On June 20, 2013, the American Journal of Epidemiology sponsored a symposium at the Society for Epidemiologic Research's 46th Annual Meeting in Boston, Massachusetts, entitled, “What Is the Role of Epidemiology in the Era of Molecular Biology and Genomics?” The future of epidemiology depends on innovation in generating interesting and important testable hypotheses that are relevant to population health. These new strategies will depend on new technology, both in measurement of agents and environment and in the fields of pathophysiology and outcomes, such as cellular epidemiology and molecular pathology. The populations to be studied, sample sizes, and study designs should be selected based on the hypotheses to be tested and include case-control, cohort, and clinical trials. Developing large mega cohorts without attention to specific hypotheses is inefficient, will fail to address many associations with high-quality data, and may well produce spurious results.
immunology; pathology; study design
Systematic review and meta-analysis to investigate the association between maternal AGTR1 gene single nucleotide polymorphisms (SNPs) and preeclampsia (PE).
A systematic literature search was performed using PubMed, EMBASE, Scopus, and HuGE Literature Finder databases. The review was conducted according to PRISMA guidelines. Summary odds ratios (ORs) for the allelic and genotypic contrasts were calculated and compared to indicate the most appropriate genetic model for the polymorphism of interest. Among-study heterogeneity was assessed using the I2 statistic and publication bias was evaluated visually using funnel plots.
Seven maternal SNPs investigated with PE were found, but only AGTR1 +1166A>C accumulated sufficient evidence for meta-analysis. Summary ORs calculated from eight studies (10 populations involving 845 PE cases and 1150 controls) did not reveal an association between the +1166A>C polymorphism and PE (allelic OR = 1.19, 95% CI: 0.96–1.47). No evidence of publication bias and among-study heterogeneity was detected.
Meta-analysis findings did not support AGTR1 +1166A>C as a susceptibility locus for PE. Other AGTR1 SNPs require more study.
angiotensin II receptor type 1; genetic association study; pregnancy; single nucleotide polymorphism
A genome-wide association study was undertaken to identify maternal single nucleotide polymorphisms (SNPs) and copy-number variants (CNVs) associated with preeclampsia. Case-control analysis was performed on 1070 Afro-Caribbean (n=21 cases and 1049 controls) and 723 Hispanic (n=62 cases and 661 controls) mothers and 1257 mothers of European ancestry (n=50 cases and 1207 controls) from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study. European ancestry subjects were genotyped on Illumina Human610-Quad and Afro-Caribbean and Hispanic subjects were genotyped on Illumina Human1M-Duo BeadChip microarrays. Genome-wide SNP data were analyzed using PLINK. CNVs were called using three detection algorithms (GNOSIS, PennCNV, and QuantiSNP), merged using CNVision, and then screened using stringent criteria. SNP and CNV findings were compared to those of the Study of Pregnancy Hypertension in Iowa (SOPHIA), an independent preeclampsia case-control dataset of Caucasian mothers (n=177 cases and 116 controls). A list of top SNPs were identified for each of the HAPO ethnic groups, but none reached Bonferroni-corrected significance. Novel candidate CNVs showing enrichment among preeclampsia cases were also identified in each of the three ethnic groups. Several variants were suggestively replicated in SOPHIA. The discovered SNPs and copy-number variable regions present interesting candidate genetic variants for preeclampsia that warrant further replication and investigation.
copy-number variant; genome-wide association study; microarray analysis; preeclampsia; single nucleotide polymorphism
To assess whether folic acid intake during the first trimester of pregnancy is related to asthma in the offspring by the age of 6 years.
Prospective cohort study of 1,499 women who were followed from first trimester of pregnancy. Their children were followed until they were 6 years old.
