Hypophosphatasia : diagnosis and clinical signs - a dental surgeon perspective

Hypophosphatasia (HPP) is a rare inherited metabolic disease in which mutations in the ALPL gene (encoding tissue-nonspecific alkaline phosphatase) result in varying degrees of enzyme deficiency. HPP manifests in a spectrum of symptoms, including early primary tooth loss (root intact) and alveolar bone mineralisation defects.To provide an overview of HPP for dental professionals to help recognise and differentially diagnose patients for appropriate referral to a specialist team.A non-systematic review of publications on HPP was performed.Different forms of HPP are described, along with characteristic symptoms and laboratory findings. Diagnosis is challenging due to the rareness and variable presentation of symptoms. Low alkaline phosphatase levels are a signature of HPP, but reference ranges vary according to gender and age. Key features are defined and management strategies discussed, focusing on enzyme replacement therapy. Finally, a patient registry aimed at better defining the prevalence of HPP and raising awareness is described.HPP is a rare disease with a wide spectrum of manifestations, with orodental symptoms featuring prominently in the natural history. Dental professionals may be positioned at the beginning of the diagnostic pathway; thus, recognition of HPP features for timely referral and optimal disease management is important.reviewjournal article2016 Nov2016 03 31importe

Evolutionary Analysis Predicts Sensitive Positions of MMP20 and Validates Newly- and Previously-Identified MMP20 Mutations Causing Amelogenesis Imperfecta

Amelogenesis imperfecta (AI) designates a group of genetic diseases characterized by a large range of enamel disorders causing important social and health problems. These defects can result from mutations in enamel matrix proteins or protease encoding genes. A range of mutations in the enamel cleavage enzyme matrix metalloproteinase-20 gene (MMP20) produce enamel defects of varying severity. To address how various alterations produce a range of AI phenotypes, we performed a targeted analysis to find MMP20 mutations in French patients diagnosed with non-syndromic AI. Genomic DNA was isolated from saliva and MMP20 exons and exon-intron boundaries sequenced. We identified several homozygous or heterozygous mutations, putatively involved in the AI phenotypes. To validate missense mutations and predict sensitive positions in the MMP20 sequence, we evolutionarily compared 75 sequences extracted from the public databases using the Datamonkey webserver. These sequences were representative of mammalian lineages, covering more than 150 million years of evolution. This analysis allowed us to find 324 sensitive positions (out of the 483 MMP20 residues), pinpoint functionally important domains, and build an evolutionary chart of important conserved MMP20 regions. This is an efficient tool to identify new- and previously-identified mutations. We thus identified six functional MMP20 mutations in unrelated families, finding two novel mutated sites. The genotypes and phenotypes of these six mutations are described and compared. To date, 13 MMP20 mutations causing AI have been reported, making these genotypes and associated hypomature enamel phenotypes the most frequent in AI

A New SLC10A7 Homozygous Missense Mutation Responsible for a Milder Phenotype of Skeletal Dysplasia With Amelogenesis Imperfecta

Amelogenesis imperfecta (AI) is a heterogeneous group of rare inherited diseases presenting with enamel defects. More than 30 genes have been reported to be involved in syndromic or non-syndromic AI and new genes are continuously discovered (Smith et al., 2017). Whole-exome sequencing was performed in a consanguineous family. The affected daughter presented with intra-uterine and postnatal growth retardation, skeletal dysplasia, macrocephaly, blue sclerae, and hypoplastic AI. We identified a homozygous missense mutation in exon 11 of SLC10A7 (NM_001300842.2: c.908C>T; p.Pro303Leu) segregating with the disease phenotype. We found that Slc10a7 transcripts were expressed in the epithelium of the developing mouse tooth, bones undergoing ossification, and in vertebrae. Our results revealed that SLC10A7 is overexpressed in patient fibroblasts. Patient cells display altered intracellular calcium localization suggesting that SLC10A7 regulates calcium trafficking. Mutations in this gene were previously reported to cause a similar syndromic phenotype, but with more severe skeletal defects (Ashikov et al., 2018;Dubail et al., 2018). Therefore, phenotypes resulting from a mutation in SLC10A7 can vary in severity. However, AI is the key feature indicative of SLC10A7 mutations in patients with skeletal dysplasia. Identifying this important phenotype will improve clinical diagnosis and patient management

