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Saccadic slowing in myotonic dystrophy and CTG repeat expansion
R Osanai1, M Kinoshita, K Hirose
1Department of Otolaryngology, Saitama Medical Centre, Saitama Medical School, Kawagoe, Japan.
Journal of Neurology
|October 17, 1998
Summary
Myotonic dystrophy (DM) patients exhibit significantly slower saccadic eye movements compared to controls, particularly horizontally. Saccadic velocity strongly correlates with CTG repeat expansion size, indicating its utility in assessing DM severity.
Area of Science:
- Ophthalmology
- Neurology
- Genetics
Background:
- Myotonic dystrophy (DM) symptom severity is linked to CTG triplet repeat size in the myotonin protein kinase gene.
- Previous research noted neurotological findings like saccadic slowing in DM patients, but its correlation with CTG repeat expansion remained unexplored.
Purpose of the Study:
- To investigate the relationship between saccadic velocity and CTG triplet repeat expansion size in myotonic dystrophy patients.
- To assess the utility of saccadic velocity testing in evaluating DM clinical severity and detecting subtle eye movement abnormalities.
Main Methods:
- A case-control study comparing saccadic velocity in 13 DM patients and 13 age/sex-matched controls.
- Examination of eye position, ocular movement range, and nystagmus.
- Correlation analysis between saccadic velocity and expanded DNA fragment (EF) size determined by Southern blot.
Main Results:
- DM patients showed significantly lower horizontal and vertical saccadic velocities than controls, with horizontal slowing being more pronounced.
- Horizontal saccadic velocity demonstrated a strong negative correlation with EF size (r = 0.801 with EcoRI, r = 0.756 with BglI; P < 0.01).
- Two patients with the longest EF sizes exhibited hypometric horizontal saccades; one with the longest EF also had hypometric vertical saccades.
Conclusions:
- Saccadic velocity testing is a valuable tool for detecting subtle eye movement abnormalities in myotonic dystrophy.
- The strong correlation between reduced saccadic velocity and CTG repeat expansion suggests its utility in quantitatively assessing DM clinical severity.
- Absence of gaze-evoked nystagmus suggests extraocular muscle atrophy may contribute to saccadic slowing more than central oculomotor system involvement.