51% of the women used folic acid in the month before conception and 88% in the third month of pregnancy. The adjusted OR per 100 microgram increase in average daily intake of folic acid was 0.98 (95% CI:0.93-1.04). For categories of daily folate intake, there was no evidence of associations with childhood asthma nor evidence of any dose response relation for any time period (all ptrend>0.05)
Our results do not support any association of folic acid supplementation in pregnancy and asthma risk in offspring by age 6 years.
childhood asthma; folic acid; pregnancy
Many studies have reported that antibiotic use may be associated with increased risk of childhood asthma. Respiratory tract infections in small children may be difficult to distinguish from early symptoms of asthma, and studies may have been confounded by “protopathic” bias, where antibiotics are used to treat early symptoms of asthma. These analyses of a cohort including 1,401 US children assess the association between antibiotic use within the first 6 months of life and asthma and allergy at 6 years of age between 2003 and 2007. Antibiotic exposure was associated with increased risk of asthma (adjusted odds ratio = 1.52, 95% confidence interval (CI): 1.07, 2.16). The odds ratio if asthma was first diagnosed after 3 years of age was 1.66 (95% CI: 0.99, 2.79) and, in children with no history of lower respiratory infection in the first year of life, the odds ratio was 1.66 (95% CI: 1.12, 3.46). The adverse effect of antibiotics was particularly strong in children with no family history of asthma (odds ratio = 1.89, 95% CI: 1.00, 3.58) (Pinteraction = 0.03). The odds ratio for a positive allergy blood or skin test was 1.59 (95% CI: 1.10, 2.28). The results show that early antibiotic use was associated with asthma and allergy at 6 years of age, and that protopathic bias was unlikely to account for the main findings.
anti-bacterial agents; asthma; child; cohort studies; hypersensitivity
To estimate whether prenatal exposure to acetaminophen is associated with risk of diagnosed asthma and asthma symptoms in children.
The authors prospectively followed 1,505 pregnant women and their children until 6 years (±3 months) of life. Acetaminophen use in the first and third trimesters of pregnancy was assessed before 24 weeks of gestation and within 1 month of delivery, and asthma in children was assessed when the child was 6 years old. Adjusted odds ratios (aORs) were derived from logistic regression models controlling for potential confounders.
Acetaminophen was used by 69% of women during pregnancy. Use of acetaminophen did not significantly increase the risk of asthma (aOR 0.76, 95% confidence interval [CI] 0.53–1). Acetaminophen use during both the first and the third trimester was associated with a significantly reduced risk of asthma (aOR 0.59, 95% CI 0.36–0.98). There was no evidence of a dose response, and consumption greater than 10,400 mg (32 tablets) a month did not increase risk (aOR 0.99, 95% CI 0.19–5.30).
Our results suggest that acetaminophen use during pregnancy does not increase risk of asthma in children.
Childhood asthma and obesity prevalence have increased in recent years suggesting a potential association. However, the direction of any association is poorly understood and the potential causal-relationship is unknown.
We examined the association between overweight/obesity, defined by body mass index (BMI) <18 years of age, and subsequent physician-diagnosed incident asthma at least one year after BMI assessment. We sought to explore potential effect modification by sex. PubMed and Embase were searched using keywords and restricted to subjects aged 0–18 years. There were no date or language restrictions. From each study we extracted: authors, publication date, location, overweight/obesity definitions, asthma definitions, number of participants, recruitment duration, description of cohort, follow-up time, adjusted effect estimates (with 95% CI) and estimates of subgroup analysis.
Six prospective cohort studies which focused on children <18 years of age met criteria for inclusion. The combined risk ratio (RR) of overweight was associated with asthma (RR = 1.35; 95% CI = 1.15, 1.58). In boys, the combined RR of overweight on asthma was significant (RR = 1.41; 95% CI = 1.05, 1.88). For girls, when BMI was defined by Z-score, the combined RR of overweight on asthma was also significant (RR = 1.19; 95% CI = 1.06, 1.34). The combined risk ratio (RR) of obesity was associated with asthma in both boys and girls (RR = 1.50; 95% CI = 1.22, 1.83), in boys only (RR = 1.40; 95% CI = 1.01, 1.93) and in girls only (RR = 1.53; 95% CI = 1.09, 2.14).
