Generalized epilepsy syndromes include seizures with myoclonic and tonic features. They can be idiopathic, cryptogenic or symptomatic.
Benign 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 or not a baby loses consciousness; the baby usually does not stop what they are doing, but if they are 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-epileptic drugs.
Epilepsy with myoclonic astatic seizures
This syndrome may be idiopathic or symptomatic, and 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 another idiopathic generalized epilepsy syndrome, such as juvenile myoclonic epilepsy, later on.
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 has 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-epileptic drugs may or may not control seizures in this syndrome. 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-epileptic drugs. Children with this syndrome may be hyperactive, with a short attention span and volatile emotions.
Epilepsy with myoclonic absences
Epilepsy with myoclonic absences may be idiopathic, cryptogenic, or rarely symptomatic. 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% have some degree of developmental delay.
The syndrome is treated with anti-epileptic drugs, 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 atypical absence seizures or tonic seizures.
Epilepsy with generalized tonic-clonic seizures on awakening
This syndrome usually begins between the ages of 11 and 20. The child has generalized tonic-clonic seizures. More than 90% of the time, these occur shortly after they wake up or in the evening. They may have other seizure types as well; these are usually absence seizures or myoclonic seizures, as seen in juvenile myoclonic epilepsy.
The seizures may be triggered by sleep deprivation and other factors, including photosensitivity.
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 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 partial 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.
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% 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 GEFS+ to severe myoclonic epilepsy in infancy (Dravet syndrome). Rarely, they are associated with familial migraine.
Genetic testing may be suggested for children and families with a strong history of seizures with or without fever.