Pathogenesis of Enamel-Renal Syndrome Associated Gingival Fibromatosis: A Proteomic Approach

The enamel renal syndrome (ERS) is a rare disorder featured by amelogenesis imperfecta, gingival fibromatosis and nephrocalcinosis. ERS is caused by bi-allelic mutations in the secretory pathway pseudokinase FAM20A. How mutations in FAM20A may modify the gingival connective tissue homeostasis and cause fibromatosis is currently unknown. We here analyzed conditioned media of gingival fibroblasts (GFs) obtained from four unrelated ERS patients carrying distinct mutations and control subjects. Secretomic analysis identified 109 dysregulated proteins whose abundance had increased (69 proteins) or decreased (40 proteins) at least 1.5-fold compared to control GFs. Proteins over-represented were mainly involved in extracellular matrix organization, collagen fibril assembly, and biomineralization whereas those under-represented were extracellular matrix-associated proteins. More specifically, transforming growth factor-beta 2, a member of the TGFβ family involved in both mineralization and fibrosis was strongly increased in samples from GFs of ERS patients and so were various known targets of the TGFβ signaling pathway including Collagens, Matrix metallopeptidase 2 and Fibronectin. For the over-expressed proteins quantitative RT-PCR analysis showed increased transcript levels, suggesting increased synthesis and this was further confirmed at the tissue level. Additional immunohistochemical and western blot analyses showed activation and nuclear localization of the classical TGFβ effector phospho-Smad3 in both ERS gingival tissue and ERS GFs. Exposure of the mutant cells to TGFB1 further upregulated the expression of TGFβ targets suggesting that this pathway could be a central player in the pathogenesis of the ERS gingival fibromatosis. In conclusion our data strongly suggest that TGFβ -induced modifications of the extracellular matrix contribute to the pathogenesis of ERS. To our knowledge this is the first proteomic-based analysis of FAM20A-associated modifications.

Long-term dental intervention and laboratory examination in a patient with Vitamin D-dependent rickets type I: A case report

RATIONALE

Vitamin D-dependent rickets type I (VDDR-I) is a rare form of rickets, which is an autosomal recessive disease caused by 1α-hydroxylase enzyme deficiency. However, long-term dental management and microscopic morphology of teeth remain largely unclear.

PATIENT CONCERNS

We report the case of a 10-year-old Chinese boy complaining of yellowish-brown teeth with extensive caries.

DIAGNOSES

Clinical and laboratory examinations were performed, and VDDR-I was confirmed. Scanning electron microscopy confirmed amelogenesis imperfecta.

INTERVENTIONS

The patient had been taking drugs intervention for VDDR-I from the age of 3 years. The decayed teeth were treated, and metal-preformed crowns were placed to prevent further impairment. Sequence tooth extraction and remineralization therapy were also performed.

OUTCOMES

After 3 years of follow-up, the patient exhibited normal tooth replacement and an acceptable oral hygiene status. However, the new erupted teeth had amelogenesis imperfecta.

LESSONS

This case is the first to confirm amelogenesis imperfecta in a patient with VDDR-I that was not prevented by drug intervention. Importantly, it provides evidence that long-term dental intervention in patients with VDDR-I can result in an acceptable oral hygiene status. Therefore, early and long-term dental intervention is necessary in VDDR-I patients.

Whole-exome sequencing, without prior linkage, identifies a mutation in LAMB3 as a cause of dominant hypoplastic amelogenesis imperfecta

The conventional approach to identifying the defective gene in a family with an inherited disease is to find the disease locus through family studies. However, the rapid development and decreasing cost of next generation sequencing facilitates a more direct approach. Here, we report the identification of a frameshift mutation in LAMB3 as a cause of dominant hypoplastic amelogenesis imperfecta (AI). Whole-exome sequencing of three affected family members and subsequent filtering of shared variants, without prior genetic linkage, sufficed to identify the pathogenic variant. Simultaneous analysis of multiple family members confirms segregation, enhancing the power to filter the genetic variation found and leading to rapid identification of the pathogenic variant. LAMB3 encodes a subunit of Laminin-5, one of a family of basement membrane proteins with essential functions in cell growth, movement and adhesion. Homozygous LAMB3 mutations cause junctional epidermolysis bullosa (JEB) and enamel defects are seen in JEB cases. However, to our knowledge, this is the first report of dominant AI due to a LAMB3 mutation in the absence of JEB.

