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PubMed1985

Hereditary amelogenesis imperfecta. I. Epidemiology and clinical classification in a Swedish child population.

This study was performed in order to classify different hereditary enamel defects and to estimate their prevalence in a Swedish population. 425,000 children 3-19 years of age were screened in the Public Dental Service for suspected hereditary enamel defects in a well-defined region of Sweden. 182 of the 193 affected children were available for a thorough examination performed by one of the authors. 105 (58%) of these children could be diagnosed as Hereditary Amelogenesis Imperfecta (H.A.I.). 62 (34%) children exhibited enamel defects not related to H.A.I. and in 15 (8%) children no definite diagnosis could be made concerning H.A.I. The group of children diagnosed as H.A.I. could be classified into 12 different clinical subgroups based on two basic types, the hypoplastic and the hypomineralized. 63 of the 105 children showed the hypoplastic type of H.A.I. and 42 the hypomineralized type of H.A.I. Hypomineralized areas of the teeth were a common secondary finding in the hypoplastic type of H.A.I. Usually clinical signs of hereditary enamel defects could be identified both in the primary and in the permanent dentition. The prevalence of H.A.I. in the population studied was estimated to be 1 in 4,000.

Adolescent↗

PubMed2006

Analysis of the COL17A1 in non-Herlitz junctional epidermolysis bullosa and amelogenesis imperfecta.

Non-Herlitz junctional epidermolysis bullosa (nH-JEB) disease manifests with skin blistering, atrophy and tooth enamel hypoplasia. The majority of patients with nH-JEB harbor mutations in COL17A1, the gene encoding type XVII collagen. Heterozygotes with a single COL17A1 mutation, nH-JEB defect carriers, may exhibit only enamel hypoplasia. In this study, to further elucidate COL17A1 mutation phenotype/ genotype correlations, we examined two unrelated families with nH-JEB. Furthermore, we hypothesized that COL17A1 mutations might underlie or worsen the enamel hypoplasia seen in amelogenesis imperfecta (AI) patients that are characterized by defects in tooth enamel formation without other systemic manifestations. We therefore conducted COL17A1 mutational analysis in three patients from two AI families. One nH-JEB patient showed no COL17A1 expression and was a compound heterozygote for the novel premature termination codon (PTC) mutations 1285delA and Q1387X. In addition, reduced COL17A1 expression was found in a second nH-JEB patient who was homozygous for the novel PTC mutation 4335delC, the most carboxyl terminal PTC mutation thus far identified. Due to nonsense mediated mRNA decay, the position of these PTC mutations is thought not to influence the effect of COL17A1 transcript loss and hence the severity of the nH-JEB phenotype. This study is the first to suggest that type XVII collagen carboxyl PTC mutations lead to restoration of truncated polypeptide expression and to a milder clinical disease severity in nH-JEB. Conversely, we failed to detect any pathogenic COL17A1 defects in AI patients, in either exon or within the intron-exon borders of AI patients. This study furthers the understanding of mutations in COL17A1 causing nH-JEB, and clearly demonstrates that the mechanism of enamel hypoplasia differs between nH-JEB and AI diseases.

Adult↗

PubMed2002

Altered amelogenin self-assembly based on mutations observed in human X-linked amelogenesis imperfecta (AIH1).

A hallmark of biological systems is a reliance on protein assemblies to perform complex functions. We have focused attention on mammalian enamel formation because it relies on a self-assembling protein complex to direct mineral habit. The principle protein of enamel is amelogenin, a 180-amino acid hydrophobic protein that self-assembles to form nanospheres. We have used independent technical methods, consisting of the yeast two-hybrid (Y2H) assay and surface plasmon resonance (SPR), to demonstrate the importance of amelogenin self-assembly domains. In addition, we have analyzed mutations in amelogenin observed in patients with amelogenesis imperfecta who demonstrate defects in enamel formation. Assessments of self-assembly of these mutant amelogenins by either SPR or Y2H assay yield concordant data. These data support the conclusion that the amelogenin amino-terminal self-assembly domain is essential to the creation of an enamel extracellular organic matrix capable of directing mineral formation. It also suggests that a pathway through which point mutations in the amelogenin protein can adversely impact on the formation of the enamel organ is by disturbing self-assembly of the organic matrix. These data support the utilization of the Y2H assay to search for protein interactions among extracellular matrix proteins that contribute to biomineralization and provide functional information on protein-protein and protein-mineral interactions.

Amelogenesis Imperfecta↗

PubMed1997

Tuftelin: enamel mineralization and amelogenesis imperfecta.

Tuftelin is a novel acidic enamel protein thought to play a major role in enamel mineralization. Its identity and localization has been confirmed by amino acid composition, enzyme-linked immunosorbant assay, Western blots, indirect immunohistochemistry and high resolution protein-A gold immunocytochemistry. The deduced tuftelin protein (pI 5.2) contains 389 amino acids and has a calculated peptide molecular mass of 43,814 Da. Immunological studies suggest conservation of tuftelin structure between species throughout vertebrate evolution. The cDNA sequence encodes for several putative post-translation sites including one N-glycosylation consensus site, seven O-glycosylation sites and seven phosphorylation sites, as well as an EF-hand calcium-binding domain (with mismatch), localized towards the N-terminal region. At the C-terminal region (residues 252-345) tuftelin contains structurally relevant determinants for self assembly. We recently cloned and partially sequenced the human tuftelin gene (four exons have now been sequenced). These sequences include exon 1 and over 1000 bases of the putative promoter region. Employing fluorescent in situ hybridization, we mapped the human tuftelin gene to chromosome 1q 21-31. Localization of the human tuftelin gene to a well-defined cytogenetic region may be important in understanding the aetiology of autosomally inherited amelogenesis imperfecta, the most common enamel hereditary disease.

Amelogenesis↗

PubMed2003

Subunit structures in hydroxyapatite crystal development in enamel: implications for amelogenesis imperfecta.

Previous freeze-etching studies of developing enamel revealed collinear arrays of spherical structures (approximately 50 nM dia) of similar width to the crystals of mature tissue. Concomitant with matrix degradation/processing, spherical structures became less distinct until, coincident with massive matrix loss, only crystal outlines were seen. More recently, using Atomic force microscopy technology, early crystals exhibited topology reminiscent of these collinear spherical structures. After matrix loss these were replaced by similarly sized bands of positive charge density on the crystal surfaces. The data suggest enamel crystals may form from mineral-matrix spherical subunits. Matrix processing may generate mineral nuclei and lead to their fusion and transformation into long apatite crystals. Support for this view derives from the appearance of short crystal segments in amelogenesis imperfecta (hypoplastic AI) or abnormally large crystals alongside 50 nM diameter spherical mineral subunits (hypomaturation AI). Mutation of matrix or processing enzymes leading to defective processing may have impaired mineral initiation, fusion, and subsequent growth.

Amelogenesis Imperfecta↗

PubMed1976