The Mexico Childhood Asthma Study is a case-parent triad study of childhood asthma in Mexico City. The study’s emphasis is on candidate genes that may be involved in ozone response. The team completed data collection after enrollment of approximately 600 triads, comprised of children with asthma (age 4-17 years) and their parents. The asthmatic children were diagnosed at the allergy referral clinic at Hospital Infantil de Mexico Frederico Gomez, a large public hospital in central Mexico City. The researchers collected blood from cases, parents of the case, and, when available, a sibling. Pulmonary function measurements and skin prick test results to 24 aeroallergens are available on these children.
The study collaborators chose the case-parent triad design based on work done by Clarice Weinberg, Ph.D., and Allen Wilcox, M.D., Ph.D., at NIEHS. The design enabled the examination of maternal genetic effects that possibly worked through modification of the in-utero environment in contrast to genetic effects due to transmission to the fetus. In addition, the design allowed for the examination of gene-environment interaction as long as the assumption of independence could be made. The case-parent triad design offers strong practical advantages in cases where clinically confirmed cases are required. In a referral clinic setting, the optimal population control sampling frame is not clear. Another advantage of the case-parent triad approach is protection against population stratification, which can be a modest source of bias in admixed populations, such as the case in Mexico City with its mix of Caucasian and Native Indian ethnicities.
Mexico City has the highest ozone levels in North America. This study has examined asthma candidate genes that are plausibly involved in ozone response, ozone response genes that have emerged from animal models and other asthma candidates in various pathways.