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Published on: September 3, 2020
Electroretinogram abnormalities in FKRP-related limb-girdle muscular dystrophy (LGMDR9)
Joshua L Hagedorn1,2, Taylor M Dunn2,3, Sajag Bhattarai2
1University of Iowa Carver College of Medicine, Iowa City, USA.
Background:
Dystroglycanopathies are a heterogeneous group of membrane-related muscular dystrophies. The dystroglycanopathy phenotype includes a spectrum of severity ranging from severe congenital muscular dystrophy to adult-onset limb-girdle muscular dystrophy (LGMD). LGMDR9 is a dystroglycanopathy caused by mutations in the FKRP gene. Previous studies have characterized electroretinogram findings of dystroglycanopathy mouse models but have not been reported in humans.
Purpose:
This study set out to characterize the electroretinogram in eight participants with LGMDR9.
Methods:
Eight participants were recruited from an ongoing dystroglycanopathy natural history study at the University of Iowa (NCT00313677). Inclusion criteria for the current study were children and adults > 6 years old with confirmed LGMDR9. Age similar controls were identified from our electrophysiology service normative control database. Full-field electroretinograms were recorded using ISCEV standards. Six of the eight participants underwent light-adapted ON/OFF testing.
Results:
The electronegative electroretinogram was not seen in any participants with LGMDR9. An unusual sawtooth pattern in the 30 Hz flicker with faster rise than descent was noted in all 8 participants. Our cases showed a decreased b-wave amplitude in light-adapted ON responses (p = 0.011) and decreased d-wave amplitude in light-adapted OFF responses (p = 0.015). Decreased b-wave amplitude in light-adapted 3.0 testing (p = 0.015) and decreased flicker ERG amplitudes were also detected (p = 0.0018). Additionally, compared to controls, participants with LGMDR9 had decreased a-wave amplitudes on dark-adapted 10 testing (p = 0.026).
Conclusions:
Abnormal ON/OFF bipolar cell responses and sawtooth 30 Hz flicker waveforms on full-field electroretinogram may be specific for LGMDR9. If confirmed in a larger population and if related to disease stage, these tests are potential biomarkers which could be useful as endpoints in clinical treatment trials.
Insights
Electroretinogram (ERG) testing in Limb-Girdle Muscular Dystrophy type R9 (LGMDR9) revealed abnormal ON/OFF bipolar cell responses and a unique sawtooth pattern in flicker ERG. These findings may serve as potential biomarkers for LGMDR9, aiding in clinical trial development.
Area of Science:
- Ophthalmology
- Neurology
- Genetics
Background:
- Dystroglycanopathies are a group of muscular dystrophies affecting the cell membrane.
- Limb-Girdle Muscular Dystrophy type R9 (LGMDR9) is a dystroglycanopathy caused by mutations in the FKRP gene.
- Previous research on electroretinogram (ERG) findings has focused on mouse models, with limited human data available for LGMDR9.
Purpose of the Study:
- To characterize the electroretinogram (ERG) findings in human participants diagnosed with LGMDR9.
- To investigate potential visual biomarkers associated with LGMDR9.
Main Methods:
- Eight participants with confirmed LGMDR9 were recruited from a natural history study.
- Full-field electroretinograms (FF-ERG) were performed according to International Society for Clinical Electrophysiology of Vision (ISCEV) standards.
- Light-adapted ON/OFF testing was conducted on six participants, and results were compared to age-matched controls.
Main Results:
- No electronegative ERG patterns were observed in LGMDR9 participants.
- A distinctive sawtooth pattern in the 30 Hz flicker ERG was present in all eight participants.
- Significant reductions in b-wave amplitude (light-adapted ON responses and 3.0 testing), d-wave amplitude (light-adapted OFF responses), and flicker ERG amplitudes were noted.
- Decreased a-wave amplitudes were observed in dark-adapted 10 testing compared to controls.
Conclusions:
- Abnormal ON/OFF bipolar cell responses and sawtooth 30 Hz flicker waveforms on FF-ERG may be specific indicators for LGMDR9.
- These ERG findings show potential as biomarkers for LGMDR9.
- Further validation in larger populations and correlation with disease stage could establish these ERG tests as valuable endpoints for LGMDR9 clinical trials.
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