Characteristic dental pattern with hypodontia and short roots in Fraser syndrome

Dental abnormalities in rare genetic bone diseases: Literature review

Currently, over 500 rare genetic bone disorders are identified. These diseases are often accompanied by dental abnormalities, which are sometimes the first clue for an early diagnosis. However, not many dentists are sufficiently familiar with phenotypic abnormalities and treatment approaches when they encounter patients with rare diseases. Such patients often need dental treatment but have difficulties in finding a dentist who can treat them appropriately. Herein we focus on major dental phenotypes and summarize their potential causes and mechanisms, if known. We discuss representative diseases, dental treatments, and their effect on the oral health of patients and on oral health-related quality of life. This review can serve as a starting point for dentists to contribute to early diagnosis and further investigate the best treatment options for patients with rare disorders, with the goal of optimizing treatment outcomes.

[The tooth: A marker of developmental abnormalities]

Tooth formation results from specific epithelial-mesenchymal interactions, which summarize a number of developmental processes. Tooth anomalies may thus reflect subclinical diseases of the kidney, bone and more broadly of the mineral metabolism, skin or nervous system. Odontogenesis starts from the 3rd week of intrauterine life by the odontogenic orientation of epithelial cells by a first PITX2 signal. The second phase is the acquisition of the number, shape, and position of teeth. It depends on multiple transcription and growth factors (BMP, FGF, SHH, WNT). These ecto-mesenchymal interactions guide cell migration, proliferation, apoptosis and differentiation ending in the formation of the specific dental mineralized tissues. Thus, any alteration will have consequences on the tooth structure or shape. Resulting manifestations will have to be considered in the patient phenotype and the multidisciplinary care, but also may contribute to identify the altered genetic circuity.

Tooth agenesis: An overview of diagnosis, aetiology and management

Patients with one or more developmentally absent teeth are routinely encountered in dental practice. Tooth agenesis can be associated with significant functional, aesthetic and psycho-social problems. The present article provides an overview of the prevalence and aetiology of tooth agenesis, as well as the condition's clinical characteristics and management options with reference to the evidence base. A timely diagnosis can facilitate the appropriate planning and management which might not be straightforward, and patient care will likely require multi- and inter-disciplinary input. It is critical that dental care practitioners are aware of the clinical characteristics and management options for tooth agenesis.

Heterozygous Variants in FREM2 Are Associated with Mesiodens, Supernumerary Teeth, Oral Exostoses, and Odontomas

BACKGROUND

Supernumerary teeth refer to extra teeth that exceed the usual number of dentitions. A mesiodens is a particular form of supernumerary tooth, which is located in the premaxilla region. The objective of the study was to investigate the genetic etiology of extra tooth phenotypes, including mesiodens and isolated supernumerary teeth.

METHODS

Oral and radiographic examinations and whole-exome sequencing were performed on every patient in our cohort of 122 patients, including 27 patients with isolated supernumerary teeth and 94 patients with mesiodens. A patient who had multiple supernumerary teeth also had odontomas.

RESULTS

We identified a novel (c.8498A>G; p.Asn2833Ser) and six recurrent (c.1603C>T; p.Arg535Cys, c.5852G>A; p.Arg1951His, c.6949A>T; p.Thr2317Ser; c.1549G>A; p.Val517Met, c.1921A>G; p.Thr641Ala, and c.850G>C; p.Val284Leu) heterozygous missense variants in FREM2 in eight patients with extra tooth phenotypes.

CONCLUSIONS

Biallelic variants in FREM2 are implicated in autosomal recessive Fraser syndrome with or without dental anomalies. Here, we report for the first time that heterozygous carriers of FREM2 variants have phenotypes including oral exostoses, mesiodens, and isolated supernumerary teeth.

Presentation of a Case of Short Root Anomaly in an 11-Year-Old Child

Short root anomaly (SRA) is a developmental anomaly in which the affected teeth present morphologically normal crowns and short, round roots. The exact cause of SRA is unknown. A case of an 11-year-old female patient with SRA is described. The patient presented short, round roots of all permanent teeth but first molars. Maxillary lateral incisors presented severe root resorption and mobility. Treatment plan included preservation of the maxillary lateral incisors by splinting them to their adjacent teeth using a stainless steel coaxial wire. A custom mouthguard for dental trauma protection was also constructed using a computer-aided design - computer-aided manufacturing (CAD-CAM) system in order to fabricate 3D-printed dental casts. At 2-year follow-up, the mobility of maxillary lateral incisors decreased, and the patient's dentition remained stable. Considerations regarding differential diagnosis, orthodontic management, and treatment options after an eventual loss of teeth are thoroughly discussed.

Cryptophthalmos, dental anomalies, oral vestibule defect, and a novel FREM2 mutation

FREM2 is a member of the FREM2-FRAS1-FREM1 protein complex which contributes to epithelial-mesenchymal coupling. We report a Thai woman with cryptophthalmos, dental anomalies, and oral vestibule defect. A compound heterozygous mutation (c.6499C>T; p.Arg2167Trp and c.641_642del; p.Glu214GlyfsTer135) in the FREM2 gene was identified. The frameshift variant p.Glu214GlyfsTer135 is de novo and novel. It is predicted to result in the loss of most of the functional domains. The p.Arg2167Trp mutation was predicted to disrupt both Ca²⁺ binding and conformational change. The Arg2167Trp mutant protein has been shown to cause partial loss of function, decrease its interaction with FREM1 and result in impaired function of the FRAS1-FREM2-FREM1 complex. Frem2 was shown to be expressed in the developing tooth and vestibular lamina. It is hypothesized that these mutations resulted in aberration of the FRAS1-FREM2-FREM1 protein complex, resulting in loss of nephronectin, basement membrane disruption, and abnormal epithelial-mesenchymal interactions leading to dental and oral vestibule malformations.

The first adolescent case of Fraser syndrome 3, with a novel nonsense variant in GRIP1

Fraser syndrome is characterized by cryptophthalmos, syndactyly and other autopod defects, and abnormalities of the respiratory and urogenital tracts. Biallelic variants in GRIP1 can cause Fraser syndrome 3 (FRASRS3), and five unrelated FRASRS3 cases have been reported to date. Four cases are fetuses with homozygous truncating variants. The remaining case is an almost 9-year-old Turkish girl compound heterozygous for a truncation variant and a possibly frame-shift intragenic deletion. We present a 15.5-year old Pakistani boy with homozygous truncating variant c.1774C>T (p.Gln592Ter). Of the hallmarks of the disease, the boy has cryptophthalmia, midface retrusion, very low anterior hairline, hair growth on temples extending to the supraorbital line and also on alae nasi, agenesis of right kidney, and cutaneous syndactyly of fingers and toes but no symptoms in any other organs, including lungs, anorectal system, genitalia, and umbilical system. This case is the oldest known individual with FRASRS3, and our findings show that a homozygous GRIP1 truncating variant can manifest with a non-lethal phenotype than in the reported cases with such variants, expanding the phenotypic and mutational spectrum of GRIP1.