NORTHERN EPILEPSY SYNDROME - AN INHERITED CHILDHOOD-ONSET EPILEPSY WITH ASSOCIATED MENTAL DETERIORATION

A new autosomal recessively inherited disease of the central nervous s ystem involving childhood epilepsy and mental deterioration is describ ed. Twenty three patients (11 males and 12 females) belonging to 11 fa milies from northern Finland have been identified. A common ancestor h as been found for nine families. The mean age of onset of epilepsy was 6.7 years (range 5-10 years) and the epilepsy was characterised by ge neralised tonic-clonic seizures increasing in frequency up to puberty. One third of the patients also had complex partial seizures during ch ildhood. During young adulthood the epileptic activity began to decrea se, but complete remission did not occur. Electroencephalography showe d progressive slowing of the background activity with relatively scant y epileptiform activity. Out of four ictal recordings the paroxysmal a ctivity was initiated focally in two cases. Clonazepam and sodium valp roate had some antiepileptic effect, clonazepam being the more benefic ial of the two. Mental development, which was originally normal, began to deteriorate two to five years after the onset of epilepsy, and the deterioration continued during adulthood in spite of good epilepsy co ntrol, leading to mental retardation by middle age. The pathogenesis o f the disorder, called the Northern epilepsy syndrome, is unknown. Lin kage analysis using DNA markers linked to the EPM1 gene for progressiv e myoclonus epilepsy of Unverricht-Lundborg type showed that the North ern epilepsy syndrome is not allelic to EPM1.