POU3F4 and deafness: Previous studies have indicated that deafness is transmitted with an inheritance pattern consistent with autosomal recessive transmission in 75–77% of cases and with autosomal dominant transmission in 15–20% of cases; 2–3% of human hereditary HL is caused by X-linked mutations [2, 3].To date, six deafness loci (DFNX1–6) have been mapped to chromosome X, with five of the corresponding genes identified: PRPS1 for DFNX1 [4], POU3F4 for DFNX2 [5], SMPX for DFNX4, AIFM1 for DFNX5 [6] and COL4A6 for DFNX6 [7–9] .