asthma in Chinese population. Our results associating TGFB1 and TLE4 with clinical features of asthma suggest potential application of these parameters in the management of asthma children.

Refined phenotyping identifies links between preeclampsia and related diseases in a Norwegian preeclampsia family cohort

OBJECTIVE

Preeclampsia is a complex genetic disease of pregnancy with a heterogenous presentation, unknown cause and potential severe outcomes for both mother and child. Preeclamptic women have increased risk for atherothrombotic cardiovascular disease. We aimed to identify heritabilities and phenotypic correlations of preeclampsia and related conditions in the Norwegian Preeclampsia Family Biobank.

METHODS

By applying a variance components model, a total of 493 individuals (from 138 families with increased occurrence of preeclampsia) were classified according to 30 disease-related phenotypes.

RESULTS

Of parous women, 75.7% (263/338) had experienced preeclampsia and 35.7% of women with and 22.4% without preeclampsia delivered children small for gestational age (SGA). We identified 11 phenotypes as heritable. The increased occurrence of preeclampsia was reflected by the presence [heritability (H2r) = 0.60)] and severity (H2r = 0.15) of preeclampsia and being born in a preeclamptic pregnancy (H2r = 0.25). Other heritable phenotypes identified included SGA (H2r = 0.40), chronic hypertension (H2r = 0.57), severity of atherothrombotic cardiovascular disease (H2r = 0.31), BMI (H2r = 0.60) and pulmonary disease (H2r = 0.91). The heritable phenotype preeclampsia overlapped with SGA (P = 0.03), whereas pulmonary disease was phenotypically correlated with atherothrombotic cardiovascular disease (P < 0.01), SGA (P = 0.02) and BMI (P = 0.02).

CONCLUSION

This is the first study identifying the H2r of a range of health-related conditions in preeclamptic families. Our study demonstrates how refinement of phenotypes leads to better H2r estimation and the identification of a biological relationship between preeclampsia and related traits.

Subsequent brain tumors in patients with autoimmune disease

BACKGROUND

Previous studies have reported increased risk of brain tumors after allergic conditions, but no systematic analyses of these tumors in patients with autoimmune disease (AId) have been performed. No data are available on survival among patients with AId from brain tumors. We analyzed systematically risks and survival in histological types of brain tumors among patients who received a diagnosis of 33 different AIds.

PATIENTS AND METHODS

Standardized incidence ratios (SIRs) for brain tumors or hazard ratios (HRs) of deaths after brain tumors were calculated up to 2008 in 402 462 patients hospitalized for AId after 1964 and were compared with data on the population not hospitalized for AIds.

RESULTS

Brain tumors were diagnosed in 880 patients with AId. No increased or decreased risks (SIRs) were noted for glioma, whereas the increased SIRs for meningioma after many AIds were likely to be attributable to surveillance bias. The data on survival showed overall decreases for glioma (HR, 1.15) and meningioma (HR, 1.26). The survival in both was decreased in patients with chronic rheumatic heart disease, multiple sclerosis, and rheumatoid arthritis. Overall, HRs were increased for glioma after 6 AIds and for meningioma after 7 AIds.

CONCLUSIONS

The present data showed that none of the 33 AIds influenced the risk of glioma. However, many AIds negatively influence survival in glioma and meningioma, probably through added physical burden or therapeutic limitations. Information of an existing AId in patients with newly diagnosed brain tumors should help the prognostic assessment and the design of treatment.

Validation of asthma and eczema in population-based Swedish drug and patient registers

PURPOSE

Validated measures of asthma and eczema at the population level remain a challenge. Our aim was to ascertain if register-based information on asthma/eczema medication can function as a proxy for an asthma/eczema diagnosis and to validate register-based asthma diagnoses.

METHODS

Information was requested on all 0-45-year-old individuals with reported asthma/eczema medication and/or diagnoses in the Swedish Prescribed Drug Register and National Patient Register, between July 2005 and December 2009 (N = 250 691). Medical records for 1952 randomly selected individuals were reviewed to estimate the proportion of individuals with the following: (1) asthma/eczema medication that fulfilled predefined criteria of asthma/eczema (positive predictive value (PPV)) and (2) a register-based asthma diagnosis verified as asthma by predefined criteria.

