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.

Rare and de novo variants in 827 congenital diaphragmatic hernia probands implicate LONP1 as candidate risk gene.

Congenital diaphragmatic hernia (CDH) is a severe congenital anomaly that is often accompanied by other anomalies. Although the role of genetics in the pathogenesis of CDH has been established, only a small number of disease-associated genes have been identified. To further investigate the genetics of CDH, we analyzed de novo coding variants in 827 proband-parent trios and confirmed an overall significant enrichment of damaging de novo variants, especially in constrained genes. We identified LONP1 (lon peptidase 1, mitochondrial) and ALYREF (Aly/REF export factor) as candidate CDH-associated genes on the basis of de novo variants at a false discovery rate below 0.05. We also performed ultra-rare variant association analyses in 748 affected individuals and 11,220 ancestry-matched population control individuals and identified LONP1 as a risk gene contributing to CDH through both de novo and ultra-rare inherited largely heterozygous variants clustered in the core of the domains and segregating with CDH in affected familial individuals. Approximately 3% of our CDH cohort who are heterozygous with ultra-rare predicted damaging variants in LONP1 have a range of clinical phenotypes, including other anomalies in some individuals and higher mortality and requirement for extracorporeal membrane oxygenation. Mice with lung epithelium-specific deletion of Lonp1 die immediately after birth, most likely because of the observed severe reduction of lung growth, a known contributor to the high mortality in humans. Our findings of both de novo and inherited rare variants in the same gene may have implications in the design and analysis for other genetic studies of congenital anomalies.

Two loss-of-function ANKRD11 variants in Chinese patients with short stature and a possible molecular pathway.

KBG syndrome is a rare genetic disease characterized mainly by skeletal abnormalities, distinctive facial features, and intellectual disability. Heterozygous mutations in ANKRD11 gene, or deletion of 16q24.3 that includes ANKRD11 gene are the cause of KBG syndrome. We describe two patients presenting with short stature and partial facial features, whereas no intellectual disability or hearing loss was observed in them. Two ANKRD11 variants, c.4039_4041del (p. Lys1347del) and c.6427C > G (p. Leu2143Val), were identified in this study. Both of them were classified as variants of uncertain significance (VOUS) by ACMG/AMP guidelines and were inherited from their mothers. ANKRD11 could enhance the transactivation of p21 gene, which was identified to participate in chondrogenic differentiation. In this study, we demonstrated that the knockdown of ANKRD11 could reduce the p21-promoter luciferase activities while re-introduction of wild type ANKRD11, but not ANKRD11 variants (p. Lys1347del or p. Leu2143Val), could restore the p21 levels. Thus, our study report two loss-of-function ANKRD11 variants which might provide new insight on pathogenic mechanism that correlates ANKRD11 variants with the short stature phenotype of KBG syndrome.

Fine Breakpoint Mapping by Genome Sequencing Reveals the First Large X Inversion Disrupting the NHS Gene in a Patient with Syndromic Cataracts.

Inversions are structural variants that are generally balanced. However, they could lead to gene disruptions or have positional effects leading to diseases. Mutations in the NHS gene cause Nance-Horan syndrome, an X-linked disorder characterised by congenital cataracts and dental anomalies. Here, we aimed to characterise a balanced pericentric inversion X(p22q27), maternally inherited, in a child with syndromic bilateral cataracts by breakpoint mapping using whole-genome sequencing (WGS). 30× Illumina paired-end WGS was performed in the proband, and breakpoints were confirmed by Sanger sequencing. EdU assays and FISH analysis were used to assess skewed X-inactivation patterns. RNA expression of involved genes in the breakpoint boundaries was evaluated by droplet-digital PCR. We defined the breakpoint position of the inversion at Xp22.13, with a 15 bp deletion, disrupting the unusually large intron 1 of the canonical NHS isoform, and also perturbing topologically-associated domains (TADs). Moreover, a microhomology region of 5 bp was found on both sides. RNA analysis confirmed null and reduced NHS expression in the proband and his unaffected mother, respectively. In conclusion, we report the first chromosomal inversion disrupting NHS, fine-mapped by WGS. Our data expand the clinical spectrum and the pathogenic mechanisms underlying the NHS defects.

Fucoidan inhibits tooth movement by promoting restorative macrophage polarization through the STAT3 pathway.

Retention after treatment and effective anchorage control are two essential factors in orthodontics. Our study aimed to explore the effects of fucoidan on orthodontic tooth movement (OTM) and the involvement of macrophages. We established a murine OTM model to test the effect of fucoidan administration. We found that mice injected with fucoidan had a deceleration in OTM and a higher bone mineral density. Moreover, fucoidan increased the proportion of F4/80+ CD206+ macrophages and promoted the messenger RNA expression of Arg-1, CD206, and IL-10 at both in vivo and in vitro levels. In addition, macrophages showed lower expression of TNF-α, IL-1ß, and IL-6 and a decrease in F4/80+ CD11c+ cells. Mechanistically, the level of phosphorylated STAT3 was elevated in unpolarized and restorative macrophages after treatment with fucoidan. Taken together, our findings suggest that fucoidan treatment inhibits OTM and enhances the stability of teeth after movement by promoting restorative macrophages through the STAT3 pathway.

Mice harbouring an oculodentodigital dysplasia-linked Cx43 G60S mutation have severe hearing loss.

Given the importance of connexin43 (Cx43, encoded by GJA1) function in the central nervous system and sensory organ processing, we proposed that it would also be crucial in auditory function. To that end, hearing was examined in two mouse models of oculodentodigital dysplasia that globally express GJA1 mutations resulting in mild or severe loss of Cx43 function. Although Cx43I130T/+ mutant mice, with ∼50% Cx43 channel function, did not have any hearing loss, Cx43G60S/+ mutant mice, with ∼20% Cx43 channel function, had severe hearing loss. There was no evidence of inner ear sensory hair cell loss, suggesting that the mechanism for Cx43-linked hearing loss lies downstream in the auditory pathway. Since evidence suggests that Cx26 function is essential for hearing and may be protective against noise-induced hearing loss, we challenged Cx43I130T/+ mice with a loud noise and found that they had a similar susceptibility to noise-induced hearing loss to that found in controls, suggesting that decreased Cx43 function does not sensitize the mice for environmentally induced hearing loss. Taken together, this study suggests that Cx43 plays an important role in baseline hearing and is essential for auditory processing.This article has an associated First Person interview with the first author of the paper.

Effects of Reduced Connexin43 Function on Mandibular Morphology and Osteogenesis in Mutant Mouse Models of Oculodentodigital Dysplasia.

Mutations in the gene encoding the gap-junctional protein connexin43 (Cx43) are the cause of the human disease oculodentodigital dysplasia (ODDD). The mandible is often affected in this disease, with clinical reports describing both mandibular overgrowth and conversely, retrognathia. These seemingly opposing observations underscore our relative lack of understanding of how ODDD affects mandibular morphology. Using two mutant mouse models that mimic the ODDD phenotype (I130T/+ and G60S/+), we sought to uncover how altered Cx43 function may affect mandibular development. Specifically, mandibles of newborn mice were imaged using micro-CT, to enable statistical comparisons of shape. Tissue-level comparisons of key regions of the mandible were conducted using histomorphology, and we quantified the mRNA expression of several cartilage and bone cell differentiation markers. Both G60S/+ and I130T/+ mutant mice had altered mandibular morphology compared to their wildtype counterparts, and the morphological effects were similarly localized for both mutants. Specifically, the biggest phenotypic differences in mutant mice were focused in regions exposed to mechanical forces, such as alveolar bone, muscular attachment sites, and articular surfaces. Histological analyses revealed differences in ossification of the intramembranous bone of the mandibles of both mutant mice compared to their wildtype littermates. However, chondrocyte organization within the secondary cartilages of the mandible was unaffected in the mutant mice. Overall, our results suggest that the morphological differences seen in G60S/+ and I130T/+ mouse mandibles are due to delayed ossification and suggest that mechanical forces may exacerbate the effects of ODDD on the skeleton.

Oral, dental, and craniofacial features in chronic acid sphingomyelinase deficiency.

The aim of this study was to evaluate the oral, dental, and craniofacial features of individuals affected by the chronic forms of acid sphingomyelinase deficiency (ASMD). This study comprised a sample of adult and pediatric patients (n = 8) with chronic ASMD. The individuals underwent oral examinations to evaluate the occurrence of caries, as well as full-mouth periodontal examinations, to assess the occurrence and severity of periodontal diseases. Panoramic and profile radiographs were obtained to analyze dental conditions and craniofacial parameters. Participants also answered questionnaires to identify systemic impairment, parafunctional habits, and bruxism. Dental anomalies of size, shape, and number were found, with agenesis and microdontia being the predominant findings. The average of caries experience was 11.75 (±8.1). Only one patient had periodontal health and all adult individuals had periodontitis at different stages and degrees. Bruxism was found in 87.5% of the sample. The convex profile and maxillary and mandibular retrusion were the most relevant findings in the cephalometric analysis. It is concluded that individuals with chronic ASMD, in addition to several systemic manifestations, present significant modifications in their oral health, from a greater occurrence of dental anomalies, caries, periodontal disease, in addition to skeletal changes.

KBG syndrome: Common and uncommon clinical features based on 31 new patients.

KBG syndrome (MIM #148050) is an autosomal dominant disorder characterized by developmental delay, intellectual disability, distinct craniofacial anomalies, macrodontia of permanent upper central incisors, skeletal abnormalities, and short stature. This study describes clinical features of 28 patients, confirmed by molecular testing of ANKRD11 gene, and three patients with 16q24 deletion encompassing ANKRD11 gene, diagnosed in a single center. Common clinical features are reported, together with uncommon findings, clinical expression in the first years of age, distinctive associations, and familial recurrences. Unusual manifestations emerging from present series include juvenile idiopathic arthritis, dysfunctional dysphonia, multiple dental agenesis, idiopathic precocious telarche, oral frenula, motor tics, and lipoma of corpus callosum, pilomatrixoma, and endothelial corneal polymorphic dystrophy. Facial clinical markers suggesting KBG syndrome before 6 years of age include ocular and mouth conformation, wide eyebrows, synophrys, long black eyelashes, long philtrum, thin upper lip. General clinical symptoms leading to early genetic evaluation include developmental delay, congenital malformations, hearing anomalies, and feeding difficulties. It is likely that atypical clinical presentation and overlapping features in patients with multiple variants are responsible for underdiagnosis in KBG syndrome. Improved knowledge of common and atypical features of this disorder improves clinical management.

KBG syndrome in two patients from Egypt.

KBG syndrome is an intellectual disability (ID) associated with multiple congenital anomalies in which the macrodontia could be the clue for the diagnosis. It is caused either by heterozygous variant in ANKRD11 gene or 16q24.3 microdeletions that involve the ANKRD11 gene. Here, we report on two unrelated male patients who presented with ID, short stature, webbing of neck, and cryptorchidism. Noonan syndrome was suspected first but the presence of macrodontia in both patients pointed to KBG syndrome which was confirmed thereafter by the identification of a novel pathogenic variant in ANKRD11 gene, c.5488G>T (p.E1830*). Macrodontia was noticed in all the deciduous anterior teeth in Patient 1. This observation was reported previously in few patients, but it seems to be a common feature that could be misdiagnosed as premature eruption of teeth. Therefore, our results confirm that maxillary permanent central incisors may not be the only teeth affected in KBG but also all the deciduous teeth. Interestingly, desquamative gingivitis was additionally noted in Patient 1, which has not been reported previously, however; it could be a coincidental finding. To the best of our knowledge, this is the first report from Egypt.

CDH1-related blepharocheilodontic syndrome is associated with diffuse gastric cancer risk.

We report the first case of diffuse gastric cancer in an individual with familial blepharocheilodontic syndrome (BCD) due to a germline CDH1 likely pathogenic variant. To date, other BCD affected relatives are nonpenetrant for diffuse gastric cancer posing challenges to counseling regarding gastric and breast cancer surveillance, and preventative total gastrectomy.

Peripheral compound odontoma: A rare case report and literature review.

Peripheral odontoma is a very rare odontogenic hamartoma arising in soft tissues. Here, we report a case of peripheral odontoma in a pediatric patient and review the cases published in the literature. An 11-year-old male patient presented a nodular lesion in the anterior region of the palate for over 1 year. Under the clinical hypothesis of fibroma, an excisional biopsy was performed. Histopathological examination revealed the presence of tooth-like structures, formed by enamel, and dentin matrix, occasionally associated with the dental papilla and surrounding pulp tissue, thus, the histopathological diagnosis of peripheral odontoma was established. The patient has been undergoing follow-up for 6 months without any signs of lesion recurrence. Peripheral odontomas are uncommon lesions that usually affect young patients and display a preference for the maxilla and limited growth potential. The recognition of the clinical and histopathological features of the peripheral odontoma is indispensable for the establishment of its diagnosis.

Dental Manifestations of Ehlers-Danlos Syndromes: A Systematic Review.

Ehlers-Danlos syndromes (EDS) are a group of inherited connective tissue disorders characterized by joint hypermobility, skin hyperextensibility, and variable tissue fragility. However, there are limited published data on the dental manifestations of EDS. This review systematically assessed the spectrum of published dental anomalies in various types of EDS. Twenty-four individual case reports/series and 3 longer case-control studies, reporting on a total of 84 individuals with a clinical diagnosis of EDS, were included in the data analysis. The main dental features listed in classical EDS were pulp calcification and localized root hypoplasia. Common dental abnormalities observed in vascular EDS were pulp shape modifications (52.2%), exceeding root length (34.8%), and molar root fusion (47.8%). Dentinogenesis imperfecta is a consistent finding in osteogenesis imperfecta/EDS overlap syndrome. Data on dental manifestations in other types of EDS are both rare and generally inconclusive.

A contiguous microdeletion syndrome at Xp23.13 with non-obstructive azoospermia and congenital cataracts.

Non-obstructive azoospermia accounts for 10-15% of male infertility, resulting in 60% of all cases of azoospermia and affecting about 1% of the male population. About 30% of these cases are due to Y chromosome microdeletions, chromosome abnormalities, or hormonal disorders. Pathogenic variants in genes on the sex chromosomes have key roles in spermatogenic failure. The co-occurrence of azoospermia and congenital cataracts ranges between 1 in 165,000 and 1 in 500,000. Our 28-year-old patient with normal intelligence and abnormally shaped teeth presented with both disorders. A microarray revealed a microdeletion at Xp23.13 with a whole NHS gene deletion as well as a contiguous deletion of two other genes [SCML1 and RAI2]. This observation represents the first report of non-obstructive azoospermia with congenital cataracts and a contiguous deletion of the SCML1 gene, a transcript of which is exclusively expressed in the testis. SCML1 is the putative culprit gene, which requires functional study or animal experiments. Our analysis of 60 known spermatogenesis failure-related genes by whole-exome sequencing revealed no other candidate. The Nance-Horan syndrome due to pathogenic variants in the NHS gene at Xp23.13 including whole gene deletion does not have azoospermia as a feature. Our report adds to the completeness of genetic counseling for an individual with azoospermia and congenital cataracts.

Living naked: first case of lack of skin-related structures in an elasmobranch, the blackmouth catshark (Galeus melastomus).

As far as is known, in this paper the first case of lacking of skin-related structures (epidermis, stratum laxum, dermal denticles and teeth) in a free-swimming elasmobranch, the blackmouth catshark, Galeus melastomus, is reported. The individual was caught by trawl in Sardinian waters (central-western Mediterranean) in July 2019 at a depth of 500 m. Although this kind of morphological abnormality is potentially fatal, the observations suggested that the specimen was in good health and well developed.

Evolution of the phenotype of craniosynostosis with dental anomalies syndrome and report of IL11RA variant population frequencies in a Crouzon-like autosomal recessive syndrome.

In 2011, biallelic loss-of-function variants in the interleukin receptor 11 alpha gene IL11RA were found to be associated with a Crouzon-like craniosynostosis syndrome with associated dental anomalies (CRSDA). Since then, a total of 41 similar patients have been reported with IL11RA variants. We report two adult brothers diagnosed with Crouzon syndrome as children, in which the clinical diagnosis of CRSDA was made on reevaluation. Laboratory testing detected biallelic IL11RA variants, c.916_924dup (p.Thr306_Ser308dup) and c.781C > T (p.Arg261Cys), both of which have now been reported in other families. Protein modeling and conservation analysis show that these two mutation sites cluster together near a WSXWS motif that likely plays a significant role in regulating IL11RA protein function. Population analysis from gnomAD shows that Non-Finnish Europeans (similar to ethnicity of this family), have an allele frequency for p.Thr306_Ser308dup of 0.014% and p.Arg261Cys of 0.008%. We found other ethnicities have functional IL11RA missense variants at higher frequencies. With this report, we provide a summary of the clinical findings including details of middle ear anomalies associated with conductive hearing loss. We also provide data supporting the populations at risk for this condition to increase recognition and diagnosis of this rare autosomal recessive craniosynostosis syndrome.