Orodental phenotype and genotype findings in all subtypes of hypophosphatasia

<p>Abstract</p> <p>Background</p> <p>Hypophosphatasia (HP) is a rare inherited disorder characterized by a wide spectrum of defects in mineralized tissues and caused by deficiency in the tissue non-specific alkaline phosphatase gene (<it>ALPL</it>). The symptoms are highly variable in their clinical expression, and relate to numerous mutations in this gene. The first clinical sign of the disease is often a premature loss of deciduous teeth, mostly in the moderate forms.</p> <p>Aim</p> <p>The purpose of this study was to document the oral features of HP patients and to relate theses features to the six recognized forms of HP in 5 patients with known genotype and to investigate the genotype-phenotype correlations.</p> <p>Methods</p> <p>Clinical and radiographic examinations were carried out. We collected medical and dental history in the kindred and biochemical data. Finally, mutations in the <it>ALPL </it>gene were tested by DNA sequencing in SESEP laboratory.</p> <p>Results</p> <p>We have for the first time related the known dental anomalies which occur as integral features of HP to the recognized clinical forms of HP. We also pointed out striking dental abnormalities which were never described in association with this rare disease. Accurate genotype-phenotype severity correlations were observed.</p> <p>Conclusion</p> <p>This work allowed us to compare orodental manifestations in all the clinical forms of HP within the patient's sample. According to the severity of the disorder, some dental defects were infrequent, while other were always present. The long term prognosis of the permanent teeth varies from a patient to another. As premature loss of primary teeth is often the first, and sometimes the only visible symptom of the milder forms, the paediatric dentist plays a critical role in the detection and diagnosis of the disease.</p

Effects of retinoids on tooth morphogenesis and cytodifferentiations, in vitro.

The first embryonic lower mouse molar was used as a model system to investigate the effects of two retinoids, retinoic acid (RA) and a synthetic analogue, Ch55, on morphogenesis and cytodifferentiations in vitro. Exogenous retinoids were indispensable for morphogenesis of bud, cap and bell-stage molars in serum-free, chemically-defined, culture media. Transferrin and RA or transferrin and Ch55 acted synergistically in promoting morphogenesis from bud and cap-stage explants. Transferrin, per se, had no morphogenetic effect. Epithelial histogenesis, odontoblast functional differentiation and ameloblast polarization always occurred in RA-depleted explants. Comparison of the distributions of bromodeoxyuridine (BrdU) incorporation between explants cultured in the absence or presence of RA revealed that RA could modify the patterns of cell proliferation in the inner dental epithelium and dental mesenchyme. Inner dental epithelium cell proliferation is regulated by the dental mesenchyme through basement membrane-mediated interactions, and tooth morphogenesis is controlled by the dental mesenchyme. Laminin is a target molecule of retinoid action. Using a monospecific antibody, we immunolocalized laminin and/or structurally-related molecules sharing the laminin B chain in the embryonic dental mesenchyme and in the dental basement membrane and showed that RA could promote the synthesis or secretion of these molecules. Based on previous in situ hybridization data, it was speculated that CRABPs might regulate the effects of RA on embryonic dental cell proliferation. The fact that Ch55, a retinoid which does not bind to CRABPs, is 100 times more potent than RA in promoting tooth morphogenesis in vitro seems to rule out this hypothesis. On the other hand, the stage-specific inhibition of tooth morphogenesis by excess RA is consistent with the hypothesis that CRABPs might protect embryonic tissues against potentially teratogenic concentrations of free retinoids.comparative studyjournal articleresearch support, non-u.s. gov't1992 Decimporte

