Functional study of novel PAX9 variants: the paired domain and non-syndromic oligodontia.

OBJECTIVES To investigate pathogenic variants of the paired box 9 (PAX9) gene in patients with non-syndromic oligodontia, and the functional impact of these variants. SUBJECTS AND METHODS Whole exome sequencing and Sanger sequencing were utilised to detect gene variants in a cohort of 80 patients diagnosed with non-syndromic oligodontia. Bioinformatic and conformational analyses, fluorescence microscopy and luciferase reporter assay were employed to explore the functional impact. RESULTS We identified three novel variants in the PAX9, including two frameshift variants (c.211_212insA; p.I71Nfs*246 and c.236_237insAC; p.T80Lfs*6), and one missense variant (c.229C>G; p.R77G). Familial co-segregation verified an autosomal dominant inheritance pattern. Conformational analyses revealed that the variants resided in the paired domain, and could cause corresponding structural impairment of the PAX9 protein. Fluorescence microscopy showed abnormal subcellular localisations of frameshift variants, and luciferase assay showed impaired downstream transactivation activities of the bone morphogenetic protein 4 (BMP4) gene in all variants. CONCLUSIONS Our findings broaden the spectrum of PAX9 variants in patients with non-syndromic oligodontia, and support that paired domain structural impairment and the dominant-negative effect are likely the underlying mechanisms of PAX9-related non-syndromic oligodontia. Our findings will facilitate genetic diagnosis and counselling, and help lay the foundation for precise oral health therapies.