title: A twin study of early-childhood asthma in Puerto Ricans.
abstract: BACKGROUND
  The relative contributions of genetics and environment to asthma in Hispanics or to asthma in children younger than 3 years are not well understood.
  
  
  OBJECTIVE
  To 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.
  
  
  METHODS
  678 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.
  
  
  RESULTS
  The 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.
  
  
  CONCLUSIONS
  Our 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.
authors.affiliation: Department of Pediatrics, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America. supinda@post.harvard.edu
authors.forename: Supinda
authors.initials: S
authors.lastname: Bunyavanich
authors.forename: Judy L
authors.initials: JL
authors.lastname: Silberg
authors.forename: Jessica
authors.initials: J
authors.lastname: Lasky-Su
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Gillespie
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Lange
authors.forename: Glorisa
authors.initials: G
authors.lastname: Canino
authors.forename: Juan C
authors.initials: JC
authors.lastname: Celedón
mesh_terms: D000367:Age Factors; D000704:Analysis of Variance; D001249:Asthma / Q000453:epidemiology* / Q000209:etiology; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D010641:Phenotype; D015995:Prevalence; D011647:Puerto Rico / Q000453:epidemiology; D012042:Registries; D012307:Risk Factors; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic