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Mild myotonic dystrophy is associated with memory impairment in the context of normal general intelligence
J S Rubinsztein1, D C Rubinsztein, P J McKenna
1Section of Developmental Psychiatry, University of Cambridge, UK.
Abstract:
Previous investigations of cognitive function in myotonic dystrophy (DM) suggested that DM subjects have impairment of general intelligence and severe defects in executive function. These studies had to neglect patients with mild clinical disease, since they were generally performed before the availability of DNA testing for DM. We have investigated a group of milder DM cases (defined both by their degree of disability and CTG expansion size) and have not found any defect in general intelligence using the National Adult Reading Test, Standard Progressive Matrices, and Mini-Mental State examination. Three executive function tests were used. The cognitive estimates test and the Wisconsin Card Sorting Test showed tendencies towards impairment, which were of borderline significance, but the verbal fluency task was performed normally. However, in the face of normal general intelligence, mild DM subjects as a group show impairment of memory function. This suggests that memory function may be more sensitive to small CTG repeat expansions than general intelligence.
Insights
Mild myotonic dystrophy (DM) patients show normal general intelligence but impaired memory function. This suggests memory deficits may be an early indicator of DM, even with smaller CTG repeat expansions.
Area of Science:
- Neurology
- Genetics
- Cognitive Science
Background:
- Previous studies indicated general intelligence and executive function deficits in myotonic dystrophy (DM).
- Earlier research excluded patients with mild clinical disease due to lack of DNA testing.
- Mild DM cases require specific investigation for accurate cognitive assessment.
Purpose of the Study:
- To investigate cognitive function in mild myotonic dystrophy (DM) cases.
- To assess general intelligence and executive functions in DM patients with milder clinical presentation.
- To determine if memory function is affected in mild DM.
Main Methods:
- Recruited mild DM patients defined by disability and CTG expansion size.
- Administered National Adult Reading Test, Standard Progressive Matrices, and Mini-Mental State Examination for general intelligence.
- Utilized Cognitive Estimates Test, Wisconsin Card Sorting Test, and verbal fluency tasks for executive function assessment.
Main Results:
- No significant defects in general intelligence were found in mild DM subjects.
- Tendencies towards impairment were observed in cognitive estimates and Wisconsin Card Sorting Test, but were borderline significant.
- Verbal fluency task performance was normal.
- Mild DM subjects exhibited impaired memory function despite normal general intelligence.
Conclusions:
- Mild myotonic dystrophy (DM) does not impair general intelligence.
- Memory function impairment may be a more sensitive indicator of early-stage DM than general intelligence.
- Smaller CTG repeat expansions in DM may affect memory function preferentially.