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An amelogenin gene defect associated with human X-linked amelogenesis imperfecta.

Dental enamel is a product of ameloblast cells, which secrete a mineralizing organic matrix, composed primarily of amelogenin proteins. The amelogenins are thought to be crucial for development of normal, highly mineralized enamel. The X-chromosomal amelogenin gene is a candidate gene for those cases of amelogenesis imperfecta, resulting in defective enamel, in which inheritance is X-linked. In this report, a kindred is described that has a C to A mutation resulting in a pro to thr change in exon 6 of the X-chromosomal amelogenin gene in three affected individuals, a change not found in unaffected members of the kindred. The proline that is changed by the mutation is conserved in amelogenin genes from all species examined to date.

Adenine↗

Amelogenin p.M1T and p.W4S mutations underlying hypoplastic X-linked amelogenesis imperfecta.

Mutations in the human amelogenin gene (AMELX, Xp22.3) cause a phenotypically diverse set of inherited enamel malformations. We hypothesize that the effects of specific mutations on amelogenin protein structure and expression will correlate with the enamel phenotype, clarify amelogenin structure/function relationships, and improve the clinical diagnosis of X-linked amelogenesis imperfecta (AI). We have identified two kindreds with X-linked AI and characterized the AMELX mutations underlying their AI phenotypes. The two missense mutations are both in exon 2 and affect the translation initiation codon and/or the secretion of amelogenin (p.M1T and p.W4S), resulting in hypoplastic enamel. Primary anterior teeth from affected females with the p.M1T mutation were characterized by light and scanning electron microscopy. The thin enamel had defective prism organization, and the surface was rough and pitted. Dentin was normal. The severity of the enamel phenotype correlated with the predicted effects of the mutations on amelogenin expression and secretion.

Amelogenesis Imperfecta↗

Evidence of amelogenesis imperfecta in an early African Homo erectus.

The teeth of the Homo erectus child (Garba IV) recovered from Melka Kunture Ethiopia and dated to 1.5 Ma are characterized by generalized enamel dysplasia, reduced enamel radio-opacity, and severe attrition. This combination of features is found in a large group of hereditary, generalized enamel dysplasias known as amelogenesis imperfecta (AI). SEM studies carried out on epoxy replicas of teeth from the Garba IV child, confirmed that the defects noted were developmental and not due to diagenesis. The enamel prism arrangement is abnormal and there are deep vertical furrows lacking enamel on both buccal and lingual surfaces of all molars. The lesions differ from those characteristic of linear enamel hypoplasia that form discrete horizontal lesions or pits within otherwise normal enamel. We propose that the Garba IV child is the earliest example of AI and provides a link between palaeoanthropology and molecular biology in investigations of the evolutionary history of genetic disorders.

Amelogenesis Imperfecta↗

Amelogenesis imperfecta with enamel opacities and taurodontism: an alternative diagnosis for 'idiopathic dental fluorosis'.

A retrospective study of 32 children (mean age 10.3 years) attending the Children's Department, Eastman Dental Hospital with enamel opacities resembling dental fluorosis in the majority showed that these changes were probably genetically determined and had a close association with taurodontism of permanent molar teeth. It seems likely that these enamel defects should be classified as hypomaturation types of amelogenesis imperfecta (AI) conveyed by mutant auto-somal genes. The clinical expression (phenotype) of these mutant genes has a greater heterogeneity than previously described.

Adolescent↗

Oral rehabilitation of a young adult with hypoplastic amelogenesis imperfecta: a clinical report.

This clinical report describes the oral rehabilitation of a young adult patient diagnosed with hypoplastic amelogenesis imperfecta. The specific objectives of this treatment were to eliminate tooth sensitivity while enhancing esthetics and restoring masticatory function. Treatment included removal of several teeth, lengthening of the maxillary and mandibular clinical crowns, and placement of anterior and posterior metal-ceramic fixed partial dentures. The 2-year recall examination revealed no pathology associated with the rehabilitation, and the patient's esthetic and functional expectations were satisfied.

Adult↗

Autosomal recessive rough hypoplastic amelogenesis imperfecta. A case report with clinical, light microscopic, radiographic, and electron microscopic observations.

A case is presented of a 12-year-old Japanese girl with nearly complete lack of enamel in the deciduous and the permanent dentitions, coupled with a gross abnormality in the pattern of eruption. There was no family history of a similar condition. Deciduous molars were extracted, and hyperplastic gingival tissue was resected. On the basis of clinical, radiographic, and microscopic findings, a diagnosis of autosomal recessive rough hypoplastic amelogenesis imperfecta was made. The configuration of the abnormal enamel was examined with scanning and transmission electron microscopy as well as with light microscopy. Prismatic structure was virtually absent, and the scant enamel showed globular protrusions superficially. Two different surface structures were identified as covering parts of the enamel. At the ultrastructural level, calcified bodies located in the gingival tissue appeared to be composed, in part, of a dense enamel-like substance and, in part, of a tissue with features of afibrillar cementum.

Amelogenesis Imperfecta↗