RESULTS

Positive predictive value for asthma by predefined criteria ranged between 0.75 (95%CI: 0.70-0.78) to 0.94 (95%CI: 0.91-0.96), depending on age group. In pre-school children, PPV for asthma in combination with obstructive bronchitis was 0.87 (95%CI: 0.83-0.90), and PPV for eczema was estimated to 0.45 (95%CI: 0.38-0.51). Eighty percent of children 0-4.5 years and 99% of children >4.5-17 years with a register-based diagnosis of asthma were verified as asthmatics.

CONCLUSION

Asthma medication is a suitable proxy for asthma in older children and adults; the same approach is insufficient for eczema. This validation study of two Swedish registers opens for future large nation-wide register-based studies on asthma.

Subsequent leukaemia in autoimmune disease patients

Previous studies have shown that patients diagnosed with some autoimmune (AI) diseases are at an increased risk of leukaemia but limited data are available on survival. We systematically analysed the risks (standardized incidence ratio, SIR) and survival (hazard ratio, HR) in nine types of leukaemia among 402 462 patients hospitalized for any of 33 AI diseases and compared to persons not hospitalized for AI diseases. Risk for all leukaemia was increased after 13 AI diseases and survival was decreased after six AI diseases. SIRs were increased after all AI diseases for seven types of leukaemia, including SIR 1·69 (95% confidence interval (CI): 1·29-2·19) for acute lymphoblastic leukaemia (ALL), 1·85 (95% CI: 1·65-2·07) for acute myeloid leukaemia, 1·68 (95% CI: 1·37-2·04) for chronic myeloid leukaemia, 2·20 (95% CI: 1·69-2·81) for 'other myeloid leukaemia', 2·45 (95% 1·99-2·98) for 'other and unspecified leukaemia', 1·81 (95% CI: 1·11-2·81) for monocytic leukaemia, and 1·36 (95% CI: 1·08-1·69) for myelofibrosis. The HRs were increased for four types of leukaemia, most for myelofibrosis (1·74, 95% CI: 1·33-2·29) and ALL (1·42, 95% CI: 1·03-1·95). Some AI diseases, including rheumatoid arthritis, were associated with increased SIRs and HRs in many types of leukaemia. The present data showed increases in risk and decreases in survival for many types of leukaemia after various AI diseases. Leukaemia is a rare complication in AI disease but findings about this comorbidity at the time of leukaemia diagnosis may help to optimize the treatment and improve survival.

The impact of improved microarray coverage and larger sample sizes on future genome-wide association studies

Genome-wide association studies (GWAS) have identified many single nucleotide polymorphisms (SNPs) associated with complex traits. However, the genetic heritability of most of these traits remains unexplained. To help guide future studies, we address the crucial question of whether future GWAS can detect new SNP associations and explain additional heritability given the new availability of larger GWAS SNP arrays, imputation, and reduced genotyping costs. We first describe the pairwise and imputation coverage of all SNPs in the human genome by commercially available GWAS SNP arrays, using the 1000 Genomes Project as a reference. Next, we describe the findings from 6 years of GWAS of 172 chronic diseases, calculating the power to detect each of them while taking array coverage and sample size into account. We then calculate the power to detect these SNP associations under different conditions using improved coverage and/or sample sizes. Finally, we estimate the percentages of SNP associations and heritability previously detected and detectable by future GWAS under each condition. Overall, we estimated that previous GWAS have detected less than one-fifth of all GWAS-detectable SNPs underlying chronic disease. Furthermore, increasing sample size has a much larger impact than increasing coverage on the potential of future GWAS to detect additional SNP-disease associations and heritability.

Fetal growth and risk of childhood asthma and allergic disease

Introduction

Early genetic and environmental factors have been discussed as potential causes for the high prevalence of asthma and allergic disease in the western world, and knowledge on fetal growth and its consequence on future health and disease development is emerging.

Objective

This review article is an attempt to summarize research on fetal growth and risk of asthma and allergic disease. Current knowledge and novel findings will be reviewed and open research questions identified, to give basic scientists, immunologists and clinicians an overview of an emerging research field.

Methods

PubMed-search on pre-defined terms and cross-references.

Results

Several studies have shown a correlation between low birth weight and/or gestational age and asthma and high birth weight and/or gestational age and atopy. The exact mechanism is not yet clear but both environmental and genetic factors seem to contribute to fetal growth. Some of these factors are confounders that can be adjusted for, and twin studies have been very helpful in this context. Suggested mechanisms behind fetal growth are often linked to the feto-maternal circulation, including the development of placenta and umbilical cord. However, the causal link between fetal growth restriction and subsequent asthma and allergic disease remains unexplained. New research regarding the catch-up growth following growth restriction has posited an alternative theory that diseases later on in life result from rapid catch-up growth rather than intrauterine growth restriction per se. Several studies have found a correlation between a rapid weight gain after birth and development of asthma or wheezing in childhood.

