This study evaluates relationships among balance, biochemical, hormonal, kinetic and densitometric parameters of bone mineral metabolism in early adolescent girls. Comparisons will be made between White and Black girls and between healthy girls and those with precocious puberty. The specific aims of the project have not changed since the original project was begun. To summarize, these were to: 1) Assess changes in calcium absorption and bone mineral utilization during puberty in healthy girls; 2) To evaluate racial differences in pubertal girls in calcium metabolism; 3) To assess the changes in calcium metabolism associated with the precocious puberty; and 4) To assess the relationship between body composition changes during puberty and calcium metabolism. Studies were begun during early 1996. Our goals for the pat renewal period were to 1) complete 7 day studies in virtually all the girls 2) continue follow-up studies in healthy girls and 3) continue studies of girls with precocious puberty 4) to complete all sample analysis by 12/97 of all studies performed by 8/97. These goals have been met. The original study was to assess 15 Hispanic and 15 Black girls. Due to the possibility of drop-outs, it was also planned to study 2-4 additional girls in each racial group. These initial studies have all been completed. A total of 18 White, 16 Black, and 17 Hispanic girls have been studied at least twice and are continuing in the study at this time. Total numbers of dropouts (girls who received one or two studies and then withdrew) have been 3 White, and 2 Hispanic girls. Including follow-up visits, a total of 201 calcium absorption and kinetic studies have been completed on these girls by October 30, 1998. Virtually all of the approximately 5500 samples from these 201 studies have been analyzed by mass spectrometry for calcium isotope ratios. Data analysis including modeling of the kinetics has also been completed for virtually all the studies or will be completed by the end of December, 1998. A total of 11 girls with precocious puberty have also been studied. These have included 3 White or Asian girls, 2 Hispanic girls and 6 Black girls. One of these girls was bound to not have central precocious puberty. Six of these 11 girls have completed at least two studies. An important area in which we have utilized the data was the evaluation of the relationship between putative genetic markers related to calcium metabolism and calcium absorption and kinetics. These results turned up a positive associated between Fok 1 site polymorphism and calcium absorption and bone density. These findings have been tentatively accepted (pending revisions) for publication in the Journal of Bone and Mineral Research. The following conclusions may be drawn from our study to date. 1. There is evidence for genetic regulation of calcium absorption by the Fok 1 site polymorphism consistent with limited data in adults showing a relationship between bone mass and this polymorphism. In contrast, no relationship was found between the Bsm1 polymorphism and any marker of calcium metabolism. 2. Absorption of calcium in prepubertal girls is similar among White, Black, and Hispanic girls. Bone mineral content and bone calcium deposition (determined from the stable isotope studies) is increased in the Black relative to the White girls. Both of these are comparable in the Hispanic compared to the White girls. 3. There is a positive correlation between calcium kinetic values, bone density and certain hormonal values including IGF-1. These relationships are currently being evaluated in more detail. 4. Girls with precocious puberty demonstrate very high rates of bone calcium deposition which may not be readily affected by the administration of a GnRH analogue (Lupron). Our study is longitudinal in nature and is not possible to assign final interpretation or significance from a 5 year study which is only 2.5 years completed. However, our study has to date provided evidence for a significant interaction between genetics and calcium metabolism. Furthermore, our data continue to identify racial difference in mineral metabolism distinguish Black from both White and Hispanic girls. Primary plans for the next year include analysis of the longitudinal data to evaluate the rate of change of calcium metabolic parameters and their interrelationship. As all subjects have completed multiple studies, these longitudinal comparisons are possible. Study plans for the next year include completion of the next approximately 100 follow-up studies in the already enrolled girls. Several girls will likely complete their studies during this fourth year although it is anticipated that most will not complete the study (by reaching menarche) until the fifth year or shortly thereafter.