Forteo for the Treatment of Unexplained Osteoporosis in Premenopausal Women

Inclusion Criteria: * Premenopausal women of all races. * Ages 20 to 48. * Regular menses (at least 8 periods in the last 12 months). * FSH \< 20 mIU/ml during the early follicular phase, to exclude women in the perimenopause. * Fracture subjects: documented low trauma fracture(s) at age \>= 18 (e.g., fracture associated with a fall from a standing height or less). * Low BMD subjects: DXA BMD T score less than or equal to 2.5 at the LS, total hip, femoral neck or distal radius, who have not had a fracture. * Control subjects: DXA BMD T score greater than or equal to 1.0 at the LS, total hip, femoral neck and distal radius, who have not had a fracture. * All subjects must use appropriate birth control methods to prevent pregnancy for the duration of teriparatide treatment. Exclusion Criteria: * Secondary Causes of Osteoporosis. * Disorders of mineral metabolism: primary or secondary hyperparathyroidism (serum intact PTH \> 65 pg/ml), vitamin D deficiency (serum 25OHD \< 30 ng/ml), hypercalciuria (\>300 mg/g creatinine), Paget's disease, clinical osteomalacia, osteogenesis imperfecta (OI). * Recent pregnancy or lactation (within past year). * Prolonged amenorrhea (\> 6 months) during reproductive years (except during pregnancy or lactation). * History of anorexia nervosa. * Malignancy, except cured basal or squamous cell skin carcinoma. * Endocrinopathy: hyperthyroidism (elevated serum thyroxine and/or suppressed TSH), untreated hypothyroidism, Cushing's syndrome, prolactin-secreting pituitary adenoma. * Renal insufficiency (serum creatinine above upper limit of female normal range). * Liver disease (AST, ALT, bilirubin, total alkaline phosphatase activity above upper normal limit). * Intestinal disorders (celiac disease, pancreatic insufficiency, inflammatory bowel disease). * History or current use of glucocorticoids, anticonvulsants, anticoagulants, diuretics, methotrexate. * Current use of depot preparations of progesterone or GnRH agonists. * Current use of drug therapies for osteoporosis (estrogen preparations other than contraceptives, raloxifene, bisphosphonates, calcitonin, PTH). Subjects who agree to discontinue use of these medications will be eligible to participate 6 months after discontinuing raloxifene or calcitonin, and 12 months after discontinuing bisphosphonates. Total exposure to bisphosphonates must be \< 1 year. Subjects who have taken PTH at any time in the past will not be eligible. * Additional contraindications to teriparatide use: Unexplained elevated total or bone specific alkaline phosphatase or prior external beam or implant radiation therapy involving the skeleton.