Through a large international collaboration, we identified more than a thousand genetic factors that are associated with how much of a person’s weight is fat mass and how much is lean mass. We subdivided these genetic factors into six groups based on how they affect multiple aspects of body size, composition and shape (e.g., body mass index, height, waist-to-hip circumference). These six clusters of genetic factors each have distinct effects on obesity-related diseases, such as type 2 diabetes and cardiovascular disease. In addition, we found that the clusters also had differential effects on body size at birth and in childhood. We would like to use the data from the ALSPAC study to investigate if these six groups of genetic factors affect trajectories of body size and composition throughout the development of a child, from birth until early adulthood.