Since PTN over-expression in transgenic mice is associated with an increased bone mass and mineralization and may protect from experimentally-induced osteoporosis [8]–[9], the mice drawer system (MDS) experiment was designed to accommodate PTN-overexpressing mice aboard the International Space Station (ISS) with the aim to verify whether PTN can also protect mice from space related osteoporosis [10]. This evidence concerns the gene PTN and osteoporosis.