Protocol for a longitudinal twin birth cohort study to unravel the complex interplay between early-life environmental and genetic risk factors in health and disease: the Chongqing Longitudinal Twin Study (LoTiS).

Introduction: Non-communicable diseases (NCD) now represent the major burden of adverse health in most countries. It is clear that much of the risk of such conditions begins very early in life, potentially in utero. Given their complex aetiology, an understanding of the origins of NCD requires an in-depth analysis of the interplay between genetic variation and environment, preferably over time. For decades, twin studies have played a key role in understanding such traits. Their strength lies in the ability to disentangle genetic and environmental factors that contribute to a phenotype. This is done by comparing genetically identical monozygotic (MZ) with dizygotic twins, who share on average 50% of genetic variation, or by comparing MZ twins within a pair. This study aims to determine the relative contributions of genes and environment to early-onset intermediate phenotypes related to later adult onset disease (such as growth and neurodevelopment) and to identify specific biomarkers and time points for emergence of phenotypes from infancy, largely independent of underlying genetic factors.

Methods/design: The Chongqing Longitudinal Twin Study () will recruit 300 women pregnant with twins, enriched for MZ pregnancies, with follow-up to 3 years of age. Data collection will be undertaken at key time points in gestation (×3), at delivery and postnatally (×9). Maternal and infant biospecimens including blood, urine, hair, nails and buccal swabs along with measures such as fetal scans and body measurements will be collected. Additional information from questionnaires and medical records includes pregnancy, diet, sociodemographics, maternal stress, and infant growth and neurodevelopment.

Ethics And Dissemination: This study has been approved by the Ethics Committee of Chongqing Medical University (record no: 201530) and has been registered with the Chinese Clinical Trial Registry (registry no: ChiCTR-OOC-16008203). Results of the recruitment and all subsequent analyses will be submitted for publication in peer-reviewed journals.

Trial Registration Number: ChiCTR-OOC-16008203; Results.