Conclusion and clinical relevance

Asthma and allergic disease are multifactorial. Several mechanisms seem to influence their development. Additional studies are needed before we fully understand the causal links between fetal growth and development of asthma and allergic diseases.

Effect of autoimmune diseases on incidence and survival in subsequent multiple myeloma

Background

Patients with many types of autoimmune diseases (AIDs) are at an increased risk of cancer, which may depend on underlying dysregulation of the immune system or treatment. We systematically analyzed myeloma risk and survival in patients diagnosed with 33 different AIDs.

Methods

Data on patients with AIDs were retrieved from the Swedish Hospital Discharge Register and were linked to myeloma diagnoses from the Cancer Registry. Standardized incidence ratios (SIR) and hazard ratios (HRs) were calculated for subsequent myeloma between 1964 and 2008.

Results

Among patients with the 33 AIDs analyzed, 457 cases of myeloma were diagnosed. The overall SIR for myeloma was 1.12 and the overall HR was 0.92 and non-significant. SIRs for myeloma were significantly increased after ankylosing spondylitis (2.02) and systemic sclerosis (2.63). Only the HR for myeloma after rheumatic fever (5.27) was significantly increased. The SIR for myeloma before age 60 years was 1.45; the SIR for myeloma was only increased in the period 1964–1990 (1.31) and not later (1.04). Only the SIR for myeloma after ankylosing spondylitis was increased in the period 1991–2008 (2.09); the HRs for myeloma were increased after polymyositis/dermatomyositis (6.44) and rheumatic fever (4.43) but there were only three deaths of myeloma after these AIDs.

Conclusions

The present data showed an increase in myeloma SIR after two AIDs, ankylosing spondylitis and systemic sclerosis, and in HR after rheumatic fever. The overall myeloma risk after any AID was no longer increased in the latter follow-up period of 1991 through 2008.

Effect of autoimmune diseases on mortality and survival in subsequent digestive tract cancers

BACKGROUND

Patients with some autoimmune diseases (AIDs) are at increased risk of cancer, possibly a result of an underlying dysregulation of the immune system, medication, treatment or, probably, surveillance bias. Data on cancer mortality and survival in patients previously diagnosed with AIDs would provide novel information on these comorbidities and their clinical implications.

PATIENTS AND METHODS

Standardized mortality ratios (SMRs) and hazard ratios (HRs) were calculated for subsequent deaths from seven digestive tract cancers between 1964 and 2008 in patients hospitalized for any of 33 AIDs.

RESULTS

There were 33 increased SMRs for specific cancers after a defined AID; similarly, 21 HRs were increased. Both the SMR and HR were increased after 10 autoimmune disorders, including pernicious anemia, systemic lupus erythematosus and psoriasis. Increased SMRs and unchanged HRs were noted for 23 cancers. Myasthenia gravis was associated with SMRs for five cancers but no increases in HRs. For nine cancers, including esophageal cancer after ulcerative colitis and rheumatoid arthritis, the SMR was unchanged but the HR increased.

CONCLUSIONS

The increases in SMRs provide evidence that cancer risks were truly increased and largely unaffected by surveillance bias. The prognostic survival data should contribute to clinical evaluation and therapeutic planning.

Risk of asthma and autoimmune diseases and related conditions in patients hospitalized for obesity

BACKGROUND

Although there are putative mechanistic links between obesity and autoimmune diseases, obesity is not considered a risk factor for most autoimmune diseases.

METHODS

Using the nation-wide Hospital Discharge Register we defined a cohort of 29,665 patients hospitalized for obesity since year 1964. The patients were followed for hospitalization for any of 34 autoimmune or related conditions through year 2007. Standardized incidence ratios (SIRs) were calculated for autoimmune diseases in obese individuals compared to those who had not been hospitalized for obesity.

