Electrophysiological findings in two young patients with Bothnia dystrophy and a mutation in the RLBP1 gene.
OBJECTIVE
To characterize the clinical phenotype, with emphasis on electrophysiology, of two children with suspected Bothnia dystrophy.


METHODS
Two unrelated affected patients, 10 and 11 years old, were studied. Ophthalmological examination included testing of visual acuity, fundus inspection and fundus photography, kinetic perimetry, full-field electroretinogram (ERG), and multifocal ERG. The presence of a mutation in exon 7 of the RLBP1 gene was investigated by DNA sequencing.


RESULTS
Both patients were homozygous for the Arg234Trp-causing mutation in the RLBP1 gene, but the resulting disease phenotype appeared to vary somewhat between them. Visual acuity was moderately reduced in one patient and normal in the other. Fundus inspection at this age revealed no pathology in either patient and there were no signs of retinitis punctata albescens, which has been described previously as a frequent clinical feature of Bothnia dystrophy. The result of kinetic perimetry was normal. The final rod threshold was moderately elevated. Full-field ERG demonstrated the uncommon combination of absent rod response and normal cone response after 40 minutes of dark adaptation. However, after prolonged dark adaptation (20-24 h), both the rod response and the dark adaptation threshold became normal. Multifocal ERG was performed in one of the patients (the one with normal visual acuity and normal fundus appearance) and showed a reduced cone response in the central region of the tested area. There was no improvement of the multifocal ERG result after 20-24 h of dark adaptation.


CONCLUSIONS
Patients with mutations in the RLBP1 gene (Arg234Trp) may have a normal fundus appearance early in the disease course. Multifocal ERG can be used for the objective documentation of the disturbed macular function, especially when the patient's visual acuity and fundus appearance are normal. The rod response is absent in the electroretinogram; however, after prolonged dark adaptation (20-24 hours), the rods recover completely. The central cones do not seem to recover.
Gränse
L
L
Department of Ophthalmology, University of Lund, Lund, Sweden. lotta.granse@brevet.nu
Abrahamson
M
M
Ponjavic
V
V
Andréasson
S
S
D002352:Carrier Proteins / Q000235:genetics*; D002648:Child; D003623:Dark Adaptation; D003937:Diagnosis, Differential; D004596:Electroretinography; D005260:Female; D005451:Fluorescein Angiography; D005654:Fundus Oculi; D006801:Humans; D007091:Image Processing, Computer-Assisted; D009154:Mutation; D010641:Phenotype; D020419:Photoreceptor Cells, Vertebrate / Q000502:physiology*; D016133:Polymerase Chain Reaction; D012162:Retinal Degeneration / Q000208:ethnology / Q000235:genetics / Q000503:physiopathology*; D012684:Sensory Thresholds; D013548:Sweden / Q000453:epidemiology; D014792:Visual Acuity; D014794:Visual Fields
C020932:11-cis-retinal-binding protein; D002352:Carrier Proteins