In short
Epilepsy with myoclonic-atonic seizures is a rare childhood condition that brings sudden drops and multiple types of seizures, challenging young children and their families with waves of intense seizure activity that can affect how they learn and grow.
Key points
- Epilepsy with myoclonic-atonic seizures affects one to two percent of childhood epilepsy cases and occurs two to three times more often in boys than girls.
- The condition typically begins suddenly between ages two and six in previously healthy children, though mild delays may exist before seizures start.
- Myoclonic-atonic seizures combine a brief jerk with sudden muscle limpness, causing dangerous falls or head drops that can result in injuries.
- Most children experience a "stormy phase" with multiple seizure types occurring very frequently, along with developmental setbacks in language, behavior, and motor skills.
- The underlying cause is unknown in most cases but may involve multiple genes, though specific mutations in genes like SLC6A1, CHD2, and AP2M1 have been identified in some children.
- Approximately two-thirds of children eventually achieve seizure freedom within three years, while one-third continue to face ongoing seizures and developmental challenges.
- Nonconvulsive status epilepticus, where prolonged abnormal brain activity occurs without obvious physical seizures, can cause drowsiness and impaired function lasting hours to days.
- EEG testing showing characteristic brain wave patterns is essential for diagnosis, and brain imaging is typically normal, helping distinguish this condition from other epilepsy types.
Epidemiology
Epilepsy with myoclonic-atonic seizures, also known as Doose syndrome or EMAS, is an uncommon form of childhood epilepsy that affects a small but significant number of young children worldwide. This condition accounts for approximately one to two percent of all childhood epilepsy cases, making it relatively rare in the broader spectrum of neurological conditions affecting young people.
The condition shows a clear preference for affecting boys more than girls. Medical data reveals that boys develop epilepsy with myoclonic-atonic seizures at a rate that is roughly two to three times higher than girls, with the male to female ratio ranging from 2.7 to 3.1 boys for every girl diagnosed with this condition. This gender difference is one of the distinctive features that helps doctors recognize and understand this particular epilepsy syndrome.
The typical age when children experience their first seizure from this condition falls between two and six years of age, with the peak occurrence happening around three to four years old. Some sources note that onset can occur as early as six months or as late as eight years, though these cases are less common. Before seizures begin, most children develop normally without any obvious signs of neurological problems, though a smaller portion may show mild developmental delays before their first seizure appears.
Causes
The exact cause of epilepsy with myoclonic-atonic seizures remains unknown in the majority of children who develop this condition. Researchers believe that in many cases, the disorder likely involves multiple genes working together, a pattern called polygenic inheritance, where several different genetic factors contribute to making a child more vulnerable to developing this type of epilepsy.
In some cases, scientists have identified specific genetic mutations that can cause this epilepsy syndrome. The most common single-gene causes include changes in genes called SLC6A1, CHD2, and AP2M1. Other genetic variations that have been reported in children with this condition involve genes such as SLC2A1, SCN1A, SYNGAP1, KCNA2, and NEXMIF. When a specific genetic cause is identified, it helps doctors understand why the condition occurred and can provide families with information about the likelihood of having another child with the same condition.
Understanding the underlying genetic cause can sometimes influence treatment decisions and help predict how the condition might progress over time. However, because most cases do not have an identifiable single-gene cause, the condition appears to result from a complex interaction of multiple genetic and possibly environmental factors that are not yet fully understood by medical science.
Risk Factors
Several factors can increase a child's likelihood of developing epilepsy with myoclonic-atonic seizures. One notable risk factor is having a family history of epilepsy or febrile seizures, which are seizures triggered by fever. Approximately one in four children with this condition experience simple febrile seizures before the onset of their epilepsy syndrome, suggesting that children who have had fever-related seizures may be at somewhat higher risk.
Being male is itself a clear risk factor, as boys are significantly more likely than girls to develop this condition. The reason for this gender difference is not completely understood but may relate to how the developing brain responds to genetic and environmental triggers during early childhood.
Children who carry specific genetic mutations in the genes mentioned earlier face a higher risk of developing this epilepsy syndrome. However, even when these genetic changes are present, not every child will necessarily develop the full syndrome, indicating that other factors also play a role in whether the condition manifests.
Symptoms
The hallmark symptom of epilepsy with myoclonic-atonic seizures is the myoclonic-atonic seizure itself, which gives the condition its name. These distinctive seizures begin with a brief, sudden jerk of the muscles, known as the myoclonic component. This is immediately followed by a loss of muscle tone, called the atonic component, which causes the muscles to go limp. The combination of these two movements can result in dramatic and dangerous falls to the ground or more subtle downward movements of the head onto the chest, often called head drops.
