Injecting stem cells into a developing fetus might sound risky, but it could prolong the lives of children with brittle bone disease.Nicholas Fisk and colleagues at Imperial College London studied mouse models of human type III brittle bone disease, or osteogenesis imperfecta (OI). The genetic defect - detected in human fetuses by DNA testing or ultrasound - disrupts collagen production, leading to weak bones and stunted growth. Those with type III OI suffer fractures while in the womb and rarely survive beyond early adulthood.