Understanding Heritable Variation Among Hosts in Infectious Diseases Through the Lens of Twin Studies

Genetic factors have been hypothesized to contribute to the heterogeneity in the response to infectious diseases (IDs). The classical twin design provides a powerful tool to estimate the role of genetic contributions to variation in infection outcomes. With this design, the impact of heritability on the proneness as well as infection- and vaccine-induced immune responses have been documented for multiple infections, including tuberculosis, malaria, leprosy, otitis media, polio, mumps, measles, rubella, influenza, hepatitis B, and human papillomavirus infections, and recently, SARS-CoV-2. The current data show the heritable aspect in nearly all infections considered. In this contribution, we review and discuss human twin studies on the heritability of host characteristics in liability and response to IDs. This review emphasizes the importance of considering factors such as sex, disease stages, and disease presentation when assessing heritability and argues that the classical twin design provides a unique circumstance for exploring the genetic contribution as twins share levels of maternal antibodies, ancestral background, often the dates and number of vaccine doses, differences in vaccines' manufacturing and storage, age, family environment, and other exposures. Additionally, we highlight the value of twin studies and the usefulness of combining the twin model with contemporary genomics technologies and advanced statistical tools to grasp a comprehensive and nuanced understanding of heritability in IDs.