Dental anomalies in syndromes displaying hypertrichosis in the clinical spectrum

Abstract Hypertrichosis and dental anomalies may occur alone or in combination in the spectrum of many syndromes. To identify genetic entities characterized by hypertrichosis and dental anomalies, a search was performed in the Mendelian Inheritance in Man database with the terms “hypertrichosis” or “hirsutism” and “tooth” or “dental abnormalities.” Nondependent androgen metabolism disturbances were classified as hypertrichosis. Genetic entities with hypertrichosis and dental anomalies were included in the study. Additional searches were performed in the PubMed and Orphanet databases, when necessary, in order to include data from scientific articles. An integrative analysis of the genes associated with the identified syndromes was conducted using STRING to characterize biological processes, pathways, and interactive networks. The p-values were subjected to the false discovery rate for the correction of multiple tests. Thirty-nine syndromes were identified, and dental agenesis was the most frequent dental anomaly present in 41.02% (n = 16) of the syndromes. Causative genes were identified in 33 out of 39 genetic syndromes. Among them, 39 genes were identified, and 38 were analyzed by STRING, which showed 148 biological processes and three pathways that were statistically significant. The most significant biological processes were the disassembly of the nucleosome (GO:0006337, p = 1.09e-06), chromosomal organization (GO:0051276, p = 1.09e-06) and remodeling of the chromatin (GO: 0006338, p = 7.86e-06), and the pathways were hepatocellular carcinoma (hsa05225, p = 5.77e-05), thermogenesis (hsa04714, p = 0.00019), and cell cycle (hsa04110, p = 0.0433). Our results showed that the identification of hypertrichosis and dental anomalies may raise the suspicion of one of the thirty-nine syndromes with both phenotypes.


Introduction
Hypertrichosis is characterized by an abnormal increase in hair anywhere in the body and is independent of androgens.It can result from the use of drugs, hereditary factors, or metabolic disorders, and occurs in an isolated form or is associated with other clinical Declaration of Interests: The authors certify that they have no commercial or associative interest that represents a conflict of interest in connection with the manuscript.
manifestations constituting a syndrome.The isolated form is infrequent, with an unknown incidence, but its frequency increases when it participates as a phenotype of syndromes. 1lthough important genetic features can be found in syndromic forms, which provide data for the definition of the phenotype, 2 clinical descriptions are useful for patient care, especially in complex cases.Dental anomalies are common clinical manifestations associated with hypertrichosis, including variations in color, eruption, number, size, and form of teeth, and their occurrence varies based on the type of anomaly, dentition, and population.Dental anomalies are relevant clinical signs and can provide important clues for the suspicion of a genetic entity and for the differential diagnosis of the syndromes with hypertrichosis. 3Thus, the aim of this study was to identify the set of genetic syndromes with dental anomalies coinciding with the clinical presence of hypertrichosis.

Methodology
A search was performed from June 2020 to October 2021 in the Mendelian Inheritance in Man database (OMIM, https://www.omim.org)with the associations of the terms "hypertrichosis" or "hirsutism" and "tooth" or "dental abnormalities".Nondependent androgen metabolism disturbances were classified as hypertrichosis.An additional search was performed using the PubMed and Orphanet databases (https://pubmed.ncbi.nlm.nih.gov and https://www.orpha.net/consor/cgi-bin/index.php,respectively), using the same search terms, in order to include data from scientific articles.Phenotypic and genotypic manifestations were predominantly collected at OMIM by a single collaborator.Dental anomalies were grouped according to the classification established by De La Dure-Molla et al. 3 STRING, protein-protein interaction network functional enrichment analysis (http://string-db.org), was used to investigate the biological processes, pathways, and interaction network.The p-values were subjected to the false discovery rate to correct multiple tests, and values ≤ 0.05 were considered significant.

Results
Seventy-seven entries were identified; however, 39 syndromes with hypertrichosis and dental anomalies in the clinical spectrum were included in the study (Table 1).Entries with a description of genes or those related to hirsutism were excluded; however, overlapping syndromes were also included.Only segmental odontomaxillary dysplasia was not found in OMIM, but was found in scientific articles in PubMed.

