Phenotypic diversity and revision of the nomenclature for autosomal recessive amelogenesis imperfecta

Association between malocclusions and amelogenesis imperfecta genotype and phenotype: A systematic review

INTRODUCTION

The aim of this systematic review (Prospero CRD42022323188) is to investigate whether an association exists in patients with amelogenesis imperfecta (AI) between occlusal characteristics and genotype on the one hand and enamel structural phenotype on the other.

MATERIAL AND METHODS

Reports up to May 2023 assessing occlusion of individuals with AI were browsed in a systematic search using Medline, Embase, ISI Web of Science, and the grey literature. Randomised control trials, case control studies, and case series specifying both occlusion, assessed by cephalometric or clinical analysis, and genotype or dental phenotype in patients with AI were included without any age limitation. Two authors independently selected the publications and extracted the data in accordance with the PRISMA statement. The risk of bias was assessed with the Critical Appraisal Checklists from the Johanna Briggs Institute.

RESULTS

Twenty-five articles were chosen from the 261 results. Most of the included publications were case series (n=22) and case control studies (n=3). Thirteen studies reported both a genotype (ENAM, FAM83H, FAM20A, DLX3, CNMM4, WDR72) and occlusal diagnostic. The methodological quality of the studies was moderate. All AI phenotypes showed an open bite (OB) rate around 35%, except mixed form. The other malocclusions were not often mentioned. No correlation between occlusal phenotype and genotype or AI phenotype could be identified in patients with AI, as most studies had short occlusal descriptions and small sample sizes.

CONCLUSION

OB malocclusions were more frequently reported in AI. This review highlighted the need for a more accurate description of orofacial features associated with AI, to better clarify the role of amelogenesis genes in the regulation of craniofacial morphogenesis and identify patients requiring orthognathic surgery at an early stage.

A novel FAM83H variant causes familial amelogenesis imperfecta with incomplete penetrance

Background

Amelogenesis imperfecta (AI) is known to be a monogenic genetic disease caused by a variety of genes demonstrating a wide spectrum of penetrance. FAM83H is reported to be involved in AI: however, whether FAM83H causes AI with incomplete penetrance is unclear.

Methods

Whole‐exome sequencing was performed on two patients with AI, and putative disease‐related variants were validated by Sanger sequencing. Bioinformatic and in vitro functional analyses were performed to functionally characterize the identified disease‐causing variants.

Results

We identified a novel heterozygous nonsense variant of FAM83H (NM_198488: c.1975G > T, p.Glu659Ter); in vitro functional analysis showed that this mutant produced mislocalized proteins and was deleterious. Surprisingly, the clinical manifestations of each of the six individuals carrying this variant were different, with one carrier appearing to be completely asymptomatic for AI.

Conclusion

Our findings expand the variant spectrum for FAM83H and the phenotypic spectrum for FAM83H‐associated AI and suggest that FAM83H‐mediated AI exhibits incomplete penetrance.

The Human Genetics of Dental Anomalies

The development of tooth is a highly complex procedure and mastered by specific genetic programs. Genetic alterations, environmental factors, and developmental timing can disturb the execution of these programs, and result in various dental anomalies like hypodontia/oligodontia, and supernumerary teeth, which are commonly seen in our clinical practice. Advances in molecular research enabled the identification of various genes involved in the pathogenesis of dental anomalies. In the near future, it will help provide a more accurate diagnosis and biological-based treatment for these anomalies. In this article, we present the molecular phenomenon of tooth development and the genetics of various dental anomalies.

Restorative Treatment of Amelogenesis Imperfecta with Prefabricated Composite Veneers

This case report presents the use of prefabricated composite veneers for restorative treatment of amelogenesis imperfecta (AI). This technique bridges the gap between a conventional direct technique and a conventional indirect technique and introduces an alternative semidirect restorative technique for AI patients. The aim of this case report is to describe restoration of a young girl with severe AI using prefabricated composite veneers and to discuss the benefits and limitations of this technique compared to the alternative restorative techniques.

Restorative treatment in a case of amelogenesis imperfecta and 9-year follow-up: a case report

Background

Amelogenesis imperfecta is a hereditary malformation showing various manifestations regarding enamel dysplasia. This case report shows a 9-year follow-up after restorative treatment of a 16-year old female patient affected by a hypoplastic type of amelogenesis imperfecta. The caries-free, hypersensitive teeth of the patient were restored by direct dentin adhesive composite restorations performed in total etch technique.

Case presentation

After rehabilitation the patient reported a marked improvement of the mastication ability and quality of life especially during food intake. Accumulation of plaque was reduced and the ability to perform adequate oral hygiene was improved. During follow-up of 9 years recurring secondary caries and debonding of fillings were recognized and retreated.

Conclusions

The retrospective assessment exhibits that the performed restorative treatment prolonged the time until further treatment has to be considered, such as prosthetic treatment.

Amelogenesis imperfecta with Class III malocclusion, reduced crown size and decreased OVD: A multi-disciplinary management and a 5-year follow-up

This clinical report describes the oral rehabilitation of a 22-year-old-man diagnosed with a variant of hypoplastic amelogenesis imperfecta. The treatment approach was multi-disciplinary, and it included the surgical procedure of Lefort I osteotomy, surgical crown lengthening, and metal-ceramic-fixed dental prostheses. The patient was satisfied with the esthetic and functional outcome.

