Abstract
ObjectiveThe aim of this neuropsychological study of a large cohort of patients with progressive myoclonus epilepsy type 1 (Unverricht-Lundborg disease, EPM1) was to characterize the cognitive function of EPM1 patients and to explore the association between the disability caused by the disease and cognitive performance. MethodSixty-eight genetically verified EPM1 patients homozygous for the expansion mutation in the CSTB gene (37 males and 31 females aged 35 ± 11) participated in a neuropsychological assessment of intellectual ability, verbal memory, and executive and psychomotor function. The clinical evaluation comprised administering (and video-recording) the unified myoclonus rating scale (UMRS) to assess the severity of each patient’s myoclonus. Forty-six healthy volunteers (19 males and 27 females aged 32 ± 11) served as the control group for the neuropsychological tests. ResultsThe cognitive performance of the EPM1 patient group was impaired. Verbal Intelligence Quotient (VIQ) was below the average range (VIQ < 85) in 49% of the patients; further, Performance Intelligence Quotient (PIQ) was below average in 75% of the patients. The patients performed worse than the controls in both immediate and delayed story recall (p = 0.001); however, in the word list learning task, the patients performed only slightly worse than the controls. The one-hour delayed recall of the learned words was similar in both groups, and the percentage of retained words and story contents did not differ between the patients and controls. The patients were impaired in all of the executive function tests as well as in the psychomotor speed tests (p < 0.001 for all). Also, the patients’ simple psychomotor speed in the tapping task was significantly slowed in comparison to controls (p < 0.001). ConclusionThe patients had impaired performance in the majority of the cognitive measures; they showed the highest level of impairment in all the executive function tests and in the psychomotor speed tests. The measures of these cognitive domains are timed—therefore, it is clear that severe myoclonus limits patients’ performance. In contrast, verbal memory, especially delayed recall, was the least affected cognitive domain.
Highlights
Progressive myoclonus epilepsy type 1 (Unverricht-Lundborg disease, EPM1, OMIM 254800) is an autosomal recessive disorder caused by mutations in the gene encoding cystatin B (CSTB), a cysteine protease inhibitor
This cross-sectional study evaluated the cognitive functioning of genetically confirmed EPM1 patients and its relationship to disease-related clinical characteristics
Giovagnoli et al [18] concluded that the cognitive profile of patients with EPM1 was characterized by impaired processing and executive functions with the preservation of verbal memory, praxis, and theory of mind
Summary
Progressive myoclonus epilepsy type 1 (Unverricht-Lundborg disease, EPM1, OMIM 254800) is an autosomal recessive disorder caused by mutations in the gene encoding cystatin B (CSTB), a cysteine protease inhibitor. Among the progressive myoclonus epilepsies, EPM1 has the highest worldwide incidence [1]. It is clustered in Finland, with an age-standardized prevalence of 1.53/100,000 [2]. It is common in Western Mediterranean regions but has. Disease onset is in late childhood or adolescence (anywhere between the ages of 6–18 years). Myoclonus causes major disability—all EPM1 patients have involuntary action-activated or stimulus-sensitive myoclonus, which may be induced by light, sound, touch, physical exertion, or stress. A recent study showed that on average, disabling myoclonus occurred 32 years after disease onset, and cognitive impairment occurred a little later than this [5].
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