RESULTS

Among 22 immune diseases diagnosed after hospitalization for obesity and in at least 5 patients, the overall SIR was 2.05. Of the individual diseases studied, the risk of 16 was significantly increased; none displayed a decreased risk. Psoriasis (4.54) and Behçet's disease (4.49) exhibited the highest risks, followed by Hashimoto's disease/hypothyroidism (4.12) and asthma (3.39). Small but significant increases in SIRs were also noted for the common autoimmune diseases Graves's disease/hyperthyroidism (1.28) and rheumatoid arthritis (1.37).

CONCLUSIONS

The present population of obese individuals, subsequently diagnosed with a number of autoimmune diseases and related conditions, was hospitalized at a relatively young age. Further studies are needed to describe the morbidity in the obese population at large.

Autoimmune disease and subsequent digestive tract cancer by histology

BACKGROUND

Dysregulation of the immune function in autoimmune diseases could potentially lead to cancer development and there is definite evidence linking some autoimmune mechanisms with cancer. We analyzed systematically the occurrence of histology-specific digestive tract cancers in patients diagnosed with 33 different autoimmune diseases in order to address the question of shared susceptibility.

PATIENTS AND METHODS

Standardized incidence ratios (SIRs) were calculated for subsequent digestive tract cancers up to the year 2008 and in patients hospitalized for autoimmune disease after the year 1964.

RESULTS

Myasthenia gravis associated with five different cancers with SIRs ranging from 1.35 to 2.78. Pernicious anemia, Crohn disease, ulcerative colitis, systemic lupus erythematosis and psoriasis were also associated with cancers at multiple sites. Rheumatoid arthritis associated with no cancer and the standardized incidence ratio was decreased for colon adenocarcinoma, also in ankylosing spondylitis patients.

CONCLUSIONS

Increased risks of cancer were observed in patients with several autoimmune diseases. Myasthenia gravis and pernicious anemia were associated with many cancers; this is possibly related to immunosuppressant medication in myasthenia gravis. The decreased risks in colon and rectal adenocarcinomas in rheumatoid arthritis and ankylosing spondylitis suggest underlying inflammatory mechanisms as the risks may have been suppressed by the use of anti-inflammatory medication.

The impact of type 2 diabetes mellitus on cancer-specific survival: a follow-up study in Sweden

BACKGROUND

Earlier studies have suggested that type 2 diabetes mellitus (T2DM) alters the risk of developing a variety of cancers, but little has been known about the impact of T2DM on cancer prognosis. On the basis of nationwide population-based Swedish registries, the authors of this report compared the cause-specific survival among cancer patients with and without T2DM.

METHODS

Patients with T2DM were identified from the nationwide Swedish Hospital Discharge Register, and cancers were recorded from the Swedish Cancer Registry. Hazard ratios (HRs) were calculated using Cox regression models to compare variations in cause-specific survival between cancer patients with and without T2DM.

RESULTS

Of the 1016,105 cancer patients, 16,123 had been hospitalized with T2DM before their diagnosis of cancer. The mortality rate was significantly higher among cancer patients with T2DM than among those without T2DM (cause-specific HR, 1.38; 95% confidence interval, 1.35-1.41). There were no differences in TNM stage distribution among cancer patients with or without T2DM for the main cancers, with an exception of tumor and metastatic classifications for breast cancer and prostate cancer, respectively.

CONCLUSIONS

The current results indicated that patients with T2DM who are diagnosed with a subsequent cancer are at an increased risk for cause-specific mortality compared with patients who have cancer without T2DM.

The genetic interpretation of area under the ROC curve in genomic profiling

Genome-wide association studies in human populations have facilitated the creation of genomic profiles which combine the effects of many associated genetic variants to predict risk of disease. The area under the receiver operator characteristic (ROC) curve is a well established measure for determining the efficacy of tests in correctly classifying diseased and non-diseased individuals. We use quantitative genetics theory to provide insight into the genetic interpretation of the area under the ROC curve (AUC) when the test classifier is a predictor of genetic risk. Even when the proportion of genetic variance explained by the test is 100%, there is a maximum value for AUC that depends on the genetic epidemiology of the disease, i.e. either the sibling recurrence risk or heritability and disease prevalence. We derive an equation relating maximum AUC to heritability and disease prevalence. The expression can be reversed to calculate the proportion of genetic variance explained given AUC, disease prevalence, and heritability. We use published estimates of disease prevalence and sibling recurrence risk for 17 complex genetic diseases to calculate the proportion of genetic variance that a test must explain to achieve AUC = 0.75; this varied from 0.10 to 0.74. We provide a genetic interpretation of AUC for use with predictors of genetic risk based on genomic profiles. We provide a strategy to estimate proportion of genetic variance explained on the liability scale from estimates of AUC, disease prevalence, and heritability (or sibling recurrence risk) available as an online calculator.

