Target gene analyses of 39 amelogenesis imperfecta kindreds

Abstract

Previously, mutational analyses identified six disease-causing mutations in 24 amelogenesis imperfecta (AI) kindreds. 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). All four of the X-linked AI families (100%) had disease-causing mutations in AMELX, suggesting that AMELX is the only gene involved in the aetiology of X-linked AI. Eighteen families showed an autosomal-dominant pattern of inheritance. Disease-causing mutations were identified in 12 (67%): eight in FAM83H, and four in ENAM. No FAM83H coding-region or splice-junction mutations were identified in three probands with autosomal-dominant hypocalcification AI (ADHCAI), suggesting that a second gene may contribute to the aetiology of ADHCAI. Six families showed an autosomal-recessive pattern of inheritance, and disease-causing mutations were identified in three (50%): two in MMP20, and one in WDR72. No disease-causing mutations were found in 11 families with only one affected member. We conclude that mutation analyses of the current candidate genes for AI have about a 50% chance of identifying the disease-causing mutation in a given kindred.

Fig. 1

Oral photographs of probands and pedigrees of eight amelogenesis imperfecta (AI) families of unknown aetiology. A dot on the pedigree marks subjects recruited in the study. Numbering starts with 25, as a continuation of previous work reporting mutational analyses of 24 AI kindreds (11). Pedigree analyses showed that families 25 and 26 have a dominant pattern of inheritance. Families 27–32 have either a recessive pattern of transmission or are de novo mutations.

Fig. 2

Oral photographs of probands and pedigrees of four amelogenesis imperfecta (AI) families of known genetic aetiology. The proband of family 33 has autosomal-recessive hypomaturation AI, resulting from a p.W34X mutation in both enamelysin (MMP20) alleles (18). The proband of family 34 has X-linked dominant hypoplastic hypomaturation AI, resulting from a complete deletion of amelogenin (AMELX) (H-C. Chan, unpublished data). The proband of family 35 has autosomal-dominant hypocalcified AI caused by a p.Q398X mutation in one allele of family with sequence similarity 83, member H (FAM83H) (19). The proband of family 36 has a severe form of hypoplastic AI resulting from different mutations (p.422FsX448 and p.S216L) in both enamelin (ENAM) alleles (20). The father (p.422FsX448) and mother (p.S216L) had only one affected ENAM allele and both showed a very mild, but detectable, enamel phenotype.

Fig. 3

Pedigree and sequencing chromatograms for family 37 [with the amelogenin (AMELX) missense mutation, p.P70T] and oral photographs of the proband’s affected mother. The pedigree is consistent with an X-linked pattern of inheritance. The AMELX DNA sequencing chromatogram shows a doublet of C and A (c.208C > A; arrowhead). (A) Maxillary occlusal, (B) mandibular occlusal, (C) frontal, (D) right buccal, (E) left buccal, (F) frontal/buccal views of mandibular teeth, and (G) occlusal/incisal views of mandibular teeth.

Fig. 4

Pedigree and sequencing chromatograms for family 38 (FAM83H, p.Q677X) and oral photographs and radiographs of the proband. This 3-yr-old Caucasian boy showed hypocalcified amelogenesis imperfecta (AI) in his primary dentition. (A) Maxillary occlusal, (B) mandibular occlusal, (C) frontal, (D) left buccal, (E) right buccal, (F) radiographs, (G) DNA-sequencing chromatograms showing a C/T doublet demonstrating the c.2029C > T mutation in the proband, but not in the unaffected mother, and (H) a pedigree showing the autosomal-dominant pattern of inheritance (a dot marks each person recruited in the study).

Fig. 5

Pedigree and DNA-sequencing chromatograms for family 39 (FAM83H, p.Q452X) and oral photographs of the 8-yr-old proband. The sequencing chromatogram shows a C/T doublet demonstrating the c.1354C > T mutation in one FAM83H allele. (A) maxillary occlusal, (B) mandibular occlusal, (C) frontal, (D) left buccal, and (E) right buccal. The phenotype in this Caucasian family is representative of autosomal-dominant hypocalcified amelogenesis imperfecta (ADHCAI).