Osteogenesis imperfecta (OI) type I is characterized by bone fragility without significant deformity, osteopenia, normal stature, blue sclerae, and autosomal dominant inheritance. Dermal fibroblasts from most affected individuals produce about half the expected amount of type I collagen, suggesting that the OI type I phenotype results from a variety of mutations which alter the apparent expression of either COL1A1 or COL1A2, the genes encoding the chains of type I collagen.