Overweight and, especially, obese children are at increased risk of subsequent physician diagnosed asthma in comparison to normal weight children. Except for sex, no studies reported any other potential effect modifiers. The observed sex effects were inconsistent.
Asthma; Overweight; Obesity; Body mass index; Body weight; Pediatric
Chocolate consumption is associated with favorable levels of blood pressure and other cardiovascular disease risk markers. We analyzed a prospective cohort study to determine if regular chocolate intake during pregnancy is associated with reduced risks of preeclampsia and gestational hypertension (GH).
Subjects were recruited from 13 prenatal care practices in Connecticut (1988-1991). In-person interviews were administered at <16 weeks gestation to ascertain risk factors for adverse pregnancy outcomes. Hospital delivery and prenatal records were abstracted to classify preeclampsia (n=58), GH (n=158), and normotensive pregnancies (n=2351). Chocolate consumption (servings/week) during the 1st and 3rd trimesters was ascertained at initial interview and immediately postpartum, respectively. Consumers of <1 serving/week comprised the referent group. Adjusted odds ratios (aOR) were estimated using logistic regression.
Chocolate intake was more frequent among normotensives (80.7%) than preeclamptics (62.5%) or GH women (75.8%), and associated with reduced odds of preeclampsia (1st trimester: aOR=0.55, 95% CI: 0.32-0.95; 3rd trimester: aOR=0.56, 95% CI: 0.32-0.97). Only 1st trimester intake was associated with reduced odds of GH (aOR=0.65, 95% CI: 0.45-0.87).
These findings provide additional evidence of the benefits of chocolate. Prospective studies are needed to confirm and delineate protective effects of chocolate intake on risk of preeclampsia.
Chocolate; Gestational Hypertension; Preeclampsia; Pregnancy
The innate immune pathway is important in the pathogenesis of asthma and eczema. However, only a few variants in these genes have been associated with either disease. We investigate the association between polymorphisms of genes in the innate immune pathway with childhood asthma and eczema. In addition, we compare individual associations with those discovered using a multivariate approach.
Using a novel method, case control based association testing (C2BAT), 569 single nucleotide polymorphisms (SNPs) in 44 innate immune genes were tested for association with asthma and eczema in children from the Boston Home Allergens and Asthma Study and the Connecticut Childhood Asthma Study. The screening algorithm was used to identify the top SNPs associated with asthma and eczema. We next investigated the interaction of innate immune variants with asthma and eczema risk using Bayesian networks.
After correction for multiple comparisons, 7 SNPs in 6 genes (CARD25, TGFB1, LY96, ACAA1, DEFB1, and IFNG) were associated with asthma (adjusted p-value<0.02), while 5 SNPs in 3 different genes (CD80, STAT4, and IRAKI) were significantly associated with eczema (adjusted p-value < 0.02). None of these SNPs were associated with both asthma and eczema. Bayesian network analysis identified 4 SNPs that were predictive of asthma and 10 SNPs that predicted eczema. Of the genes identified using Bayesian networks, only CD80 was associated with eczema in the single-SNP study. Using novel methodology that allows for screening and replication in the same population, we have identified associations of innate immune genes with asthma and eczema. Bayesian network analysis suggests that additional SNPs influence disease susceptibility via SNP interactions.
Our findings suggest that innate immune genes contribute to the pathogenesis of asthma and eczema, and that these diseases likely have different genetic determinants.
asthma; Bayesian network; genetic association; eczema; innate immunity
Asthma is a complex disease characterized by striking ethnic disparities not explained entirely by environmental, social, cultural, or economic factors. Of the limited genetic studies performed on populations of African descent, notable differences in susceptibility allele frequencies have been observed.
To test the hypothesis that some genes may contribute to the profound disparities in asthma.
We performed a genome-wide association study in two independent populations of African ancestry (935 African American asthma cases and controls from the Baltimore-Washington, D.C. area, and 929 African Caribbean asthmatics and their family members from Barbados) to identify single-nucleotide polymorphisms (SNPs) associated with asthma.
