Direct visualization of affected collagen molecules synthesized by cultured fibroblasts from an osteogenesis imperfecta patient.

Human skin fibroblasts obtained from normal controls and a patient with osteogenesis imperfecta were cultured in the presence of ascorbic acid 2-phosphate, a long-acting vitamin C derivative. Crude collagen samples extracted from the cell layer were made to form lateral aggregates of collagen molecules, segment-long-spacing crystallites. Under the electron microscope, normal and abnormal crystallites of type I collagen were identified with the patient's collagen. While the carboxyl-terminal half of the abnormal crystallite was tightly packed, the amino-terminal half was loose and spreading, indicating the site of abnormality in the amino-terminal half of one of type I collagen alpha chains. The method is simple and useful to detect abnormal collagen and to predict the site of mutation.