Children with this condition typically experience multiple types of seizures, not just myoclonic-atonic ones. The first seizure that occurs is usually a generalized tonic-clonic seizure, also known as a grand-mal seizure. These seizures cause the entire body to stiffen briefly and then shake rhythmically. After days or months following the first seizure, additional seizure types begin to appear with increasing frequency, including myoclonic seizures (brief jerking movements), atonic seizures (sudden drops due to loss of muscle tone), and atypical absence seizures (staring or unresponsiveness).
Many children enter what doctors call the "stormy phase," a period when seizures become very frequent and multiple seizure types occur together. During this challenging time, children may experience dozens or even hundreds of seizures in a single day. This intense seizure activity can be exhausting for both the child and their caregivers, and often requires urgent medical attention and treatment adjustments.
A particularly concerning symptom is nonconvulsive status epilepticus, a condition where abnormal brain electrical activity continues for a prolonged period without the obvious physical signs of a seizure like jerking or shaking. During these episodes, children may appear drowsy, have difficulty walking, show erratic muscle movements, and be less responsive than usual. These episodes can last for hours or even days if not recognized and treated.
Developmental setbacks represent another major symptom of this condition. When seizures begin, most children have normal or only mildly delayed development. However, as the epilepsy progresses, many children experience regression, meaning they lose skills they had previously mastered, or developmental plateau, where they fail to gain new abilities at the expected rate. Parents may notice their child losing language skills, having more difficulty with balance and coordination, showing changes in behavior, experiencing sleep problems, or struggling with tasks that require planning and organization.
Some children with this condition may also develop brief tonic seizures, which cause stiffening of the whole body and can result in falls. Additionally, absence seizures (petit-mal seizures) may occur, causing episodes of staring, unresponsiveness, or slow responses that can be mistaken for daydreaming or not paying attention.
Prevention
Because the exact causes of epilepsy with myoclonic-atonic seizures remain largely unknown and the condition appears to have strong genetic components, there are no proven methods to prevent the syndrome from developing in susceptible children. The genetic factors involved are typically present from birth, and in many cases occur as new mutations that cannot be predicted or prevented with current medical knowledge.
For families who have had one child diagnosed with this condition, genetic counseling can be valuable. Genetic testing can sometimes identify whether a specific gene mutation is responsible for the epilepsy. If a genetic cause is found and it occurred as a new mutation in the affected child rather than being inherited from a parent, the risk of having another child with the same condition may be lower than if one parent carries the genetic change.
While the onset of the epilepsy syndrome itself cannot be prevented, early recognition and treatment of seizures can potentially reduce the severity of the stormy phase and may help minimize developmental setbacks. Parents and caregivers who notice unusual movements, sudden falls, head drops, or periods of unresponsiveness in young children should seek medical evaluation promptly.
Once a child is diagnosed with epilepsy with myoclonic-atonic seizures, preventing injury from falls becomes an important focus. Because the condition causes sudden drops, protective measures such as wearing helmets, removing sharp furniture corners, and supervising activities can help reduce the risk of head injuries and other trauma from seizure-related falls.
Pathophysiology
Epilepsy with myoclonic-atonic seizures involves abnormal electrical activity in the brain that disrupts normal neurological function. In this condition, the seizures are generalized, meaning they affect the whole brain rather than just one specific area. This widespread brain involvement explains why children experience sudden loss of muscle control affecting their entire body rather than just one limb or one side.
The characteristic myoclonic-atonic seizure occurs when neurons in the brain fire abnormally in two distinct phases. First, a brief burst of excessive electrical activity causes the myoclonic jerk, where muscles suddenly contract. This is immediately followed by a second phase where electrical activity is suddenly inhibited or suppressed, causing the atonic component where muscles lose their tone and go limp. These rapid changes in brain electrical patterns, happening within fractions of a second, explain the distinctive two-part nature of the seizures.
The developmental setbacks that many children experience appear to be related to the ongoing abnormal electrical activity in the brain, even between obvious seizures. The brain activity of children with this condition can be continuously disrupted by electrical disturbances that interfere with normal learning, memory formation, and skill development. This is why controlling seizures quickly and effectively is considered crucial for protecting a child's developmental progress.
In nonconvulsive status epilepticus, the brain experiences prolonged abnormal electrical discharges that don't produce obvious physical seizure symptoms but significantly impair consciousness and brain function. During these episodes, the normal communication between different brain regions is disrupted, leading to drowsiness, confusion, and impaired motor coordination. These prolonged periods of abnormal brain activity can contribute to the cognitive and behavioral difficulties that some children with this condition experience.
