Amelogenesis imperfecta: Next-generation sequencing sheds light on Witkop's classification

ENAM Mutations Can Cause Hypomaturation Amelogenesis Imperfecta

Amelogenesis imperfecta (AI) is a diverse group of inherited diseases featured by various presentations of enamel malformations that are caused by disturbances at different stages of enamel formation. While hypoplastic AI suggests a thickness defect of enamel resulting from aberrations during the secretory stage of amelogenesis, hypomaturation AI indicates a deficiency of enamel mineralization and hardness established at the maturation stage. Mutations in ENAM, which encodes the largest enamel matrix protein, enamelin, have been demonstrated to cause generalized or local hypoplastic AI. Here, we characterized 2 AI families with disparate hypoplastic and hypomaturation enamel defects and identified 2 distinct indel mutations at the same location of ENAM, c588+1del and c.588+1dup. Minigene splicing assays demonstrated that they caused frameshifts and truncation of ENAM proteins, p.Asn197Ilefs*81 and p.Asn197Glufs*25, respectively. In situ hybridization of Enam on mouse mandibular incisors confirmed its restricted expression in secretory stage ameloblasts and suggested an indirect pathogenic mechanism underlying hypomaturation AI. In silico analyses indicated that these 2 truncated ENAMs might form amyloid structures and cause protein aggregation with themselves and with wild-type protein through the added aberrant region at their C-termini. Consistently, protein secretion assays demonstrated that the truncated proteins cannot be properly secreted and impede secretion of wild-type ENAM. Moreover, compared to the wild-type, overexpression of the mutant proteins significantly increased endoplasmic reticulum stress and upregulated the expression of unfolded protein response (UPR)-related genes and TNFRSF10B, a UPR-controlled proapoptotic gene. Caspase, terminal deoxynucleotidyl transferase UTP nick-end labeling (TUNEL), and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays further revealed that both truncated proteins, especially p.Asn197Ilefs*81, induced cell apoptosis and decreased cell survival, suggesting that the 2 ENAM mutations cause AI through ameloblast cell pathology and death rather than through a simple loss of function. This study demonstrates that an ENAM mutation can lead to generalized hypomaturation enamel defects and suggests proteinopathy as a potential pathogenesis for ENAM-associated AI.

Orofacial Anomalies in Kindler Epidermolysis Bullosa

Importance

Kindler epidermolysis bullosa is a genetic skin-blistering disease associated with recessive inherited pathogenic variants in FERMT1, which encodes kindlin-1. Severe orofacial manifestations of Kindler epidermolysis bullosa, including early oral squamous cell carcinoma, have been reported.

Objective

To determine whether hypoplastic pitted amelogenesis imperfecta is a feature of Kindler epidermolysis bullosa.

Design, Settings, and Participants

This longitudinal, 2-center cohort study was performed from 2003 to 2023 at the Epidermolysis Bullosa Centre, University of Freiburg, Germany, and the Special Care Dentistry Clinic, University of Chile in association with DEBRA Chile. Participants included a convenience sampling of all patients with a diagnosis of Kindler epidermolysis bullosa.

Main Outcomes and Measures

The primary outcomes were the presence of hypoplastic pitted amelogenesis imperfecta, intraoral wounds, gingivitis and periodontal disease, gingival hyperplasia, vestibular obliteration, cheilitis, angular cheilitis, chronic lip wounds, microstomia, and oral squamous cell carcinoma.

Results

The cohort consisted of 36 patients (15 female [42%] and 21 male [58%]; mean age at first examination, 23 years [range, 2 weeks to 70 years]) with Kindler epidermolysis bullosa. The follow-up ranged from 1 to 24 years. The enamel structure was assessed in 11 patients, all of whom presented with enamel structure abnormalities. The severity of hypoplastic pitted amelogenesis imperfecta varied from generalized to localized pitting. Additional orofacial features observed include gingivitis and periodontal disease, which was present in 90% (27 of 30 patients) of those assessed, followed by intraoral lesions (16 of 22 patients [73%]), angular cheilitis (24 of 33 patients [73%]), cheilitis (22 of 34 patients [65%]), gingival overgrowth (17 of 26 patients [65%]), microstomia (14 of 25 patients [56%]), and vestibular obliteration (8 of 16 patients [50%]). Other features included chronic lip ulcers (2 patients) and oral squamous cell carcinoma with lethal outcome (2 patients).

