The role of PAX9 promoter gene polymorphisms in causing hypodontia: a study in the Jordanian population

The clinical significance and correlative signaling pathways of paired box gene 9 in development and carcinogenesis

Paired box 9 (PAX9) gene belongs to the PAX family, which encodes a family of metazoan transcription factors documented by a conserved DNA binding paired domain 128-amino-acids, critically essential for physiology and development. It is primarily expressed in embryonic tissues, such as the pharyngeal pouch endoderm, somites, neural crest-derived mesenchyme, and distal limb buds. PAX9 plays a vital role in craniofacial development by maintaining the odontogenic potential, mutations, and polymorphisms associated with the risk of tooth agenesis, hypodontia, and crown size in dentition. The loss-of-function of PAX9 in the murine model resulted in a short life span due to the arrest of cleft palate formation and skeletal abnormalities. According to recent studies, the PAX9 gene has a significant role in maintaining squamous cell differentiation, odontoblast differentiation of pluripotent stem cells, deregulation of which is associated with tumor initiation, and malignant transformation. Moreover, PAX9 contributes to promoter hypermethylation and alcohol- induced oro-esophageal squamous cell carcinoma mediated by downregulation of differentiation and apoptosis. Likewise, PAX9 activation is also reported to be associated with drug sensitivity. In summary, this current review aims to understand PAX9 function in the regulation of development, differentiation, and carcinogenesis, along with the underlying signaling pathways for possible cancer therapeutics.

Study of rs12532, rs8670 Polymorphism of Msh Homeobox 1 (MSX1), rs61754301, rs4904155 Polymorphism of Paired Box Gene 9 (PAX9), and rs2240308 Polymorphism of Axis Inhibitor Protein 2 (AXIN2) Genes in Nonsyndromic Hypodontia

The etiology of hypodontia is complex, in which both genetic and environmental factors can be related. The main objective of our study was to contribute to elucidating the genetic background of nonsyndromic hypodontia (NSH). In this order, we selected 97 NSH subjects (70 females and 27 males) from patients referred to orthodontic treatment, and we matched to each NSH subject a control by age and sex. DNA was obtained from epithelial cells from the oral mucosa. Genotyping of the PAX9 (rs4904155 and rs61754301), MSX1 (rs8670 and rs12532), and AXIN2 (rs2240308) SNPs was performed by using TaqMan SNP Genotyping Assays on a real-time PCR system. Single-nucleotide polymorphisms (SNPs) were studied for the whole NSH group and for frontal and lateral agenesis NSH subjects separately. Our results showed that the variant genotype (p=0.0008, OR = 2.9, 95% CI = 1.58–5.3) and variant T allele (p=0.0002, OR = 2.65, 95% CI = 1.6–4.39) of the MSX1 rs8670 SNP increased the risk of hypodontia in the studied population when the whole NSH group was compared with controls. The variant genotype of the MSX1 rs8670 SNP was the most frequent in frontal agenesis; meanwhile in the lateral agenesis NSH group, the AXIN2 rs2240308 SNP showed a higher frequency of the variant genotype, with a trend towards statistical significance. In conclusion, the results of the present study showed that the variant genotype and variant T allele of the MSX1 rs8670 SNP increased the risk of hypodontia in the studied population. The presence of the variant A allele of AXIN2 rs2240308 is associated with frontal agenesis but not with lateral agenesis.