['We applied mutation screening in seven cochlear implant users to identify those persons with GJB2-related deafness to determine whether etiology of deafness was predictive of speech performance after implantation.', 'Direct sequence of GJB2 was conducted over seven cochlear implant users with prelingual hearing impairment and their speech, language and cognitive performance was examined.', 'The three persons with GJB2-related deafness had a mean vocabulary of 1243 words compared to a mean vocabulary of 195 words in the four children with GJB2-unrelated deafness, although the number of patients examined here was limited. The developmental quotient (DQ) of cognitive ability also was higher in those children with GJB2-related deafness.'] Do better speech performance in cochlear implant patients with GJB2-related deafness?