Genome-wide association studies in human populations have facilitated the creation of genomic profiles that combine the effects of many associated genetic variants to predict risk of disease. However, genomic profiles are inherently constrained in their ability to classify diseased from non-diseased individuals dictated by the genetic epidemiology of the disease. In this paper, we use a genetic interpretation to provide insight into the constraints on genomic profiles for risk prediction. We provide a strategy to estimate proportion of genetic variance explained on the liability scale from estimates of AUC, disease prevalence, and heritability available as an online calculator.

Familial association of inflammatory bowel diseases with other autoimmune and related diseases

OBJECTIVES

Familial risk estimates are useful for genetic counseling, etiological understanding, and design of gene identification studies. We wanted to estimate the associations of ulcerative colitis (UC) and Crohn's disease (CD) with 32 autoimmune and related diseases among parents and offspring, singleton siblings, twins, and spouses.

METHODS

The Multigeneration Register in Sweden provides reliable access to information on families among 11.5 million individuals throughout the last century. The diseases in individual family members were obtained through linkage to the Hospital Discharge Register. Standardized incidence ratios (SIRs) and 95% confidence intervals were calculated as relative risks for UC/CD in family members of patients diagnosed with any of the 34 diseases compared with those lacking affected family members through years 1964-2004.

RESULTS

Among a total of 441,642 patients diagnosed with autoimmune and related conditions, 25,846 were diagnosed with UC and 18,885 with CD. Familial cases amounted to 5.4% of all UC patients and 6.5% of CD patients. SIR for UC was 3.9 (95% confidence interval 3.5-4.3) in offspring of affected parents, 4.6 (3.0-7.4) in siblings, 10.4 (6.5-15.8) in families of affected parents and siblings, and 6.3 (1.9-17.7) for monozygotic twins. The respective SIRs for CD were 6.0 (5.4-6.7), 6.3 (4.1-9.8), 34.0 (24.9-45.3), and 23.4 (10.1-51.1). All discordant associations, i.e., those between CD and other diseases, were also found for UC, including ankylosing spondylitis, asthma, polymyalgia rheumatica, psoriasis, and sarcoidosis. For UC, six additional associations were observed. No correlations between specific diseases were found among spouses, but between UC or CD and any disease it was 1.1 (1.0-1.1).

CONCLUSIONS

The concordant familial risks for UC and CD were lower than those commonly cited. Both diseases are associated with several autoimmune and related diseases, suggesting genetic sharing.

Sporadic cases are the norm for complex disease

The results of genome-wide association studies have revealed that most human complex diseases (for example, cancer, diabetes and psychiatric disorders) are affected by a large number of variants, each of which explains a small increase in disease risk, suggesting a pattern of polygenic inheritance. At the same time, it has been argued that most complex diseases are genetically heterogeneous because many sporadic cases are observed, as well as cases with a family history. In this study, under the assumption of polygenic inheritance, we derive the expected proportion of sporadic cases using analytical methods and simulation. We show how the proportion of sporadic cases depends on disease prevalence (K) and heritability on the underlying liability scale (h(L)(2)). We predict the underlying heritability and the proportion of sporadic cases for a range of human complex diseases, and show that this proportion is typically large. For a disease with h(L)(2)=63% and K=0.4%, such as schizophrenia, >83% of proband cases are predicted to be sporadic (no affected first-, second- and third-degree relatives) in typical families (on an average, two children per couple). For the majority of these diseases, a large proportion of sporadic cases is expected under the polygenic model, implying that the observed large proportion of sporadic cases is not informative to the causal mechanism of a complex genetic disease.

Familial factors do not confound the association between birth weight and childhood asthma

OBJECTIVE

Studies have found associations between low birth weight and asthma. However, this association could be due to familial confounding. Our objective was to investigate whether fetal growth and birth weight affect the risk of asthma in childhood, controlling for gestational age (GA), and shared (familial) environment and genetic factors.

PATIENT AND METHODS

Information on asthma, zygosity, birth characteristics, and potential confounders was collected for all 9- and 12-year-old twins through the Swedish Twin Register and Medical Birth Register. To obtain an overall effect of birth weight on risk of asthma, we performed cohort analyses on all twins (N = 10918). To address genetic and shared environmental confounding, we performed a co-twin control analysis by using the 157 monozygotic and 289 dizygotic same-sex twin pairs who were discordant for asthma.

