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Premature Stop Codon in MMP20 Causing Amelogenesis Imperfecta

¹ Department of Biologic and Materials Sciences,
⁴ Department of Orthodontics and Pediatric Dentistry, University of Michigan School of Dentistry, 1011 N. University, Ann Arbor, MI 48109-1078, USA;
² Department of Prosthodontics, and
³ Department of Pediatric Dentistry, Taipei Medical University Hospital, No. 15, Sec. 5, Xinyi Rd., Xinyi 11049, Taipei, Taiwan, ROC; and
⁵ Department of Cytokine Biology, The Forsyth Institute, 140 The Fenway, Boston, MA 02115, USA

^* corresponding author, University of Michigan Dental Research Lab, 1210 Eisenhower Place, Ann Arbor, MI 48108, USA; janhu{at}umich.edu

Proteolytic enzymes are necessary for the mineralization of dental enamel during development, and mutations in the kallikrein 4 (KLK4) and enamelysin (MMP20) genes cause autosomal-recessive amelogenesis imperfecta (ARAI). So far, only one KLK4 and two MMP20 mutations have been reported. 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. The G to A transition changes the tryptophan (W) codon (TGG) at amino acid position 34 into a translation termination (X) codon (TGA). No disease-causing sequence variations were detected in KLK4. The affected enamel is thin, with mild spacing in the anterior dentition. The enamel layer is hypomineralized, does not contrast with dentin on radiographs, and tends to chip away from the underlying dentin. An intrinsic yellowish pigmentation is evident, even during eruption. The phenotype supports current ideas concerning the function of enamelysin.

KEY WORDS: enamelysin • MMP20 • enamel • tooth • amelogenesis imperfecta