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Journal of Medical Genetics Jun 2024Plexins are large transmembrane receptors for the semaphorin family of signalling proteins. Semaphorin-plexin signalling controls cellular interactions that are critical...
BACKGROUND
Plexins are large transmembrane receptors for the semaphorin family of signalling proteins. Semaphorin-plexin signalling controls cellular interactions that are critical during development as well as in adult life stages. Nine plexin genes have been identified in humans, but despite the apparent importance of plexins in development, only biallelic and variants have so far been associated with Mendelian genetic disease.
METHODS
Eight individuals from six families presented with a recessively inherited variable clinical condition, with core features of amelogenesis imperfecta (AI) and sensorineural hearing loss (SNHL), with variable intellectual disability. Probands were investigated by exome or genome sequencing. Common variants and those unlikely to affect function were excluded. Variants consistent with autosomal recessive inheritance were prioritised. Variant segregation analysis was performed by Sanger sequencing. RNA expression analysis was conducted in C57Bl6 mice.
RESULTS
Rare biallelic pathogenic variants in plexin B2 (), a large transmembrane semaphorin receptor protein, were found to segregate with disease in all six families. The variants identified include missense, nonsense, splicing changes and a multiexon deletion. expression was detected in differentiating ameloblasts.
CONCLUSION
We identify rare biallelic pathogenic variants in as a cause of a new autosomal recessive, phenotypically diverse syndrome with AI and SNHL as core features. Intellectual disability, ocular disease, ear developmental abnormalities and lymphoedema were also present in multiple cases. The variable syndromic human phenotype overlaps with that seen in knockout mice, and, together with the rarity of human variants, may explain why pathogenic variants in have not been reported previously.
Topics: Humans; Animals; Male; Female; Mice; Intellectual Disability; Pedigree; Amelogenesis Imperfecta; Receptors, Cell Surface; Nerve Tissue Proteins; Alleles; Child; Hearing Loss; Hearing Loss, Sensorineural; Adult; Mutation; Adolescent; Child, Preschool; Phenotype
PubMed: 38458752
DOI: 10.1136/jmg-2023-109728 -
Scientific Reports Oct 2022Human ACP4 (OMIM*606362) encodes a transmembrane protein that belongs to histidine acid phosphatase (ACP) family. Recessive mutations in ACP4 cause non-syndromic...
Human ACP4 (OMIM*606362) encodes a transmembrane protein that belongs to histidine acid phosphatase (ACP) family. Recessive mutations in ACP4 cause non-syndromic hypoplastic amelogenesis imperfecta (AI1J, OMIM#617297). While ACP activity has long been detected in developing teeth, its functions during tooth development and the pathogenesis of ACP4-associated AI remain largely unknown. Here, we characterized 2 AI1J families and identified a novel ACP4 disease-causing mutation: c.774_775del, p.Gly260Aspfs*29. To investigate the role of ACP4 during amelogenesis, we generated and characterized Acp4 mice that carry the p.(Arg110Cys) loss-of-function mutation. Mouse Acp4 expression was the strongest at secretory stage ameloblasts, and the protein localized primarily at Tomes' processes. While Acp4 heterozygous (Acp4) mice showed no phenotypes, incisors and molars of homozygous (Acp4) mice exhibited a thin layer of aplastic enamel with numerous ectopic mineralized nodules. Acp4 ameloblasts appeared normal initially but underwent pathology at mid-way of secretory stage. Ultrastructurally, sporadic enamel ribbons grew on mineralized dentin but failed to elongate, and aberrant needle-like crystals formed instead. Globs of organic matrix accumulated by the distal membranes of defective Tomes' processes. These results demonstrated a critical role for ACP4 in appositional growth of dental enamel probably by processing and regulating enamel matrix proteins around mineralization front apparatus.
