Abstracts

Rationale: Chromosomal abnormalities are often associated with mental retardation, dysmorphic features and seizures. Interstitial deletions of the long arm of chromosome 6 (chr 6q) are relatively rare, and usually not associated with epilepsy. Adult onset myoclonus has not been reported, to our knowledge. Methods: A 30-year-old patient had a history of a single febrile seizure at the age of 8 months. He had mild to moderate developmental delay, dysmorphic features and no further history of seizures. In his late twenties, he developed jerky movements with some features of low amplitude myoclonus and a possible intentional component. Detailed examination and family history was performed. The patient had prolonged day and night telemetry recording, as well as MRI studies. Karyotype was performed, as well as FISH studies and array comparative genomic hybridization (array CGH) Results: On examination, the patient has mild dysmetria and frequent myoclonic jerks involving the upper extremities. According to the parents, there has been no evidence of recent cognitive deterioration. Prolonged video-telemetry revealed extremely frequent myoclonic jerks arising from the right or left upper extremity, with occasional eye closure and head deviation, at times occurring in small runs. Some of these jerks were elicited by startle, and some involved axial musculature as well. The jerks were associated with muscle artifact on the EEG, but no epileptiform abnormality was noted during these events or interictally. Background rhythm showed mild to moderate persistent dysfunction of cerebral activity. MRI showed mild cerebellar vermian atrophy or hypoplasia with slight dilatation of the fourth ventricle. Karyotype revealed a subtle interstitial deletion of chr 6q. This was at the limit of detection at the level of resolution obtained by conventional cytogenetics. Array CGH employing an oligonucleotide array confirmed a deletion of chr 6q at 6q21-6q22.31. The extent of the deletion is estimated to be 7.6 Mb. Family history revealed no neurological disorders except for a few distant relatives on the paternal side with developmental delay or mental retardation Conclusions: Although deletions of chromosome 6q are usually not associated with epilepsy, one patient with a different deletion had intractable seizures. Phenotypic variation is in large part due to differences in size and location of the segmental aneuploidy. The exact deletion described in our patient has not been reported previously, to our knowledge. However, overlapping deletions without a history of seizures or myoclonus have been described. Thus the relationship between the patient’s late-onset myoclonus and the deletion must await further reports of similar deletions. The patient does not have evidence for progressive myoclonus epilepsy, although Kufs’ disease cannot be entirely ruled out