Population stratification confounds genetic association studies among Latinos.

In the United States, asthma prevalence and mortality are the highest among Puerto Ricans and the lowest among Mexicans. Case-control association studies are a powerful strategy for identifying genes of modest effect in complex diseases. However, studies of complex disorders in admixed populations such as Latinos may be confounded by population stratification.

Genetic admixture and asthma-related phenotypes in Mexican American and Puerto Rican asthmatics.

Genetic association studies in admixed populations may be biased if individual ancestry varies within the population and the phenotype of interest is associated with ancestry. However, recently admixed populations also offer potential benefits in association studies since markers informative for ancestry may be in linkage disequilibrium across large distances. In particular, the enhanced LD in admixed populations may be used to identify alleles that underlie a genetically determined difference in a phenotype between two ancestral populations.

ADAM33 is not associated with asthma in Puerto Rican or Mexican populations.

A recent study identified the ADAM33 gene as a promising candidate contributing to asthma. In Puerto Rican and Mexican populations, we have genotyped six single nucleotide polymorphisms (SNPs) that were used in the Genetics of Asthma in Latino Americans Study. We chose to study these two populations because in the United States, Puerto Ricans have the highest asthma prevalence, morbidity, and mortality and Mexicans the lowest.