RESULTS

The overall rate of asthma ever was 13.7%. In the cohort analysis, the adjusted odds ratio (OR) for asthma in relation to a 1000-g decrease in birth weight was 1.57 (95% confidence interval [CI]: 1.38-1.79), and for each reduced gestational week the OR was 1.10 (95% CI: 1.07-1.13). In the co-twin control analyses, a 1000-g decrease in birth weight corresponded to an OR of 1.25 (95% CI: 0.74-2.10) for dizygotic same-sex twins and 2.42 (95% CI: 1.00-5.88) for monozygotic twins.

CONCLUSIONS

There is an association between fetal growth and childhood asthma that is independent of GA and shared (familial) environment and genetic factors, which indicates that fetal growth restriction affects lung development, supporting additional studies on the early metabolic and physiologic mechanisms of childhood asthma.

Familial association between type 1 diabetes and other autoimmune and related diseases

AIMS/HYPOTHESIS

In the era of genome-wide association studies, familial risks are used to estimate disease heritability and success in gene identification. We wanted to estimate associations between type 1 diabetes mellitus and 33 autoimmune and related diseases in parents, offspring, singleton siblings and twins.

METHODS

The availability of a Multigeneration Register in Sweden provides reliable access to families throughout the last century. The diseases in individual family members were obtained through linkage to the Hospital Discharge Register. Standardised incidence ratios (SIRs) were calculated as relative risks of contracting type 1 diabetes in family members of affected patients compared with those lacking affected family members.

RESULTS

Among a total of 450,899 patients, 21,168 were diagnosed with type 1 diabetes. Familial cases amounted to 10.3% of all type 1 diabetes patients. SIR for type 1 diabetes was 8.23 in offspring of affected parents, 11.92 in singleton siblings, 39.22 in multiplex families and 21.88 in twins; the calculated risk for monozygotic twins was 32.33. Type 1 diabetes in offspring was associated with 13 diseases in parents, including Addison's disease (SIR 2.41), asthma (1.38), coeliac disease (2.73), Graves' disease/hyperthyroidism (1.86), Hashimoto disease/hypothyroidism (2.35), pernicious anaemia (3.09), primary biliary cirrhosis (3.63), rheumatoid arthritis (2.12), sarcoidosis (1.62), systemic lupus erythematosus (2.04), ulcerative colitis (1.23) and Wegener's granulomatosis (2.12).

CONCLUSIONS/INTERPRETATION

The concordant familial risks for type 1 diabetes were high and the calculated risk for multiplex families and monozygotic twins may be explained by epistatic gene x gene or gene x environment interactions. Familial associations with several autoimmune and related diseases suggest genetic sharing and challenge to gene identification.

Is the association between low birth weight and asthma independent of genetic and shared environmental factors?

Epidemiologic evidence linking birth weight and asthma is inconsistent. The authors examined the association between birth weight and asthma during childhood and adult life in twins. Using prospectively collected data on 21,588 like-sexed Swedish twins of known zygosity born in 1928-1952, they first conducted a cohort study to examine the risk of asthma in relation to birth weight. Next, they conducted nested co-twin control analyses among 643 dizygotic and 365 monozygotic twin pairs discordant for asthma to ascertain whether the association between birth weight and asthma could be confounded by genetic and shared environmental exposures. In the cohort analysis, birth weight of <2,500 g was associated with significantly greater risk of asthma independent of perinatal characteristics and within-twin-pair correlations. In the co-twin control analyses, birth weight of <2,500 g was significantly related to increased risk of asthma among monozygotic twins (relative risk for 2,000 g vs. 2,500 g = 1.58, 95% confidence interval: 1.06, 2.38). A negative association between birth weight and asthma, albeit not statistically significant, was also found among dizygotic twins. In conclusion, there is a negative association between birth weight and asthma in twins that is unlikely to be confounded by genetic or shared environmental factors.

Familial associations of rheumatoid arthritis with autoimmune diseases and related conditions

OBJECTIVE

In the era of genome-wide association studies, familial risks are used to estimate disease heritability and the likelihood of candidate-gene identification. This study was undertaken to estimate associations of rheumatoid arthritis (RA) with any of 33 autoimmune diseases and related conditions among parents and offspring, singleton siblings, twins, and spouses.