Meta-analysis combining these two African-ancestry populations yielded three SNPs with a combined P-value <10-5 in genes of potential biological relevance to asthma and allergic disease: rs10515807, mapping to alpha-1B-adrenergic receptor (ADRA1B) gene on chromosome 5q33 (3.57×10-6); rs6052761, mapping to prion-related protein (PRNP) on chromosome 20pter-p12 (2.27×10-6); and rs1435879, mapping to dipeptidyl peptidase 10 (DPP10) on chromosome 2q12.3-q14.2. The generalizability of these findings was tested in family and case-control panels of UK and German origin, respectively, but none of the associations observed in the African groups were replicated in these European studies.
Evidence for association was also examined in four additional case-control studies of African Americans; however, none of the SNPs implicated in the discovery population were replicated. This study illustrates the complexity of identifying true associations for a complex and heterogeneous disease such as asthma in admixed populations, especially populations of African descent.
Asthma; GWAS; ADRA1B; PRNP; DPP10; African ancestry; ethnicity; polymorphism; genetic association
We have attempted to quantify the most up-to-date estimate of the association between cigarette smoking by the mother and preterm delivery. Studies were selected for inclusion in this review if they were prospective, reported data stratified across at least two levels of maternal smoking, and defined preterm delivery on the basis of gestational age. In a meta-analysis we combined results from multiple studies that reported on preterm delivery and maternal smoking during pregnancy. Pooled odds ratios were computed for various strata of smoking intensity with the Mantel-Haenszel fixed-effects model. Twenty studies met all inclusion criteria and were included in meta-analysis. The pooled point estimate from 20 prospective studies on any maternal smoking versus no maternal smoking was 1.27 (95% confidence interval, 1.21-1.33). Subgroup analyses stratifying maternal smoking on number of cigarettes per day suggest a dose-response relationship at low to moderate levels of smoking, which was not further increased at high levels of smoking. A nonsignificant level of publication bias appears to exist in the smoking-preterm delivery literature. Cigarette smoking is a preventable risk factor that is associated with preterm delivery. Consistent results across many study populations and research designs and evidence of a dose-response relationship support its causal role in preterm delivery.
Preterm delivery; cigarette smoking; meta-analysis
The x-ray cross complementing group 1 gene (XRCC1) is crucial to proper repair of DNA damage such as single-strand DNA breaks. A non-synonymous polymorphism in XRCC1, 399 G → A, has been shown to reduce effectiveness of such DNA repair and has been associated with the risk of certain cancers. The known risk for glioma from high dose ionizing radiation makes associations between this polymorphism and glioma of particular interest.
A systematic literature review and meta-analysis was conducted to explore the association between XRCC1 399 G → A and glioma. Subgroup analyses by grade, gender, genotyping method, country in which study was conducted, and study size were conducted when data were available and validity of the results were assessed by influence analyses and exploration of potential publication bias.
Six studies were eligible for meta-analysis including data on 2,362 Caucasian glioma cases and 3,085 Caucasian controls. Pooled analysis yielded a significant association between the variant of interest and risk of glioma (OR = 1.17, 95% CI: 1.05-1.30) which was found to be disproportionately driven by a single study. Exclusion of this study, in an influence analysis, produced no statistically significant evidence of association with glioma (OR = 1.10, 95% CI: 0.98-1.23), and no evidence of publication bias.
This meta-analysis does not suggest a major role of the XRCC1 399 G → A polymorphism in influencing risk of glioma among Caucasians. Future studies should report data separately for glioma subtypes to permit stratified analyses for Grade III and Grade IV glioma and examine other polymorphisms in this gene.
Glioma; XRCC1; Polymorphisms; Meta-analysis
Despite the success of genome-wide association studies for asthma, few, if any, definitively causal variants have been identified and there is still a substantial portion of the heritability of the disease yet to be discovered. Some of this “missing heritability” may be accounted for by family-specific coding variants found to be segregating with asthma.