Amelogenesis Imperfecta with Nephrocalcinosis: A Rare Association in Siblings

Enamel hypoplasia secondary to amelogenesis imperfect (AI) is one of the common developmental disturbances associated with the oral cavity. AI in association with multiple unerupted teeth is a rare entity, and in adolescence it not only has an affect on esthetics but also has an impact on the psychological status of the person. AI has been reported with other systemic anomalies previously. We report a case of AI in association with multiple unerupted teeth and nephrocalcinosis in siblings. The present case also highlights the importance of systemic examination and investigations in planning the treatment of a patient with AI.

Association of enamel-renal syndrome with sialolith: A rare entity

Amelogenesis imperfecta (AI) is a disease primarily affecting amelogenesis, but other various aberrations have been reported in association with this entity. Enamel-renal syndrome (ERS) is a very rare disorder associating AI with nephrocalcinosis. It is known by various synonyms such as AI nephrocalcinosis syndrome, MacGibbon syndrome, Lubinsky syndrome and Lubinsky–MacGibbon syndrome. The purposes of this article are to describe other dental anomalies which are rarely associated with AI making the diagnosis of AI a complex disorder and also to report a rare case of MacGibbon syndrome presented with sialolith of submandibular gland duct which is the first reported case in the literature.

Diversity of clinical, radiographic and genealogical findings in 41 families with amelogenesis imperfecta

Amelogenesis imperfecta (AI) is a group of enamel development disorders that alter the structure and chemical composition of the tissue. There is great variability in the clinical presentation; according to Witkop, AI can be categorized into 14 subtypes, which makes its diagnosis extremely complex.

OBJECTIVE

This study aimed to describe and determine the frequency of clinical and radiographic features and inheritance patterns found in 41 Chilean families diagnosed with diverse types of AI.

MATERIAL AND METHODS

We analyzed the clinical records, photographs, pedigrees and radiographs of 121 individuals recruited between 2003 and 2016. All of the information was included in a database that was analyzed using the application Stata 14.

RESULTS

The 72 affected individuals had average age of 16 years, and no sex association with the presence of AI was found. The most frequent clinical subtypes were as follows: 43% hypomature, 25% hypoplastic, 21% hypomature/hypoplastic, 7% hypocalcified and 4% hypocalcified/hypoplastic. The number of severely affected teeth was 22, which occurred in the patients with hypocalcified and hypocalcified/hypoplasic AI who presented the highest number of damaged teeth. Caries and periodontal disease were found in 47 and 32% of the patients, respectively. Malocclusions were observed in 43% of the individuals with AI, with open bite being the most frequent. Radiographically, the thickness of the enamel decreased in 51% of the patients, and 80% showed decreased radiopacity of the enamel compared to that of dentin. Autosomal dominant inheritance pattern was found in 37% of the families with hypoplastic AI, and autosomal recessive pattern was present in 56% of the other clinical subtypes, but more frequently in those affected with hypomature and hypocalcified AI.

CONCLUSION

Of the five clinical subtypes, autosomal recessive hypomature, autosomal dominant hypoplastic and autosomal recessive hypomature/hypoplastic AI were the most prevalent subtypes in this group.

DENTAL ENAMEL FORMATION AND IMPLICATIONS FOR ORAL HEALTH AND DISEASE

Dental enamel is the hardest and most mineralized tissue in extinct and extant vertebrate species and provides maximum durability that allows teeth to function as weapons and/or tools as well as for food processing. Enamel development and mineralization is an intricate process tightly regulated by cells of the enamel organ called ameloblasts. These heavily polarized cells form a monolayer around the developing enamel tissue and move as a single forming front in specified directions as they lay down a proteinaceous matrix that serves as a template for crystal growth. Ameloblasts maintain intercellular connections creating a semi-permeable barrier that at one end (basal/proximal) receives nutrients and ions from blood vessels, and at the opposite end (secretory/apical/distal) forms extracellular crystals within specified pH conditions. In this unique environment, ameloblasts orchestrate crystal growth via multiple cellular activities including modulating the transport of minerals and ions, pH regulation, proteolysis, and endocytosis. In many vertebrates, the bulk of the enamel tissue volume is first formed and subsequently mineralized by these same cells as they retransform their morphology and function. Cell death by apoptosis and regression are the fates of many ameloblasts following enamel maturation, and what cells remain of the enamel organ are shed during tooth eruption, or are incorporated into the tooth's epithelial attachment to the oral gingiva. In this review, we examine key aspects of dental enamel formation, from its developmental genesis to the ever-increasing wealth of data on the mechanisms mediating ionic transport, as well as the clinical outcomes resulting from abnormal ameloblast function.

Pathognomonic oral profile of Enamel Renal Syndrome (ERS) caused by recessive FAM20A mutations

Amelogenesis imperfecta (AI) is a genetically and clinically heterogeneous group of inherited dental enamel defects. Commonly described as an isolated trait, it may be observed concomitantly with other orodental and/or systemic features such as nephrocalcinosis in Enamel Renal Syndrome (ERS, MIM#204690), or gingival hyperplasia in Amelogenesis Imperfecta and Gingival Fibromatosis Syndrome (AIGFS, MIM#614253). Patients affected by ERS/AIGFS present a distinctive orodental phenotype consisting of generalized hypoplastic AI affecting both the primary and permanent dentition, delayed tooth eruption, pulp stones, hyperplastic dental follicles, and gingival hyperplasia with variable severity and calcified nodules. Renal exam reveals a nephrocalcinosis which is asymptomatic in children affected by ERS. FAM20A recessive mutations are responsible for both syndromes. We suggest that AIGFS and ERS are in fact descriptions of the same syndrome, but that the kidney phenotype has not always been investigated fully in AIGFS. The aim of this review is to highlight the distinctive and specific orodental features of patients with recessive mutations in FAM20A. We propose ERS to be the preferred term for all the phenotypes arising from recessive FAM20A mutations. A differential diagnosis has to be made with other forms of AI, isolated or syndromic, where only a subset of the clinical signs may be shared. When ERS is suspected, the patient should be assessed by a dentist, nephrologist and clinical geneticist. Confirmed cases require long-term follow-up. Management of the orodental aspects can be extremely challenging and requires the input of multi-disciplinary specialized dental team, especially when there are multiple unerupted teeth.