Topics: Acid Phosphatase; Ameloblasts; Amelogenesis; Amelogenesis Imperfecta; Animals; Dental Enamel Proteins; Histidine; Humans; Mice; Mutation
PubMed: 36183038
DOI: 10.1038/s41598-022-20684-9 -
Molecular Genetics & Genomic Medicine Sep 2019Ameloblastin (AMBN) is a secreted matrix protein that is critical for the formation of dental enamel and is enamel-specific with respect to its essential functions....
BACKGROUND
Ameloblastin (AMBN) is a secreted matrix protein that is critical for the formation of dental enamel and is enamel-specific with respect to its essential functions. Biallelic AMBN defects cause non-syndromic autosomal recessive amelogenesis imperfecta. Homozygous Ambn mutant mice expressing an internally truncated AMBN protein deposit only a soft mineral crust on the surface of dentin.
METHODS
We characterized a family with hypoplastic amelogenesis imperfecta caused by AMBN compound heterozygous mutations (c.1061T>C; p.Leu354Pro/ c.1340C>T; p.Pro447Leu). We generated and characterized Ambn knockout/NLS-lacZ (Ambn ) knockin mice.
RESULTS
No AMBN protein was detected using immunohistochemistry in null mice. ß-galactosidase activity was specific for ameloblasts in incisors and molars, and islands of cells along developing molar roots. Ambn 7-week incisors and unerupted (D14) first molars showed extreme enamel surface roughness. No abnormalities were observed in dentin mineralization or in nondental tissues. Ameloblasts in the Ambn mice were unable to initiate appositional growth and started to degenerate and deposit ectopic mineral. No layer of initial enamel ribbons formed in the Ambn mice, but pockets of amelogenin accumulated on the dentin surface along the ameloblast distal membrane and within the enamel organ epithelia (EOE). NLS-lacZ signal was positive in the epididymis and nasal epithelium, but negative in ovary, oviduct, uterus, prostate, seminal vesicles, testis, submandibular salivary gland, kidney, liver, bladder, and bone, even after 15 hr of incubation with X-gal.
CONCLUSIONS
Ameloblastin is critical for the initiation of enamel ribbon formation, and its absence results in pathological mineralization within the enamel organ epithelia.
Topics: Ameloblasts; Amelogenesis Imperfecta; Animals; Dental Enamel Proteins; Dentin; Gene Knock-In Techniques; Humans; Mice; Mice, Transgenic; Mutation; Organ Specificity
PubMed: 31402633
DOI: 10.1002/mgg3.929 -
Molecular Genetics & Genomic Medicine Jun 2019Truncation FAM83H mutations cause human autosomal dominant hypocalcified amelogenesis imperfecta (ADHCAI), an inherited disorder characterized by severe hardness defects...
BACKGROUND
Truncation FAM83H mutations cause human autosomal dominant hypocalcified amelogenesis imperfecta (ADHCAI), an inherited disorder characterized by severe hardness defects in dental enamel. No enamel defects were observed in Fam83h null mice suggesting that Fam83h truncation mice would better replicate human mutations.
METHODS
We generated and characterized a mouse model (Fam83h ) expressing a truncated FAM83H protein (amino acids 1-296), which recapitulated the ADHCAI-causing human FAM83H p.Tyr297* mutation.
RESULTS
Day 14 and 7-week Fam83h molars exhibited rough enamel surfaces and slender cusps resulting from hypoplastic enamel defects. The lateral third of the Fam83h incisor enamel layer was thinner, with surface roughness and altered enamel rod orientation, suggesting disturbed enamel matrix secretion. Regular electron density in mandibular incisor enamel indicated normal enamel maturation. Only mildly increased posteruption attrition of Fam83h molar enamel was observed at 7-weeks. Histologically, the Fam83h enamel organ, including ameloblasts, and enamel matrices at sequential stages of amelogenesis exhibited comparable morphology without overt abnormalities, except irregular and less evident ameloblast Tomes' processes in specific areas.
CONCLUSIONS
Considering Fam83h mice showed no enamel phenotype, while Fam83h (p.Tyr297*) mice displayed obvious enamel malformations, we conclude that FAM83H truncation mutations causing ADHCAI in humans disturb amelogenesis through a neomorphic mechanism, rather than haploinsufficiency.
