Genetic Architecture of Heart Disease in Rural Brazil

BACKGROUND:

Chagas' disease is a leading cause of heart disease throughout Latin America, affecting between 16 and 18 million individuals. The disease, named after the Brazilian physician Carlos Chagas who first described it in 1909, exists only on the American Continents. It is caused by a flagellate protozoan parasite, Trypanosoma cruzi, transmitted to humans by blood-sucking triatomine insects known popularly in the different countries as "vinchuca", "barbeiro", "chipo" etc. The geographical distribution of the human T.cruzi infection extends from Mexico to the south of Argentina. In Brazil alone, approximately 10 percent of the population is seropositive for T. cruzi. Given the large pool of primary hosts for this zoonotic disease, complete eradication of Chagas' disease through control of the arthropod vector is unlikely. Research with humans and animal models indicates that there is variation in susceptibility to infection, and disease outcome, and that this variation may be due to genetic factors. Thus, this form of heart disease represents a complex phenotype with potential genetic determinants to both susceptibility to infection and differential disease pathogenesis.

DESIGN NARRATIVE:

The genetic epidemiology project studies an estimated 1,125 Black individuals age 18 years or older from a small community in Posse, Brazil in which the study population may be drawn from as few as four to five large pedigrees with varying blood relationships. Preliminary pilot data appear very promising regarding the primary hypothesis that specific genetic factors influence the susceptibility to this complex zoonotic disease. The investigation will be divided into three parts involving phenotypic characterization, statistical genetic analyses to determine the relative proportion of the phenotypic variance due to additive genetic effects, and localization of genes influencing the development of Chagas' disease.

The phenotypic characterization will involve clinical history, infection status, immunologic studies, and cardiac status. The chronic phase of T. cruzi infection results in Chagas' disease manifest as a cardiomyopathy with heart block, conduction disturbance, ventricular tachyarrhythmia, heart failure, and sudden arrhythmic death. The cardiac phenotyping will involve electrocardiographic time intervals (PR interval, QRS duration, QT interval duration) as well as abnormal patterns (left anterior fascicular block, left ventricular hypertrophy, right bundle branch block), and possibly some measure of heart failure in terms of New York Heart Association functional classification. Right bundle branch block is probably the most frequent early manifestation of chronic cardiac involvement.