We suggest that the pathogenesis of this form of AI may be due to ineffective ligand binding of ITGB6 resulting in either compromised cell-matrix interaction or compromised ITGB6 activation of transforming growth factor-β (TGF-β) impacting indirectly on ameloblast-ameloblast interactions and proteolytic processing of extracellular matrix proteins via MMP20.
Amelogenesis imperfecta (AI) is an inherited disorder that is associated with mutations in five genes (AMEL; ENAM; MMP20; KLK4 and FAM83H) with a wide range of clinical presentations (phenotypes).
We have since expanded the number of AI kindreds to 39, and performed mutation analyses covering the coding exons and adjoining intron sequences for the six proven AI candidate genes [amelogenin (AMELX), enamelin (ENAM), family with sequence similarity 83, member H (FAM83H), WD repeat containing domain 72 (WDR72), enamelysin (MMP20), and kallikrein-related peptidase 4 (KLK4)] and for ameloblastin (AMBN) (a suspected candidate gene).
We have identified an ARAI-causing point mutation (c.102G>A, g.102G>A, and p.W34X) in exon 1 of MMP20 in a proband with autosomal-recessive hypoplastic-hypomaturation amelogenesis imperfecta.
Our study supports a model in which the P41T mutation reduces the interactions between amelogenin and MMP20, leading to decreased degradation of amelogenin by MMP20, and resulting in AI.
Genes expressed by odontoblasts (COL1A1, COL1A2, and DSPP), and ameloblasts (AMELX, ENAM, MMP20, and KLK4) during the crown formation stage, are associated with dentinogenesis imperfecta, dentin dysplasia, and amelogenesis imperfecta.
To determine the frequency of mutations in these genes, we analyzed 15 Turkish probands with autosomal-recessive hypomaturation AI for MMP20 and KLK4 gene mutations.No KLK4 mutations were found.
This study suggests that the reduced rate of TRAP formation by a single amino acid substitution alters enamel matrix hydrolysis by MMP-20, which may result in amelogenesis imperfecta.