Exome Sequencing of Aggressive Periodontitis in a Japanese Population

Objectives: Objective: Periodontitis is an inflammatory disease causing destruction of periodontal tissue. The disease susceptibility to aggressive periodontitis (AgP) is thought to be influenced by genetic risk factors. However, the specific genetic variants has not been fully clarified yet. In this study, we aimed to identify a novel genetic risk factor for AgP in a Japanese population by exome sequencing.
Methods: Methods: We extracted genomic DNA from peripheral whole blood and conducted whole exome sequencing of 44 unrelated AgP patients. We constructed the expressing vectors of wild-type Sphingomyelin phosphodiesterase 3 (SMPD3) and mutant SMPD3 containing single nucleotide polymorphism rs145616324 [c.412 C>T (p.Leu138Phe)]. The expressing vectors were introduced into human periodontal ligament (HPDL) cells, and sphingomyelinase activity and mRNA expression of calcification-related genes were assessed by sphingomyelinase assay kit and real-time PCR, respectively.
Results: Results: We found that single nucleotide polymorphism rs145616324 in the gene encoding SMPD3 was putatively associated with AgP, with P-value: 1.42 × 10^-2 and odds ratio 2.39 (95% confidence interval: 1.17–4.89). Interestingly, while wild-type SMPD3 increased sphingomyelinase activity, mutant SMPD3 containing rs145616324 decreased the activity. Similarly, wild-type SMPD3 significantly increased the expression of calcification-related genes such as type I collagen and alkaline phosphatase in HPDL cells, while mutant SMPD3 had no effect on the expression of these genes. These data suggested that SMPD3 with rs145616324 lacks sphingomyelinase activity, leading to the inability to regulate the cytodifferentiation of HPDL cells.
Conclusions: Conclusion: SMPD3 is important in the homeostatic maintenance of periodontal ligament tissues, and the presence of rs145616324 polymorphism may cause the imbalance of destroy this homeostasis, leading to the onset and progress of AgP.