PubMed · 5274849
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R Luberti, G Moize. 1970. [Amelogenesis imperfecta].. https://pubmed.ncbi.nlm.nih.gov/5274849/
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Amelogenins are an heterogenous family of proteins produced by ameloblasts of the enamel organ during tooth development. Disturbances of enamel formation occur in amelogenesis imperfecta, a clinically heterogenous group of inherited disorders characterised by defective enamel biomineralisation. An amelogenin gene, AMGX, has been mapped to the short of the X chromosome (Xp22.1-p22.3) and has been implicated in the molecular pathology of X-linked amelogenesis imperfecta (AIH1). We have identified three families exhibiting AIH1 and screened the AMGX gene for mutations using single-strand conformational polymorphism analysis and DNA sequencing. Three novel mutations were identified: a C-T substitution in exon 5, and a G-T substitution and single cytosine deletion in exon 6, confirming the existence of extensive allelic heterogeneity in this condition. The identification of family-specific mutations will enable early identification of affected individuals and correlation of clinical phenotype with genotype will facilitate an objective system of disease classification.
This editorial reviews the history of the classification of amelogenesis imperfecta (AI). The limitations of the existing classification systems are discussed. An alternative classification is proposed based upon the molecular defect, biochemical result, mode of inheritance and phenotype in the family involved. While not all of the criteria for the proposed classification can yet be addressed, this scheme is proposed for future classification of AI cases and families.
The purpose of this investigation was to characterize the enamel composition of teeth affected with the hereditary enamel disorders known as amelogenesis imperfecta. Teeth from 10 individuals representing all 3 major AI types (hypocalcified, n = 3; hypomaturation, n = 3; hypoplastic, n = 4) and 10 normal teeth were studied. Half of each tooth was used for histological and biochemical studies. The enamel protein content was estimated by amino acid analysis. The enamel mineral content (volume %) was determined from the calcium and/or phosphorus content. Calcium was measured using atomic absorption and phosphorus was determined colorimetrically. The mean enamel mineral content was reduced for all hypomaturation and hypocalcified AI teeth while hypoplastic AI enamel varied from normal to reduced compared with normal enamel. The enamel protein content was increased in all but one AI case (7 cases were examined for protein) compared with the normal enamel. The mineral and protein content in AI enamel showed a significant inverse relationship (R = -0.939, P = 0.001). This study shows that all three of the major AI groups can have subtypes associated with substantial decreases in the enamel mineral content, although hypomineralization appears most severe in the hypomaturation and hypocalcified AI types. The decreased mineral content was associated with an increased protein content in AI enamel. These findings provide further evidence that altered enamel mineralization in AI teeth likely involves abnormal post-secretory processing of the enamel proteins.