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Oral and craniofacial disorders
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
Enamel defects are seen in a number of generalised genetic disorders; defects occurring in isolation are termed amelogenesis imperfecta. Classifications have tended to be based on the apparent phenotype, either hypoplasia (a reduction in thickness of the enamel) or hypomineralisation (a reduction in the degree of calcification of the enamel), the latter often subdivided into hypocalcification and hypomineralisation according to the severity of the defect. In all probability, both hypoplasia and hypomineralisation occur together in the majority of cases.
Hereditary Defects of Enamel
Published in Colin Robinson, Jennifer Kirkham, Roger Shore, Dental Enamel, 2017
Amelogenesis imperfecta (AI) represents a group of hereditary conditions that manifest enamel defects without evidence of a generalized or systemic disorder. The term amelogenesis imperfecta has been generally accepted as being specific for those enamel disorders that are limited primarily to enamel. Enamel defects are referred to as enamel hypoplasia when they occur as part of a syndrome or condition with manifestations other than enamel. The reported prevalence of AI varies from one in 14—16,000 to 1.4 in 1000, depending on the specific population studied.18,63,64
Micromorphology, microstructure and micro-Raman spectroscopy of a case of amelogenesis imperfecta
Published in J. Belinha, R.M. Natal Jorge, J.C. Reis Campos, Mário A.P. Vaz, João Manuel, R.S. Tavares, Biodental Engineering V, 2019
Sebastiana Arroyo Bote, Alfonso Villa-Vigil, M.C. Manzanares Céspedes, Esteban Brau-Aguadé
Amelogenesis Imperfecta (AI) is characterized by presenting enamel defects, without defects in others tissues (Witkop, 1988). Hereditary defects in the enamel development or environmental exposure to chemicals and drugs can damage the ameloblasts (Ferreira et al., 2005). AI is characterized by its heterogeneous phenotypical clinical patterns of variable severity, as well as for its complex genetype (Wright, 2006; Gibson, 2008; Wang et al., 2013) and/or environmental aetiology (Hedge, 2012; Malik et al., 2012). Based on its heredity and clinical evidences, four types and numerous subtypes of AI were described in 1988 by Witkop (hypoplastic, hypomaturation, hypocalcified AI and a combination of them), and today this is the most widely used classification in the clinical practice. The development of enamel starts with the secretion of the enamel protein matrix by the ameloblasts, followed by its calcification and maturation (Sapp et al., 2005; Malik et al., 2012). Less than 1% of the mature enamel is constituted by organic components, while the mineral components constitute more than a 95%. The enamel mineral crystals are deposited in compact hexagonal rod-shaped structure, making this tissue the hardest in the human body (Nanci, 2012). Numerous genes have been reported as responsible of the regulation of this complex process (Sapp et al., 2005; Bailleul-Forestier et al., 2008; Lee et al., 2008; Misiadis & Luder, 2011; Luder et al., 2013; Simmer et al., 2013; Wang et al., 2014; Zhang et al., 2015; Prasad et al., 2016). Mutations of AMELX (amelogenin), ENAM (enamelin) (Misiadis & Luder, 2011), COL17A1 (Prasad et al., 2016) and FAM20A (Wang et al., 2014) have been proven as causes of hypoplastic AI, either with smooth or rough enamel; while the AI with hypomature phenotype has been attributed to genetic defects in AMELX, MMP20, KLK4 and WDR72. Hypocalcified AI have been reported to be caused by FAM83H or C4orf26 (Kim et al., 2008; Parry et al., 2012; Luder et al., 2013) in humans. Additionally, some studies indicate that a mutation in one gene could be related to more than one type of AI; thus CNNM4 mutation is related to hypoplastic/hypomineralized types (Lee et al., 2008), DLX3 mutation is related with and hypomature/hypoplastic types (Wang et al., 2014) and C4orf26 hypomineralized-hypoplastic types (Prasad et al., 2016).
Two siblings with Heimler syndrome caused by PEX1 variants: follow-up of ophthalmologic findings
Published in Ophthalmic Genetics, 2021
Dorien Herijgers, Ellen Denayer, Irina Balikova, Peter Witters, Julie Jacob, Ingele Casteels
Heimler syndrome was first described by Heimler et al as a combination of nail abnormalities (Beau’s lines or leukonychia), dental abnormalities, SNHL and often visual problems (1). This rare genetic diagnosis can clinically be confused with Usher syndrome since patients present with the combination of SNHL and visual loss (2). Amelogenesis imperfecta can help to differentiate between these two conditions. However, symptoms do not become apparent until eruption of the secondary dentition (3). In addition, full-field electroretinogram shows cone-rod dysfunction in Heimler syndrome whereas in Usher syndrome it shows rod – cone dysfunction. This publication describes two new cases, a brother and sister of non-consanguineous parents, with Heimler syndrome caused by a homozygous likely pathogenic variant in the PEX1 gene. So far, only 31 cases of Heimler syndrome have been published (4).
Ophthalmic manifestations of Heimler syndrome due to PEX6 mutations
Published in Ophthalmic Genetics, 2018
Nutsuchar Wangtiraumnuay, Waleed Abed Alnabi, Mai Tsukikawa, Avrey Thau, Jenina Capasso, Reuven Sharony, Chris F. Inglehearn, Alex V. Levin
Heimler syndrome exhibits phenotypic variability. SNHL can be unilateral or bilateral and nails can be normal (7–9). Amelogenesis imperfecta usually manifests in secondary teeth, with posterior (premolar and molar) teeth more severely affected than anterior (incisor) teeth. Amelogenesis imperfecta is also seen in Jalili syndrome (9), hyperbilirubinemia, premature birth, hypoparathyroidism, viral infections and in response to excessive fluoride or tetracycline. Jalili syndrome is associated with cone-rod dystrophy and is therefore relevant to the differential diagnosis in our patient, although our patient did not have mutations in CNNM4.
Sex-specific differences in the salivary microbiome of caries-active children
Published in Journal of Oral Microbiology, 2019
Stephanie Ortiz, Elisa Herrman, Claudia Lyashenko, Anne Purcell, Kareem Raslan, Brandon Khor, Michael Snow, Anna Forsyth, Dongseok Choi, Tom Maier, Curtis A. Machida
Genes expressed in enamel mineralization, AMELX (amelogenin) and AMNB, as well as ESRRB were found to be associated with calcium levels in saliva. Genetic mutations in enamel mineralization are directly responsible for X-linked Amelogenesis Imperfecta, which supports their contribution in enamel matrix formation and caries vulnerability [52]. Deeley et al. [53] found that ‘higher caries experience’ was associated with irregular amelogenin allele markers. This may occur in the presence of X-inactivation and mosaicism and may contribute to female caries susceptibility [53].