A second family with nonsyndromic sensorineural hearing loss linked to Xp21.2: refinement of the DFN4 locus within DMD.

X-linked inherited hearing impairment is a group of heterogeneous disorders accounting for less than 2% of hereditary hearing loss. DFN4, a sex-linked hearing impairment associated with profound sensorineural hearing loss, has been previously mapped to Xp21.2, a region containing the DMD locus. We have identified a family from Turkey with deafness in which the disease maps to and refines the DFN4 locus. In contrast to the previous family, the crossover points are entirely within the DMD locus. Two-point lod score analysis for the markers DXS 997, DXS 1214, and DXS 1219 showed a lod score of 2. 59. 5' and 3' crossovers were between DMD 44 and DXS 1219 and between DXS 1214 and DXS 985, respectively, suggesting that DFN4 is either an allele of DMD or a mutation in a DMD nested gene. The restriction of the DFN4 locus to DMD suggests that dystrophin may play an important role in hearing.