Pathognomonic (diagnostic) ERGs. A review and update.

Area of Science:

• Ophthalmology
• Genetics
• Neuroscience

Background:

• Inherited retinal disorders (IRDs) present diagnostic challenges.
• Electroretinogram (ERG) abnormalities are key indicators for specific IRDs.
• Understanding ERG patterns aids in genetic diagnosis and management.

Purpose of the Study:

• To review three inherited retinal disorders with pathognomonic ERG abnormalities: cone dystrophy with supernormal rod ERG (KCNV2), enhanced S-cone syndrome (NR2E3), and bradyopsia (RGS9/R9AP).
• To correlate specific ERG findings with genetic mutations.
• To highlight the role of standard and nonstandard ERG techniques in diagnosis.

Main Methods:

• Review of clinical, genetic, and electrophysiological data for KCNV2, NR2E3, and RGS9/R9AP disorders.
• Analysis of standard and specialized electroretinogram (ERG) techniques.
• Correlation of ERG patterns with causative gene mutations.

Main Results:

• Pathognomonic ERG features were identified for each of the three disorders, allowing for gene specification.
• Nonstandard electrophysiological testing beyond international standards is necessary for diagnosing cone dystrophy with supernormal rod ERG and bradyopsia.
• Clinical phenotypes can be variable, with NR2E3 mutations potentially causing other conditions besides enhanced S-cone syndrome.

Conclusions:

• Characteristic ERG changes are diagnostic for cone dystrophy with supernormal rod ERG, enhanced S-cone syndrome, and bradyopsia, guiding genetic screening.
• Additional nonstandard ERG testing is essential for accurate diagnosis in at least two of these conditions.
• ERG analysis combined with genetic testing provides a robust approach to diagnosing these inherited retinal disorders.