Lafora progressive myoclonus epilepsy is a brain disorder characterized by recurrent seizures (epilepsy) and a decline in intellectual function. The signs and symptoms of the disorder usually appear in late childhood or adolescence and worsen with time.

Myoclonus is a term used to describe episodes of sudden, involuntary muscle jerking or twitching that can affect part of the body or the entire body. Myoclonus can occur when an affected person is at rest, and it is made worse by motion, excitement, or flashing light (photic stimulation). In the later stages of Lafora progressive myoclonus epilepsy, myoclonus often occurs continuously and affects the entire body.

Several types of seizures commonly occur in people with Lafora progressive myoclonus epilepsy. Generalized tonic-clonic seizures (also known as grand mal seizures) affect the entire body, causing muscle rigidity, convulsions, and loss of consciousness. Affected individuals may also experience occipital seizures, which can cause temporary blindness and visual hallucinations. Over time, the seizures worsen and become more difficult to treat. A life-threatening seizure condition called status epilepticus may also develop. Status epilepticus is a continuous state of seizure activity lasting longer than several minutes.

About the same time seizures begin, intellectual function starts to decline. Behavioral changes, depression, confusion, and speech difficulties (dysarthria) are among the early signs and symptoms of this disorder. As the condition worsens, a continued loss of intellectual function (dementia) impairs memory, judgment, and thought. Affected people lose the ability to perform the activities of daily living by their mid-twenties, and they ultimately require comprehensive care. People with Lafora progressive myoclonus epilepsy generally survive up to 10 years after symptoms first appear.

Lafora progressive myoclonus epilepsy can be caused by mutations in either the EPM2A gene or the NHLRC1 gene. These genes provide instructions for making proteins called laforin and malin, respectively. Laforin and malin play a critical role in the survival of nerve cells (neurons) in the brain.

Studies suggest that laforin and malin work together and may have several functions. One of these is to help regulate the production of a complex sugar called glycogen, which is a major source of stored energy in the body. The body stores this sugar in the liver and muscles, breaking it down when it is needed for fuel. Laforin and malin may prevent a potentially damaging buildup of glycogen in tissues that do not normally store this molecule, such as those of the nervous system.

Researchers have discovered that people with Lafora progressive myoclonus epilepsy have distinctive clumps called Lafora bodies within their cells. Lafora bodies are made up of an abnormal form of glycogen that cannot be broken down and used for fuel. Instead, it builds up to form clumps that can damage cells. Neurons appear to be particularly vulnerable to this type of damage. Although Lafora bodies are found in many of the body's tissues, the signs and symptoms of Lafora progressive myoclonus epilepsy are limited to the nervous system.

Mutations in the EPM2A gene prevent cells from making functional laforin, while NHLRC1 gene mutations prevent the production of functional malin. It is unclear how a loss of either of these proteins leads to the formation of Lafora bodies. However, a loss of laforin or malin ultimately results in the death of neurons, which interferes with the brain's normal functions. The condition tends to progress more slowly in some people with NHLRC1 gene mutations than in those with EPM2A gene mutations.

Mutations in the EPM2A and NHLRC1 genes account for 80 percent to 90 percent of all cases of Lafora progressive myoclonus epilepsy. In the remaining cases, the cause of the condition is unknown. Researchers are searching for other genetic changes that may underlie this disease.

Normal Function

The EPM2A gene provides instructions for making a protein called laforin. Although this protein is active in cells throughout the body, it appears to play a critical role in the survival of nerve cells (neurons) in the brain.

Studies suggest that laforin has multiple functions within cells. To carry out these functions, laforin interacts with several other proteins, including malin (which is produced from the NHLRC1 gene). These proteins are part of complex networks that transmit chemical signals and break down unneeded or abnormal proteins. Additionally, laforin may act as a tumor suppressor protein, which means that it keeps cells from growing and dividing in an uncontrolled way.

Laforin and malin likely play a critical role in regulating the production of a complex sugar called glycogen. Glycogen is a major source of stored energy in the body. The body stores this sugar in the liver and muscles, breaking it down when it is needed for fuel. Researchers believe that laforin and malin may prevent a potentially damaging buildup of glycogen in tissues that do not normally store this molecule, such as those of the nervous system.

Health Conditions Related to Genetic Changes

Lafora progressive myoclonus epilepsy

More than 50 mutations in the EPM2A gene have been identified in people with Lafora progressive myoclonus epilepsy. Many of these mutations change single protein building blocks (amino acids) in the laforin protein. Other mutations delete or insert genetic material in the EPM2A gene. Almost all mutations in this gene prevent cells from producing any laforin or lead to the production of a nonfunctional version of the protein.

It is unclear how mutations in the EPM2A gene lead to the major features of Lafora progressive myoclonus epilepsy. Studies suggest that a loss of laforin prevents cells from regulating the production of glycogen. As a result, distinctive clumps called Lafora bodies form within many types of cells. Lafora bodies are made up of an abnormal form of glycogen (called polyglucosan) that cannot be broken down and used for fuel. Instead, polyglucosans build up to form clumps that can damage cells. Neurons appear to be particularly vulnerable to this type of damage. Although Lafora bodies are found in many of the body's tissues, the signs and symptoms of Lafora progressive myoclonus epilepsy are limited to the nervous system.