To identify family-specific variants segregating with asthma, we recruited one family from a previous study of asthma as reporting multiple asthmatic and non-asthmatic children. We performed whole-exome sequencing on all four children and both parents and identified coding variants segregating with asthma that were not found in other variant databases.
Ten novel variants were identified that were found in the two affected offspring and affected mother, but absent in the unaffected father and two unaffected offspring. Of these ten, variants in three genes (PDE4DIP, CBLB, and KALRN) were deemed of particular interest based on their functional prediction scores and previously reported function or asthma association. We did not identify any common risk variants segregating with asthma, however, we did observe an increase in the number of novel, nonsynonymous variants in asthma candidate genes in the asthmatic children compared to the non-asthmatic children.
This is the first report applying exome sequencing to identify asthma susceptibility variants. Despite having sequenced only one family segregating asthma, we have identified several potentially functional variants in interesting asthma candidate genes. This will provide the basis for future work in which more families will be sequenced to identify variants across families that cluster within genes.
Asthma; Whole-exome sequencing; PDE4DIP; CBLB; KALRN
Specific genetic contributions for preeclampsia (PE) are currently unknown. This genome-wide association study (GWAS) aims to identify maternal single nucleotide polymorphisms (SNPs) and copy-number variants (CNVs) involved in the etiology of PE.
A genome-wide scan was performed on 177 PE cases (diagnosed according to National Heart, Lung and Blood Institute guidelines) and 116 normotensive controls. White female study subjects from Iowa were genotyped on Affymetrix SNP 6.0 microarrays. CNV calls made using a combination of four detection algorithms (Birdseye, Canary, PennCNV, and QuantiSNP) were merged using CNVision and screened with stringent prioritization criteria. Due to limited DNA quantities and the deleterious nature of copy-number deletions, it was decided a priori that only deletions would be selected for assay on the entire case-control dataset using quantitative real-time PCR.
The top four SNP candidates had an allelic or genotypic p-value between 10-5 and 10-6, however, none surpassed the Bonferroni-corrected significance threshold. Three recurrent rare deletions meeting prioritization criteria detected in multiple cases were selected for targeted genotyping. A locus of particular interest was found showing an enrichment of case deletions in 19q13.31 (5/169 cases and 1/114 controls), which encompasses the PSG11 gene contiguous to a highly plastic genomic region. All algorithm calls for these regions were assay confirmed.
CNVs may confer risk for PE and represent interesting regions that warrant further investigation. Top SNP candidates identified from the GWAS, although not genome-wide significant, may be useful to inform future studies in PE genetics.
Copy-number variant; Genome-wide association study; Microarray analysis; Preeclampsia; Single nucleotide polymorphism
Respiratory symptoms; wheeze; asthma; maternal anemia
Polymorphisms in the endotoxin-mediated TLR4 pathway genes have been associated with asthma and atopy. We aimed to examine how genetic polymorphisms in innate immunity pathways interact with endotoxin to influence asthma risk in children.
In a previous analysis of 372 children from the Boston Home Allergens and the Connecticut Childhood Asthma studies, 7 SNPs in 6 genes (CARD15, TGFB1, LY96, ACAA1, DEFB1 and IFNG) involved in innate immune pathways were associated with asthma, and 5 SNPs in 3 genes (CD80, STAT4, IRAK2) were associated with eczema. We tested these SNPs for interaction with early life endotoxin exposure (n = 291), in models for asthma and eczema by age 6.
We found a significant interaction between endotoxin and a SNP (rs156265) in ACAA1 (p = 0.0013 for interaction). Increased endotoxin exposure (by quartile) showed protective effects for asthma in individuals with at least one copy of the minor allele (OR = 0.39 per quartile increase in endotoxin, 95% CI 0.15 to 1.01). Endotoxin exposure did not reduce the risk of asthma in children homozygous for the major allele.
Our findings suggest that protective effects of endotoxin exposure on asthma may vary depending upon the presence or absence of a polymorphism in ACAA1.