Mouse genetic background influences the dental phenotype

Dental enamel covers the crown of the vertebrate tooth and is considered to be the hardest tissue in the body. Enamel develops during secretion of an extracellular matrix by ameloblast cells in the tooth germ, prior to eruption of the tooth into the oral cavity. Secreted enamel proteins direct mineralization patterns during the maturation stage of amelogenesis as the tooth prepares to erupt. The amelogenins are the most abundant enamel proteins and are required for normal enamel development. Phenotypic differences were observed between incisors from individual Amelx (amelogenin) null mice that had a mixed 129xC57BL/6J genetic background and between inbred wild-type (WT) mice with different genetic backgrounds (C57BL/6J, C3H/HeJ, FVB/NJ). We hypothesized that this could be due to modifier genes, as human patients with a mutation in an enamel protein gene causing the enamel defect amelogenesis imperfecta (AI) can also have varied appearance of dentitions within a kindred. Enamel density measurements varied for all WT inbred strains midway during incisor development. Enamel thickness varied between some WT strains, and, unexpectedly, dentin density varied extensively between incisors and molars of all WT and Amelx null strains studied. WTFVB/NJ incisors were more similar to those of Amelx null mice than to those of the other WT strains in terms of incisor height/width ratio and pattern of enamel mineralization. Strain-specific differences led to the conclusion that modifier genes may be implicated in determining both normal development and severity of enamel appearance in AI mouse models and may in future studies be related to phenotypic heterogeneity within human AI kindreds reported in the literature.

Candidate-gene exclusion in a family with inherited non-syndromic dental disorders

OBJECTIVES

Amelogenesis imperfecta, dentinogenesis imperfecta, and dentin dysplasia are the most common non-syndromic dental disorders. In this study, we analysed and localised the gene(s) responsible for inherited non-syndromic dental disorders in a Chinese family.

METHODS

This study identified and researched non-syndromic dental disorders in a four-generation Chinese family, including four affected individuals whose clinical phenotype was atypical. Linkage analysis with seven polymorphic markers that localise to six different autochromosomes showed that the family was linked through chromosome 4q. All exons and exon-intron boundaries of dentin sialophosphoprotein (DSPP), enamelin (ENAM), and ameloblastin (AMBN), which are located on chromosome 4q, were sequenced in nine of the family members.

RESULTS

Direct DNA sequence analysis revealed the existence of a G to A transversion in exon 4 (g.13081786G>A, c.727G>A, p.Asp243Asn, based on reference sequences NM_014208.3) of the DSPP gene, and this sequence variation correlated exactly with the presence of the disease.

CONCLUSION

These results indicate that mutation p.Asp243Asn is a highly probable cause of non-syndromic dental disorder in this Chinese family. The presence of symptom heterogeneity is possible, as the clinical classification system is hampered by the lack of close correlation between the subtype and the molecular defect.

An interdisciplinary approach for rehabilitating a patient with amelogenesis imperfecta: a case report

Amelogenesis imperfecta (AI) has been defined as a group of hereditary enamel defects. It can be characterized by enamel hypoplasia, hypomaturation, or hypocalcification of the teeth. AI may be associated with some other dental and skeletal developmental defects. Restoration for patients with this condition should be oriented toward the functional and esthetic rehabilitation. This clinical report describes the oral rehabilitation of a young patient diagnosed with the hypoplastic type of AI in posterior teeth and hypomatured type of AI in anterior teeth.

Amelogenesis imperfecta and other biomineralization defects in Fam20a and Fam20c null mice

The FAM20 family of secreted proteins consists of three members (FAM20A, FAM20B, and FAM20C) recently linked to developmental disorders suggesting roles for FAM20 proteins in modulating biomineralization processes. The authors report here findings in knockout mice having null mutations affecting each of the three FAM20 proteins. Both Fam20a and Fam20c null mice survived to adulthood and showed biomineralization defects. Fam20b (-/-) embryos showed severe stunting and increased mortality at E13.5, although early lethality precluded detailed investigations. Physiologic calcification or biomineralization of extracellular matrices is a normal process in the development and functioning of various tissues (eg, bones and teeth). The lesions that developed in teeth, bones, or blood vessels after functional deletion of either Fam20a or Fam20c support a significant role for their encoded proteins in modulating biomineralization processes. Severe amelogenesis imperfecta (AI) was present in both Fam20a and Fam20c null mice. In addition, Fam20a (-/-) mice developed disseminated calcifications of muscular arteries and intrapulmonary calcifications, similar to those of fetuin-A deficient mice, although they were normocalcemic and normophosphatemic, with normal dentin and bone. Fam20a gene expression was detected in ameloblasts, odontoblasts, and the parathyroid gland, with local and systemic effects suggesting both local and/or systemic effects for FAM20A. In contrast, Fam20c (-/-) mice lacked ectopic calcifications but were severely hypophosphatemic and developed notable lesions in both dentin and bone to accompany the AI. The bone and dentin lesions, plus the marked hypophosphatemia and elevated serum alkaline phosphatase and FGF23 levels, are indicative of autosomal recessive hypophosphatemic rickets/osteomalacia in Fam20c (-/-) mice.