[Phenotype analysis and the molecular mechanism of enamel hypoplasia]

Enamel hypoplasia is a surface defect of the tooth crown caused by a disturbance of enamel matrix secretion. Enamel hypoplasia may be inherited, or result from illness, malnutrition, trauma, or high concentrations of fluorides or strontium in the drinking water or food. Different types of enamel hypoplasia have been distinguished, such as pit-type, plane-type, and linear enamel hypoplasia. Hypoplasia has been related to the intensity and duration of stress events, the number of affected ameloblasts, and their position along the forming tooth crown. Amelogenesis imperfecta (AI) is a heterogeneous group of inherited defects in dental enamel formation, most teeth are affected in both the primary and permanent dentition. 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. Since the enamel is formed according to a strict chronological sequence, and once formed, undergoes no repair or regeneration. Then the analysis the phenotype of enamel hypoplasia can provide insights of the severity of inherited or environmental stress and the molecular mechanism during the period of enamel formation.

An atomic force microscopic study of the ultrastructure of dental enamel afflicted with amelogenesis imperfecta

The ultrastructure of human tooth enamel from a patient diagnosed to have amelogenesis imperfecta (AI) was investigated using atomic force microscopy (AFM) and compared with normal human tooth enamel. AI is a hereditary defect of dental enamel in which the enamel is deficient in either quality or quantity. Tissue-specific proteins, especially amelogenins, have been postulated to play a central role in amelogenesis. The secondary structure of amelogenin has been assigned an important role in directing the architecture of hydroxyapatite (HA) enamel crystallites and an alteration of the secondary structure of amelogenin is expected to result in an altered architecture of the mineral phase in human enamel. Previous studies have shown that the human amelogenin gene encodes for a mutant protein in which a conserved Pro is mutated to a Thr residue (Pro-->Thr); such a mutation should be expected to cause a disoriented pattern of the mineral phase in enamel. AFM results presented for the AI tooth enamel clearly demonstrate that the apatite crystal morphology in AI tooth enamel is perturbed in the diseased state; this might result from a defective synthesis of the extracellular matrix proteins, e.g. amelogenin, by the ameloblasts.

Enamel biomineralization defects result from alterations to amelogenin self-assembly

Enamel formation is a powerful model for the study of biomineralization. A key feature common to all biomineralizing systems is their dependency upon the biosynthesis of an extracellular organic matrix that is competent to direct the formation of the subsequent mineral phase. The major organic component of forming mouse enamel is the 180-amino-acid amelogenin protein (M180), whose ability to undergo self-assembly is believed to contribute to biomineralization of vertebrate enamel. Two recently defined domains (A and B) within amelogenin appear essential for this self-assembly. The significance of these two domains has been demonstrated previously by the yeast two-hybrid system, atomic force microscopy, and dynamic light scattering. Transgenic animals were used to test the hypothesis that the self-assembly domains identified with in vitro model systems also operate in vivo. Transgenic animals bearing either a domain-A-deleted or domain-B-deleted amelogenin transgene expressed the altered amelogenin exclusively in ameloblasts. This altered amelogenin participates in the formation an organic enamel extracellular matrix and, in turn, this matrix is defective in its ability to direct enamel mineralization. At the nanoscale level, the forming matrix adjacent to the secretory face of the ameloblast shows alteration in the size of the amelogenin nanospheres for either transgenic animal line. At the mesoscale level of enamel structural hierarchy, 6-week-old enamel exhibits defects in enamel rod organization due to perturbed organization of the precursor organic matrix. These studies reflect the critical dependency of amelogenin self-assembly in forming a competent enamel organic matrix and that alterations to the matrix are reflected as defects in the structural organization of enamel.

