Amelogenesis imperfecta (AI) describes a heterogeneous group of inherited dental enamel defects reflecting failure of normal amelogenesis. Ameloblastin (AMBN) is the second most abundant enamel matrix protein expressed during amelogenesis. The pivotal role of AMBN in amelogenesis has been confirmed experimentally using mouse models. However, no AMBN mutations have been associated with human AI. Using autozygosity mapping and exome sequencing, we identified genomic deletion of AMBN exon 6 in a second cousin consanguineous family with three of the six children having hypoplastic AI. The genomic deletion corresponds to an in-frame deletion of 79 amino acids, shortening the protein from 447 to 368 residues. Exfoliated primary teeth (unmatched to genotype) were available from family members. The most severely affected had thin, aprismatic enamel (similar to that reported in mice homozygous for Ambn lacking exons 5 and 6). Other teeth exhibited thicker but largely aprismatic enamel. One tooth had apparently normal enamel. It has been suggested that AMBN may function in bone development. No clinically obvious bone or other co-segregating health problems were identified in the family investigated. This study confirms for the first time that AMBN mutations cause non-syndromic human AI and that mouse models with disrupted Ambn function are valid.
Amelogenesis imperfecta (AI) is a heterogeneous group of genetic conditions that result in defective dental enamel formation. Amelotin (AMTN) is a secreted protein thought to act as a promoter of matrix mineralization in the final stage of enamel development, and is strongly expressed, almost exclusively, in maturation stage ameloblasts. Amtn overexpression and Amtn knockout mouse models have defective enamel with no other associated phenotypes, highlighting AMTN as an excellent candidate gene for human AI. However, no AMTN mutations have yet been associated with human AI. Using whole exome sequencing, we identified an 8,678 bp heterozygous genomic deletion encompassing exons 3-6 of AMTN in a Costa Rican family segregating dominant hypomineralised AI. The deletion corresponds to an in-frame deletion of 92 amino acids, shortening the protein from 209 to 117 residues. Exfoliated primary teeth from an affected family member had enamel that was of a lower mineral density compared to control enamel and exhibited structural defects at least some of which appeared to be associated with organic material as evidenced using elemental analysis. This study demonstrates for the first time that AMTN mutations cause non-syndromic human AI and explores the human phenotype, comparing it with that of mice with disrupted Amtn function.
Amelogenesis imperfecta (AI) is a heterogeneous group of inherited disorders characterized by abnormal formation of dental enamel, either in isolation or as part of a syndrome. Heterozygous variants in laminin subunit beta 3 (LAMB3) cause AI with dominant inheritance in the absence of other cosegregating clinical features. In contrast, biallelic loss-of-function variants in LAMB3 cause recessive junctional epidermolysis bullosa, characterized by life-threatening skin fragility. We identified 2 families segregating autosomal dominant AI with variable degrees of a distinctive hypoplastic phenotype due to pathogenic variants in LAMB3. Whole exome sequencing revealed a nonsense variant (c.3340G>T, p.E1114*) within the final exon in family 1, while Sanger sequencing in family 2 revealed a variant (c.3383-1G>A) in the canonical splice acceptor site of the final exon. Analysis of cDNA from family 2 revealed retention of the final intron leading to a premature termination codon. Two unerupted third molar teeth from individual IV:5 in family 2 were subject to computerized tomography and scanning electron microscopy. LAMB3 molar teeth have a multitude of cusps versus matched controls. LAMB3 enamel was well mineralized but pitted. The architecture of the initially secreted enamel was abnormal, with cervical enamel appearing much less severely affected than coronal enamel. This study further defines the variations in phenotype-genotype correlation for AI due to variants in LAMB3, underlines the clustering of nonsense and frameshift variants causing AI in the absence of junctional epidermolysis bullosa, and highlights the shared AI phenotype arising from variants in genes coding for hemidesmosome proteins.
