Decreased osteogenic activity and mineralization of alveolar bone cells from a patient with amelogenesis imperfecta and FAM83H 1261G>T mutation

FAM83H mutations lead to autosomal dominant hypocalcified amelogenesis imperfecta(ADHCAI).However,the biological role of FAM83H remains unclear.The present study aimed to characterize the alveolar bone cells isolated from a patient with ADHCAI having the mutation,c.1261G>T,p.E421*,in FAM83H.We showed that FAM83H mutant cells had proliferation ability and morphology similar to the controls.The F-actin staining revealed that FAM83H mutant cells were remained in the earlier stages of cell spreading compared to the controls at 30 min,but their spreading was advanced comparable to the controls at later stages.After osteogenic induction,a significant decrease in mRNA levels of RUNX2 and ALP was observed in FAM83H mutant cells at day 7 compared with day 3 while their expressions were increased in the controls.The OPN levels in FAM83H mutant cells were not significantly changed at day 7 compared to day 3 while the controls showed a significant increase.After 14 days,the mineral deposition of FAM83H mutant cells was slightly lower than that of the controls.In conclusion,we identify that FAM83H bone cells have lower expression of osteogenic marker genes and mineralization while they maintain their morphology,proliferation,and spreading.Consistent with previous studies in the ameloblasts and periodontal ligamental cells,these evidences propose that FAM83H influences osteogenic differentiation across different cell types in oral cavity.

A novel mutation in COL1A2 leads to osteogenesis imperfecta/Ehlers-Danlos overlap syndrome with brachydactyly

Osteogenesis imperfecta(OI)is mainly characterized by bone fragility and Ehlers-Danlos syndrome(EDS)by connective tissue defects.Mutations in COL1A1 or COL1A2 can lead to both syndromes.OI/EDS overlap syndrome is mostly caused by helical mutations near the amino-proteinase cleavage site of type Ⅰ procollagen.In this study,we identified a Thai patient having OI type Ⅲ,EDS,brachydactyly,and dentinogenesis imperfecta.His dentition showed delayed eruption,early exfoliation,and severe malocclusion.For the first time,ultrastructural analysis of the tooth affected with OI/EDS showed that the tooth had enamel inversion,bonelike dentin,loss of dentinal tubules,and reduction in hardness and elasticity,suggesting severe developmental disturbance.These severe dental defects have never been reported in OI or EDS.Exome sequencing identified a novel de novo heterozygous glycine substitution,c.3296G>A,p.Gly1099Glu,in exon 49 of COL1A2.Three patients with mutations in the exon 49 of COL1A2 were previously reported to have OI with brachydactyly and intracranial hemorrhage.Notably,two of these three patients did not show hyperextensible joints and hypermobile skin,while our patient at the age of 5 years had not developed intracranial hemorrhage.Here,we demonstrate that the novel glycine substitution in the carboxyl region of alpha2(Ⅰ)collagen triple helix leads to OI/EDS with brachydactyly and severe tooth defects,expanding the genotypic and phenotypic spectra of OI/EDS overlap syndrome.