Researchers are uncertain how a loss of functional laforin contributes to the formation of Lafora bodies. However, a lack of this protein ultimately results in the death of neurons, which interferes with the brain's normal functions. The degeneration of neurons likely underlies the seizures, movement abnormalities, intellectual decline, and other neurological problems seen with Lafora progressive myoclonus epilepsy.

Other Names for This Gene

• epilepsy, progressive myoclonus type 2, Lafora disease (laforin)
• epilepsy, progressive myoclonus type 2A, Lafora disease (laforin)
• EPM2
• EPM2A_HUMAN
• laforin
• LD
• LDE
• MELF

Genomic Location

Normal Function

The NHLRC1 gene provides instructions for making a protein called malin. Although this protein is active in cells throughout the body, it appears to play a critical role in the survival of nerve cells (neurons) in the brain.

Malin is part of the cell machinery that breaks down (degrades) unwanted proteins within cells. The protein tags damaged and excess proteins with a molecule called ubiquitin, which serves as a signal to degrade these proteins. This process, which is known as the ubiquitin-proteasome system, acts as the cell's quality control system by disposing of damaged, misshapen, and excess proteins. This system also regulates the level of proteins involved in several critical cell activities such as the timing of cell division and growth. Malin belongs to a group of proteins in the ubiquitin-proteasome system called E3 protein-ubiquitin ligases.

Malin targets several proteins for degradation, including laforin (which is produced from the EPM2A gene). The interaction between malin and laforin likely plays a critical role in regulating the production of a complex sugar called glycogen. Glycogen is a major source of stored energy in the body. The body stores this sugar in the liver and muscles, breaking it down when it is needed for fuel. Researchers believe that malin and laforin may prevent a potentially damaging buildup of glycogen in tissues that do not normally store this molecule, such as those of the nervous system.

Health Conditions Related to Genetic Changes

Lafora progressive myoclonus epilepsy

More than 45 mutations in the NHLRC1 gene have been identified in people with Lafora progressive myoclonus epilepsy. Many of these mutations change single protein building blocks (amino acids) in the malin protein. Other mutations delete or insert genetic material in the NHLRC1 gene. Almost all mutations in this gene prevent cells from producing any malin or lead to the production of a nonfunctional version of the protein.

The most common NHLRC1 gene mutation replaces the amino acid proline with the amino acid alanine at position 69 in the malin protein (written as Pro69Ala or P69A). This mutation has been found in many affected individuals of Portuguese, Italian, and Spanish heritage. The second most common NHLRC1 gene mutation replaces the amino acid glycine with a premature stop signal in the instructions for making malin (written as Gly158Ter or G158X). This mutation has been seen in affected individuals from several different ethnic groups.

It is unclear how mutations in the NHLRC1 gene lead to the major features of Lafora progressive myoclonus epilepsy. Studies suggest that a loss of malin prevents cells from regulating the production of glycogen. As a result, distinctive clumps called Lafora bodies form within many types of cells. Lafora bodies are made up of an abnormal form of glycogen (called polyglucosan) that cannot be broken down and used for fuel. Instead, polyglucosans build up to form clumps that can damage cells. Neurons appear to be particularly vulnerable to this type of damage. Although Lafora bodies are found in many of the body's tissues, the signs and symptoms of Lafora progressive myoclonus epilepsy are limited to the nervous system.

Researchers are uncertain how a loss of functional malin contributes to the formation of Lafora bodies. However, a lack of this protein ultimately results in the death of neurons, which interferes with the brain's normal functions. The degeneration of neurons likely underlies the seizures, movement abnormalities, intellectual decline, and other neurological problems seen with Lafora progressive myoclonus epilepsy.

Other Names for This Gene

• bA204B7.2
• EPM2B
• MALIN
• MGC119262
• MGC119264
• MGC119265
• NHL repeat containing 1
• NHLC1_HUMAN

Genomic Location

A diagnosis of Lafora disease is often suspected based on the presence of characteristic signs and symptoms. Additional testing can then be ordered to confirm the diagnosis and rule out other conditions that may cause similar features. For example, a skin biopsy may be performed to detect "Lafora bodies" (clumps of abnormal glycogen that cannot be broken down and used for fuel) which are found in most people with the condition. Genetic testing for changes (mutations) in either the EPM2A gene or the NHLRC1 gene may be used to confirm the diagnosis in some cases. An EEG and an MRI of the brain are generally recommended in all people with recurrent seizures and are useful in investigating other conditions in the differential diagnosis.

The prevalence of Lafora progressive myoclonus epilepsy is unknown. Although the condition occurs worldwide, it appears to be most common in Mediterranean countries (including Spain, France, and Italy), parts of Central Asia, India, Pakistan, North Africa, and the Middle East.