A multidisciplinary approach for the diagnosis of hypocalcified amelogenesis imperfecta in two Chilean families

OBJECTIVE

The purpose of this study was to conduct a multidisciplinary analysis of a specific type of tooth enamel disturbance (amelogenesis imperfecta) affecting two Chilean families to obtain a precise diagnosis and to investigate possible underlying mutations.

MATERIALS AND METHODS

Two non-related families affected with amelogenesis imperfecta were evaluated with clinical, radiographic and histopathological methods. Furthermore, pedigrees of both families were constructed and the presence of eight mutations in the enamelin gene (ENAM) and three mutations in the enamelysin gene (MMP-20) were investigated by PCR and direct sequencing.

RESULTS

In the two affected patients, the dental malformation presented as soft and easily disintegrated enamel and exposed dark dentin. Neither of the affected individuals presented with a dental and skeletal open bite. Histologically, a high level of an organic matrix with prismatic organization was found. Genetic analysis indicated that the condition is autosomal recessive in one family and either autosomal recessive or due to a new mutation in the other family. Molecular mutational analysis revealed that none of the eight mutations previously described in the ENAM gene or the three mutations in the MMP-20 gene were present in the probands.

CONCLUSION

A multidisciplinary analysis allowed for a diagnosis of hypocalcified amelogenesis imperfecta, Witkop type III, which was unrelated to previously described mutations in the ENAM or MMP-20 genes.

Target gene analyses of 39 amelogenesis imperfecta kindreds

Previously, mutational analyses identified six disease-causing mutations in 24 amelogenesis imperfecta (AI) kindreds. We have since expanded the number of AI kindreds to 39, and performed mutation analyses covering the coding exons and adjoining intron sequences for the six proven AI candidate genes [amelogenin (AMELX), enamelin (ENAM), family with sequence similarity 83, member H (FAM83H), WD repeat containing domain 72 (WDR72), enamelysin (MMP20), and kallikrein-related peptidase 4 (KLK4)] and for ameloblastin (AMBN) (a suspected candidate gene). All four of the X-linked AI families (100%) had disease-causing mutations in AMELX, suggesting that AMELX is the only gene involved in the aetiology of X-linked AI. Eighteen families showed an autosomal-dominant pattern of inheritance. Disease-causing mutations were identified in 12 (67%): eight in FAM83H, and four in ENAM. No FAM83H coding-region or splice-junction mutations were identified in three probands with autosomal-dominant hypocalcification AI (ADHCAI), suggesting that a second gene may contribute to the aetiology of ADHCAI. Six families showed an autosomal-recessive pattern of inheritance, and disease-causing mutations were identified in three (50%): two in MMP20, and one in WDR72. No disease-causing mutations were found in 11 families with only one affected member. We conclude that mutation analyses of the current candidate genes for AI have about a 50% chance of identifying the disease-causing mutation in a given kindred.

Amelogenesis imperfecta: A challenge to restoring esthetics and function

Rehabilitation of complicated cases poses difficulty in clinical practice, both with respect to restoring function and with esthetics. One such clinical condition where the dentist has to give importance to proper planning of the treatment and execution of the plan is amelogenesis imperfecta (AI), a condition where both function and esthetics are accommodated. This article discusses both the functional and esthetic rehabilitation of a patient with AI. Both the esthetics and function were hampered in this patient due to the condition. As a result, the treatment was properly planned and executed. A number of treatment options are available for us today to treat such a case. There is no one technique to be followed as such. However, the aim was to properly diagnose the case and provide good function and esthetics to the patient.

Amelogenesis imperfecta: genotype-phenotype studies in 71 families

Amelogenesis imperfecta (AI) represents hereditary conditions affecting the quality and quantity of enamel. Six genes are known to cause AI (AMELX, ENAM, MMP20, KLK4, FAM83H, and WDR72). Our aim was to determine the distribution of different gene mutations in a large AI population and evaluate phenotype-genotype relationships. Affected and unaffected family members were evaluated clinically and radiographically by one examiner. Genotyping was completed using genomic DNA obtained from blood or saliva. A total of 494 individuals were enrolled, with 430 (224 affected, 202 unaffected, and 4 not definitive) belonging to 71 families with conditions consistent with the diagnosis of AI. Diverse clinical phenotypes were observed (i.e. hypoplastic, hypocalcified, and hypomaturation). Genotyping revealed mutations in all 6 candidate genes. A molecular diagnosis was made in 132 affected individuals (59%) and in 26 of the families (37%). Mutations involved 12 families with FAM83H (46%), 6 families with AMELX (23%), 3 families with ENAM (11%), 2 families with KLK4 and MMP20 (8% for each gene), and 1 family with a WDR72 mutation (4%). Phenotypic variants were associated with allelic FAM83H and AMELX mutations. Two seemingly unrelated families had the same KLK4 mutation. Families affected with AI where candidate gene mutations were not identified could have mutations not identifiable by traditional gene sequencing (e.g. exon deletion) or they could have promoter sequence mutations not evaluated in this study. However, the results suggest that there remain new AI causative genes to be identified.

Case series: clinical findings and oral rehabilitation of patients with amelogenesis imperfecta

BACKGROUND

Children with amelogenesis imperfecta (AI) experience many oral difficulties including sensitivity and aesthetics. The methods of treating AI children are limited and therefore a program of care was evaluated in order to assess the clinical efficacy of providing preventive and restorative treatments.

