Analysis of human enamel genes: insights into genetic disorders of enamel

Gingival inflammation, enamel defects, and tooth sensitivity in children with amelogenesis imperfecta: a case-control study

Gingival conditions and tooth sensitivity of young patients with amelogenesis imperfecta lack in depth studies. This case-control study aimed to compare (1) the gingival inflammation, the presence of enamel defects, and tooth sensitivity in young patients with and without amelogenesis imperfecta and (2) to investigate if any difference exists between subtypes of amelogenesis imperfecta.

Qualitative assessment of the dental groove pattern and its uniqueness for forensic identification

Introduction:

Teeth are invaluable in both the living and the deceased for forensic identification and profiling purposes. The occlusal surface patterns in the molars of an individual depend on both intrinsic and extrinsic factors. The individualistic nature of the groove pattern can be used to determine the identity of an individual by the process of comparative identification.

Aim and Objective:

The objective of this study is to determine the uniqueness of the groove pattern among individuals by the means of digital analysis.

Materials and Methods:

An experimental study was conducted on 80 dental casts where the occlusal groove patterns of 1^st and 2^nd molars from each cast were traced digitally using image analysis software GIMP (v 2.10.6). The traced patterns were then examined to determine their uniqueness.

Results:

The most common groove patterns for the maxillary 1^st and 2^nd molars were found to resemble “Branched H” and “H”, respectively. “Y” pattern was observed to be the most common in mandibular 1^st molar, whereas mandibular 2^nd molar most commonly exhibited “+” pattern. No two groove patterns were similar in the analysis.

Conclusion:

Digital method of analysis is preferable over conventional manual methods as it is noninvasive and precise. The individualistic nature of occlusal groove patterns may play an important role in comparative forensic identification.

Amelogenin gene influence on enamel defects of cleft lip and palate patients

The aim of this study was to investigate the occurrence of mutations in the amelogenin gene (AMELX) in patients with cleft lip and palate (CLP) and enamel defects (ED). A total of 165 patients were divided into four groups: with CLP and ED (n=46), with CLP and without ED (n = 34), without CLP and with ED (n = 34), and without CLP or ED (n = 51). Genomic DNA was extracted from saliva followed by conducting a Polymerase Chain Reaction and direct DNA sequencing of exons 2 through 7 of AMELX. Mutations were found in 30% (n = 14), 35% (n = 12), 11% (n = 4) and 13% (n = 7) of the subjects from groups 1, 2, 3 and 4, respectively. Thirty seven mutations were detected and distributed throughout exons 2 (1 mutation - 2.7%), 6 (30 mutations - 81.08%) and 7 (6 mutations - 16.22%) of AMELX. No mutations were found in exons 3, 4 or 5. Of the 30 mutations found in exon 6, 43.34% (n = 13), 23.33% (n = 7), 13.33% (n = 4) and 20% (n = 6) were found in groups 1, 2, 3 and 4, respectively. c.261 C > T (rs2106416), a silent mutation, was detected in 26 subjects, and found more significantly (p = 0.003) in patients with CLP (groups 1 and 2 - 23.75%), compared with those without CLP (groups 3 and 4 - 8.23%). In the groups without ED, this silent mutation was also found more significantly (p = 0.032) among subjects with CLP (17.65% in group 2), compared with those without CLP (7.8% in group 4). In conclusion, this study suggested that AMELX may be a candidate gene for cleft lip and palate.

Sex determination in highly fragmented human DNA by high-resolution melting (HRM) analysis

Sex identification in ancient human remains is a common problem especially if the skeletons are sub-adult, incomplete or damaged. In this paper we propose a new method to identify sex, based on real-time PCR amplification of small fragments (61 and 64 bp) of the third exon within the amelogenin gene covering a 3-bp deletion on the AMELX-allele, followed by a High Resolution Melting analysis (HRM). HRM is based on the melting curves of amplified fragments. The amelogenin gene is located on both chromosomes X and Y, showing dimorphism in length. This molecular tool is rapid, sensitive and reduces the risk of contamination from exogenous genetic material when used for ancient DNA studies. The accuracy of the new method described here has been corroborated by using control samples of known sex and by contrasting our results with those obtained with other methods. Our method has proven to be useful even in heavily degraded samples, where other previously published methods failed. Stochastic problems such as the random allele drop-out phenomenon are expected to occur in a less severe form, due to the smaller fragment size to be amplified. Thus, their negative effect could be easier to overcome by a proper experimental design.