Conclusions and Relevance

These findings suggest that hypoplastic pitted amelogenesis imperfecta is a feature of Kindler epidermolysis bullosa and underscore the extent and severity of oral manifestations in Kindler epidermolysis bullosa and the need for early and sustained dental care.

Isolated dentinogenesis imperfecta: Novel DSPP variants and insights on genetic counselling

OBJECTIVE

Dentinogenesis imperfecta (DI) is an inherited dentin defect and may be isolated or associated with disorders such as osteogenesis imperfecta, odontochondrodysplasia Ehler-Danlos and others. Isolated DI is caused mainly by pathogenic variants in DSPP gene and around 50 different variants have been described in this gene. Herein, we report on 19 patients from two unrelated Egyptian families with isolated DI. Additionally, we focused on genetic counselling of the two families.

MATERIALS AND METHODS

The patients were examined clinically and dentally. Panoramic X-rays were done to some patients. Whole exome sequencing (WES) and Sanger sequencing were used.

RESULTS

WES revealed two new nonsense variants in DSPP gene, c.288T > A (p.Tyr96Ter) and c.255G > A (p.Trp85Ter). Segregation analysis by Sanger sequencing confirmed the presence of the first variant in all affected members of Family 1 while the second variant was confirmed to be de novo in the patient of Family 2.

CONCLUSIONS AND CLINICAL RELEVANCE

Our study extends the number of DSPP pathogenic variants and strengthens the fact that DSPP is the most common DI causative gene irrespective of patients' ethnicity. In addition, we provide insights on genetic counseling issues in patients with inherited DSPP variants taking into consideration the variable religion, culture and laws in our society.

Heterozygous COL17A1 variants are a frequent cause of amelogenesis imperfecta

BACKGROUND

Collagen XVII is most typically associated with human disease when biallelic COL17A1 variants (>230) cause junctional epidermolysis bullosa (JEB), a rare, genetically heterogeneous, mucocutaneous blistering disease with amelogenesis imperfecta (AI), a developmental enamel defect. Despite recognition that heterozygous carriers in JEB families can have AI, and that heterozygous COL17A1 variants also cause dominant corneal epithelial recurrent erosion dystrophy (ERED), the importance of heterozygous COL17A1 variants causing dominant non-syndromic AI is not widely recognised.

METHODS

Probands from an AI cohort were screened by single molecule molecular inversion probes or targeted hybridisation capture (both a custom panel and whole exome sequencing) for COL17A1 variants. Patient phenotypes were assessed by clinical examination and analyses of affected teeth.

RESULTS

Nineteen unrelated probands with isolated AI (no co-segregating features) had 17 heterozygous, potentially pathogenic COL17A1 variants, including missense, premature termination codons, frameshift and splice site variants in both the endo-domains and the ecto-domains of the protein. The AI phenotype was consistent with enamel of near normal thickness and variable focal hypoplasia with surface irregularities including pitting.

CONCLUSION

These results indicate that COL17A1 variants are a frequent cause of dominantly inherited non-syndromic AI. Comparison of variants implicated in AI and JEB identifies similarities in type and distribution, with five identified in both conditions, one of which may also cause ERED. Increased availability of genetic testing means that more individuals will receive reports of heterozygous COL17A1 variants. We propose that patients with isolated AI or ERED, due to COL17A1 variants, should be considered as potential carriers for JEB and counselled accordingly, reflecting the importance of multidisciplinary care.

Standardization of the protocol for oral cavity examination and collecting of the biological samples for microbiome research using the next-generation sequencing (NGS): own experience with the COVID-19 patients