CASE REPORTS

A non-randomised convenience sample of 12 patients with AI was evaluated. A comprehensive patient history was recorded, followed by a clinical and radiographic assessment of oral health. In 8/12 patients a hypoplastic form of AI was diagnosed, in 2/12 cases hypomaturation and in 2/12 cases hypocalcified form were noted. Chief complaints were mainly related to unsatisfactory aesthetics and dental sensitivity. In 8 patients there was active dental caries. Most of the patients had gingivitis and showed fair oral hygiene. The presence of non-enamel dental anomalies was recorded in 9 patients.

TREATMENT

All patients received meticulous preventive care. Initial treatment depended on AI type and oral health of the patient. During the transition period, both conventional and resin modified glassionomer cements, as well as composite resin materials, were used to restore posterior teeth. Direct composite resin restorations were used to improve the appearance of anterior teeth. In 4 patients a long-lasting interdisciplinary approach including orthodontics, metal-ceramic crowns and fixed partial dentures, and direct composite restorations was required.

FOLLOW-UP

Follow-up periods varied between 2-11 years. All children have been regularly recalled at 3 monthly intervals. Caries prevalence has remained low during the follow-up postoperative period and patients have reported satisfaction with the treatment they have received.

CONCLUSION

AI is associated with multiple non-enamel anomalies and requires a complex treatment. Treatment planning is related to the age of the patient, the type and severity of the disorder, and the oral health of the patient. Early diagnosis, preventive care and timely treatment are of foremost importance to improve oral health in children with AI.

Mutations in the beta propeller WDR72 cause autosomal-recessive hypomaturation amelogenesis imperfecta

Healthy dental enamel is the hardest and most highly mineralized human tissue. Though acellular, nonvital, and without capacity for turnover or repair, it can nevertheless last a lifetime. Amelogenesis imperfecta (AI) is a collective term for failure of normal enamel development, covering diverse clinical phenotypes that typically show Mendelian inheritance patterns. One subset, known as hypomaturation AI, is characterised by near-normal volumes of organic enamel matrix but with weak, creamy-brown opaque enamel that fails prematurely after tooth eruption. Mutations in genes critical to enamel matrix formation have been documented, but current understanding of other key events in enamel biomineralization is limited. We investigated autosomal-recessive hypomaturation AI in a consanguineous Pakistani family. A whole-genome SNP autozygosity screen identified a locus on chromosome 15q21.3. Sequencing candidate genes revealed a point mutation in the poorly characterized WDR72 gene. Screening of WDR72 in a panel of nine additional hypomaturation AI families revealed the same mutation in a second, apparently unrelated, Pakistani family and two further nonsense mutations in Omani families. Immunohistochemistry confirmed intracellular localization in maturation-stage ameloblasts. WDR72 function is unknown, but as a putative β propeller is expected to be a scaffold for protein-protein interactions. The nearest homolog, WDR7, is involved in vesicle mobilization and Ca²⁺-dependent exocytosis at synapses. Vesicle trafficking is important in maturation-stage ameloblasts with respect to secretion into immature enamel and removal of cleaved enamel matrix proteins via endocytosis. This raises the intriguing possibility that WDR72 is critical to ameloblast vesicle turnover during enamel maturation.

Case reports of a new syndrome associating gingival fibromatosis and dental abnormalities in a consanguineous family

BACKGROUND

Gingival fibromatosis (GF) is characterized by fibrotic enlargement of the gingiva that can be inherited as an isolated trait (named hereditary gingival fibromatosis) or as a component of a syndrome. This article reports one kindred affected by a syndrome characterized by GF associated with dental abnormalities (DA) including generalized thin hypoplastic amelogenesis imperfecta (AI).

METHODS

To characterize the pattern of inheritance and the clinical features, 70 family members were examined. Hematoxylin and eosin staining, immunohistochemistry, and scanning electronic microscopy (SEM) were performed to identify the alterations on gingiva, teeth, and dental follicles.

RESULTS

Examination of the family pedigree demonstrated multiple consanguineous first-cousin marriages and an autosomal recessive trait of inheritance. Four members demonstrated mild GF in association with DA, including generalized thin hypoplastic AI, intrapulpal calcifications, delay of tooth eruption, and pericoronal radiolucencies involving unerupted teeth. One of those four patients also had mental retardation (MR). MR as an isolated feature was observed in six members, whereas isolated GF was found in one individual. A combination of gingivectomy and gingivoplasty followed by regular dental procedures were performed in these patients. Histologic examination of the gingival enlargement revealed a dense connective tissue containing myofibroblasts, islands of odontogenic epithelium, and calcified psammomatous deposits, which resembled cementicle-like structures by SEM. Pericoronal lesions also showed calcified psammomatous deposits in association with islands of odontogenic epithelium. Enamel ultrastructure analysis revealed normal surface alternating with irregular and porous areas.

CONCLUSION

To the best of our knowledge, these cases represent a new syndrome within the spectrum of those including GF.

Fixed rehabilitation of an ACP PDI class III patient with amelogenesis imperfecta

This clinical report describes the oral rehabilitation of a 19-year-old woman diagnosed with hypoplastic-type amelogenesis imperfecta (AI). She presented with discolored and mutilated teeth, missing teeth, anterior open bite, and posterior short crowns. She was classified as an American College of Prosthodontists Prosthodontic Diagnostic Index (ACP PDI) class III patient. The aim of treatment was to restore esthetics and improve masticatory function. The patient's esthetic and functional expectations were successfully attained with porcelain laminate veneers and all-ceramic and metal-ceramic restorations after extensive crown lengthening. The patient was regularly recalled during the postoperative period. Loss of retention of one all-ceramic crown and minimal recession of the gingiva of one laminate veneer were noted at 4-year recall.

