Epilepsy is a disorder of the central nervous system (CNS) characterized by nerve cell activity disruption resulting in seizures. In a previous article, we introduced what seizures are and how they manifest and develop. Here in this series of the A-Z Common and Rare Types of Epilepsy, we are running through approximately 40 distinct types of the condition. It is hoped that this will act as a useful source for those looking for an introduction to the topic.

For those who are new to the series, let’s recap. Our understanding of epilepsy is still evolving but around 40 different types of epilepsy have been described thus far. Each form has a unique seizure profile. The 40 or so types of epilepsy can be grouped into 4 categories which describe the electrical activity pattern of the brain during a seizure. The categories are:

  1. Focal Epilepsy
  2. Idiopathic Generalized Epilepsy
  3. Progressive Myoclonic Syndromes
  4. Reflex Epilepsy

We covered the first two categories previously and will cover the last two here.

  1. Progressive Myoclonic Syndromes: characterized by involuntary muscle spasms and twitches that often get worse over time.

Lafora Disease

Alternative names Features Include Triggers

Lafora progressive myoclonic epilepsy, MELF, Lafora body disease, myoclonic epilepsy of Lafora and progressive myoclonic epilepsy type 2.

Occipital and/or myoclonic seizures that start in late childhood or early adolescence and worsen over time. Seizures are accompanied by changes in behavior, depression, confusion, problems with speech (dysarthria) which progress into dementia, spasticity and sometimes status epilepticus (prolonged seizure activity). This form of epilepsy is fatal. It presents in childhood or adolescence.

Motion, excitement, and flashing lights

Prevalence Genetics Brain Area Affected Prognosis

Unknown but MELF is more common in certain areas of the world.

Caused by mutations in the EPM2A gene or the NHLRC1 gene. It is an autosomal recessive disorder (see below).

Generalized to more than one part of the brain.

The life expectancy after the first symptoms appear is up to 10 years.

 

Jargon Alert!

Autosomal recessive disorder = both copies of a defective gene are required for the person to have the disease, disorder or trait.

 

Myoclonic Epilepsy with Ragged Red Fibers (MERFF)

Alternative names Features Include Triggers

Merrf syndrome.

Myoclonus (twitching muscle spasms), ataxia (limited coordination), peripheral neuropathy, generalized epileptic seizures and mitochondrial dysfunction seen as ragged-red fibers in muscle biopsies. Other MERFF symptoms can include hearing and sight loss, limited stature and heart problems.

None specific to MERFF.

Prevalence Genetics Brain Area Affected Prognosis

Rare. Exact prevalence is unknown.

Caused by mutations in the MT-TK gene in 80% of cases. Other genes have been reported but they are commonly cited in other mitochondrial disorders (see below) as well.

Generalized to more than one part of the brain.

Varies but often poor with limited life expectancy.

 

Jargon Alert!

Mitochondrial disorders = mitochondria  are the power generators of the cell. These organelles make over 90% of the body’s energy supply. If they are functioning suboptimally, the cell has less energy available to it and may die. If this occurs systemically, the body will experience organ failure. Mitochondrial disorders is the name given to an extensive group of heterogeneous diseases, including MERFF.

 

Neuronal Ceroid Lipofuscinoses (NCLs)

Alternative names Features Include Triggers

Batten disease.

Progressive intellectual and motor deterioration, seizures, and early death. Vision problems are common. NCLs are a group of inherited, neurodegenerative, lysosomal storage disorders. The clinical phenotype of NCLs are classified into four main types according to age of onset and and subgroups by the gene responsible.

None specific to NCLs.

Prevalence Genetics Brain Area Affected Prognosis

Up to 1 in 12,500 people in some populations but 2 to 4 of every 100,000 in the US.

Autosomal recessive or dominant inheritance depending on the type. There are many genes involved depending on the subtype of the disorder.

Generalized to more than one part of the brain.

Life expectancy varies with the type of the disorder but it is fatal but no cure found thus far.

 

Unverricht-Lundborg Disease

Alternative names Features Include Triggers

Baltic myoclonic epilepsy.

Increasingly severe myoclonic seizures. Within 5-10 years, symptoms may affect everyday activities such as walking. Tonic-clonic seizures are also common. Decreasing mental function, intention tremors and depression may develop over time. Symptoms manifest in late childhood to early adolescence.

