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Novel MSX1 Frameshift Causes Autosomal-dominant Oligodontia

¹ Department of Orthodontics and Pediatric Dentistry, University of Michigan Dental Research Lab, 1210 Eisenhower Place, Ann Arbor, MI 48108, USA;
² Seoul National University, College of Dentistry, Department of Pediatric Dentistry & Dental Research Institute, 28-2 Yongon-Dong, Chongno-Gu, Seoul, Korea 110-768; and
³ University of California at San Francisco, School of Dentistry, Department of Growth and Development, Division of Pediatric Dentistry, 513 Parnassus Avenue, S-630, San Francisco, CA 94143-0430, USA

View larger version (88K): [in a new window]   Figure 1. Oral photographs of the unaffected mother (II-2) and the proband (III-1; age 11) show that the MSX1 mutation (g.62dupG) has no apparent effect on tooth size (top). Panorex radiographs demonstrate that the unaffected mother (II-2) has all of her permanent teeth except the third molars, while the proband (III-1) is missing 6 teeth, and his affected sister (III-2; age 9) is missing 12 teeth, not counting the third molars. A white dot indicates the expected location of a congenitally absent tooth. The pedigree indicates that the oligodontia trait in this family was transmitted from the father to the offspring in an autosomal-dominant pattern of inheritance. DNA sequencing chromatograms (bottom) identified the specific MSX1 frameshift mutation (arrows) in both the forward and reverse directions. This mutation was not observed in the wild-type (Wt) MSX1 gene in the unaffected members of the kindred.

View larger version (51K): [in a new window]   Figure 2. Quadrant diagram (Palmer notation system) indicating the teeth missing in the two affected members (III-1 and III-2) of the MSX1 kindred (A). The number of missing teeth in people with defined MSX1 mutations was compiled for each position in the human dentition (32 teeth) based on the data from this report, as well as from the six previous reports of MSX1 mutations. The MSX1 mutations are summarized in the chart (D) as fractions, with the numerators being the number of missing teeth and the denominators being the number of individuals. There were no statistically significant differences between the numbers of teeth missing on the left and right, so the data for equivalent teeth on the left and right were combined (bottom of D). We plotted the percentage of teeth missing for each position in the maxillary and mandibular arches (B top), and indicated statistically significant differences (p < 0.001) between the maxillary and mandibular arches with asterisks. The number of missing teeth at each position in people with defined PAX9 mutations was compiled from the 8 previous reports of 10 PAX9 mutations (E). As with MSX1, there were no statistically significant differences between the numbers of teeth missing on the left and right, so the data for equivalent teeth on the left and right were combined (bottom of E). In subsequent analyses, we averaged the values for the mandibular central and lateral incisors, since which tooth is missing is often ambiguous. We plotted the percentage of teeth missing for each position in the maxillary and mandibular arches (B bottom), with statistically significant differences (p < 0.001) between the maxillary and mandibular arches marked with asterisks. We plotted the percentage of missing teeth at each maxillary and mandibular position for people with defined MSX1 and PAX9 mutations (C). For each tooth position in the bar graphs (B,C), the bars for the maxillary teeth are on the right, and bars for the mandibular teeth are on the left. Statistically significant differences (p < 0.001) between MSX1 and PAX9 are marked with asterisks in C, and by bold type in D and E. Note that the absence of maxillary first bicuspids (#4) is the most distinguishing feature of an MSX1 mutation, while the absence of second molars (#7) is the most distinguishing feature of PAX9 mutations. Key: 1, central incisor; 2, lateral incisor; 3, cuspid; 4, first bicuspid; 5, second bicuspid; 6, first molar; 7, second molar 8, third molar; ?, not able to be determined; x axis = tooth position; y axis = percent missing.