METHODS

Patients: This study was approved by the ethics committee of the University Hospital of Cologne, and written informed consent was obtained from all five participants from the family investigated herein. DNA from 106 healthy Caucasian control individuals (all had negative family history for Usher syndrome) was extracted from EDTA blood (10 ml). Audiometric examination of the three patients consisted of otoscopic exploration, pure-tone and speech audiometry. Testing of the vestibular system was done by electronystagmography (ENG). Ocular examinations included measurement of visual acuity, fundus ophthalmoscopy, visual field examination, color vision testing, course of dark adaptation, Ganzfeld-electroretinogram (ERG) and multifocal ERG (mfERG; II: 2, and II: 3) according to ISCEV-standards. DNA samples were available from the three patients and both parents. Genotyping/linkage analysis: DNA was isolated as follows: 5-10 ml of EDTA-blood were added up with lysis buffer (155 mM NH4Cl, 10 mM KHCO3, 0, 1 mM EDTA in aqua dest., pH 7, 4) to a total volume of 40 ml and incubated on ice