Brent Lin

ENAM Mutations in Autosomal-dominant Amelogenesis Imperfecta

To date, 4 unique enamelin gene (ENAM) defects have been identified in kindreds with amelogenesis imperfecta. To improve our understanding of the roles of enamelin in normal enamel formation, and to gain information related to possible genotype/phenotype correlations, we have identified 2 ENAM mutations in kindreds with hypoplastic ADAI, 1 novel (g.4806A>C, IVS6-2A>C) and 1 previously identified (g.8344delG), and have characterized the resulting enamel phenotypes. The IVS6-2A>C mutation caused a severe enamel phenotype in the proband, exhibiting horizontal grooves of severely hypoplastic enamel. The affected mother had several shallow hypoplastic horizontal grooves in the lower anterior teeth. In the case of the g.8344delG mutation, the phenotype was generalized hypoplastic enamel with shallow horizontal grooves in the middle 1/3 of the anterior teeth. In general, mutations in the human enamelin gene cause hypoplastic enamel, often with horizontal grooves, but the severity of the enamel defects is variable, even among individuals with the same mutation.

Novel MSX1 Frameshift Causes Autosomal-dominant Oligodontia

Can kindreds with tooth agenesis caused by MSX1 or PAX9 mutations be distinguished by their phenotypes? We have identified an MSX1second bicuspids and mandibular central incisors. The dominant phenotype is apparently due to haploinsufficiency. We analyzed patterns of partial tooth agenesis in seven kindreds with defined MSX1 mutations and ten kindreds with defined PAX9 mutations. The probability of missing a particular type of tooth is always bilaterally symmetrical, but differences exist between the maxilla and mandible. MSX1-associated oligodontia typically includes missing maxillary and mandibular second bicuspids and maxillary first bicuspids. The most distinguishing feature of MSX1-associated oligodontia is the frequent (75%) absence of maxillary first bicuspids, while the most distinguishing feature of PAX9-associated oligodontia is the frequent (> 80%) absence of the maxillary and mandibular second molars.

Mutational Spectrum of FAM83H: The C-Terminal Portion is Required for Tooth Enamel Calcification

Dental enamel forms through the concerted activities of specialized extracellular matrix proteins, including amelogenin, enamelin, MMP20, and KLK4. Defects in the genes encoding these proteins cause non‐syndromic inherited enamel malformations collectively designated as amelogenesis imperfecta (AI). These genes, however, account for only about a quarter of all AI cases. Recently we identified mutations in FAM83H that caused autosomal dominant hypocalcified amelogenesis imperfecta (ADHCAI). Unlike other genes that cause AI, FAM83 H does not encode an extracellular matrix protein. Its location inside the cell is completely unknown, as is its function. We here report novel FAM83H mutations in four kindreds with ADHCAI. All are nonsense mutations in the last exon (c.1243G>T, p.E415X; c.891T>A, p.Y297X; c.1380G>A, p.W460X; and c.2029C>T, p.Q677X). These mutations delete between 503 and 883 amino acids from the C‐terminus of a protein normally comprised of 1179 residues. The reason these mutations cause such extreme defects in the enamel layer without affecting other parts of the body is not known yet. However it seems evident that the large C‐terminal part of the protein is essential for proper enamel calcification.

ITGB6 loss-of-function mutations cause autosomal recessive amelogenesis imperfecta

Integrins are cell-surface adhesion receptors that bind to extracellular matrices (ECM) and mediate cell-ECM interactions. Some integrins are known to play critical roles in dental enamel formation. We recruited two Hispanic families with generalized hypoplastic amelogenesis imperfecta (AI). Analysis of whole-exome sequences identified three integrin beta 6 (ITGB6) mutations responsible for their enamel malformations. The female proband of Family 1 was a compound heterozygote with an ITGB6 transition mutation in Exon 4 (g.4545G > A c.427G > A p.Ala143Thr) and an ITGB6 transversion mutation in Exon 6 (g.27415T > A c.825T > A p.His275Gln). The male proband of Family 2 was homozygous for an ITGB6 transition mutation in Exon 11 (g.73664C > T c.1846C > T p.Arg616*) and hemizygous for a transition mutation in Exon 6 of Nance-Horan Syndrome (NHS Xp22.13; g.355444T > C c.1697T > C p.Met566Thr). These are the first disease-causing ITGB6 mutations to be reported. Immunohistochemistry of mouse mandibular incisors localized ITGB6 to the distal membrane of differentiating ameloblasts and pre-ameloblasts, and then ITGB6 appeared to be internalized by secretory stage ameloblasts. ITGB6 expression was strongest in the maturation stage and its localization was associated with ameloblast modulation. Our findings demonstrate that early and late amelogenesis depend upon cell-matrix interactions. Our approach (from knockout mouse phenotype to human disease) demonstrates the power of mouse reverse genetics in mutational analysis of human genetic disorders and attests to the need for a careful dental phenotyping in large-scale knockout mouse projects.