R-twist gene expression during rat palatogenesis

Palatal clefting is often associated with premature fusion of cranial sutures in human craniosynostosis syndromes, many of which are characterised by mutations affecting the fibroblast growth factor receptor (FGFR) gene family. In palatal fusion, epithelio-mesenchymal transition (EMT) contributes to the dispersion of the midline epithelial seam. EMT has also been observed in neoplastic epithelial cells in relation to the acquisition of malignant characteristics where morphological changes are accompanied by rapid switching in the expression of fgfr2 from the epithelial type (kgfr) to the mesenchymal type (bek). The twist gene codes for a basic helix-loop-helix transcription factor putatively involved in regulation of transcription of fgfr2. Mutations in the TWIST gene have been described as being responsible for the Saethre-Chotzen syndrome, an autosomal dominant craniosynostosis associated with cleft palate as well as other disturbances of the facial skeleton. In this study we have analysed the distribution of twist transcripts during rat palatogenesis in vivo from 14.5 to 17.5 days post coitum by in situ hybridisation with digoxygenin-labelled ssDNA probes. twist transcripts were found to be concentrated in mesenchymal cells beneath the epithelium at the tip of the palatal shelves immediately prior to, and during fusion as well as in a localised epithelial area at the tip of the shelves prior to fusion, thereby implicating twist gene expression in the process of palatogenesis. This pattern of expression illuminates the disturbances of maxillary growth that occur in human craniosynostotic syndromes.journal articleresearch support, non-u.s. gov't2001 Aprimporte

Molars and incisors: show your microarray IDs.

BACKGROUND: One of the key questions in developmental biology is how, from a relatively small number of conserved signaling pathways, is it possible to generate organs displaying a wide range of shapes, tissue organization, and function. The dentition and its distinct specific tooth types represent a valuable system to address the issues of differential molecular signatures. To identify such signatures, we performed a comparative transcriptomic analysis of developing murine lower incisors, mandibular molars and maxillary molars at the developmental cap stage (E14.5). RESULTS: 231 genes were identified as being differentially expressed between mandibular incisors and molars, with a fold change higher than 2 and a false discovery rate lower than 0.1, whereas only 96 genes were discovered as being differentially expressed between mandibular and maxillary molars. Numerous genes belonging to specific signaling pathways (the Hedgehog, Notch, Wnt, FGF, TGFβ/BMP, and retinoic acid pathways), and/or to the homeobox gene superfamily, were also uncovered when a less stringent fold change threshold was used. Differential expressions for 10 out of 12 (mandibular incisors versus molars) and 9 out of 10 selected genes were confirmed by quantitative reverse transcription-PCR (qRT-PCR). A bioinformatics tool (Ingenuity Pathway Analysis) used to analyze biological functions and pathways on the group of incisor versus molar differentially expressed genes revealed that 143 genes belonged to 9 networks with intermolecular connections. Networks with the highest significance scores were centered on the TNF/NFκB complex and the ERK1/2 kinases. Two networks ERK1/2 kinases and tretinoin were involved in differential molar morphogenesis. CONCLUSION: These data allowed us to build several regulatory networks that may distinguish incisor versus molar identity, and may be useful for further investigations of these tooth-specific ontogenetic programs. These programs may be dysregulated in transgenic animal models and related human diseases leading to dental anomalies.journal articleresearch support, non-u.s. gov't2013 Mar 262013 03 26importe

Midline fusion in the formation of the secondary palate anticipated by upregulation of keratin K5/6 and localized expression of vimentin mRNA in medial edge epithelium

Secondary palatal fusion is dependent on targeted removal of the epithelium between the palatal shelves. Aseptically delivered rat embryos 15 through 18 days post coitum (dpc) were probed with DIG-labeled antisense and sense ssDNA probes for spliced exon sequences flanking intron E of cytokeratins K5/6 and spliced exon sequences flanking intron F of vimentin. Cytokeratin K5/6 expression was upregulated in the medial edge epithelium (MEE) prior to rotation of the palatal shelves and in the vomerine epithelium in the region of fusion with the palate. K5/6 expression continued in the medial epithelial seam (MES) and in epithelial islands during breakdown of the MES. Vimentin expression was not detected in the MEE prior to rotation but was specifically upregulated in the MEE following rotation and prior to midline contact and continued in the MES and in epithelial cells identifiable during the breakdown of the MES. Initiation of vimentin upregulation in the MEE prior to contact of the palatal shelves was tested by serum-free organ culture of palates from embryos at 15.5 dpc with the shelves separated by a biocompatible membrane. Vimentin upregulation occurred in the epithelium specifically in the region of anticipated contact. These results are interpreted as indicating that i) cytokeratin K5/6 expression may play a critical role in the integration of the epithelial layers of the MES to ensure subsequent merging of the mesenchyme and ii) epithelial cells in the MEE are specifically 'primed' to upregulate expression of mesenchymal genes prior to integration into and breakdown of the MES.journal articleresearch support, non-u.s. gov't1999 Mayimporte