Amelogenesis imperfecta (AI) is a heterogeneous group of genetic diseases characterised by dental enamel malformation. Pathogenic variants in at least 33 genes cause syndromic or non-syndromic AI. Recently variants in RELT, encoding an orphan receptor in the tumour necrosis factor (TNF) superfamily, were found to cause recessive AI, as part of a syndrome encompassing small stature and severe childhood infections. Here we describe four additional families with autosomal recessive hypomineralised AI due to previously unreported homozygous mutations in RELT. Three families carried a homozygous missense variant in the fourth exon (c.164C>T, p.(T55I)) and a fourth family carried a homozygous missense variant in the 11th exon (c.1264C>T, p.(R422W)). We found no evidence of additional syndromic symptoms in affected individuals. Analyses of tooth microstructure with computerised tomography and scanning electron microscopy suggest a role for RELT in ameloblasts' coordination and interaction with the enamel matrix.Microsatellite genotyping in families segregating the T55I variant reveals a shared founder haplotype. These findings extend the RELT pathogenic variant spectrum, reveal a founder mutation in the UK Pakistani population and provide detailed analysis of human teeth affected by this hypomineralised phenotype, but do not support a possible syndromic presentation in all those with RELT-variant associated AI. K E Y W O R D S amelogenesis imperfecta, enamel, RELT, tumour necrosis factor receptor
RESUMENAmelogénesis imperfecta (AI) describe defectos en el esmalte derivados de mutaciones genéticas que se manifiestan en anormalidades estructurales en la dentición temporal y permanente. A pesar del amplio conocimiento que aumenta día tras día a nivel mundial sobre las mutaciones genéticas asociadas a la AI, existe poca investigación en su efecto sobre la calidad de vida de los pacientes. El objetivo de este estudio es determinar, en un cohorte de pacientes costarricenses afectados por esta patología, la percepción emocional sobre su calidad de vida que esta condición ha generado. Miembros de varias familias portadoras de AI se entrevistaron y sus experiencias sirvieron de base para desarrollar un instrumento (cuestionario), el cual se utilizó para evaluar el impacto de este padecimiento, en su calidad de vida. Se incluyeron 18 personas afectadas de AI, provenientes de 17 familias. Los resultados más relevantes revelaron que un 100 % de los participantes han sufrido burlas y rechazo; 77.8 % se mostraron preocupados por la herencia a sus hijos; 66.7 % les preocupa el costo del tratamiento; 89 % le atribuyen alta importancia a sus dientes, siendo no estadísticamente significativo por sexo (p = 0.732). El estudio indica que los profesionales en Odontología deben entender la AI no solo como un defecto en la estructura del esmalte dental, que demanda un manejo clínico especializado, sino como una condición que causa impacto negativo en la calidad de vida de quienes la padecen. Esto se debe considerar en la comunicación e interacción del profesional, los sujetos afectados y sus familias. PALABRAS CLAVEAmelogénesis imperfecta, Percepción emocional, Autoestima, Familias costarricenses. ODOVTOS-International Journal of Dental SciencesABSTRACT "Amelogenesis imperfecta" (AI) (prevalence up to 1 in 700) describes largely Mendelian enamel defects arising from gene mutations that present as structural abnormalities of the temporary and permanent teeth as a result of defective enamel formation. AI has a wide range of clinical presentations and phenotypes and affects both sexes. Despite increasing knowledge of the genetic mutations underlying AI there has been little research focussing on the effect of AI on the quality of life of AI patients. This study aimed to investigate the effects of AI on patient quality of life in a Costa Rican AI cohort. Affected family members were interviewed and their experiences used to develop an instrument (questionnaire) that was subsequently used to evaluate the impact of AI on their quality of life. 18 AI patients from 17 families were included in the study. Our findings showed that 100% had been teased and had suffered social rejection; 77.8% were concerned about their children´s inheritance and 66.7 % were concerned by the cost of treatment; 89% placed a high importance on their teeth. Results were not statistically significant when sorted by sex (p = 0.732). The results of this study indicate that dental professionals need to understand AI not only as defective tooth enamel structure d...
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