title: Amelogenesis imperfecta in two families with defined AMELX deletions in ARHGAP6.
abstract: Amelogenesis imperfecta (AI) is a group of inherited conditions featuring isolated enamel malformations. About 5% of AI cases show an X-linked pattern of inheritance, which are caused by mutations in AMELX. In humans there are two, non-allelic amelogenin genes: AMELX (Xp22.3) and AMELY (Yp11.2). About 90% of amelogenin expression is from AMELX, which is nested within intron 1 of the gene encoding Rho GTPase activating protein 6 (ARHGAP6). We recruited two AI families and determined that their disease-causing mutations were partial deletions in ARHGAP6 that completely deleted AMELX. Affected males in both families had a distinctive enamel phenotype resembling "snow-capped" teeth. The 96,240 bp deletion in family 1 was confined to intron 1 of ARHGAP6 (g.302534_398773del96240), but removed alternative ARHGAP6 promoters 1c and 1d. Analyses of developing teeth in mice showed that ARHGAP6 is not expressed from these promoters in ameloblasts. The 52,654 bp deletion in family 2 (g.363924_416577del52654insA) removed ARHGAP6 promoter 1d and exon 2, precluding normal expression of ARHGAP6. The male proband of family 2 had slightly thinner enamel with greater surface roughness, but exhibited the same pattern of enamel malformations characteristic of males in family 1, which themselves showed minor variations in their enamel phenotypes. We conclude that the enamel defects in both families were caused by amelogenin insufficiency, that deletion of AMELX results in males with a characteristic snow-capped enamel phenotype, and failed ARHGAP6 expression did not appreciably alter the severity of enamel defects when AMELX was absent.
authors.affiliation: Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, Michigan, USA. janhu@umich.edu
authors.forename: Jan C-C
authors.initials: JC
authors.lastname: Hu
authors.forename: Hui-Chen
authors.initials: HC
authors.lastname: Chan
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Simmer
authors.forename: Figen
authors.initials: F
authors.lastname: Seymen
authors.forename: Amelia S
authors.initials: AS
authors.lastname: Richardson
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Hu
authors.forename: Rachel N
authors.initials: RN
authors.lastname: Milkovich
authors.forename: Ninna M R P
authors.initials: NM
authors.lastname: Estrella
authors.forename: Mine
authors.initials: M
authors.lastname: Yildirim
authors.forename: Merve
authors.initials: M
authors.lastname: Bayram
authors.forename: Chiung-Fen
authors.initials: CF
authors.lastname: Chen
authors.forename: James P
authors.initials: JP
authors.lastname: Simmer
mesh_terms: D000293:Adolescent; D000567:Amelogenesis Imperfecta / Q000235:genetics*; D053523:Amelogenin / Q000235:genetics*; D000818:Animals; D002648:Child; D002675:Child, Preschool; D003743:Dental Enamel / Q000473:pathology; D003746:Dental Enamel Proteins / Q000235:genetics; D005091:Exons / Q000235:genetics; D020690:GTPase-Activating Proteins / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D006801:Humans; D007438:Introns; D008297:Male; D051379:Mice; D010641:Phenotype; D011401:Promoter Regions, Genetic; D017384:Sequence Deletion; D014070:Tooth / Q000473:pathology
chemical_list: C507199:AMELX protein, human; C109971:ARHGAP6 protein, human; D053523:Amelogenin; D003746:Dental Enamel Proteins; D020690:GTPase-Activating Proteins