A New SLC10A7 Homozygous Missense Mutation Responsible for a Milder Phenotype of Skeletal Dysplasia With Amelogenesis Imperfecta

International audienceAmelogenesis imperfecta (AI) is a heterogeneous group of rare inherited diseases presenting with enamel defects. More than 30 genes have been reported to be involved in syndromic or non-syndromic AI and new genes are continuously discovered (Smith et al., 2017). Whole-exome sequencing was performed in a consanguineous family. The affected daughter presented with intra-uterine and postnatal growth retardation, skeletal dysplasia, macrocephaly, blue sclerae, and hypoplastic AI. We identified a homozygous missense mutation in exon 11 of SLC10A7 (NM_001300842.2: c.908C>T; p.Pro303Leu) segregating with the disease phenotype. We found that Slc10a7 transcripts were expressed in the epithelium of the developing mouse tooth, bones undergoing ossification, and in vertebrae. Our results revealed that SLC10A7 is overexpressed in patient fibroblasts. Patient cells display altered intracellular calcium localization suggesting that SLC10A7 regulates calcium trafficking. Mutations in this gene were previously reported to cause a similar syndromic phenotype, but with more severe skeletal defects (Ashikov et al., 2018;Dubail et al., 2018). Therefore, phenotypes resulting from a mutation in SLC10A7 can vary in severity. However, AI is the key feature indicative of SLC10A7 mutations in patients with skeletal dysplasia. Identifying this important phenotype will improve clinical diagnosis and patient management

Retinoic Acid Excess Impairs Amelogenesis Inducing Enamel Defects.

Abnormalities of enamel matrix proteins deposition, mineralization, or degradation during tooth development are responsible for a spectrum of either genetic diseases termed Amelogenesis imperfecta or acquired enamel defects. To assess if environmental/nutritional factors can exacerbate enamel defects, we investigated the role of the active form of vitamin A, retinoic acid (RA). Robust expression of RA-degrading enzymes Cyp26b1 and Cyp26c1 in developing murine teeth suggested RA excess would reduce tooth hard tissue mineralization, adversely affecting enamel. We employed a protocol where RA was supplied to pregnant mice as a food supplement, at a concentration estimated to result in moderate elevations in serum RA levels. This supplementation led to severe enamel defects in adult mice born from pregnant dams, with most severe alterations observed for treatments from embryonic day (E)12.5 to E16.5. We identified the enamel matrix proteins enamelin (Enam), ameloblastin (Ambn), and odontogenic ameloblast-associated protein (Odam) as target genes affected by excess RA, exhibiting mRNA reductions of over 20-fold in lower incisors at E16.5. RA treatments also affected bone formation, reducing mineralization. Accordingly, craniofacial ossification was drastically reduced after 2 days of treatment (E14.5). Massive RNA-sequencing (RNA-seq) was performed on E14.5 and E16.5 lower incisors. Reductions in Runx2 (a key transcriptional regulator of bone and enamel differentiation) and its targets were observed at E14.5 in RA-exposed embryos. RNA-seq analysis further indicated that bone growth factors, extracellular matrix, and calcium homeostasis were perturbed. Genes mutated in human AI (ENAM, AMBN, AMELX, AMTN, KLK4) were reduced in expression at E16.5. Our observations support a model in which elevated RA signaling at fetal stages affects dental cell lineages. Thereafter enamel protein production is impaired, leading to permanent enamel alterations.journal article20162017 01 06importe