Ameloblastin gene (AMBN) maps within the critical region for autosomal dominant amelogenesis imperfecta at chromosome 4q21

Amelogenesis imperfecta (AI) is a broad group of hereditary enamel defects that is characterized by a high degree of clinical diversity. Recently, the local hypoplastic form of autosomal dominant AI (AIH2) has been mapped to human chromosome 4q in a 17.6-cM region. This locus has been further refined to a 4-Mb interval between D4S2421 and Albumin. Recently, a cDNA clone for an enamel matrix protein, ameloblastin (AMBN), has been isolated. In this report, we have isolated a PAC human genomic clone containing the human AMBN gene. The AMBN was mapped by two color fluorescence in situ hybridization using two P1 genomic clones for sequence tagged site (STS) markers, D4S400 and D4S409, which flank the critical AIH2 region. Our results place AMBN at 4q21 between D4S409 (4q13) and D4S400 (4q21). Furthermore, the AMBN PAC genomic clone was shown to contain three STS markers, D4S2604, D4S2670, and D4S2609, which are contained within the critical region defined by six Swedish families with AIH2. AMBN is therefore a strong candidate gene for AIH2.

Mapping of the locus for autosomal dominant amelogenesis imperfecta (AIH2) to a 4-Mb YAC contig on chromosome 4q11-q21

Amelogenesis imperfecta (AI) is a clinically and genetically heterogeneous group of inherited enamel defects. We recently mapped a locus for autosomal dominant local hypoplastic amelogenesis imperfecta (AIH2) to the long arm of chromosome 4. The disease gene was localized to a 17.6-cM region between the markers D4S392 and D4S395. The albumin gene (ALB), located in the same interval, was a candidate gene for autosomal dominant AI (ADAI) since albumin has a potential role in enamel maturation. Here we describe refined mapping of the AIH2 locus and the construction of marker maps by radiation hybrid mapping and yeast artificial chromosome (YAC)-based sequence tagged site-content mapping. A radiation hybrid map consisting of 11 microsatellite markers in the 5-cM interval between D4S409 and D4S1558 was constructed. Recombinant haplotypes in six Swedish ADAI families suggest that the disease gene is located in the interval between D4S2421 and ALB. ALB is therefore not likely to be the disease-causing gene. Affected members in all six families share the same allele haplotypes, indicating a common ancestral mutation in all families. The AIH2 critical region is less than 4 cM and spans a physical distance of approximately 4 Mb as judged from radiation hybrid maps. A YAC contig over the AIH2 critical region including several potential candidate genes was constructed.

Genetic heterogeneity of autosomal dominant amelogenesis imperfecta demonstrated by its exclusion from the AIH2 region on human chromosome 4Q

Amelogenesis imperfecta (AI) is a group of hereditary enamel defects, characterized by large clinical diversity. On the basis of differences in clinical manifestation and inheritance pattern, 14 different subtypes have been recognized. A locus for autosomal dominant AI (ADAI) of local hypoplastic type was recently mapped to the region between D4S392 and D4S395 on the long arm of chromosome 4. To test whether the chromosome 4 locus is responsible for other forms of AI as well, a linkage study was carried out with 17 families representing at least five clinical forms of ADAI. Admixture tests for heterogeneity performed with the marker D4S2456 gave statistical support for genetic heterogeneity of ADAI with the odds 78:1. Linkage to the ADAI locus on chromosome 4q (AIH2) could only be demonstrated with families expressing the local hypoplastic type, and there was no support for heterogeneity within that group of families. Furthermore, linkage could be excluded for five families with other clinical forms of ADAI. The data therefore demonstrated that ADAI is genetically heterogeneous, and that at least two loci for it exist.