Abstract
Amelogenesis imperfecta is a group of rare inherited disorders that affect tooth enamel formation, quantitatively and/or qualitatively. The aim of this study was to identify the genetic etiologies of two families presenting with hypomaturation amelogenesis imperfecta. DNA was isolated from peripheral blood samples obtained from participating family members. Whole exome sequencing was performed using DNA samples from the two probands. Sequencing data was aligned to the NCBI human reference genome (NCBI build 37.2, hg19) and sequence variations were annotated with the dbSNP build 138. Mutations in MMP20 were identified in both probands. A homozygous missense mutation (c.678T>A; p.His226Gln) was identified in the consanguineous Family 1. Compound heterozygous MMP20 mutations (c.540T>A, p.Tyr180* and c.389C>T, p.Thr130Ile) were identified in the non-consanguineous Family 2. Affected persons in Family 1 showed hypomaturation AI with dark brown discoloration, which is similar to the clinical phenotype in a previous report with the same mutation. However, the dentition of the Family 2 proband exhibited slight yellowish discoloration with reduced transparency. Functional analysis showed that the p.Thr130Ile mutant protein had reduced activity of MMP20, while there was no functional MMP20 in the Family 1 proband. These results expand the mutational spectrum of the MMP20 and broaden our understanding of genotype-phenotype correlations in amelogenesis imperfecta.
Highlights
Non-syndromic amelogenesis imperfecta (AI), hereditary enamel defects, can be divided into 3 major categories based on the quantity and quality of the enamel (Witkop, 1988)
In hypoplastic AI, the enamel is thin with interdental spacing and the affected individuals are often sensitive to thermal changes and possess an increased tendency of anterior open bite (Ravassipour et al, 2005)
Hypomaturation AI is caused by failures during the maturation stage of amelogenesis
Summary
Non-syndromic amelogenesis imperfecta (AI), hereditary enamel defects, can be divided into 3 major categories based on the quantity and quality of the enamel (Witkop, 1988). In hypoplastic AI, the enamel is thin with interdental spacing and the affected individuals are often sensitive to thermal changes and possess an increased tendency of anterior open bite (Ravassipour et al, 2005). In hypocalcification AI, the affected enamel is extremely soft with normal thickness. Hypomaturation AI is caused by failures during the maturation stage of amelogenesis. The resulting phenotype is characteristically (dark) brown or yellowish discolored less mineralized enamel with normal thickness. Because the enamel is not matured well, prolonged attrition can result in excessive enamel wear facets or localized enamel fractures (Wright et al, 2011). A broader classification scheme with two categories has been used: hypoplastic AI and hypomineralized AI. The hypomineralized AI includes hypocalcification AI and hypomaturation AI (Prasad et al, 2016)
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