METHODS

The Multigeneration Register in Sweden was used as a reliable source of information on Swedish families throughout the last century. Data on autoimmune diseases in individual family members were obtained through linkage to the Hospital Discharge Register. The standardized incidence ratio (SIR) was calculated as a measure of the relative risk of RA in family members of patients with RA or any of 33 other autoimmune diseases or related conditions, as compared with the relative risk of RA in those lacking an affected family member.

RESULTS

Among a total of 447,704 patients, 47,361 were diagnosed as having RA. The SIRs for RA were 3.02 in offspring of affected parents, 4.64 in siblings, 9.31 in multiplex families, 6.48 in twins, and 1.17 in spouses. Significant associations with the familial risk of RA in offspring according to parental proband were observed for ankylosing spondylitis (SIR 2.96), localized scleroderma (SIR 2.40), Sjögren's syndrome (SIR 2.25), systemic lupus erythematosus (SIR 2.13), systemic sclerosis (SIR 1.65), Hashimoto thyroiditis/hypothyroidism (SIR 1.54), pernicious anemia (SIR 1.53), sarcoidosis (SIR 1.40), psoriasis (SIR 1.36), Wegener's granulomatosis (SIR 1.34), and asthma or polymyalgia rheumatica (SIR 1.32).

CONCLUSION

This is the first study to compare the familial risks of RA in relation to a large number of autoimmune diseases and related conditions using data from a single population. The high discordant familial risks in this population suggest that there is extensive genetic sharing between RA and the associated diseases.

Large scale genotyping study for asthma in the Japanese population

Background

Asthma is a complex phenotype that is influenced by both genetic and environmental factors. Genome-wide linkage and association studies have been performed to identify susceptibility genes for asthma. These studies identified new genes and pathways implicated in this disease, many of which were previously unknown.

Objective

To perform a large-scale genotyping study to identify asthma-susceptibility genes in the Japanese population.

Methods

We performed a large-scale, three-stage association study on 288 atopic asthmatics and 1032 controls, by using multiplex PCR-Invader assay methods at 82,935 single nucleotide polymorphisms (SNPs) (1^st stage). SNPs that were strongly associated with asthma were further genotyped in samples from asthmatic families (216 families, 762 members, 2^nd stage), 541 independent patients, and 744 controls (3^rd stage).

Results

SNPs located in the 5' region of PEX19 (rs2820421) were significantly associated with P < 0.05 through the 1^st to the 3^rd stage analyses; however, the P values did not reach statistically significant levels (combined, P = 3.8 × 10^-5; statistically significant levels with Bonferroni correction, P = 6.57 × 10^-7). SNPs on HPCAL1 (rs3771140) and on IL18R1 (rs3213733) were associated with asthma in the 1^st and 2^nd stage analyses, but the associations were not observed in the 3^rd stage analysis.

Conclusion

No association attained genome-wide significance, but several loci for possible association emerged. Future studies are required to validate these results for the prevention and treatment of asthma.

Familial risks for hospitalization with endocrine diseases

CONTEXT

Familial clustering of a disease is an indicator of a possible heritable cause. In the era of genome scans, the consideration of data on heritability should be important in the assessment of the likely success of the scans.

OBJECT

The objective of the study was to carry out a family study on nonthyroid endocrine diseases to search familial clustering of these diseases beyond the known syndromes.

DESIGN AND SETTING

The Swedish Multigeneration Register on 0- to 72-yr-old subjects was linked to the Hospital Discharge Register from years 1964 to 2004.

MAIN OUTCOME MEASURE

Standardized incidence ratios were calculated for offspring of affected parents and siblings by comparing with those whose relatives had no hospitalization for nonthyroid endocrine diseases.

RESULTS

A total of 11,948 hospitalized cases and 443 familial cases were identified. The familial standardized incidence ratios were increased for parathyroid, pituitary, and adrenal hyperfunctions and hypofunctions, some findings consistent with known syndromes, most clearly that for adrenal cortical hypofunction showing recessive inheritance described for autoimmune polyendocrine syndrome 1. The sibling risks were very high for many diseases, but some of these affecting young individual may be due to bias caused by selective hospitalization. A high sibling risk observed for anterior pituitary hypofunction may represent a yet-unknown recessive syndrome.