The frequency of occurrence of abnormal frenal attachment of lips and enamel defects in Turner syndrome

OBJECTIVE

The aim of the work was to register the frequency of occurrence of abnormal frenal attachment of lips and enamel defects and find the correlation between these anomalies and three types of Turner syndrome.

MATERIALS AND METHODS

Fifty patients (aged 20-40 years) were clinically and cytogenetically diagnosed and divided into three groups, according to karyotype: 45,X (17 cases), with structural aberrations of chromosome X (12 cases) and with mosaic karyotype (21 cases). The control group consisted of 51 healthy woman aged 21-40 years. Subjects were screened for developmental anomalies in the labial frenula and enamel defects in three groups of Turner syndrome.

RESULTS

Some significant anomalies of soft and hard tissues were found in studied patients: abnormal frenal attachments (42% of cases), enamel opacities (58% of cases) and enamel hypoplasia (38% of cases). Differences in the occurrence of these anomaly in all group with Turner syndrome in comparison with the control group were significantly different. Enamel defects were prevalent in the patients with karyotype 45,X and patients with structural aberrations of chromosome X in comparison with the mosaic karyotype.

CONCLUSION

The results of the present study have shown, that abnormal attachment of lips and enamel defects were more frequent in Turner syndrome patients than in the control group. Enamel defects were correlated with the karyotypes of Turner syndrome and abnormal attachment of lips was not correlated with the karyotypes of Turner syndrome.

Root morphology of mandibular premolars in 40 patients with Turner syndrome

AIM

To analyse root morphology of mandibular premolars in 40 females with Turner syndrome.

METHODOLOGY

All patients aged 18-50 years (mean+/-SD: 26.2+/-6.22) were clinically and cytogenetically diagnosed and divided into three groups according to karyotype: I-with 45,X (n=19); II-with 46,X,i(Xq) and other structural changes of this chromosome (n=8); III-with mos45,X/46,XX and other mosaic karyotype (n=13). The control group consisted of 30 healthy women aged 20-50 years (mean+/-SD: 31.52+/-5.21) who underwent dental treatment at the Department of Conservative Dentistry and Department of Periodontology and Oral Mucosa Diseases, Medical University of Gdańsk, Poland. The root morphology of mandibular premolars was studied based on orthopantomogram X-ray images. The results were analysed using chi-square test with Yates's adjustment.

RESULTS

Separate mesial and distal root canals and separate root apices were noted on orthopantomograms in patients with Turner syndrome. Two-rooted mandibular first premolars were observed in 34% of cases in group 45,X (group I), in 31% of cases in the group with structural aberrations of chromosome X (group II) and in 31% of cases with mosaic karyotypes (group III). Two-rooted mandibular second premolars were observed in 39% cases in group 45,X and in 31% of cases in the group with structural aberrations of chromosome X and in 35% of cases with mosaic karyotypes. This type of root morphology was not observed in the control group. No significant difference was found between the three groups of Turner syndrome.

CONCLUSION

Highly significant differences in root morphology of mandibular premolars between patients with Turner syndrome and a population control group were found.

Dental anomalies associated with amelogenesis imperfecta: a radiographic assessment

Amelogenesis imperfecta, a group of hereditary conditions primarily affecting the enamel, has been associated with dental anomalies, including taurodontism, congenitally missing teeth, delayed eruption, crown resorption, and abnormal enamel density. The purpose of this study was to assess the prevalence of these anomalies in an amelogenesis imperfecta population. The study group consisted of members of 9 unrelated families--22 family members with amelogenesis imperfecta and 13 unaffected family members. Panoramic radiographs were evaluated for taurodontism, congenitally missing teeth, delayed tooth eruption, pathologic dental resorption, pulp calcification, and radiographic enamel density. The prevalence of taurodontism was similar in people with amelogenesis imperfecta and normal people; all of the remaining parameters were more commonly observed in people with amelogenesis imperfecta. The radiographic enamel density was quantitatively reduced in teeth affected by amelogenesis imperfecta in comparison with teeth with normal enamel. These findings suggest that some of the features associated with amelogenesis imperfecta result from abnormal enamel formation (eg, decreased enamel density, crown resorption) whereas others may occur as a result of expression of the genetic mutation in cells other than ameloblasts (eg, abnormal eruption, pulp calcification).

