The importance of mediated transport proteins is visualized with the presence of mutations that render the transport proteins nonfunctional. A prime example of this are mutations found within the Archain 1 gene which codes for the transport proteins COPI and COPII. The main function of these transport proteins is to facilitate the passage of molecules from the endoplasmic reticulum to the golgi apparatus, and vice versa. The mutated ARCN1 gene gives rise to abnormal COPI who fails to transport type I collagen and leads to the secretion of collagen. Due to the fact that type I collagen is the main ingredient of connective tissue, such mutations are the cause of numerous severe skeletal disorders such as osteogenesis imperfecta and cranio-lenticulo-sutural dysplasia. Various variations of these disorders are characterized by visible physical dysplasia. This example highlights the importance of transport proteins, not only as a means for the passage of specific molecules across a membrane, but for proper bodily development.