Baltic myoclonus.

It has been found that PME without Lafora bodies is more common in Finland than elsewhere. The incidence is 1:20,000. The mode of inheritance is autosomal recessive. At first the children are healthy. Stimulus-sensitive myoclonic jerks and grand mal seizures appear at the age of 6 to 15 years. The EEG shows a generalized disturbance with spike-wave or polyspike-wave paroxysms which increase during photic stimulation. Myoclonic jerks incapacitate the patient. Within 5 years after the onset of the first symptoms, many patients have a disorder of gait and may become confined to bed. Sodium valproate alone or combined with clonazepam is the most effective therapy. However, the course of the disease is progressive. The mean age at death has been 24 years but appears to be increasing. The etiology and pathogenesis of PME without Lafora bodies are unknown. Increased excretion of indican has been noted, suggesting deficient intestinal absorption of L-tryptophan. A loss of Purkinje cells is the most prominent neuropathological feature. No inclusion bodies are present. Finnish PME patients are similar to the patients described by Unverricht from Estonia and by Lundborg from Sweden. Neuropathological data from these patients are not available. Clinically, these patients could form an entity with Finnish patients defined as a Baltic or Nordic type of PME. The gene is enriched in Finland, but elsewhere it is rare.