Baltic myoclonus

Area of Science:

• Neurology
• Genetics
• Pathology

Background:

• Progressive myoclonus epilepsy (PME) without Lafora bodies is notably more prevalent in Finland, with an incidence of 1:20,000.
• This specific PME subtype follows an autosomal recessive inheritance pattern, affecting individuals typically between 6 and 15 years of age.

Purpose of the Study:

• To characterize the clinical, electrophysiological, and neuropathological features of PME without Lafora bodies in a Finnish cohort.
• To explore the potential genetic enrichment and unique characteristics of this PME subtype in the Nordic region.

Main Methods:

• Clinical case review and electroencephalogram (EEG) analysis.
• Neuropathological examination focusing on Purkinje cell loss and absence of inclusion bodies.
• Comparison with historical descriptions of similar PME cases from Estonia and Sweden.

Main Results:

• Patients present with stimulus-sensitive myoclonic jerks and grand mal seizures, progressing to gait disorders and confinement to bed within five years.
• EEG reveals generalized disturbances with spike-wave paroxysms, exacerbated by photic stimulation.
• Neuropathology is characterized by significant Purkinje cell loss without Lafora bodies; increased indican excretion suggests L-tryptophan malabsorption.

Conclusions:

• Finnish PME without Lafora bodies may represent a distinct clinical entity, potentially a 'Baltic or Nordic type' of PME, characterized by genetic enrichment in Finland.
• While Sodium valproate and clonazepam offer symptomatic relief, the disease course remains progressive, with a mean age at death around 24 years, though this appears to be increasing.
• The etiology and pathogenesis remain unknown, highlighting the need for further research into the genetic and molecular underpinnings of this PME subtype.