[Syndromes 20. Tuberous sclerosis complex]

Tuberous sclerosis complex (TSC) is an autosomal dominantly inherited disease. It is clinically a very variable disorder. Hamartomas can develop in many different organs, including the skin, kidneys, heart and brain. Diagnosis of patients with minimal expression of the disease can be very difficult. The dentist can contribute to the (early) diagnosis of the disease.

[Dental complications of radiotherapy of tumors of the nasal cavity in childhood]

Authors have presented a case-report of a child with no or hardly developed roots of permanent teeth in the maxilla. Histological examinations of the removed teeth showed amelogenesis imperfecta and dentinogenesis imperfecta. The disturbance in root development is considered to be the consequence of the radiological treatment which was given to the child at the age of four because of the endodermal sinus tumor of the left middle nasal passage.

Amelogenesis imperfecta and nephrocalcinosis syndrome. Case studies of clinical features and ultrastructure of tooth enamel in two siblings

This article describes the enamel ultrastructure and clinical features in two siblings with the little known syndrome of Amelogenesis imperfecta and nephrocalcinosis. Nephrocalcinosis was diagnosed by x-ray examination of the abdomen, intravenous pyelography, ultrasonography, and computed tomography scan. Amelogenesis imperfecta was diagnosed from clinical and histologic examinations. The affected enamel was hypoplastic (approximately 0.2 mm thick), positively birefringent, generally aprismatic, porous, and consisted of loosely packed, randomly orientated, thin (approximately 10 nm wide), ribbonlike crystals. The enamel surface was rough, extensively cracked, and covered with ovoid or globular protrusions. Observations showed that in this case hypoplasia, hypocalcification, or hypomaturation defects were present in the same tooth, indicating that both secretory and maturation phases may have been affected. The study suggested the possibility of an abnormality in interstitial matrix, which could lead to dystrophic calcification in the kidney and abnormal tooth enamel formation. It also suggested the possibility of involvement of two separate but closely linked genes.

Amelogenin signal peptide mutation: correlation between mutations in the amelogenin gene (AMGX) and manifestations of X-linked amelogenesis imperfecta

Formation of tooth enamel is a poorly understood biological process. In this study we describe a 9-bp deletion in exon 2 of the amelogenin gene (AMGX) causing X-linked hypoplastic amelogenesis imperfecta, a disease characterized by defective enamel. The mutation results in the loss of 3 amino acids and exchange of 1 in the signal peptide of the amelogenin protein. This deletion in the signal peptide probably interferes with translocation of the amelogenin protein during synthesis, resulting in the thin enamel observed in affected members of the family. We compare this mutation to a previously reported mutation in the amelogenin gene that causes a different disease phenotype. The study illustrates that molecular analysis can help explain the various manifestations of a tooth disorder and thereby provide insights into the mechanisms of tooth enamel formation.

Development defects of enamel in humans with hereditary epidermolysis bullosa

Developmental defects of enamel are often reported as a feature of the more severe forms of epidermolysis bullosa (EB). The purpose of this investigation was to determine the prevalence and character of enamel defects in each of the major hereditary EB types. Clinical evaluations were made on 237 individuals representing all of the major EB types and 58 unaffected individuals. All EB cases were categorized by phenotype, mode of inheritance and skin biopsy. The frequency of individuals having developmental enamel defects ranged from 8.6% in recessive dystrophic EB to 100% in junctional EB; 27.5% of the control population had these defects. Generalized hypoplasia characterized by either severe pitting and/or thin enamel was seen in all junctional EB cases but not in any other EB type. There was a tendency for the severe Herlitz form of junctional EB to have thin enamel while non-Herlitz junctional EB cases had less severe pitting and generally no reduction in enamel thickness. The prevalence of individuals with hypoplastic enamel bands was greater in the EB population (9.7%) than controls (1.9%). Thus individuals with simplex and dominant dystrophic EB typically have enamel defects that are similar in frequency and distribution to those of unaffected individuals. Developmental defects of enamel are a consistent feature of junctional EB, although the clinical expression is highly variable.