CONCLUSIONS

To our knowledge this is a first population-based study on nonthyroid endocrine diseases. The results call for further studies to sort out the challengingly high sibling risk for many individual nonthyroid endocrine diseases, whether they are due to bias or possible recessive effects.

Early respiratory infections and asthma among New York City Head Start children

BACKGROUND

Respiratory infections in neonates have been found to predict wheeze among young children. We hypothesized that among preschool children from low-income minority communities in New York City, current asthma would be associated with a history of respiratory infection in the first few months after their birth.

METHODS

We asked parents of children in New York City Head Start centers (preschool programs for children of low-income families) to respond to a questionnaire covering demographic factors, lifestyle, home environment, and health history, including a detailed history of respiratory conditions. We used logistic regression to model the association of asthma and asthma severity with history of respiratory infections, controlling for gender, ethnicity, family history of asthma, and other factors.

RESULTS

Among 1,022 children (mean age 4+/- 0.6 years) whose parents provided information about their health history, 359 (35%) met our criteria for asthma. Overall, 22% had had a cold by 6 months and 17% an ear infection by 8 months of age. In multivariable models, children with asthma had had more colds (OR = 2.8, 95% confidence interval [CI] 1.4-6.0) and ear infections (OR = 3.4, 95% CI 1.7-6.9) in the past year than other children. Associations of respiratory infections with emergency department use for asthma (as a measure of severity) were similar. In models that did not control for infections in the past year, ages at first cold and first ear infection were associated with asthma and emergency department visits in the past year.

CONCLUSIONS

In this sample of preschool children, respiratory infections were common and were associated with asthma and health care utilization for asthma exacerbations. If these findings are confirmed, preventive measures among children who develop such infections at a very early age should be explored to help reduce the burden of asthma in this age group.

Glutathione S-transferase P1, maternal smoking, and asthma in children: a haplotype-based analysis

BACKGROUND

Glutathione S-transferase P1 (GSTP1) plays a role in a spectrum of respiratory diseases; however, the effects of sequence variation across the entire locus in asthma pathogenesis have yet to be determined.

OBJECTIVES

This study was designed to investigate whether sequence variations in the GSTP1 coding and promoter regions are associated with asthma and wheezing outcomes and to determine whether variants affect susceptibility to maternal smoking.

METHODS

Four haplotype tagging SNPs were selected that accounted for 83% of the common haplotypic variation in GSTP1. The associations of GSTP1 variants with asthma and wheezing were assessed among white children in the Children's Health Study (CHS).

RESULTS

The Ile105Val allele and a SNP in the upstream promoter region (SNP1: rs6591255, putative transcription factor 1 binding site) were associated with asthma and wheezing outcomes, an association observed in two cohorts of the CHS recruited in different years. Haplotypes that included both the promoter SNP (i.e., rs6591255) and the 105 Val variant were associated with an increased risk for asthma in non-Hispanic whites. Using SNP- and haplotype-based approaches, the effect of maternal smoking on wheezing was largest in children with the Ile105Val allele.

CONCLUSIONS

Variants in both the promoter and coding regions of the GSTP1 locus may contribute to the occurrence of childhood asthma and wheezing and may increase susceptibility to adverse effects of tobacco-smoke exposure.

Familial risks for common diseases: etiologic clues and guidance to gene identification

Familial clustering of a disease is a direct indicator of a possible heritable cause, provided that environmental sharing can be excluded. If the familial clustering is lacking, the likelihood of a heritable influence is also small. In the era of genome scans, the consideration of data on heritability should be important in the assessment of the likely success of the genome scan. The availability of a Multigeneration Register in Sweden provides a reliable access to families throughout the last century. This Register has been extensively used to study a number of different diseases through linkage to the Hospital Discharge Register. In the present article we review the obtained and some unpublished results for nine main disease classes. For each of these, familial risks are given for four disease subtypes. As measures of familial clustering we use risks between siblings, twins and spouses. Disease correlation between spouses suggests environmental sharing and a higher correlation between siblings and particularly twins shows heritable effects. We will also comment on the established susceptibility genes and the risks conferred by them. The data suggest high heritabilities for chronic obstructive pulmonary disease, asthma, noninfective enteritis and colitis, cerebral palsy and endocrine and metabolic diseases. Among the performed first-generation genome scans on various diseases, the success appears to be related to the a priori heritability estimates. To our knowledge this is a first attempt to summarize familial risks for a large number of diseases using data from a single population on which reasonable uniform diagnostic criteria have been applied.