To date, publications have shown that compositions of oral microbiota differ depending on their habitats (e.g. tongue, tonsils, pharynx). The absence of set standards for the choice of the areas and conditions of material collection makes the oral microbiome one of the most difficult environments for a comparative analysis with other researchers, which is a meaningful limitation during an assessment of the potential effects of microorganisms as biomarkers in the courses of various human diseases. Therefore, standardisation of basic conditions of a dental examination and collection of material for the next generation sequencing (NGS) is worth attempting. The standardisation of the dental exam and collection of the clinical materials: saliva, swab from the tongue ridge, hard palate, palatine tonsils and oropharynx, supragingival plaque and subgingival plaque. Protocol involved the patients (n = 60), assigned to 3 groups: I-COVID-19 convalescents who received antibiotics, n = 17, II-COVID-19 convalescents, n = 23 and III-healthy individuals, n = 20. The collected biological samples were used to conduct NGS (16S rRNA). The conditions of patient preparation for collecting biological materials as well as the schedule of dental examination, were proposed. Based on the research conducted, we have indicated the dental indicators that best differentiate the group of COVID-19 patients (groups I and II) from healthy people (group III). These include the DMFT, D and BOP indices. The use of alpha and beta diversity analysis provided an overall insight into the diversity of microbial communities between specific niches and patient groups. The most different diversity between the studied group of patients (group II) and healthy people (group III) was noted in relation to the supragingival plaque. The order of activities during the dental exam as well as while collecting and securing clinical materials is particularly important to avoid technical errors and material contamination which may result in erroneous conclusions from the analyses of the results of sensitive tests such as the NGS. It has been shown that the dental indices: DMFT, D number, PI and BOP are the best prognostic parameters to assess the oral health. Based on beta diversity the most sensitive niche and susceptible to changes in the composition of the microbiota is the supragingival plaque. The procedures developed by our team can be applied as ready-to-use forms in studies conducted by other researchers.

The Rogdi knockout mouse is a model for Kohlschütter-Tönz syndrome

Kohlschütter-Tönz syndrome (KTS) is a rare autosomal recessive disorder characterized by severe intellectual disability, early-onset epileptic seizures, and amelogenesis imperfecta. Here, we present a novel Rogdi mutant mouse deleting exons 6-11- a mutation found in KTS patients disabling ROGDI function. This Rogdi-/- mutant model recapitulates most KTS symptoms. Mutants displayed pentylenetetrazol-induced seizures, confirming epilepsy susceptibility. Spontaneous locomotion and circadian activity tests demonstrate Rogdi mutant hyperactivity mirroring patient spasticity. Object recognition impairment indicates memory deficits. Rogdi-/- mutant enamel was markedly less mature. Scanning electron microscopy confirmed its hypomineralized/hypomature crystallization, as well as its low mineral content. Transcriptomic RNA sequencing of postnatal day 5 lower incisors showed downregulated enamel matrix proteins Enam, Amelx, and Ambn. Enamel crystallization appears highly pH-dependent, cycling between an acidic and neutral pH during enamel maturation. Rogdi-/- teeth exhibit no signs of cyclic dental acidification. Additionally, expression changes in Wdr72, Slc9a3r2, and Atp6v0c were identified as potential contributors to these tooth acidification abnormalities. These proteins interact through the acidifying V-ATPase complex. Here, we present the Rogdi-/- mutant as a novel model to partially decipher KTS pathophysiology. Rogdi-/- mutant defects in acidification might explain the unusual combination of enamel and rare neurological disease symptoms.

[The tooth: A marker of developmental abnormalities]

Tooth formation results from specific epithelial-mesenchymal interactions, which summarize a number of developmental processes. Tooth anomalies may thus reflect subclinical diseases of the kidney, bone and more broadly of the mineral metabolism, skin or nervous system. Odontogenesis starts from the 3rd week of intrauterine life by the odontogenic orientation of epithelial cells by a first PITX2 signal. The second phase is the acquisition of the number, shape, and position of teeth. It depends on multiple transcription and growth factors (BMP, FGF, SHH, WNT). These ecto-mesenchymal interactions guide cell migration, proliferation, apoptosis and differentiation ending in the formation of the specific dental mineralized tissues. Thus, any alteration will have consequences on the tooth structure or shape. Resulting manifestations will have to be considered in the patient phenotype and the multidisciplinary care, but also may contribute to identify the altered genetic circuity.

Dentofacial manifestations in a child with Jalili syndrome

Jalili syndrome (JS) (MIM#217080) is a rare autosomal recessive disorder with oculo-dental malformations. The clinical phenotype is characterized by the presence of Cone-Rod Dystrophy (CRD) and Amelogenesis Imperfecta (AI). Genetic mechanism entails a mutation in the CNNM4, a metal transporter gene located on Chromosome 2q11.2. A high fluoride concentration in groundwater has also been identified as an epigenetic factor in this syndrome. JS draws the attention of dentists due to its distinct oral manifestations. To the best of our knowledge, this is the first genetically confirmed pediatric case report from the Indian subcontinent emphasizing the clinical and radiographic features of this condition and its management in a 6-year-old child.

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.