Discussion
In the current study, 39 syndromes with dental anomalies associated with hypertrichosis were identified together with other important clinical features.Despite differences in the final structures and functions, this association is possible because ectodermal organs, such as the hair and teeth, originate from the epithelium and mesenchyme.The mesenchyme typically provides the first instructive signal, which is followed by the development of an early signaling node, the epithelial placode. 4Morphogenesis is supported by placode buds into or out of the mesenchyme and subsequent proliferation, cell movements, and epithelium and mesenchyme differentiation. 4Thus, countless genes can participate in these processes.This highlights the degree to which common molecular mechanisms regulate many aspects of early hair and teeth development.This study found 7 genes in the BMP, 6 in the FGF, 7 in the Shh, and 18 in the Wnt pathways.In addition, there were significant differences between hair and teeth, especially in the spatial and temporal dynamics of placode growth, suggesting that in different  contexts, there may be specific means of modulating the signaling pathways and of the 39 genes found, 16 not participating in the four main pathways.It is likely that deregulation of these pathways (BMP, FGF, Shh, and Wnt) is responsible for the occurrence of hypertrichosis and dental anomalies.
Extensive genetic studies of defective mouse mutants have shown that signaling pathways (BMP,  FGF, Shh, and Wnt) are used reiteratively in many stages of the production of various skin appendages and of teeth, in biological processes through pathways such as the cell cycle. 5The Wnt pathway plays an essential role during hair follicle induction and in the dental development.Shh is related to morphogenesis and differentiation at an advanced stage, whereas BMP is related to cell differentiation. 5ymphoid augmentation factor 1 (Lef-1) is necessary for the development of multiple organ systems, including hair and teeth, and its role in Wnt signaling has been established.The expression of Lef-1 regulates the signaling of Wnt and target genes of Wnt, as well as mechanisms of cell proliferation, while miR-26b reduces the levels of expression of the Wnt target gene. 6Lef-1 is regulated by FGF signaling, and the overexpression of Lef-1 in cells results in increased epithelial invagination and formation of extra hair follicles.Lef-1 deficiency results in dental morphogenesis stuck in the late phase of the button, and Lef-1 is only needed temporarily in the dental epithelium for tooth development. 6At the molecular level, Lef-1 is necessary to induce an expression of FGF4, which regulates an expression of FGF3 and Shh in the tooth germ. 6hh is critical for dental epithelial cells during tooth development, and inhibition of Shh signaling results in apoptosis located in the dental epithelium.7 Hence, in both, disruption of individual signaling pathways also causes related developmental defects.Shh also promotes cell proliferation in anagen hair follicles.5 The antagonistic interactions between FGF and BMP in the oral epithelium play an important role in the positioning of the tooth formation sites.These FGF-BMP interactions control the expression of Bmp4, Pax9, Barx1, Msx1, Msx2, Dlx and other genes in the mesenchyme, whose combinatorial expression influences the type, number, size, and shape of the tooth.5 During the beginning of dental formation, the BMP signaling in the epithelium antagonizes the FGF pathways, and this interaction is designed to determine the locations of dental formation. Te interruption of BMP activity due to the excessive expression of noggin blocks the molar development and the differentiation of epithelial cells in the final stage.8 BMP signaling has an inhibitory role in hair follicle induction and morphogenesis, which needs to be antagonized mainly by noggin to facilitate placebo induction.Overexpression of noggin in the epidermis results in the thickening of the epidermis, increased hair density, and the alteration of hair types.8 Ontology analysis revealed 148 biological processes and three pathways (hepatocellular carcinoma, thermogenesis, and cell cycle) formed by genes that interact with each other and constitute a large network.In most cases, dental agenesis is caused by mutations that interrupt epithelial Wnt/ β-catenin signaling.9 It is one of the fundamental signaling pathways for the growth and development of hair follicles and teeth, but is also responsible for contributing to the development of hepatocellular carcinoma and hepatoblastoma.10,11 It is suggested that mutations in the genes found in the present study may interfere with the Wnt/β-catenin pathway.
The activation or under-activation of signaling pathways, such as Shh, Notch, TFG, BMP, and Wnt/β-catenin, plays a key role in the hair cycle. 5,8his knowledge supports the understanding of the molecular basis of disturbances and the identification of intracellular targets for the development of therapies, such as hair loss treatment. 10

Conclusion
Together, our results highlight that the identification of hypertrichosis and dental anomalies should raise the suspicion of the possibility of one of the thirtynine genetic syndromes of the health professional for the proper management and care of the patient.The main dental anomalies described in individuals with genetic alterations associated with the clinical presence of hypertrichosis are agenesis, delayed tooth eruption, and widely spaced teeth.Further studies are required to better understand these associations.

Table 1 .
Syndromes with hypertrichosis and dental anomalies.

Table 2 .
Frequency of the dental anomalies in syndromes hypertrichosis.

Table 3 .
Main biological processes characterized with the list of altered genes in syndromes with hypertrichosis and dental anomalies.

Table 4 .
Activated pathways characterized with syndromes with hypertrichosis and dental anomalies-containing-genes.