MILD MYOTONIC-DYSTROPHY IS ASSOCIATED WITH MEMORY IMPAIRMENT IN THE CONTEXT OF NORMAL GENERAL INTELLIGENCE

Previous investigations of cognitive function in myotonic dystrophy (D M) 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 perfor med before the availability of DNA testing for DM. We have investigate d a group of milder DM cases (defined both by their degree of disabili ty and CTG expansion size) and have not found any defect in general in telligence 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, but the verbal flue ncy task was performed normally. However, in the face of normal genera l 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.