Topics: Ameloblasts; Amelogenesis Imperfecta; Animals; Dental Enamel; Homozygote; Loss of Function Mutation; Mice; Mice, Inbred C57BL; Phenotype; Proteins
PubMed: 31060110
DOI: 10.1002/mgg3.724 -
Frontiers in Physiology 2021Connexin 43 (Cx43) is an integral membrane protein that forms gap junction channels. These channels mediate intercellular transport and intracellular signaling to...
Connexin 43 (Cx43) is an integral membrane protein that forms gap junction channels. These channels mediate intercellular transport and intracellular signaling to regulate organogenesis. The human disease oculodentodigital dysplasia (ODDD) is caused by mutations in Cx43 and is characterized by skeletal, ocular, and dental abnormalities including amelogenesis imperfecta. To clarify the role of Cx43 in amelogenesis, we examined the expression and function of Cx43 in tooth development. Single-cell RNA-seq analysis and immunostaining showed that is highly expressed in pre-secretory ameloblasts, differentiated ameloblasts, and odontoblasts. Further, we investigated the pathogenic mechanisms of ODDD by analyzing -null mice. These mice developed abnormal teeth with multiple dental epithelium layers. The expression of enamel matrix proteins such as ameloblastin (Ambn), which is critical for enamel formation, was significantly reduced in -null mice. TGF-β1 induces transcription in dental epithelial cells. The induction of Ambn expression by TGF-β1 depends on the density of the cultured cells. Cell culture at low densities reduces cell-cell contact and reduces the effect of TGF-β1 on Ambn induction. When cell density was high, Ambn expression by TGF-β1 was enhanced. This induction was inhibited by the gap junction inhibitors, oleamide, and 18α-grycyrrhizic acid and was also inhibited in cells expressing Cx43 mutations (R76S and R202H). TGF-β1-mediated phosphorylation and nuclear translocation of ERK1/2, but not Smad2/3, were suppressed by gap junction inhibitors. Cx43 gap junction activity is required for TGF-β1-mediated Runx2 phosphorylation through ERK1/2, which forms complexes with Smad2/3. In addition to its gap junction activity, Cx43 may also function as a Ca channel that regulates slow Ca influx and ERK1/2 phosphorylation. TGF-β1 transiently increases intracellular calcium levels, and the increase in intracellular calcium over a short period was not related to the expression level of Cx43. However, long-term intracellular calcium elevation was enhanced in cells overexpressing Cx43. Our results suggest that Cx43 regulates intercellular communication through gap junction activity by modulating TGF-β1-mediated ERK signaling and enamel formation.
PubMed: 34630166
DOI: 10.3389/fphys.2021.748574 -
PloS One 2016Patients with Amelogenesis imperfecta (AI) can present with rapid tooth loss or fractures of enamel as well as alterations in enamel thickness, color, and shape; factors...
Patients with Amelogenesis imperfecta (AI) can present with rapid tooth loss or fractures of enamel as well as alterations in enamel thickness, color, and shape; factors that may compromise aesthetic appearance and masticatory function. The aim was to explore the experiences and perceptions of adolescents and young adults living with AI and receiving early prosthetic therapy. Seven patients with severe AI aged 16 to 23 years who underwent porcelain crown therapy participated in one-to-one individual interviews. The interviews followed a topic guide consisting of open-ended questions related to experiences of having AI. Transcripts from the interviews were analyzed using thematic analysis. The analysis process identified three main themes: Disturbances in daily life, Managing disturbances, and Normalization of daily life. These themes explain the experiences of patients living with enamel disturbances caused by AI and receiving early crown therapy. Experiences include severe pain and sensitivity problems, feelings of embarrassment, and dealing with dental staff that lack knowledge and understanding of their condition. The patients described ways to manage their disturbances and to reduce pain when eating or drinking, and strategies for meeting other people. After definitive treatment with porcelain crown therapy, they described feeling like a normal patient. In conclusion the results showed that adolescents and young adults describe a profound effect of AI on several aspects of their daily life.
