A novel dominant mutation in SIX1 , affecting a highly conserved residue, result in only auditory defects in humans

Abstract Branchio-oto-renal (BOR) and Branchio-otic (BO) syndromes are dominant disorders characterized by variable hearing impairment (HI) and branchial defects. BOR includes additional kidney malformations. BO/BOR syndromes are genetically heterogeneous and caused by mutations in EYA1 and SIX1 genes. Mutation in SIX1 is responsible also for DFNA23, a locus for non-syndromic HI. Strikingly, the severity of the phenotype did not seem to correlate with the type of SIX1 mutation. Herein, we identified a novel mutation in SIX1 (p.E125K) in a Tunisian family with variable HI and preauricular pits. This mutation is located at the same position as the mutation identified in the Catwhesel ( Cwe ) mouse. No renal and branchial defects were observed in our family nor in Cwe /+ mice. A homology model revealed that the replacement of the Glutamate by a Lysine alters the electrostatic potential surface propriety which may affect the DNA-binding activity.