To investigate the pathogenic gene of one Chinese family with autosomal dominant hypocalcified amelogenesis imperfecta and to report multidisciplinary treatment process for two patients from this family, so as to provide guidance for genetic counseling and clinical treatment of hereditary amelogenesis imperfecta. The clinical data and peripheral blood of the family members were collected. Whole-exome sequencing was performed, and candidate variants were filtered out by data analysis. The identified variant was confirmed by Sanger sequencing and protein three-dimensional structure prediction. Affected members of this hereditary family exhibited yellow-brown discoloration of the dental crowns, rough tooth surfaces, and enamel erosion, consistent with hypocalcified amelogenesis imperfecta. A nonsense mutation c.1363C＞T(p.Gln455*) in exon 5 of the FAM83H gene was identified in the proband, her mother, and her sister; this mutation was predicted to cause a truncation of the FAM83H protein. This variant was not found in unaffected family members. After receiving multidisciplinary treatment based on orthodontics, the proband and her sister restored oral function and aesthetics. The nonsense variant of FAM83H caused hypocalcified amelogenesis imperfecta in this study is detected for the first time in a Chinese family. The results further validate the pathogenic variant involved in FAM83H leading to amelogenesis imperfecta. Patients with amelogenesis imperfecta can restore oral function and aesthetics through various orthodontic and restorative treatments.

Autosomal-dominant hypocalcified amelogenesis imperfecta (ADHCAI) is caused by mutations in the FAM83H gene. Mutated FAM83H genes encode truncated FAM83H proteins with amino acid lengths between amino acids 1-286 and 1-693, in contrast to wild-type FAM83H (1-1179). Deletion of the C-terminus of FAM83H results in its subcellular translocation from the cytoplasmic compartment to the nuclear speckles, where splicing factors accumulate. However, the amino acid region of FAM83H required for nuclear speckle localization has not yet been determined, and whether all FAM83H-truncated proteins associated with ADHCAI localize to nuclear speckles remains unknown. Here, we examined the subcellular localization of FAM83H mutant proteins with truncations or deletions at various amino acid positions. Deletions within residues 1-300, which corresponds to the DUF1669 domain (17-281), attenuated or abolished the nuclear speckle localization of FAM83H. Meanwhile, some ADHCAI-related FAM83H-truncated proteins did not localize to nuclear speckles, despite the presence of the DUF1669 domain. These results suggest that the DUF1669 domain is required, but not sufficient, for nuclear speckle localization of FAM83H, demonstrating that nuclear speckle localization is not a common feature among FAM83H-truncated proteins related to ADHCAI.

The study identifies a non-consanguineous multigenerational family of the Lua ethnic group in Northern Thailand with three members affected with hypoplastic-hypocalcified amelogenesis imperfecta, cone-rod dystrophy, and harboring a novel homozygous missense variant, c.1475G>A p.(Gly492Asp), in CNNM4, indicating Jalili syndrome. We report features including advanced dental age, crossbite, developmental delay, expanding genotypic and phenotypic spectra of Jalili syndrome, and perform the prenatal genetic testing that helps avoid unnecessary pregnancy termination.

