A new autosomal recessively inherited disease of the central nervous system involving childhood
epilepsy and
mental deterioration is described. Twenty three patients (11 males and 12 females) belonging to 11 families from northern Finland have been identified. A common ancestor has 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 generalised
tonic-clonic seizures increasing in frequency up to puberty. One third of the patients also had
complex partial seizures during childhood. During young adulthood the epileptic activity began to decrease, but complete remission did not occur. Electroencephalography showed progressive slowing of the background activity with relatively scanty epileptiform activity. Out of four ictal recordings the paroxysmal activity was initiated focally in two cases.
Clonazepam and
sodium valproate had some
antiepileptic effect,
clonazepam being the more beneficial 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 control, leading to
mental retardation by middle age. The pathogenesis of the disorder, called the
Northern epilepsy syndrome, is unknown. Linkage analysis using
DNA markers linked to the EPM1 gene for
progressive myoclonus epilepsy of Unverricht-Lundborg type showed that the
Northern epilepsy syndrome is not allelic to EPM1.