Topics: Adolescent; Amelogenesis Imperfecta; Crowns; Dental Enamel; Female; Humans; Interviews as Topic; Male; Patient Satisfaction; Treatment Outcome; Young Adult
PubMed: 27359125
DOI: 10.1371/journal.pone.0156879 -
Journal of Dental Sciences Jan 2024Amelogenesis imperfecta (AI), an assemblage of genetic diseases with dental enamel malformations, is generally grouped into hypoplastic, hypomaturation, and...
BACKGROUND/PURPOSE
Amelogenesis imperfecta (AI), an assemblage of genetic diseases with dental enamel malformations, is generally grouped into hypoplastic, hypomaturation, and hypocalcified types. This study aimed to identify the genetic etiology for a consanguineous Iranian family with autosomal recessive hypocalcified AI.
MATERIALS AND METHODS
Dental defects were characterized, and whole exome analysis conducted to search for disease-causing mutations. Minigene assay and RT-PCR were performed to evaluate molecular consequences of the identified mutation and expression of the causative gene in human dental tissues.
RESULTS
The defective enamel of erupted teeth showed extensive post-eruptive failure and discoloration. Partial enamel hypoplasia and indistinct dentino-enamel junction were evident on unerupted teeth, resembling hypocalcified AI. A novel homozygous (previously designated ) mutation of single-nucleotide deletion (NG_032974.1:g.5103del, NM_178497.5:c.67+1del) was identified to be disease-causing. The mutation would cause a frameshift to different transcript variant (TV) products: p.(Ala23Hisfs∗29) for TV1 and p.(Gly23Aspfs∗140) for TV2. Both dental pulps of developing and exfoliating primary teeth expressed TV2.
CONCLUSION
Loss-of-function mutations can cause AI type IIIB (the hypocalcified, autosomal recessive type), rather than type IIA4 (the hypomaturation, pigmented autosomal recessive type). This study supports a hypothesis that the product of TV2 is the single dominant ODAPH protein isoform critical for dental enamel formation and may also play an unappreciated role in development and homeostasis of dentin-pulp complex. Due to genetic heterogeneity and a nonideal genotype-phenotype correlation of AI, it is essential to perform genetic testing for patients with inherited enamel defects to make a definitive diagnosis.
PubMed: 38303846
DOI: 10.1016/j.jds.2023.09.020 -
International Journal of Oral Science Sep 2018Tooth development is a complex process that involves precise and time-dependent orchestration of multiple genetic, molecular, and cellular interactions. Ameloblastin...
Tooth development is a complex process that involves precise and time-dependent orchestration of multiple genetic, molecular, and cellular interactions. Ameloblastin (AMBN, also named "amelin" or "sheathlin") is the second most abundant enamel matrix protein known to have a key role in amelogenesis. Amelogenesis imperfecta (AI [MIM: 104500]) refers to a genetically and phenotypically heterogeneous group of conditions characterized by inherited developmental enamel defects. The hereditary dentin disorders comprise a variety of autosomal-dominant genetic symptoms characterized by abnormal dentin structure affecting either the primary or both the primary and secondary teeth. The vital role of Ambn in amelogenesis has been confirmed experimentally using mouse models. Only two cases have been reported of mutations of AMBN associated with non-syndromic human AI. However, no AMBN missense mutations have been reported to be associated with both human AI and dentin disorders. We recruited one kindred with autosomal-dominant amelogenesis imperfecta (ADAI) and dentinogenesis imperfecta/dysplasia characterized by generalized severe enamel and dentin defects. Whole exome sequencing of the proband identified a novel heterozygous C-T point mutation at nucleotide position 1069 of the AMBN gene, causing a Pro to Ser mutation at the conserved amino acid position 357 of the protein. Exfoliated third molar teeth from the affected family members were found to have enamel and dentin of lower mineral density than control teeth, with thinner and easily fractured enamel, short and thick roots, and pulp obliteration. This study demonstrates, for the first time, that an AMBN missense mutation causes non-syndromic human AI and dentin disorders.
