Unverricht–Lundborg disease (abbreviated ULD or EPM1) is the most common form of an uncommon group of genetic epilepsy disorders called the progressive myoclonus epilepsies. It is caused due to a mutation in the cystatin B gene (CSTB). The disease is named after Heinrich Unverricht, who first described it in 1891, and Herman Bernhard Lundborg, who researched it in greater detail in 1901 and 1903. ULD onsets in children between the ages of 6 and 16; there are no known cases in which the person was older than 18. Most cases originate from the Baltic region of Europe, though many have been reported from countries in the Mediterranean.Onset of the disease is characterized by myoclonic jerks and tonic-clonic seizures. Early cases often resulted in the need of a wheelchair and death before the age of 24, but new treatments and medications have increased the life expectancy of individuals with ULD, in some cases even to near that of an unaffected individual. Signs and symptoms
Patients with Unverricht–Lundborg disease exhibit myoclonic jerks and tonic-clonic seizures at a young age, between ages 6–16. The myoclonic jerks occur in the muscles of the arms and legs closest to the torso, and are triggered due to a variety of common external stimuli. Seizures begin at an average age of 10.8 years, with myoclonus beginning around 12.1 years. It is not currently possible to diagnose without a genetic test, and since early symptoms are general, it is often mistaken for another more common epilepsy, in many cases juvenile myoclonic epilepsy (JME).
This research has been performed on mice with the gene for producing cystatin B removed, to provide a similar set of symptoms to individuals with ULD. The mechanism currently supported by research is very similar to another theory of epilepsy progression known as kindling. Onset
Current research links cystatin B to production of inhibitory neurons known as GABAergic neurons. It has shown that a lack of cystatin B due to a mutation of the CSTB gene leads to a decrease in the number of inhibitory neurons, and this lack of inhibition makes the cells in the brain, particularly the hippocampus, more excitable. It is hypothesized that this increase in excitability is what causes the myoclonic jerks and tonic-clonic seizures in patients with ULD. Progression
Research also gives evidence to support the idea that cystatin B may be a type of "protecting" molecule in the brain. Normally, after a seizure, the presence of cystatin B prevents the neurons from dying due to toxic levels of neurotransmitters. Studies suggest that the absence of cystatin B leads to the death of affected neurons, leading to a damaged portion of the brain. This damage coupled with the increased excitability of the cells then leads to more damage, which is what makes Unverricht–Lundborg disease progressive. Diagnosis
The only currently available method to diagnose Unverricht–Lundborg disease is a genetic test to check for the presence of the mutated cystatin B gene. If this gene is present in an individual suspected of having the disease, it can be confirmed.