Thymus size at birth is associated with infant mortality: a community study from Guinea-Bissau

A few studies have suggested that thymus atrophy is associated with severe malnutrition and increased morbidity; however, no study of thymus size has been undertaken in countries with high mortality. This study examined the relation between thymus size at birth and subsequent mortality in an urban West African community. The size of the thymus was assessed by sonography as a volume estimate, the thymus index. A total of 278 children born at the local health centre in Bandim in Bissau, Guinea-Bissau, was enrolled in the study. Children were followed to the age of 2 y. Thymus size at birth was associated with most strongly weight, as well as with length and arm circumference. Controlling for weight and other risk factors, boys had larger thymus indices than girls [means ratio (MR) = 1.07, 95% confidence interval (95% CI) 1.01-1.14)]. Thymus size was also associated with prematurity, ethnic group, season and investigator, but not with birth order, mother's age, socioeconomic factors or the use of health services. Infant mortality was 117/1000. In a multivariate analysis, excluding premature infants and adjusting for age, gender, ethnic group, season of birth and investigator, higher birthweight (MR = 0.35, 95% CI 0.16-0.74) and larger thymus size (MR = 0.17, 95% CI 0.06-0.48) were independently associated with lower infant mortality. When both indices were estimated in the same model, the thymus index was associated with infant mortality (MR = 0.27, 95% CI 0.07-1.00), whereas birthweight had a non-significant effect (MR = 0.59, 95% CI 0.24-1.47). After 1 y of age neither birthweight nor thymus size at birth was associated with mortality.

As all deaths were due to infectious diseases, thymus size at birth may be an important predictor of immune competence. Future studies should examine the determinants of thymus growth.