Macular dysfunction and morphology in spinocerebellar ataxia type 7 (SCA 7).
OBJECTIVE
To characterize the clinical phenotype regarding retinal function and macular appearance in patients with spinocerebellar ataxia type 7 (SCA 7), with an emphasis on electrophysiological findings.


METHODS
Three patients from two Swedish families were given an ophthalmological examination including visual acuity, fundus inspection, Farnsworth's color vision test, Goldmann perimetry, full-field electroretinography (full-field ERG), multifocal electroretinography (mfERG) and optical coherence tomography (OCT). DNA was analyzed with polymerase chain reaction for CAG trinucleotide expansion repeats in the SCA 7 gene.


RESULTS
Molecular analysis demonstrated abnormally expanded CAG repeats in the gene for SCA 7, which encodes the protein ataxin-7, thus confirming the diagnosis SCA 7. In the oldest patient very discreet pigmentary changes in the maculae were found, but with that exception the patients had a normal ophthalmoscopic fundus appearance and OCT demonstrated only minor changes. MfERG indicated predominantly central involvement, especially in the early disease stages, which in pace with disease progression extended from the center to the more peripheral areas. Full-field ERG in the oldest patient demonstrated bilaterally distinctly prolonged 30-Hz flicker implicit time, verifying widespread cone photoreceptor degeneration.


CONCLUSIONS
The patients with genetically confirmed SCA 7 presented an early macular dysfunction, preceding any signs of abnormalities in fundus appearance. According to the electrophysiological findings the primary dysfunction involves the cone photoreceptors in the foveal region, however in an older patient involvement of cone photoreceptors throughout the retina was verified. This is in accordance with the theory that ataxin-7 interacts with CRX transcription, since it is known that mutations in the CRX gene cause cone-rod dystrophy.
Hugosson
Therése
T
Department of Ophthalmology, Central Hospital, Kristianstad, Sweden. Therese.Hugosson@med.lu.se
Gränse
Lotta
L
Ponjavic
Vesna
V
Andréasson
Sten
S
D000328:Adult; D000067719:Ataxin-7; D003118:Color Perception; D004596:Electroretinography; D005260:Female; D006801:Humans; D008266:Macula Lutea / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009419:Nerve Tissue Proteins / Q000235:genetics; D010641:Phenotype; D016133:Polymerase Chain Reaction; D020033:Protein Isoforms / Q000235:genetics; D012164:Retinal Diseases / Q000235:genetics / Q000503:physiopathology*; D020754:Spinocerebellar Ataxias / Q000235:genetics / Q000503:physiopathology*; D041623:Tomography, Optical Coherence; D018911:Trinucleotide Repeats / Q000235:genetics; D014792:Visual Acuity; D058609:Visual Field Tests
C000593829:ATXN7 protein, human; D000067719:Ataxin-7; D009419:Nerve Tissue Proteins; D020033:Protein Isoforms