Distribution of progressive myoclonus epilepsies in Italy; positively diagnosed and unclassified patients

Purpose: Progressive myoclonus epilepsies (PMEs) result from several genetic disorders. Few information are available about the prevalence of different PMEs. In spite of the progress in bio-molecular fields, the causative disorder remains undiagnosed in a significant fraction of the patients presenting with a PME phenotype. The aim of this study was collecting information about the frequency and geographical distribution of PMEs in Italy. Method: The Genetic Commission of the Italian League against epilepsy set up a data-base to include information dealing with PME patients referred by Italian Epilepsy Centres, including the following information: geographical origin of the parents, consanguinity, familiarity, age at the disease and myoclonus onset, general characteristics of the seizures and myoclonus and associated neurological defects, positive diagnosis, when reached. Negative results obtained in the different examinations performed during the diagnostic work-up had to be explicitly reported for the patients who didn't reach a positive diagnosis of the neurological disorder underlying the PME phenotype. Result: We collected 179 patients, including 74 with Unverricht-Lundborg disease, 33 with Lafora body disease, 25 with PME forms resulting from more rare genetic causes (neuronal ceroid-lipofuscinosis, action myoclonus renal syndrome, mitochondrial encephalopathies, other metametabolic disorders, celiac disease). Forty-seven patients were not classified, in spite of several investigations. We performed a tentative sub classification of these patients, based on details of phenotypic presentation (onset age, presence of relevant cognitive decline, seizure frequency and associated neurological signs). Conclusion: This study is expected to support further genetic studies suitable to detect new diseases giving rise to the PME phenotype.