Self-limited myoclonic epilepsy in infancy
This syndrome is rare. It begins when a child is between four months and three years old, usually before the child is one year old. The seizures consist of one or several brief myoclonic jerks, usually in the arm or the body. In young babies, they may look like head nodding or infantile spasms. It is hard to tell whether a baby loses consciousness as the baby usually does not stop what they are doing. If the child is older and walking, they may stop or stumble.
The baby’s development is not affected, although they may develop problems later if the seizures are not controlled. The seizures can usually be stopped with anti-seizure medications.
Epilepsy with myoclonic-atonic seizures
This syndrome usually has no apparent brain abnormality and likely has an underlying genetic component. There is some overlap between it and other early childhood epilepsy syndromes. About one-third of children with this syndrome have a family history of epilepsy. Children with this syndrome may develop other generalized seizure types later on in life.
The child usually begins having seizures when they are between two and five years old. The seizures are usually severe myoclonic seizures, which may be followed by atonic seizures and may cause the child to fall down. Occasionally, the child only has atonic seizures. They usually lose consciousness briefly during the seizure but have very little confusion afterwards. Three-quarters of people with this syndrome will have at least one generalized tonic-clonic seizure, and about one-third will have myoclonic status epilepticus.
Anti-seizure medications may or may not control seizures in this syndrome. The ketogenic diet is an effective treatment option and should be considered early for this condition. The outlook for children with this syndrome is difficult to predict, but about half have a good outcome with well-controlled seizures, and some may be able to discontinue their anti-seizure medications. About one-quarter of children will have difficult-to-control seizures throughout their lives. Additionally, children with this syndrome may be hyperactive, with a short attention span and volatile emotions.
Epilepsy with myoclonic absences
Epilepsy with myoclonic absences, like other generalized epilepsies, is likely to have no known cause, and has a probable genetic basis. Cases with an identified cause are rare. It usually begins when the child is about seven years old. The child has absence seizures with strong myoclonic jerks, usually in the shoulders, arms and legs. The seizures may last up to a minute and are longer than those seen in childhood absence epilepsy. They begin and end abruptly. They may happen while the child is asleep, causing them to wake up. In some cases, the child may have a generalized tonic-clonic seizure. Children with this syndrome often have learning disabilities and behavioural problems; about 50 per cent have some degree of developmental delay.
The syndrome is treated with anti-seizure medications, but the seizures may not respond well to treatment. The outlook for this syndrome is best if the child has few seizures, a normal EEG and no developmental delay. In some cases, as the child grows older, the absence seizures disappear and are replaced with tonic seizures.
Epilepsy with generalized tonic-clonic seizures alone
This syndrome usually begins between the ages of 11 and 20 years old. The child has generalized tonic-clonic seizures. More than 90 per cent of the time, these occur shortly after they wake up or in the evening. They may very rarely have other seizure types such as absences or myoclonic seizures, as seen in juvenile myoclonic epilepsy.
The seizures may be triggered by sleep deprivation, fatigue, alcohol, fever, menstrual cycles and flashing lights (photosensitivity).
The outlook is variable, but three-quarters of patients will require medications throughout their lives.
Generalized epilepsies with febrile seizures plus (GEFS+)
This is a group of several syndromes in which multiple members of a family may have different types of seizures. In most cases, some family members have febrile seizures, which often persist beyond the age of five years, when they would normally grow out of them. Other members of the family may have other types of seizures without fever, including generalized tonic-clonic, absence, myoclonic, atonic or even focal seizures. Only a small fraction of febrile seizures are caused by GEFS+.
GEFS+ is considered relatively benign. Most children with GEFS+ develop normally and eventually grow out of their seizures over time.
GEFS+ has been associated with various mutations on different genes, particularly the SCN1A, SCN1B and SCN2A genes, which help control sodium ion channels, and the GABRG2 gene, which helps control chloride ion channels. They are inherited in an autosomal dominant fashion, although they can also arise spontaneously. However, the mutations that have been identified account for fewer than 20 per cent of families with GEFS+; in most families, the cause is still unknown. Most cases involve complex inheritance.
Mutations on the SCN1A gene are associated with a spectrum of epilepsy syndromes, ranging from benign, such as GEFS+, to severe, such as myoclonic epilepsy in infancy or Dravet syndrome.
Genetic testing may be suggested for children and families with a strong history of seizures with or without fever. In a small proportion of cases, finding a genetic cause may help guide treatment.