Growth and Puberty are fundamental aspects of childhood development. Puberty is the period of transition between childhood and adulthood, resulting in the capacity to reproduce and is associated with a significant increase in rate of growth. The mechanisms underlying the control of human growth as well as initiation of human puberty are poorly understood. Knowledge of the mechanisms, as well as being of great interest, could contribute to the care and treatment of children with early and late puberty. The proposed study aims to further understanding of the control of childhood growth and triggers of pubertal onset using measures of gene activity in normal children from the ALSPAC cohort. By examining the pattern of growth and puberty in normal children and comparing this with patterns of gene activity, we hope to identify markers of pubertal onset and identify which genes influence growth rate. We aim to use this information to develop a blood test for use in children with possible disorders of puberty.