A Twin Study of Early-Childhood Asthma in Puerto Ricans

Abstract

BackgroundThe relative contributions of genetics and environment to asthma in Hispanics or to asthma in children younger than 3 years are not well understood.ObjectiveTo examine the relative contributions of genetics and environment to early-childhood asthma by performing a longitudinal twin study of asthma in Puerto Rican children ≤3 years old.Methods678 twin infants from the Puerto Rico Neo-Natal Twin Registry were assessed for asthma at age 1 year, with follow-up data obtained for 624 twins at age 3 years. Zygosity was determined by DNA microsatellite profiling. Structural equation modeling was performed for three phenotypes at ages 1 and 3 years: physician-diagnosed asthma, asthma medication use in the past year, and ≥1 hospitalization for asthma in the past year. Models were additionally adjusted for early-life environmental tobacco smoke exposure, sex, and age.ResultsThe prevalences of physician-diagnosed asthma, asthma medication use, and hospitalization for asthma were 11.6%, 10.8%, 4.9% at age 1 year, and 34.1%, 40.1%, and 8.5% at 3 years, respectively. Shared environmental effects contributed to the majority of variance in susceptibility to physician-diagnosed asthma and asthma medication use in the first year of life (84%–86%), while genetic effects drove variance in all phenotypes (45%–65%) at age 3 years. Early-life environmental tobacco smoke, sex, and age contributed to variance in susceptibility.ConclusionOur longitudinal study in Puerto Rican twins demonstrates a changing contribution of shared environmental effects to liability for physician-diagnosed asthma and asthma medication use between ages 1 and 3 years. Early-life environmental tobacco smoke reduction could markedly reduce asthma morbidity in young Puerto Rican children.

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

“…The magnitude of the additive genetic (A) components for asthma in our study was in line with previous studies including children . However, the overall pattern of variance components in asthma differs between studies.…”

“…The underlying genetic components of asthma have been demonstrated using quantitative as well as molecular genetic methods . While these principally intend to describe the same phenomenon, the perspectives are somewhat different.…”

“…In the past, the heritability of asthma was estimated to be between 50 and 90% . However, it is difficult to draw reliable conclusions regarding asthma in children based on these studies, as some concern only adults and the study populations with child subjects often include also adolescents and young adults or address only preschool years . The few studies that focus on mid‐childhood to early adolescence are comparably small.…”

Pulmonary Disease and Age at Immigration among Hispanics. Results from the Hispanic Community Health Study/Study of Latinos

“…Early life exposures may also be implicated (41), which is supported by our findings of the markedly elevated risk of asthma among Hispanics who had immigrated to the United States before age 6 years. Early-life exposures encountered in predominantly urban U.S. environments may include increased dust, cockroach-and mold-borne allergens, and air pollution exposures (45), which may increase the risk of developing asthma via eosinophilic and noneosinophilic mechanisms (50).…”

What the Genetic Background of Individuals with Asthma and Obesity Can Reveal: Is β2-Adrenergic Receptor Gene Polymorphism Important?

“…5 For asthma, this proportion was determined to be similar. 6 For at least 10 years, shared genetic background for asthma and obesity has been investigated, summarized elsewhere. 7 Between commonly shared genes, the most biologicaly plausible are those that are pleiotropic, including b2-adrenergic receptor (ADRB2), vitamin D receptor gene (VDR), leptin (LEP), protein kinase C alpha (PRKCA), and tumor necrosis factor a (TNFa).…”