Sex-linked and polygenic models of inheritance are also possible.18 Various genes including PAX9, MSX1 and AXIN2 have been implicated in the aetiology of hypodontia.19,20 The AXIN2 gene regulates the Wnt signalling pathway, which plays an important role in the cellular proliferation, differentiation and morphogenesis of most organs, and control of ß-catenin stability is central to Wnt signalling. The gene discussed is AXIN2; the disease is tooth agenesis.