We investigated if clinicians were altering their care of group B streptococcus (GBS)-positive women in labor to achieve 4 hours of intrapartum antibiotic prophylaxis based on their interpretation of the 2002 Centers for Disease Control (CDC) guidelines on prevention of perinatal GBS disease. We surveyed all clinicians with privileges on the labor floor at our institution about their interpretation and clinical application of the 2002 CDC guidelines. Seventy of 96 eligible clinicians (72.9%) completed our survey. In our survey, only 22.9% of clinicians reported not altering their management of labor in GBS-positive pregnancies that achieved less than 4 hours of prophylaxis. These alterations included “laboring down” or delaying pushing; turning off or decreasing an oxytocin infusion; or delaying or avoiding artificial rupture of membranes. Clinicians are altering their management of labor to attempt to achieve 4 hours of intrapartum prophylaxis. The 2002 CDC guidelines do not specifically recommend prolonging labor and are being interpreted differently in the clinical setting than the authors may have intended. The effects and consequences of this interpretation are unknown.
Group B streptococcus; intrapartum prophylaxis; CDC guidelines; early onset neonatal sepsis
Background and Purpose
Of the 795,000 strokes occurring in the USA each year, over 20% are recurrent events. Little is known about how the rates of recurrent stroke in the country have changed over time. Our objective was to determine national trends in 1-year recurrent ischemic stroke rates by US county among the elderly from 1994 to 2002.
One-year recurrent stroke rates following incident ischemic stroke (ICD-9 433, 434, 436) among all fee-for-service Medicare beneficiaries were determined by US county for 1994–1996, 1997–1999, and 2000–2002. Bayesian spatiotemporal Poisson modeling was used to determine county-specific trends in recurrent stroke rates over time with risk adjustment for demographics, medical history and comorbid conditions.
The analysis included more than 2.5 million beneficiaries (56% women; mean age: 78 years; 87% white; n = 957,933 for 1994–1996; n = 838,330 for 1996–1999; n = 895,916 for 2000–2002) aggregated to all 3,118 US counties. After adjustment for changing patient demographics and comorbidities, there was a 4.5% decrease in recurrent stroke rates from 1994–1996 (13.2%) to 2000–2002 (12.6%; p for trend <0.0001). The geographic and temporal patterns were not uniform; the recurrent stroke rates decreased within sections of the Southeast (the ‘stroke belt’), but increased in counties in the middle and western sections of the USA.
The overall recurrent ischemic stroke rates declined by almost 5% from 1994 to 2002, but temporal patterns varied markedly by region. Additional research is needed to identify the reasons for this geographic disparity.
Acute ischemic stroke; Geographic pattern; Time trends; Recurrent stroke
Traffic exhaust is a source of air contaminants that have adverse health effects. Quantification of traffic as an exposure variable is complicated by aerosol dispersion related to variation in layout of roads, traffic density, meteorology, and topography. A statistical model is presented which uses Geographic Information Systems (GIS) technology to incorporate variables into a generalized linear model that estimates distribution of traffic-related pollution. Exposure from a source is expressed as an integral of a function proportional to average daily traffic and a nonparametric dispersion function which takes the form of a step, polynomial or spline model. The method may be applied using standard regression techniques for fitting generalized linear models. Modifiers of pollutant dispersion such as wind direction, meteorology, and landscape features can also be included. Two examples are given to illustrate the method. The first employs data from a study in which NO2 (a known pollutant from automobile exhaust) was monitored outside of 138 Connecticut homes, providing a model for estimating NO2 exposure. In a second example, estimated levels of nitrogen dioxide (NO2) from the model, as well as a separate spatial model, were used to analyze traffic-related health effects in a study of 761 infants.