Amelogenesis imperfecta - a systematic literature review of associated dental and oro-facial abnormalities and their impact on patients

OBJECTIVE

Amelogenesis imperfecta (AI) is a disease primarily affecting amelogenesis, but other aberrations have been reported. The purposes of this review were: (1) to identify other anomalies associated with AI, and (2) to describe the impact of the disease and its associated conditions on the oral health-related quality of life of patients, and the economic consequences.

MATERIAL AND METHODS

A literature search was conducted in the following databases: PubMed, EMBASE, Bibliotek.dk, The Cochrane Library, Web of Science, and OMIM, supplemented by a search for selected authors. Based on titles and abstracts, 137 papers were identified.

RESULTS

Most articles were case reports or case series with few cases. Aberrations were reported in the eruption process, in the morphology of the crown, in the pulp-dentine organ, and in the number of teeth. Gingival conditions and oral hygiene were usually reported to be poor, and calculus was a common finding. Open bite was the most commonly reported malocclusion. A negative impact on patients' oral health-related quality of life was described, but information was scarce. No information was found on the economic impact.

CONCLUSIONS

A number of aberrations associated with AI have been reported, but not sufficiently systematic to allow for a secondary analysis and synthesis of the findings. The impact on patients in terms of reduced quality of life and economic burden needs to be studied.

A novel autosomal-recessive mutation, whitish chalk-like teeth, resembling amelogenesis imperfecta, maps to rat chromosome 14 corresponding to human 4q21

A rat mutant, whitish chalk-like teeth (wct), with white, chalk-like abnormal incisors, was discovered and morphologically and genetically characterized. The mutant rats showed tooth enamel defects that were similar to those of human amelogenesis imperfecta. The wct mutation was found to disturb the morphological transition of ameloblasts from secretory to maturation stages and to induce cyst formation. This mutation also disturbs the transfer of iron into the enamel, resulting in the whitish chalk-like incisors. A genetic linkage study indicated that the wct locus maps to a specific interval of rat chromosome 14 between D14Got13 and D14Wox2. Interestingly, the human chromosomal region orthologous to wct, a 5.5-Mb interval in human chromosome 4q21, is a critical region for the locus of human amelogenesis imperfecta AIH2. These results strongly suggest that this wct mutant is a useful model for the identification of genes responsible for amelogenesis imperfecta and molecular mechanisms of tooth development.

Interdisciplinary approach to treating a patient with amelogenesis imperfecta: a clinical report

Treatment of a patient with amelogenesis imperfecta (AI) presents a real problem from both functional and esthetic points of view. An esthetic result also will result in an improvement in the patient's quality of life. This clinical report illustrates the oral rehabilitation of a 24-year-old man diagnosed with hypomature type of AI. The aim of treatment was to both restore esthetics and improve masticatory function. Esthetic expectations of the patient were successfully attained by placing all-porcelain crowns from canine to canine in each arch, 12 crowns total. Moreover, metal-ceramic three-unit fixed partial dentures for the missing mandibular right first molars were fabricated for the patient's masticatory function. Resin composite restorations were applied to the maxillary premolars, the maxillary right first molar, the mandibular left premolars, and the right first premolar to modify the occlusion. No deterioration in the restorations and no pathology associated with the rehabilitation were found at the 1-year recall, and the patient's esthetic and functional expectations were satisfied. CLINICAL SIGNIFICANCE This article provides an overview of an interdisciplinary approach to treating the difficult condition of AI using a combination of treatments to achieve optimal esthetics and function.

Amelogenesis imperfecta

Amelogenesis imperfecta (AI) represents a group of developmental conditions, genomic in origin, which affect the structure and clinical appearance of enamel of all or nearly all the teeth in a more or less equal manner, and which may be associated with morphologic or biochemical changes elsewhere in the body. The prevalence varies from 1:700 to 1:14,000, according to the populations studied. The enamel may be hypoplastic, hypomineralised or both and teeth affected may be discoloured, sensitive or prone to disintegration. AI exists in isolation or associated with other abnormalities in syndromes. It may show autosomal dominant, autosomal recessive, sex-linked and sporadic inheritance patterns. In families with an X-linked form it has been shown that the disorder may result from mutations in the amelogenin gene, AMELX. The enamelin gene, ENAM, is implicated in the pathogenesis of the dominant forms of AI. Autosomal recessive AI has been reported in families with known consanguinity. Diagnosis is based on the family history, pedigree plotting and meticulous clinical observation. Genetic diagnosis is presently only a research tool. The condition presents problems of socialisation, function and discomfort but may be managed by early vigorous intervention, both preventively and restoratively, with treatment continued throughout childhood and into adult life. In infancy, the primary dentition may be protected by the use of preformed metal crowns on posterior teeth. The longer-term care involves either crowns or, more frequently these days, adhesive, plastic restorations.

Exclusion of known gene for enamel development in two Brazilian families with amelogenesis imperfecta

Amelogenesis imperfecta (AI) is a genetically heterogeneous group of diseases that result in defective development of tooth enamel. Mutations in several enamel proteins and proteinases have been associated with AI. The object of this study was to evaluate evidence of etiology for the six major candidate gene loci in two Brazilian families with AI. Genomic DNA was obtained from family members and all exons and exon-intron boundaries of the ENAM, AMBN, AMELX, MMP20, KLK4 and Amelotin gene were amplified and sequenced. Each family was also evaluated for linkage to chromosome regions known to contain genes important in enamel development. The present study indicates that the AI in these two families is not caused by any of the known loci for AI or any of the major candidate genes proposed in the literature. These findings indicate extensive genetic heterogeneity for non-syndromic AI.

