The weak tendons and fragile bones characteristic of osteogenesis imperfecta, or brittle bone disease, stem from a genetic mutation that causes the incorrect substitution of a single amino acid in the chain of thousands of amino acids making up a collagen molecule, the basic building block of bone and tendon. According to Professor Markus Buehler of MIT, that minuscule encoding error creates a defective collagen molecule that, at the site of the amino acid substitution, repels rather than attracts the collagen molecule alongside it. This creates a tiny rift in the tissue, which when repeated in many molecules, leads to brittle tissue, broken bones, deformity and, in the most severe form of the disease, death. For example, if healthy collagen tissue looked like a sheet of paper, diseased collagen tissue would look more like a sheet of paper full of tiny perforations. At each of these perforations, the sheet would be considerably more prone to tearing. Read release.