Neuro status: All patients will be co-enrolled in 97-CH-0064, and will be screened for Basilar Invagination through that protocol. Children who are initially screened by spiral CT scan with MRI confirmation and determined to have severe BI will be excluded from participation in this study. Severe BI is defined by NIH data as distortion of the angle between the pons and medulla and or compression of posterior fossa contents. We are only beginning to define the parameters of BI in this population, and we do not know why some children with BI progress in severity and some do not. Until those questions are answered, we feel it would not be prudent to stimulate growth in a child we know to have a severe form of BI at enrollment.