Physical exertion, stress, light, or other stimuli.

Prevalence Genetics Brain Area Affected Prognosis

Rare.

Caused by mutations in the CSTB gene. Autosomal recessive inheritance.

Generalized to more than one part of the brain.

Life expectancy may be normal depending on the severity of the disorder and the success of treatment.

 

Sialidosis

Alternative names Features Include Triggers

Mucolipidosis. Type I, normomorphic sialidosis or cherry-red spot (macular spots) myoclonus syndrome.

This is a lysosomal storage disease. Two types (I and II) distinguished by the age at which symptoms present as well as their severity. Type I present in the teens and twenties with symptoms starting with gait and vision issues progressing to myoclonus, ataxia, tremors and seizures. Myoclonus worsens and eventually requires wheelchair use. Type II is more severe, presents at various points in baby and childhood and is further divided into three types (congenital, infantile, and juvenile)

None specific to sialidosis.

Prevalence Genetics Brain Area Affected Prognosis

Very rare. Less than 1/1,000,000 is estimated but the true incidence of sialidosis is unknown.

Mutations in the NEU1 gene causes sialidosis. Autosomal recessive inheritance.

Generalized to more than one part of the brain.

Type I has no effect on life expectancy. Congenital type II is often fatal before or shortly after birth. Those with infantile type II survive up to childhood or adolescence. Those with juvenile type II have varying life spans depending on symptoms severity.

 

Dentatorubral-Pallidoluysian Atrophy (DRPLA)

Alternative names Features Include Triggers

Haw River syndrome.

Involuntary movements, mental and emotional issues, and decreasing mental ability. Symptoms are more severe if they first appear before age 20 and can appear any time from infancy to mid-adulthood.

None specific to DRPLA.

Prevalence Genetics Brain Area Affected Prognosis

Unknown worldwide but more commonly found in Japan (1/208,000).

Caused by mutations in the ATN1 gene. Autosomal dominant disorder with worse symptoms when paternally inherited.

Generalized to more than one part of the brain.

Poor. Reduced life expectancy with prognosis depending on the gene mutations present.

 

Jargon Alert!

Autosomal dominant disorder = only one copy of a defective gene is required for the person to have the disease, disorder or trait.

 

  1. Reflex Epilepsy
Reflex Epilepsy (RE)
Alternative names Features Include Triggers

Reflex epilepsy syndrome.

This form of epilepsy is very broad.  It describes a set of conditions where the common trait is epilepsy caused only by a certain trigger (unless presenting with other forms of epilepsy).  Individuals with only this form of epilepsy will have seizures exclusively provoked by their unique trigger(s). These may external forces such as visual, sensory, auditory, somatosensory or olfactory stimuli and/or internal forces (proprioceptive stimuli, such as certain thought process). Some people may be asymptomatic.

Triggers include flashing lights of a certain frequency, hot water and reading. Unexpected noises or touch may provoke seizures although this is categorized separately as reflex myoclonic epilepsy in infancy (RMEI).

Prevalence Genetics Brain Area Affected Prognosis

Very rare at only 5% of epilepsy cases.

None that cover all forms of

May be generalized or partial (in more than one or just one part of the brain).

Very good.

 
Some takeaways:

  1. Epilepsy is a very general term that tells you very little about a person so be careful not be make any presumptions.
  2. Life expectancy can range from normal to very poor depending on the condition, response to treatment, genetic make-up and many other factors.
  3. Some forms of epilepsy are more common than others with some being mainly found in certain populations.
  4. Epilepsy may require two forms of a gene to be present (autosomal recessive) or just one (autosomal dominant).
  5. Some forms of epilepsy occurs before birth while other may develop later in life and still others may come during certain windows such as early children to late adolense.
  6. Triggers can be very specific such as reading or far more general and difficult to characterize.
  7. Symptoms may stabilize, improve or worsen over time depending on the form of the condition with some forms being lifelong and others disappearing over time.

We hope you have found this series of articles useful! Please feel free to message us with any comments or questions or leave a note below.


Article by Olwen Reina. Contact Olwen at olwen@tempobioscience.com.
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