Which Genetic and Environmental Factors Affect Asthma Outcomes?

Key Point

Recent studies show that genetics, social environment, and country of residence during the first year of life can all be important influences of asthma risk and manifestation of symptoms.

Genetics, social environment, geography: Which of these factors influence asthma incidence and treatment outcomes? Recent study results published in three separate journals point to all three.
In one study, disparities between black and white adults in the number of emergency department (ED) visits and hospitalizations for asthma were independently associated with race alone, while a second study attributed differences in asthma symptoms and health behaviors among youths to the social environments within the family and the community. In the third study, which also implicates environmental factors, Mexican American children who lived in the United States during their first year of life appear to have a significantly higher incidence of physician-diagnosed asthma than their peers who lived in Mexico during their first year of life.

RACIAL DISPARITIES

In an effort to understand why asthma morbidity disproportionately affects black people, Sara E. Erickson, MD, of the University of California, San Francisco, and colleagues identified asthma patients of the managed-care Kaiser Permanente hospitals in Northern California—“a health care setting that provides uniform access to care”—and followed them for a median of 1.9 years for subsequent ED visits and hospitalizations. As reported in the September 24 Archives of Internal Medicine, only patients who self-identified their race/ethnicity as black (n = 154) or white (n = 524) were included in the analysis. Demographic and clinical information, general and asthma-related health status, and medication use were ascertained.

The demographic differences between white and black patients were significant, the study authors noted, with white patients being older and more likely to have a college or graduate degree. A larger proportion of black patients reported an annual household income of less than $20,000 and lack of a high school diploma.

Black and white patients were similar in terms of asthma severity, physical health status, and number of days of restricted activity, and the two patient groups were equally as likely to have received asthma education in the past year. However, black patients were more likely than white patients to have used or been prescribed a short-acting inhaled b-agonist or nebulizer, to have used a peak flow meter on a regular basis, and to have seen an asthma specialist in the past year.

“Black patients were significantly more likely to have had ambulatory care visits for asthma during follow-up,” the authors added. “In addition, there was a suggestion that black patients had more urgent care asthma visits as well.” About 36% of black patients and 21% of white patients had an ED visit for asthma symptoms during follow-up, and 26.6% of black patients versus 15.3% of white patients were hospitalized for asthma. These associations remained even after adjustment for individual and socioeconomic factors.

Patients’ cultural beliefs and behaviors related to asthma and provider preferences with regard to treating black patients may have been responsible for the differences between the patient groups; however, the study’s findings “also support genetic differences or predispositions, including b2-adrenergic receptor polymorphisms, as a possible explanation for racial disparities in asthma outcomes,” the researchers contended.

A PRODUCT OF THEIR ENVIRONMENT

For an observational study, 78 youths ranging in age from 9 to 18 with physician-diagnosed asthma were recruited from asthma clinics and through advertisements in newspapers and school and community center postings, said Edith Chen, PhD, of the University of British Columbia, Vancouver, and colleagues in the October 1 American Journal of Respiratory and Critical Care Medicine.

Participants completed questionnaires about family and peer support, neighborhood problems, smoking behaviors, and adherence to medications. Pulmonary function, serum biologic markers, and asthma symptoms were assessed at the laboratory and at home for two weeks.

After adjustment for age, sex, ethnicity, and disease severity, lower levels of family support were associated with higher levels of total immunoglobulin E, higher eosinophil counts, and greater production of interleukin 4—“biologic measures in a direction detrimental to asthma,” the researchers observed. Furthermore, lower levels of family support were associated with marginally lower FEV1, significantly lower at-home morning PEF, marginally greater daytime symptoms during the past two weeks, greater nighttime symptoms during the past two weeks, and greater exertional symptoms during the past two weeks.

Greater problems in the neighborhood were associated with higher incidence of smoking and exposure to secondhand smoke and less adherence to asthma medications. Greater neighborhood problems also were associated with greater daytime symptoms during the past two weeks. Although peer support was not associated with any pulmonary function or symptom variable, high levels of peer support surprisingly were associated with poor adherence to medications.

“Among youths with asthma, the family and the neighborhood [may] play a more important role than peer support,” the researchers posited. They suggested that problems within the family directly affect biological mechanisms by triggering hormonal and inflammatory processes that contribute to asthma. By contrast, neighborhood factors appear to influence youths’ behavior.

“Interventions that target family interaction patterns may help improve children’s asthma by altering biological profiles,” Dr. Chen told Pulmonary Reviews. “The neighborhood effects suggest the potential utility of making community-wide changes that could help shape the health behaviors of children with asthma.  But first, future research that manipulates social factors and tests their effects on childhood asthma morbidity is needed to confirm these study findings."

EARLY LIFE IN AMERICA LINKED TO INCREASED ASTHMA RISK

Kamal M. Eldeirawi, PhD, and Victoria W. Persky, MD, from the University of Illinois at Chicago, conducted a cross-sectional analysis of data from the Chicago Asthma School Study involving 10,106 Mexican American children from 20 Chicago public schools, prekindergarten through eighth grade. During the study, which was undertaken to identify students with asthma and respiratory symptoms and to facilitate their access to health care, participants were identified as follows:

• US-born who lived in the US in the first year of life
• US-born who lived in the Mexico in the first year of life
• Mexico-born who lived in the US in the first year of life
• Mexico-born who lived in Mexico in the first year of life.

Screening questionnaires also sought to determine participants’ length of residence in the US. As reported in the September Annals of Allergy, Asthma, and Immunology, the researchers found that about 79% of participants were born in the US, and the rest were born in Mexico; in more than 95% of cases, the children’s country of birth was where they lived during their first year of life.

After adjustment for age, sex, income, and language, “children who lived in the United States in the first year of life had a 2.39-fold … increased risk of physician-diagnosed asthma,” the researchers remarked. After further adjustment for country of birth, the increased risk diminished but was still significant (odds ratio [OR], 1.79). Children who had been residents of the US for more than 10 years had an increased risk of asthma (OR, 1.93) compared with children who had been in the country for less than 10 years. “These results suggest that the protective effect of birth in Mexico or residence in Mexico in the first year of life diminishes after prolonged residence in the United States,” the investigators noted.

Study limitations include the cross-sectional design (which made it unsuitable to establish a causal link between birth country or country of residence and asthma risk), the reliance of self-report, and the lack of information on potential confounding variables, the researchers acknowledged. However, they suggested that differences between mothers of US-born Mexican American children and mothers of Mexico-born participants in smoking habits during pregnancy, dietary factors, and breastfeeding practices may explain the differences in the children’s asthma risk.            

—Adriene Marshall

Reference
Chen E, Chim LS, Strunk RC, Miller GE. The role of the social environment in children and adolescents with asthma. Am J Respir Crit Care Med. 2007;176(7):644-649.
Eldeirawi KM, Persky VW. Associations of physician-diagnosed asthma with country of residence in the first year of life and other immigration-related factors: Chicago Asthma School Study. Ann Allergy Asthma Immunol. 2007;99(3):236-243.
Erickson SE, Iribarren C, Tolstykh IV, et al. Effect of race on asthma management and outcomes in a large, integrated managed care organization. Arch Intern Med. 2007;167(17):1846-1852.

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