In summary, the GCPCR is a unique longitudinal biorepository that links clinical data and health outcomes to biologic samples and molecular data. It provides an infrastructure for better characterization of phenotypes so that observed heterogeneity in allergic diseases can be dissected. It is unique in that children with allergic disorders are recruited in parallel to healthy controls. Subjects' asthma, allergy, and skin symptoms; past medical, family, social, diet, and environmental histories; physical activity; medication adherence; perceived quality of life; and demographics are ascertained. DNA is collected from all participants, and other biospecimens such as blood, hair, and nasal epithelial cells are collected on a subset. The GCPCR is being utilized by several ongoing studies. It is an invaluable resource for clinical and translational research in allergy as demonstrated by the broad range of research activities that the GCPCR supports, including genetics, environmental, obesity, health outcomes, health literacy, and health disparities studies.
Ongoing genetic association studies
The factors that contribute to development of asthma and other allergic diseases are diverse, but the greatest risk factor is a family history or genetic predisposition. Identifying genes associated with these complex diseases remains a fundamental challenge. Currently, the GCPCR has more than 6,317 participants predominantly of Caucasian and African American descent (). More than 93% of these participants have banked DNA samples (57% saliva, 43% buccal) collected for the purpose of genetic studies. Common biologic pathways underlie allergic diseases such as asthma, atopic dermatitis, and food allergy with the immune system and the epithelium being key links. Indeed, epithelial cells are increasingly recognized as critical participants in the pathogenesis of allergic inflammation. In fact, we previously reported that even healthy appearing skin of children with atopic dermatitis has a defective skin barrier function that is associated with disease severity18
further supporting the likely role of genetic predisposition in this disease.
As such, NIH-funded studies are underway at CCHMC to elucidate the genes and biologic pathways that contribute allergic diseases such as atopic dermatitis and asthma. As the current standard of asthma treatment is ineffective in 40–70% of patients,19
the need for novel and alternative therapies, such as those that target the epithelium, is high. Therefore, we recently designed a custom Illumina GoldenGate assay with 768 predominantly tagging SNPs within 52 genes that are located not only in pathways related to the epithelium, but also in those related to innate and adaptive immunity, inflammation, oxidative stress, microbe sensing, and protease inhibition. We genotyped 750 childhood asthmatics age 4 to 17 years old compared to 419 nonasthmatic/allergic children and 349 nonasthmatic/nonallergic controls using our custom assay in order to elucidate genetic associations with asthma.20–22
A similar Illumina GoldenGate assay has been developed targeting genes specifically involved in atopic dermatitis. Future already funded studies will further investigate genetic associations of not only asthma and atopic dermatitis, but also these diseases independent of and in combination with allergic rhinitis and food allergies. Mucosal epithelial cells provide a critical physical defense barrier against allergens, pathogens, and other exposures, and also directly promote the development of Th2 responses. Each allergic disorder involves an epithelial or mucosal surface including the lung, gastrointestinal tract, or skin, but the epithelial pathways that contribute to disease at each site and possibly across sites have not been well investigated. The GCPCR will serve as a resource to make these unique studies possible.
Ongoing environmental exposure studies
Previous studies have indicated that environmental exposures dramatically influence the phenotype of allergic diseases.23–25
For this reason, our questionnaires have detailed questions regarding primary and secondary tobacco smoke exposures, pet exposure, and early exposure to daycare. The smoking questions determine the type, the number of cigarettes per day, and the location of smoking of the participant, parents or guardians, and other members of the participant's household, as well as smoking habits of the biological mother during her pregnancy with the participant, the frequency of smoking in a car with the participant, and the average number of hours that the patient spends in the same area as someone who is smoking. Based on parental report of 850 of our asthmatic GCPCR recruits aged 5–18 years old, 33% indicated that their child lived with a smoker at the time of their child's enrollment. Of these subjects, 66% of mothers, 41% of fathers, and 29% of other adults living in the home reported smoking in the household. More than 19% of smoking households included both maternal and paternal smokers. Collection of hair samples in a subset of GCPCR participants has recently been implemented to enable future biologic measurement of nicotine and cotinine levels.
In addition to environmental tobacco smoke exposure, asthmatic and allergic children living in the Greater Cincinnati area are also greatly affected by traffic-related air pollution. Importantly, Greater Cincinnati has three converging major federal highways that cause traffic volume to be one of the largest in the nation. In fact, the level of exposure to truck related traffic is estimated to be one of the largest in the nation with 135,000–150,000 vehicles and 12,000–16,000 trucks per 24 hours traveling on each highway. Due to traffic, topography, and meteorological conditions in the Ohio Valley, air pollutants are concentrated in this area per an ongoing Environmental Protection Agency nonattainment rating. Elemental Carbon Attributable to Traffic (ECAT), a reliable surrogate for traffic related exposure, has previously been measured at 24 separate ambient air sampling sites in the greater Cincinnati area as part of the Cincinnati Childhood Allergy and Air Pollution Study (CCAAPS).26
The average daily value of ECAT was determined for each sampling site for the years 2001–2005 and a land-use regression (LUR) approach was developed to relate the average daily values of ECAT at the sampling sites to surrounding traffic and land variables in a Geographic Information System (GIS). Estimates of truck-related traffic exposure at the home addresses of repository children are determined by combining ambient air sampling data with GIS data. As a result, the LUR model developed by CCAAPS can be used to estimate truck-related air pollution exposure in GCPCR participants. Using the same definition of high levels of exposure to traffic-related air pollution as CCAAPS (>0.50
per day), in 5,550 GCPCR participants, we found that 14% of the children would be considered highly exposed to DEP. The mean value was 0.38
, the range was 0.27–0.89
, and the standard deviation was 0.12. Children with asthma in our repository commonly live along one of Cincinnati's interstates (). Currently, there are two ongoing NIH-funded case-control studies evaluating oxidative stress-related biomarkers of both truck-related traffic exposure and secondhand smoke exposure side-by-side in the context of asthma. The studies' population bases are comprised of 64% of GCPCR participants with 330 enrollees undergoing analyses in the second year of the studies.