Traffic; Dispersion models; Geographic Information Systems; Generalized Linear Models; Splines
Asthma is a chronic inflammatory disease of the lungs which affects more than 6.5 million American children. A family-based genome-wide association study of copy-number variation identified an association between decreased copy-number at TCRγ and childhood allergic asthma. TCRγ encodes the T-cell receptor gamma glycoprotein, a cell-surface protein found on T-cells and involved in cell-mediated immunity. Using quantitative real-time PCR, we sought to determine if copy-number variation at TCRα, TCRβ or TCRγ was associated with childhood allergic asthma in an independent cohort of 94 cases and 455 controls using DNA from buccal swabs. Copy-number variation at these loci is well-known, but appears to be dominated by somatic mutations. Genotyping results indicated that copy-number variants at these genes are largely somatic mutations, as inheritance did not show Mendelian consistency. In these mosaic cell populations, copy-number was significantly reduced among asthmatic children at TCRγ (p = 0.0199), but was not associated at TCRα or TCRβ (p = 0.7972 and 0.8585, respectively). These findings support the association between reduced copy-number at TCRγ and childhood allergic asthma. Further work is needed to resolve whether reduced copy-number at TCRγ predisposes individuals to asthma, or whether deletion of this gene is a somatic response to the disease.
T-cell receptor gamma; Copy Number Variant; allergic asthma; mosaicism
Asthma is a phenotypically diverse disease with genetic susceptibility. A single nucleotide polymorphism (SNP) in the CD14 gene at position -260 (also known as -159) C>T has been inconsistently associated with asthma. The aim of this study was to estimate the combined likelihood of developing asthma given the CD14 -260C>T genotype.
Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic search and meta-analysis of the literature was conducted to estimate the association between this SNP and asthma. Planned subgroup analyses were performed to detect potential sources of heterogeneity from selected study characteristics. Post-hoc sensitivity analysis was performed to identify studies exerting excessive influence on among-study heterogeneity and combined effects.
Meta-analysis of 23 studies yielded a non-significant overall association with high heterogeneity across studies. After restricting analysis to studies using atopic asthma and non-atopic non-asthma case-control phenotypes and excluding studies influencing heterogeneity, the genotype-specific odds ratios (ORs) suggested a codominant model. Carriers of the TT and CT genotypes were about 33% less likely (OR = 0.67, 95% CI: 0.54-0.84) and about 20% less likely (OR = 0.80, 95% CI: 0.66-0.95), respectively, to have atopic asthma compared to carriers of the CC genotype. Among-study heterogeneity may be explained by overly broad asthma phenotype definitions, gene-environment interactions, and gene-gene interactions.
A protective dose-response relationship between the CD14 -260T allele and atopic asthma susceptibility was observed. These results demonstrate the importance of precisely specified case-control groups as well as the need to assess interactions in the investigation of complex diseases such as asthma.
While geographic disparities in stroke mortality are well documented, there are no data describing geographic variation in recurrent stroke. Accordingly, we evaluated geographic variations in 1-year recurrent ischemic stroke rates in the USA with adjustment for patient characteristics.
One-year recurrent stroke rates for ischemic stroke (International Classification of Diseases, 9th Revision codes 433, 434 and 436) following hospital discharge were calculated by county for all fee-for-service Medicare beneficiaries from 2000 to 2002. The rates were standardized and smoothed using a bayesian conditional autoregressive model that was risk-standardized for patients’ age, gender, race/ethnicity, prior hospitalizations, Deyo comorbidity score, acute myocardial infarction, congestive heart failure, diabetes, hypertension, dementia, cancer, chronic obstructive pulmonary disease and obesity.
The overall 1-year recurrent stroke rate was 9.4% among 895,916 ischemic stroke patients (mean age: 78 years; 56.6% women; 86.6% White, 9.7% Black and 1.2% Latino/Hispanic). The rates varied by geographic region and were highest in the South and in parts of the West and Midwest. Regional variation was present for all racial/ethnic subgroups and persisted after adjustment for individual patient characteristics.
Almost 1 in 10 hospitalized ischemic stroke patients was readmitted for an ischemic stroke within 1 year. There was heterogeneity in recurrence patterns by geographic region. Further work is needed to understand the reasons for this regional variability.
Stroke, recurrent; Small-area analysis; Variation, geographic; Recurrence