Identification of Usher syndrome subtypes by ERG implicit time.
OBJECTIVE
Usher syndrome (US) is a recessively inherited disorder combining retinitis pigmentosa (RP) and a sensorineural hearing loss. The classification in subtypes is based mainly on auditory tests. The purpose of this study was to analyze implicit time (IT) differences in the electroretinogram (ERG) between RP alone, US I, and US II.


METHODS
The data of 15 control subjects and of 15 patients with US I, 15 with US II, and 15 with RP with nonzero 33-Hz flicker ERG responses were analyzed. The ITs of three signal peaks (P1-P3) were evaluated. Sensitivity and specificity of a test to distinguish between US I and II based on timing differences were determined. Multifocal (mf)ERGs were used to assess differences in disease topography.


RESULTS
Despite the similar amplitude loss with retinal eccentricity in the mfERG in all three groups, the peak delay in US I was negligible compared with that in US II and RP. In the flicker ERG data, US I and control subjects had almost identical peak times, and the same was true for subjects with US II and RP. Because of the slight overlap between US I and II, the diagnostic test achieved a sensitivity of 100% and a specificity of 93.3%.


CONCLUSIONS
Substantial timing differences between US I and II and their usefulness for a diagnostic test were demonstrated. This finding may also be the basis for further investigations regarding the structural differences of retinal impairment between US I and II on a cellular level.
Seeliger
M W
MW
Retinal Electrodiagnostics Research Group, University Eye Hospital, Tübingen, Germany. see@uni-tuebingen.de
Zrenner
E
E
Apfelstedt-Sylla
E
E
Jaissle
G B
GB
D000293:Adolescent; D000328:Adult; D002648:Child; D004596:Electroretinography / Q000379:methods*; D006319:Hearing Loss, Sensorineural / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D008875:Middle Aged; D012160:Retina / Q000502:physiology; D012174:Retinitis Pigmentosa / Q000145:classification / Q000175:diagnosis* / Q000503:physiopathology; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013577:Syndrome; D013997:Time Factors