Elevated Fibroblast Growth Factor Signaling Is Critical for the Pathogenesis of the Dwarfism in Evc2/Limbin Mutant Mice.

Ellis-van Creveld (EvC) syndrome is a skeletal dysplasia, characterized by short limbs, postaxial polydactyly, and dental abnormalities. EvC syndrome is also categorized as a ciliopathy because of ciliary localization of proteins encoded by the two causative genes, EVC and EVC2 (aka LIMBIN). While recent studies demonstrated important roles for EVC/EVC2 in Hedgehog signaling, there is still little known about the pathophysiological mechanisms underlying the skeletal dysplasia features of EvC patients, and in particular why limb development is affected, but not other aspects of organogenesis that also require Hedgehog signaling. In this report, we comprehensively analyze limb skeletogenesis in Evc2 mutant mice and in cell and tissue cultures derived from these mice. Both in vivo and in vitro data demonstrate elevated Fibroblast Growth Factor (FGF) signaling in Evc2 mutant growth plates, in addition to compromised but not abrogated Hedgehog-PTHrP feedback loop. Elevation of FGF signaling, mainly due to increased Fgf18 expression upon inactivation of Evc2 in the perichondrium, critically contributes to the pathogenesis of limb dwarfism. The limb dwarfism phenotype is partially rescued by inactivation of one allele of Fgf18 in the Evc2 mutant mice. Taken together, our data uncover a novel pathogenic mechanism to understand limb dwarfism in patients with Ellis-van Creveld syndrome.

Cervical Enamel Projection - A Rare Case Report with its Management.

A developmental anomaly like cervical enamel projection is a rare finding in the maxillary anterior region. Its ectopic presence attracts attention in literature. This type of anomaly is typically found in the furcation region of molars. The case report presented here deals with the ectopic presence of combined anomalous lesion and its management. A 18 year old male presented with pronounced bilobed cingulum extending as a cervical enamel projection on the maxillary right lateral incisor associated with pain, exudation and difficulty in mastication. Enameloplasty and regenerative procedure was performed. The possible etiology, its management and healing evaluated by CBCT are presented in this report. One year follow up showed satisfactory healing with no recurrence of abscess.

A specific IFIH1 gain-of-function mutation causes Singleton-Merten syndrome.

Singleton-Merten syndrome (SMS) is an infrequently described autosomal-dominant disorder characterized by early and extreme aortic and valvular calcification, dental anomalies (early-onset periodontitis and root resorption), osteopenia, and acro-osteolysis. To determine the molecular etiology of this disease, we performed whole-exome sequencing and targeted Sanger sequencing. We identified a common missense mutation, c.2465G>A (p.Arg822Gln), in interferon induced with helicase C domain 1 (IFIH1, encoding melanoma differentiation-associated protein 5 [MDA5]) in four SMS subjects from two families and a simplex case. IFIH1 has been linked to a number of autoimmune disorders, including Aicardi-Goutières syndrome. Immunohistochemistry demonstrated the localization of MDA5 in all affected target tissues. In vitro functional analysis revealed that the IFIH1 c.2465G>A mutation enhanced MDA5 function in interferon beta induction. Interferon signature genes were upregulated in SMS individuals' blood and dental cells. Our data identify a gain-of-function IFIH1 mutation as causing SMS and leading to early arterial calcification and dental inflammation and resorption.

Familial autosomal dominant severe ankyloglossia with tooth abnormalities.

Ankyloglossia is a congenital oral anomaly characterized by the presence of a hypertrophic and short lingual frenulum. Mutations in the gene encoding the transcription factor TBX22 have been involved in isolated ankyloglossia and X-linked cleft palate. The knockout of Lgr5 in mice results in ankyloglossia. Here, we report a five-generation family including patients with severe ankyloglossia and missing lower central incisors. Two members of this family also exhibited congenital anorectal malformations. In this report, male-to-male transmission was in favor of an autosomal dominant inheritance, which allowed us to exclude the X-linked TBX22 gene. Linkage analysis using short tandem repeat markers located in the vicinity of LGR5 excluded this gene as a potential candidate. These results indicate genetic heterogeneity for ankyloglossia. Further investigations with additional families are required in order to identify novel candidate genes.