The dentin phosphoprotein repeat region and inherited defects of dentin

Nonsyndromic dentin defects classified as type II dentin dysplasia and types II and III dentinogenesis imperfecta are caused by mutations in DSPP (dentin sialophosphoprotein). Most reported disease‐causing DSPP mutations occur within the repetitive DPP (dentin phosphoprotein) coding sequence. We characterized the DPP sequences of five probands with inherited dentin defects using single molecule real‐time (SMRT) DNA sequencing. Eight of the 10 sequences matched previously reported DPP length haplotypes and two were novel. Alignment with known DPP sequences showed 32 indels arranged in 36 different patterns. Sixteen of the 32 indels were not represented in more than one haplotype. The 25 haplotypes with confirmed indels were aligned to generate a tree that describes how the length variations might have evolved. Some indels were independently generated in multiple lines. A previously reported disease‐causing DSPP mutation in Family 1 was confirmed and its position clarified (c.3135delC; p.Ser1045Argfs*269). A novel frameshift mutation (c.3504_3508dup; p.Asp1170Alafs*146) caused the dentin defects in Family 2. A COL1A2 (c.2027G>A or p.Gly676Asp) missense mutation, discovered by whole‐exome sequencing, caused the dentin defects in Family 3. We conclude that SMRT sequencing characterizes the DPP repeat region without cloning and can improve our understanding of normal and pathological length variations in DSPP alleles.

What do parents say about their children's oral health on twitter?

Using twitter, a social networking platform, this study examined parents′ perceptions and behaviors related to their child′s oral health. Publically available tweets on twitter were extracted from 14 randomly selected nonconsecutive days in December 2012 and January 2013. A total of 1073 tweets meeting the search criteria were included and analyzed. Parents frequently described events related to their children′s dental eruption, exfoliation, and grinding on twitter, which accounted for close to half of the tweets. One in three (32%) concerns that parents raised was related to one of these events. Concerns about dental esthetics represented the largest category of concerns (28%) that parents had. The most frequent actions described were related to dental visits (61%) and caries prevention (33%). More than half of the tweets contained an associated attitude of the parents themselves or their children (57%) with 2 in 3 attitudes related to dental settings, such as dental visits, being negative. Twitter can serve as a rich source of data on parental perceptions and behaviors related to their child′s oral health. Future research is warranted to better understand how social media can facilitate parental positive attitudes and oral health promotion behaviors.

Interprofessional Oral Health Education Improves Knowledge, Confidence, and Practice for Pediatric Healthcare Providers

Dental caries is the most prevalent chronic childhood disease in the United States. Dental caries affects the health of 60–90% of school-aged children worldwide. The prevalence of untreated early childhood dental caries is 19% for children 2–5 years of age in the U.S. Some factors that contribute to the progression of dental caries include socioeconomic status, access to dental care, and lack of anticipatory guidance. The prevalence of dental caries remains highest for children from specific ethnic or racial groups, especially those living in underserved areas where there may be limited access to a dentist. Although researchers have acknowledged the various links between oral health and overall systemic health, oral health care is not usually a component of pediatric primary health care. To address this public health crisis and oral health disparity in children, new collaborative efforts among health professionals is critical for dental disease prevention and optimal oral health. This evaluation study focused on a 10-week interprofessional practice and education (IPE) course on children’s oral health involving dental, osteopathic medical, and nurse practitioner students at the University of California, San Francisco. This study’s objective was to evaluate changes in knowledge, confidence, attitude, and clinical practice in children’s oral health of the students completed the course. Thirty-one students participated in the IPE and completed demographic questionnaires and four questionnaires before and after the IPE course: (1) course content knowledge, (2) confidence, (3) attitudes, and (4) clinical practice. Results showed a statistically significant improvement in the overall knowledge of children’s oral health topics, confidence in their ability to provide oral health services, and clinical practice. There was no statistically significant difference in attitude, but there was an upward trend toward positivity. To conclude, this IPE evaluation showed that offering an interprofessional course on children’s oral health to graduate students in dentistry, nursing, and osteopathic medicine can improve their knowledge, confidence, and practice toward children’s oral health and expand their professional goals to include caring for underserved, minority children.

Assessment of simulated lesions on primary teeth with near-infrared imaging

Previous studies have demonstrated that the structural changes on enamel due to demineralization and remineralization can be exploited through optical imaging methods such as QLF, thermal and NIR imaging. The purpose of this study is to investigate whether PS-OCT and NIR reflectance imaging can be utilized to assess lesion structure in artificial enamel lesions on the smooth surfaces of primary teeth exposed to fluoride. The smooth coronal surfaces of primary teeth (n=25) were divided into 4 windows: sound, demineralization, demineralization with remineralization and APF with demineralization. Windows were treated with either acidulated phosphate fluoride (APF) for 1 minute, a demineralization solution for 4 days, and/or an acidic remineralization solution for 12 days. The samples were imaged using PS-OCT, QLF and NIR reflectance at 1400–1700 nm wavelengths. This study demonstrated that both PS-OCT and NIR reflectance imaging were suitable for assessing lesion structure in the smooth surfaces of primary dentition.