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGF alpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of the mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome (FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis. Poorly co-ordinated control of form and size of structures, or groups of structures (e.g., teeth and jaws), by regulatory genes should do much to explain the very frequent "mismatches" found in malocclusions and other dentofacial "deformities". Future directions for research, including possibilities for prevention, are discussed.

Genetic covariance structure of incisor crown size in twins

Previous studies of tooth size in twins and their families have suggested a high degree of genetic control, although there have been difficulties separating the various genetic and environmental effects. A genetic analysis of variation in crown size of the permanent incisors of South Australian twins was carried out, with structural equation modeling used to determine the relative contributions of genetic and environmental factors. Maximum mesiodistal crown dimensions of maxillary and mandibular permanent incisors were recorded from dental models of 298 pairs of twins, including 149 monozygous (MZ) and 149 dizygous (DZ) pairs. The analysis revealed that: (i) an adequate fit required additive genetic and unique environmental components; (ii) augmenting the model with non-additive genetic variation did not lead to a significant improvement in fit; (iii) there was evidence of shared environmental influences in the upper central incisors of males; (iv) the additive genetic component constituted a general factor loading on all eight teeth, with group factors loading on antimeric pairs of teeth; (v) unique environmental effects were mostly variable-specific; (vi) most factor loadings on antimeric tooth pairs could be constrained to be equal, indicating a symmetry of genetic and environmental influences between left and right sides; and (vii) estimated heritability of the incisor mesiodistal dimensions varied from 0.81 to 0.91.

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.

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGFalpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome(FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis.(ABSTRACT TRUNCATED AT 400 WORDS)

The absence of correlations between a clinical classification and ultrastructural findings in amelogenesis imperfecta

This study was performed to examine whether a clinical classification of different phenotypes of amelogenesis imperfecta could be discernible at the ultrastructural level. Seventeen primary teeth from 16 children with hypomineralization, hypomaturation, or hypoplastic variants of the disease were collected for histologic studies of the enamel by means of polarized light microscopy, scanning electron microscopy (SEM), and secondary ion mass spectrometry (SIMS). Polarization microscopy showed that the enamel was hypomineralized; in six teeth a wavy configuration of the enamel prisms also appeared. Three histomorphologic main types could be discerned. In 10 of the teeth extensive hypomineralization of the bulk of the enamel was found. One tooth had an unusually thick enamel with only a thin normally mineralized surface layer. SIMS images showed less pronounced signals from Ca2+ and Na+ but with stronger signals from Cl- and CN-, representing the organic component of enamel. The SEM images showed an irregular prism pattern with marked interprismatic areas. Irrespective of the clinical appearance or the hereditary pattern the main findings were hypomineralized enamel with or without wavy bands. Neither of the analytical methods used in this paper distinguishes between the clinical phenotypes of amelogenesis imperfecta.

Incidence of cleft lips, palates rising

About 1:700 live human births are affected by cleft lip and palate. Socio-economic factors--teenage pregnancies, pregnancies in women older than 35, increased consumption of teratogens during early months of pregnancy--have resulted in increased numbers of congenital malformations in the United States.

Tooth crown size in 46, X, i (Xq) human females

Permanent tooth crown sizes of six Finnish females with a 46, X, i(Xq) chromosome constitution (isochromosome for the long arm of the X chromosome) were measured from dental casts and compared with those of normal women, first-degree female relatives and 45, X females. Crown diameters of the 46, X, i(Xq) females were not only smaller than in the normal women but even smaller than the 45, X females. These findings can be considered indirect evidence that X chromosome gene(s) for tooth crown growth are most probably located on the short arm.