Topics: Adult; Amelogenesis Imperfecta; Cells, Cultured; China; Codon; Dentin; Female; Humans; Male; Microsatellite Repeats; Microscopy, Electron, Scanning; Middle Aged; Mutation, Missense; Pedigree; RNA; Transfection; Exome Sequencing
PubMed: 30174330
DOI: 10.1038/s41368-018-0027-9 -
International Journal of Legal Medicine Jul 2021The Y chromosome is male-specific and is important for spermatogenesis and male fertility. However, the Y chromosome is poorly characterized due to massive palindromes...
The Y chromosome is male-specific and is important for spermatogenesis and male fertility. However, the Y chromosome is poorly characterized due to massive palindromes and inverted repeats, which increase the likelihood of genomic rearrangements, resulting in short tandem repeats on the Y chromosome or long fragment deletions. The present study reports a large-scale (2.573~2.648 Mb) deletion in the Yp11.2 region in a Chinese population based on the analysis of 34 selected Y-specific sequence-tagged sites and subsequent sequencing of the breakpoint junctions on the Y chromosome from 5,068,482-5,142,391 bp to 7,715,462-7,716,695 bp. The results of sequence analysis indicated that the deleted region included part or all of the following five genes: PCDH11Y, TSPY, AMELY, TBL1Y, and RKY. These genes are associated with spermatogenesis or amelogenesis and various other processes; however, specific physiological functions and molecular mechanisms of these genes remain unclear. Notably, individuals with this deletion pattern did not have an obvious pathological phenotype but manifested some degree of amelogenesis imperfecta.
Topics: Amelogenin; Asian People; Cadherins; Cell Cycle Proteins; Chromosome Breakpoints; Chromosome Deletion; Chromosomes, Human, Pair 11; Chromosomes, Human, Y; Genetic Loci; Humans; Male; Microsatellite Repeats; Protein Serine-Threonine Kinases; Protocadherins; Sequence Tagged Sites; Transducin
PubMed: 33903958
DOI: 10.1007/s00414-021-02596-x -
Oral Diseases Jan 2019Variants in DLX3 cause tricho-dento-osseous syndrome (TDO, MIM #190320), a systemic condition with hair, nail and bony changes, taurodontism and amelogenesis imperfecta...
OBJECTIVES
Variants in DLX3 cause tricho-dento-osseous syndrome (TDO, MIM #190320), a systemic condition with hair, nail and bony changes, taurodontism and amelogenesis imperfecta (AI), inherited in an autosomal dominant fashion. Different variants found within this gene are associated with different phenotypic presentations. To date, six different DLX3 variants have been reported in TDO. The aim of this paper was to explore and discuss three recently uncovered new variants in DLX3.
SUBJECTS AND METHODS
Whole-exome sequencing identified a new DLX3 variant in one family, recruited as part of an ongoing study of genetic variants associated with AI. Targeted clinical exome sequencing of two further families revealed another new variant of DLX3 and complete heterozygous deletion of DLX3. For all three families, the phenotypes were shown to consist of AI and taurodontism, together with other attenuated features of TDO.
RESULTS
c.574delG p.(E192Rfs*66), c.476G>T (p.R159L) and a heterozygous deletion of the entire DLX3 coding region were identified in our families.
CONCLUSION
These previously unreported variants add to the growing literature surrounding AI, allowing for more accurate genetic testing and better understanding of the associated clinical consequences.
Topics: Amelogenesis Imperfecta; Craniofacial Abnormalities; Dental Enamel Hypoplasia; Female; Hair Diseases; Homeodomain Proteins; Humans; Male; Pedigree; Transcription Factors
PubMed: 30095208
DOI: 10.1111/odi.12955