Abstracts

RATIONALE: Epilepsy associated with a ring chromosome 20 mosaicism (rCh20m) is considered as a rare condition and only short series have been reported in the literature yet, with a total of less than 50 cases. We present the clinical, interictal and ictal features of a series of 27 patients.
METHODS: In every patients cytogenetic analysis showed a pool of cells with a rCh20 associated with a variable proportion of normal cells. For every patients, detailed history, neurological examination, MRI, Video-EEG with seizures characterization were obtained. In most of the patients neuropsychological assessment was performed.
RESULTS: The proportion of affected lymphocytes varied from 0.5 % to 100 % in our series. None of the patients had a familial history of epilepsy ; none of the patients had any dysmorphism except in 4 cases a microcephaly ; they all had frequent episodes of non convulsive status epilepticus with a typical EEG pattern. Cognitive performances might be normal, and were very variable and not in relation with the proportion of affected cells in the karyotype, but seemed to be more correlated with the age of onset of the epilepsy. This age of onset is also very variable (from 0 to 17 years), in one case epilepsy began a few hours after birth. In most cases diagnosis was delayed because of the unusual seizures presentation and the frequent association with psychiatric behavior.
CONCLUSIONS: This syndrome is more frequent and more heterogeneous than previously reported, the main characteristic is the ability to have long lasting electro-clinical status. A very low proportion of cells may be found on the karyotype, if the history, the electro-clinical pattern is compatible, more than one hundred of mitosis must be studied.