Secondly, we report that Slc25a21tm1a(KOMP)Wtsi homozygous mice present with profound dental, orofacial and hearing/middle ear phenotypes caused by off-target effects on the expression of the neighbouring gene Pax9. Finally, the resulting novel, hypomorphic allele of Pax9 opens the door to further studies into how Pax9 is involved in the patterning of the palatal rugae and may represent a novel model of otitis media in the mouse. Here, PAX9 is linked to otitis media.