Truncation mutations in FAM83H are the major cause of autosomal dominant hypocalcified amelogenesis imperfecta. Some studies also indicated that FAM83H could be involved in osteogenic differentiation; however, the function of FAM83H in bone formation was rarely explored. This study aimed to explore the effect of Fam83h mutation on skeletal development. We generated Fam83h c.1186C>T (p.Q396*) knockin C57/BL6J mice by CRISPR/Cas9 technology and found that the Fam83hQ396⁎/Q396⁎ male mice presented skeletal development retardation that was inconspicuous at birth but progressively worsened as they grew up. Alcian and Alizarin Red staining of the whole-mount skeleton showed Fam83hQ396⁎/Q396⁎ mice presented obvious skeletal development retardation. Moreover, Micro-computed tomography (Micro-CT) analysis and H&E staining showed that the mandible of Fam83hQ396⁎/Q396⁎ mice exhibited decreased bone trabecula and slight bone rarefaction compared with wild-type mice. Calcium and phosphorus content of serum and bone, and serum ALP activity analysis showed that the serum ALP activity and value of bone calcium were decreased in Fam83hQ396⁎/Q396⁎ mice. The reduced expression of mineralization markers of RUNX2, OSX, OCN, and COL1, the reduced ALP activity and the weakened ARS staining exhibited in osteoblasts isolated from 3-day-old Fam83hQ396⁎/Q396⁎ mice. The increased protein expression of casein kinase 1α (CK1α) in the cytoplasm and the decreased expression of β-CATENIN in the nucleus indicated the inhibiting Wnt/β-catenin signaling in osteoblasts from Fam83hQ396⁎/Q396⁎ mice. Furthermore, agonists of Wnt/β-catenin signaling and Ck1α siRNA partially reversed the mineralization inhibition and the decreased expression of key signaling molecules in osteoblasts of Fam83hQ396⁎/Q396⁎ mice. In conclusion, Fam83h mutation caused the increase of cytoplasmic CK1α (as one of the components of the degradation complex), which in turn promoted degradation of β-CATENIN in the cytoplasm and reduced β-CATENIN translocation into the nucleus, subsequently inhibited Wnt/β-catenin signaling in osteoblast differentiation, and thus resulted in the mandible underdevelopment in Fam83hQ396⁎/Q396⁎ male mice.

Truncation mutations in family with sequence similarity, member H (FAM83H) gene are considered the main cause of autosomal dominant hypocalcified amelogenesis imperfecta (ADHCAI); however, its pathogenic mechanism in amelogenesis remains poorly characterized. This study aimed to investigate the effects of truncated FAM83H on developmental defects in enamel. CRISPR/Cas9 technology was used to develop a novel Fam83h c.1186C > T (p.Q396*) knock-in mouse strain, homologous to the human FAM83H c.1192C > T mutation in ADHCAI. The Fam83hQ396⁎/Q396⁎ mice showed poor growth, a sparse and scruffy coat, scaly skin and early mortality compared to control mice. Moreover, the forelimbs of homozygous mice were swollen, exhibiting a significant inflammatory response. Incisors of Fam83hQ396⁎/Q396⁎ mice appeared chalky white, shorter, and less sharp than those of control mice, and energy dispersive X-ray spectroscopy (EDS) analysis and Prussian blue staining helped identify decreased iron and increased calcium (Ca) and phosphorus (P) levels, with an unchanged Ca/P ratio. The expression of iron transportation proteins, transferrin receptor (TFRC) and solute carrier family 40 member 1 (SLC40A1), was decreased in Fam83h-mutated ameloblasts. Micro-computed tomography revealed enamel defects in Fam83hQ396⁎/Q396⁎ mice. Fam83hQ396⁎/Q396⁎ enamel showed decreased Vickers hardness and distorted enamel rod structure and ameloblast arrangement. mRNA sequencing showed that the cell adhesion pathway was most notably clustered in LS8-Fam83h-mutated cells. Immunofluorescence analysis further revealed decreased protein expression of desmoglein 3, a component of desmosomes, in Fam83h-mutated ameloblasts. The FAM83H-casein kinase 1α (CK1α)-keratin 14 (K14)-amelogenin (AMELX) interaction was detected in ameloblasts. And K14 and AMELX were disintegrated from the tetramer in Fam83h-mutated ameloblasts in vitro and in vivo. In secretory stage ameloblasts of Fam83hQ396⁎/Q396⁎ mice, AMELX secretion exhibited obvious retention in the cytoplasm. In conclusion, truncated FAM83H exerted dominant-negative effects on gross development, amelogenesis, and enamel biomineralization by disturbing iron transportation, influencing the transportation and secretion of AMELX, and interfering with cell-cell adhesion in ameloblasts.