The investigators have currently finished conducting an international multi-center trial that compares the efficacy and safety of pamidronate and zoledronate in the treatment of moderate to severe forms of Osteogenesis Imperfecta (OI). This trial has included only children above one year of age. The aim of the current study is to extend the observations of that currently finished study to infants below 1 year of age. Moreover, it is possible to administer zoledronate in a single short infusion instead of the three-day cycles with Pamidronate, therefore decreasing patient and family burdens with shorter stays in the hospital.