FIG. 2. Estimated traffic related air pollution at residential locations of GCPCR participants by disease status. Elemental analysis of ambient samples of PM2.5 was used to estimate levels of elemental carbon attributable to traffic (ECAT; a marker of traffic (more ...)
Ongoing disparity and health literacy studies
In the United States, the prevalence of asthma continues to increase, particularly among minority and low-income groups, despite improvements in medications and treatment strategies. The GCPCR has more than1,993 African American participants and more than 1,800 participants in families with an income of less than $30,000 per year (). Geocoding maps of participants' primary residences suggest that African American asthmatics and nonasthmatics () alike are clustered in or near the downtown Cincinnati area. The role of the parent or primary caregiver of children is critical in managing asthma and in influencing the child's health outcomes. This includes a variety of characteristics that contribute to a caregiver's ability to manage their child's asthma: access to medical care, insurance coverage, the ability to acquire prescription drugs, race, ethnicity, household income, family structure, residential location27
and health literacy,28
all of which have disproportionate effects on those in minority and low-income groups. While it is well established that patient education is essential for effective disease management, health literacy issues are rarely addressed and partially understood in research studies targeting low-income and/or minority patients. Minorities and low-income patients have a higher prevalence of low health literacy and utilize primary care and community health services more often than visiting a specialist. This is despite the literature that supports that specialists are better at treating the disease.29
Recent reports also indicate that African Americans are less likely to seek the care of a specialist. Those that do seek a specialist's care, however, are among the sickest. While asthma outcomes are known to improve under specialty care, the impact of caregiver health literacy on asthma outcomes of minority children and/or children in low-income families visiting asthma and allergy specialists is not well established. In fact, in a currently enrolling study utilizing the GCPCR, nearly 30% of 145 caregivers of 4–11-year-old asthmatic children screened using the Rapid Assessment of Adult Literacy in Medicine (REALM) had less than a high school reading level,30
further suggesting a need examine social factors, in addition to biological factors, that promote asthma in highly susceptible populations and the role of poor health literacy as one of many factors that lead to disparate health outcomes.
Residential locations of GCPCR participants stratified by race and disease status. Geographic Information System software was used to obtain longitude and latitude coordinates from each repository participant's home address.
Strengths and limitations of the GCPCR and its ongoing improvement
The GCPCR is a unique resource for allergic diseases in children that can and has been continuously adapted as new opportunities arise. Limitations of the cohort include current limited longitudinal data and demographic data from subjects enrolled early in course of the GCPCR. For example, in the early years, the GCPCR focused on recruiting children at their baseline visits to the specialist and consequently has limited longitudinal data on early participants. This is particularly problematic when evaluating younger children that may have subsequently developed asthma, for example, following their baseline visit. To remedy this issue, a data capture campaign was completed in 2008 to obtain missing data and to get updates on study participants. Nearly 45% of participants recontacted responded. In addition to the recapture campaign, follow-up questionnaires were developed at that time and study coordinators began to mail these questionnaires to previously consented participants with the goal of regular collection at subsequent clinic visits. Utilization of online questionnaires is now being considered and will likely permit more rapid questionnaire completion and previously consented participants would be able complete online questionnaires from home outside of or prior to their CCHMC visits. While complete validation of all the questionnaires used by the GCPCR is not possible given the ongoing clinical needs and magnitude of the information being collected, this is a future goal.
Another limitation of the study is also routed in the early years. Early on, only the race and ethnicity of the study participant were collected. In 2008, we began collecting information about race and ethnicity on both the participants and their parents using the revised guidelines established by the Office of Management and Budget at the NIH (2001) for studies recruiting minorities. These include two ethnic categories: Hispanic or Latino, and Not Hispanic or Latino; and five racial categories: American Indian or Alaska Native, Asian, Black or African American, Native Hawaiian or Other Pacific Islander and White [NOT-OD-01-053]. In addition, we now also inquire about participants' siblings (full, half, step, and biologically unrelated) to enhance genetic and exposure-based studies. Genotyping is then used to corroborate relatedness as a second quality control measure, as well as correct gender assignment. Inclusion of a set of ancestry informative markers in genotyping studies along with principal component analysis allows us to discover misidentified ancestry, admixture and individuals that have a unique combination of ethnic backgrounds that make them outliers for population-specific studies. Recruitment of African Americans with asthma, as well as appropriate controls, is a priority of the GCPCR. The availability of these populations in the repository, as well as numerous other characteristics, makes the GCPCR a distinctive resource ().