The molecular etiologies and associated phenotypes of amelogenesis imperfecta

The amelogenesis imperfectas (AIs) are a clinically and genetically diverse group of conditions that are caused by mutations in a variety of genes that are critical for normal enamel formation. To date, mutations have been identified in four genes (AMELX, ENAM, KLK4, MMP20) known to be involved in enamel formation. Additional yet to be identified genes also are implicated in the etiology of AI based on linkage studies. The diverse and often unique phenotypes resulting from the different allelic and non-allelic mutations in these genes provide an opportunity to better understand the role of these genes and their related proteins in enamel formation. Understanding the AI phenotypes also provides an aid to clinicians in directing molecular studies aimed at delineating the genetic basis underlying these diverse clinical conditions. Our current knowledge of the known mutations and associated phenotypes of the different AI subtypes are reviewed.

Phenotype and enamel ultrastructure characteristics in patients with ENAM gene mutations g.13185-13186insAG and 8344delG

OBJECTIVE

The main clinical manifestations of amelogenesis imperfecta (AI) include alteration in the quality and quantity of enamel. AI is associated with different mutations in four genes: enamelin (ENAM), amelogenin (AMGX), kallikrein (KLK4) and enamelysin (MMP-20). Seven different mutations have been identified in the enamelin gene (ENAM).

DESIGN

In this paper, we describe the phenotype and ultrastructure of enamel observed using scanning electron microscopy (SEM) in patients with two autosomal dominant (AD) mutations in the ENAM gene: g.13185-13186insAG and g.8344delG, each in one of two unrelated families. Mutations were confirmed by sequence analysis of PCR amplified products of all 10 exons and exon/intron boundaries of the ENAM gene.

RESULTS

Phenotypic diversity was observed in patients with ENAM gene mutations g.13185-13186insAG with consecutive protein alteration designated as p.P422fsX488 within family 1. In the proband, the enamel of his entire dentition was chalky white with only mild local hypoplastic alteration, while the phenotypic appearance of his father's dentition was that of local hypoplastic AI. In patients with the ENAM gene mutation g.8344delG from family 2 with consecutive protein alteration designated as p.N197fsX277, generalised hypoplastic AI was observed.

CONCLUSIONS

Ultrastructural enamel changes in the patient with the autosomal dominant ENAM g.13185-13186insAG mutation, described for the first time in this study, were less pronounced compared to ultrastructural changes in patients with the autosomal dominant ENAM mutation 8344delG. Ultrastructural characteristics of the g.13185-13186insAG mutation revealed deformed prisms, an oval shape on the cross-section and wider interprism spaces, while enamel with the ENAM mutation 8344delG was laminated, but prismless.

The use of animal models to explore amelogenin variants in amelogenesis imperfecta

Amelogenin proteins are secreted by ameloblast cells during tooth development. Because of extensive alternative splicing of the amelogenin primary RNA transcript, and because systematic proteolysis results in many additional peptides during enamel maturation, it has been difficult to assign function to individual amelogenins. Targeted deletions and transgenic mice have been generated in order to better understand amelogenin protein function in vivo. From these murine models, we have determined that amelogenins are responsible for normal enamel thickness and structure, but not for initiation of enamel mineral formation at the dentin-enamel junction. Although it is now clear that the amelogenin (AmelX) gene exists in a nested orientation and that AmelX is expressed at a low level in various developing tissues, the significance of these findings is incompletely understood. Future studies are expected to answer remaining questions concerning structure/function relationships among these 'enamel proteins'.

Mutational analysis of candidate genes in 24 amelogenesis imperfecta families

Amelogenesis imperfecta (AI) is a heterogeneous group of inherited defects in dental enamel formation. The malformed enamel can be unusually thin, soft, rough and stained. The strict definition of AI includes only those cases where enamel defects occur in the absence of other symptoms. Currently, there are seven candidate genes for AI: amelogenin, enamelin, ameloblastin, tuftelin, distal-less homeobox 3, enamelysin, and kallikrein 4. To identify sequence variations in AI candidate genes in patients with isolated enamel defects, and to deduce the likely effect of each sequence variation on protein expression and structure, families with isolated enamel defects were recruited. The coding exons and nearby intron sequences were amplified for each of the AI candidate genes by using genomic DNA from the proband as template. The amplification products for the proband were sequenced. Then, other family members were tested to determine their genotype with respect to each sequence variation. All subjects received an oral examination, and intraoral photographs and dental radiographs were obtained. Out of 24 families with isolated enamel defects, only six disease-causing mutations were identified in the AI candidate genes. This finding suggests that many additional genes potentially contribute to the etiology of AI.

Genes and related proteins involved in amelogenesis imperfecta

Dental enamel formation is a remarkable example of a biomineralization process. The exact mechanisms involved in this process remain partly obscure. Some of the genes encoding specific enamel proteins have been indicated as candidate genes for amelogenesis imperfecta. Mutational analyses within studied families have supported this hypothesis. Mutations in the amelogenin gene (AMELX) cause X-linked amelogenesis imperfecta, while mutations in the enamelin gene (ENAM) cause autosomal-inherited forms of amelogenesis imperfecta. Recent reports involve kallikrein-4 (KLK4), MMP-20, and DLX3 genes in the etiologies of some cases. This paper focuses mainly on the candidate genes involved in amelogenesis imperfecta and the proteins derived from them, and reviews current knowledge on their structure, localization within the tissue, and correlation with the various types of this disorder.