[Anomalies of enamel structure: description of a clinical case]

The anomalies of dental structure are quite common in pediatric dentistry; these anomalies can involve separately or in the same time enamel, dentin or cementum and they are due to many factors acting during odontogenesis and istogenesis. The Authors analyse these abnormalities and describe a personal case.

[Recent concepts on amelogenesis: towards a molecular understanding of the pathology of human enamel]

Recent studies concerning amelogenesis demonstrate the key role of ameloblasts in the elaboration of mature enamel; this highly differentiated epithelial cell elaborates a specific extra-cellular proteic matrix, secondarily mineralized and participating in the elaboration of mature enamel. While the matrix of immature enamel is essentially made of two main classes of proteins--amelogenins and enamelins--specific proteins are found in mature enamel, the tuft proteins as well as enamelin-type proteins. In light of recent results concerning enamel proteins, we will review the different pathological processes of human enamel. In fact, the clinical observation of various forms of imperfect amelogenesis enables to recognize several aetiological mechanisms. This could either be a pathological process of genetic nature originating in the ameloblast--imperfect, mendelian-type amelogenesis--or secondary abnormalities of the calcification process, without anomalies of the genes responsible for the protein framework, which could be called post-ameloblastic pathological process.

Investigation of the aetiopathogenesis of amelogenesis imperfecta through microscopic, submicroscopic and cytogenetic methods--a case report

A case of hypomineralized type of amelogenesis imperfecta has been evaluated by using microscopic, submicroscopic and cytogenetic techniques. It has been observed that some of the enamel contained hydroxyapatite crystals and showed normal mineralization, but some others consisted of transparent, crystal plates of octacalcium phosphate, revealing that these enamel prisms have hypomature characteristics. Extra chromosomes which belong to D-autosomes were found in the culture obtained from the peripheral blood of the patient, suggesting that the patient has 15% hyperdiploids. It is suggested that the structural disorders in some of the enamel prisms resulted from alterations in the environmental conditions related to chromosome anomalies.

Aetiology of developmental enamel defects not related to fluorosis

The aetiological factors in enamel defects of a non-fluoride nature can be divided into systemic and local. The systemic factors comprise a variety of conditions: genetically determined, chromosomal anomalies, congenital defects, inborn errors of metabolism, neonatal disturbances, infectious diseases, neurological disturbances, endocrinopathies, nutritional deficiencies, nephropathies, enteropathies, liver diseases and intoxications. The genetically determined enamel defects include amelogenesis imperfecta, which may occur as an isolated phenomenon or as part of other disorders such as epidermolysis bullosa, pseudohypoparathyroidism and taurodontism. The congenital defects include heart disorders and unilateral facial hypoplasia and hypertrophy. Among the inborn errors of metabolism are: galactosaemia, phenylketonuria, alkaptonuria, erythropoietic porphyria and primary hyperoxaluria. Neonatal disturbances are important in the development of enamel hypoplasia, foremost among these are premature birth and hypocalcaemia. The latter causes postnatal hypoplasias, which, however, are never seen in breast-fed children. Haemolytic anaemia, mostly in conjunction with erythroblastosis foetalis, may cause enamel hypoplasia. In children with neurological disturbances a rather large number have enamel hypoplasias, and these changes may be a significant aid in neurological diagnosis. When the tetracyclines were introduced, many children had these drugs prescribed in the period when the teeth were undergoing mineralization. The result was a yellow-brown stain of the affected teeth. In recent years, however, there appears to have been a reduction in the incidence of tetracycline staining. As for local causes the most important are traumatic injuries and periapical osteitis of primary teeth.