The major objectives of this protocol focus on rehabilitation and physical therapy studies, pulmonary and cardiovascular function, neurological features, audiological studies and genetic and molecular biology aspects of OI. A major objective in this study is to expand the intensive rehabilitation and physical therapy studies of children with types III and IV OI. This objective continues the work that has been done in the Rehabilitation Department of the Clinical Center for the past 20 years on these patients. However, the focus of this objective is changing to include studies of scoliosis and its effect on function, studies of chest proportions and rib deformities, and studies of nonkinetic variables related to motor performance, such as temperament, competence, coping, and resilience in children with OI. The second major objective is the longitudinal study of pulmonary function in children with types III and IV OI. It is well known that cardiopulmonary complications are a major cause of disability and death in adults with OI; the developmental patterns of these complications, and whether susceptible individuals can be identified in childhood, is unknown. The third major objective of these studies of secondary features is to determine the incidence of basilar invagination and develop a monitoring and management plan for this neurological feature. Next, the prevalence, severity, age of onset and genotypic/phenotypic correlation of hearing loss among children with types II and IV OI remains poorly understood; therefore, the study of audiological features is our fourth major objective. The final major objective in this study is the continued study of the genetic and molecular biology aspect of OI. Patients will have skin biopsies for collagen studies at the biochemical and molecular level. Parents will have blood drawn for determination of mosaic status for the mutation that causes their child s OI. These studies will provide further information on genotype/phenotype correlation and other variables in OI genetics. As appropriate, bone chips from emergency or elective surgical procedures on the participants will be used to study osteoblast function in OI.