Phenotype of ENAM mutations is dosage-dependent

Five mutations in the ENAM gene have been found to cause hypoplastic amelogenesis imperfecta (AI), with phenotypes ranging from localized enamel pitting in carriers to severe hypoplastic AI. To determine the generality of ENAM mutations in hypoplastic AI, we sequenced the ENAM gene in ten Turkish families segregating autosomal hypoplastic AI. In two families, ENAM mutations were found. A novel nonsense mutation (g.12663C>A; p.S246X) was identified in one family segregating local hypoplastic AI as a dominant trait. Affected individuals in a second family segregating autosomal-recessive AI were compound heterozygotes for a novel insertion mutation (g.12946_12947insAGTCAGTACCAGTACTGTGTC) and a previously described insertion (g.13185_13186insAG) mutation. Heterozygous carriers of either insertion had a localized enamel-pitting phenotype. These findings substantiate that enamel phenotypes of ENAM mutations may be dose-dependent, with generalized hypoplastic AI segregating as a recessive trait and localized enamel pitting segregating as a dominant trait.

MMP20 active-site mutation in hypomaturation amelogenesis imperfecta

The Amelogenesis Imperfecta (AI) are a group of clinically and genetically heterogeneous disorders that affect enamel formation. To date, mutations in 4 genes have been reported in various types of AI. Mutations in the genes encoding the 2 enamel proteases, matrix metalloproteinase 20 (MMP20) and kallikrein 4 (KLK4), have each been reported in a single family segregating autosomal-recessive hypomaturation AI. To determine the frequency of mutations in these genes, we analyzed 15 Turkish probands with autosomal-recessive hypomaturation AI for MMP20 and KLK4 gene mutations. No KLK4 mutations were found. A novel MMP20 mutation (g.16250T>A) was found in one family. This missense mutation changed the conserved active-site His226 residue of the zinc catalytic domain to Gln (p.H226Q). Zymogram analysis demonstrated that this missense mutation abolished MMP20 proteolytic activity. No MMP20 mutations were found in the remaining 14 probands, underscoring the genetic heterogeneity of hypomaturation AI.

The genetics of amelogenesis imperfecta: a review of the literature

A melogenesis imperfecta (AI) is a group of inherited defects of dental enamel formation that show both clinical and genetic heterogeneity. Enamel findings in AI are highly variable, ranging from deficient enamel formation to defects in the mineral and protein content. Enamel formation requires the expression of multiple genes that transcribes matrix proteins and proteinases needed to control the complex process of crystal growth and mineralization. The AI phenotypes depend on the specific gene involved, the location and type of mutation, and the corresponding putative change at the protein level. Different inheritance patterns such as X-linked, autosomal dominant and autosomal recessive types have been reported. Mutations in the amelogenin, enamelin, and kallikrein-4 genes have been demonstrated to result in different types of AI and a number of other genes critical to enamel formation have been identified and proposed as candidates for AI. The aim of this article was to present an evaluation of the literature regarding role of proteins and proteinases important to enamel formation and mutation associated with AI.

Case report of a rare syndrome associating amelogenesis imperfecta and nephrocalcinosis in a consanguineous family

A rare syndrome associating amelogenesis imperfecta (AI) with nephrocalcinosis has been reported. The purpose of this study is to characterise the phenotype of a consanguineous family presenting amelogenesis imperfecta, delayed permanent teeth eruption and nephrocalcinosis. Six family members were examined. Ground sections of the case index deciduous teeth and biopsies of enlarged dental follicles were analysed. The patients's parents were first cousins. The case index had yellow discoloration and altered teeth shapes, retention of deciduous teeth, and delayed eruption. Panoramic radiographs revealed multiple enlarged pericoronal follicles in unerupted teeth and generalised intrapulpal calcifications. Renal ultrasound showed the presence of nephrocalcinosis. No other family members presented enamel defects or nephrocalcinosis. Histologically, the enamel appeared hypoplastic, and dental follicles indicated pericoronal hamartoma. The consanguineous marriage suggests an autosomal recessive mode of inheritance. Further studies are necessary to clarify the genetic defect behind this syndrome that associates AI, nephrocalcinosis and impaired tooth eruption.

Variation in dental and skeletal open bite malocclusion in humans with amelogenesis imperfecta

The amelogenesis imperfectas (AI) are a diverse group of genetic disorders primarily affecting the quality and or quantity of enamel, however, affected individuals often have an open bite malocclusion. Three main AI types are recognized based on the perceived developmental mechanisms involved and the enamel phenotype. The purpose of this investigation was to evaluate the association of the AI enamel defect with craniofacial features characteristic of an open bite malocclusion. The sample consisted of 54 AI affected and 34 unaffected family members from 18 different kindreds. Lateral cephalograms were digitized and measurements evaluated for vertical plane alterations using Z-scores. Forty two percent of AI affected individuals and 12% of unaffected family members had dental or skeletal open bite malocclusions. Skeletal open bite malocclusion was variably expressed in AI affected individuals. The enamel phenotype severity did not necessarily correspond with the presence or severity of open bite malocclussion. Open bite malocclusion occurred in individuals with AI caused by mutations in the AMELX and ENAM genes even though these genes are considered to be predominantly or exclusively expressed in teeth. Affected AI individuals with cephalometric values meeting our criteria of skeletal open bite malocclusion were observed in all three major AI types. The pathophysiological relationship between AI associated enamel defects and open bite malocclusion remains unknown.