The enamel proteins in human amelogenesis imperfecta.

Amelogenesis imperfecta comprises a unique group of hereditary conditions that result in abnormal enamel development. The purpose of this study was to characterize the enamel proteins in different amelogenesis imperfecta types and to determine if amelogenin, the principal matrix protein in normal developing enamel, was retained. Primary and/or permanent amelogenesis imperfecta teeth were analysed from 11 individuals. Normal teeth served as controls. Thin sections were cut with a diamond blade and enamel was dissected for analysis. The enamel proteins were characterized by amino acid analysis, sodium dodecyl sulphate polyacrylamide gel electrophoresis, and Western blot analysis using antiamelogenin antibodies. An increased protein content was seen in all hypocalcified and hypomaturation amelogenesis imperfecta cases. A slightly increased protein content was seen in two of four hypoplastic amelogenesis imperfecta cases. The enamel protein amino acid composition varied between the different amelogenesis imperfecta types. All three cases of hypomaturation amelogenesis imperfecta enamel showed an increased proline content compared with normal enamel or other amelogenesis imperfecta types. Hypocalcified amelogenesis imperfecta enamel had an increased tyrosine content while the other amino acids were generally similar in amount to normal enamel. Fully developed hypomaturation and hypocalcified amelogenesis imperfecta enamel showed cross-reactivity to antiamelogenin antibodies while normal enamel did not. Although both amelogenesis imperfecta types showed cross-reactivity, the banding patterns on Western blot analyses were markedly different. This investigation provides additional evidence that abnormal post-secretory processing of amelogenin is involved in hypomaturation and hypocalcified amelogenesis imperfecta. Furthermore, these results indicate that amelogenin retention can occur in a variety of amelogenesis imperfecta types. The unique amino acid compositions and distinct enamel protein species seen by electrophoresis and Western blot analyses suggest that different developmental processes might be involved in hypomaturation and hypocalcified amelogenesis imperfecta.