Ohtahara syndrome is rare and the earliest-appearing age-related epileptic encephalopathy, with seizure onset occurring within the first three months of life, and often in the first ten days. Many, but not all, cases of OS evolve into other seizure disorders, namely West syndrome and Lennox-Gastaut syndrome.

The primary outward manifestation of OS is seizures, usually presenting as tonic seizures (a generalized seizure involving a sudden stiffening of the limbs). Other seizure types that may occur include partial seizures, clusters of infantile spasms, and, rarely, myoclonic seizures. In addition to seizures, children with OS exhibit profound mental and physical retardation.

Clinically, OS is characterized by a "burst suppression" pattern on an EEG. This pattern involves high voltage spike wave discharge followed by little brain wave activity.

It is named for the Japanese neurologist Shunsuke Ohtahara (1930–2013), who identified it in 1976.

Ohtahara syndrome (OS), also known as early infantile epileptic encephalopathy with burst-suppression (EIEE), is a progressive epileptic encephalopathy. The syndrome is outwardly characterized by tonic spasms and partial seizures, and receives its more elaborate name from the pattern of burst activity on an electroencephalogram (EEG). It is an extremely debilitating progressive neurological disorder, involving intractable seizures and severe mental retardation. No single cause has been identified, although in many cases structural brain damage is present.

The age of onset of seizures is typically between three and five, though onset can occur at an earlier or later age. The syndrome shows clear parallels to West syndrome, enough to suggest a connection.

Daily multiple seizures are typical in LGS. Also typical is the broad range of seizures that can occur, larger than that of any other epileptic syndrome. The most frequently occurring seizure type is tonic seizures, which are often nocturnal (90%); the second most frequent are myoclonic seizures, which often occur when the person is over-tired.

Atonic, atypical absence, tonic, complex partial, focalized and tonic–clonic seizures are also common. Additionally, about half of patients will have status epilepticus, usually the nonconvulsive type, which is characterized by dizziness, apathy, and unresponsiveness. The seizures can cause sudden falling (or spasms in tonic, atonic and myoclonic episodes) and/or loss of balance, which is why patients often wear a helmet to prevent head injury.

In addition to daily multiple seizures of various types, children with LGS frequently have arrested/slowed psycho-motor development and behavior disorders.

The syndrome is also characterized by an (between-seizures) EEG featuring slow spike-wave complexes.

Benign occipital epilepsy of childhood (BOEC) is an idiopathic localization-related epilepsy and consists of an evolving group of syndromes. Most authorities include two subtypes, an early subtype with onset between three and five years, and a late onset between seven and 10 years. Seizures in BOEC usually feature visual symptoms such as scotoma or fortifications (brightly colored spots or lines) or amaurosis (blindness or impairment of vision). Convulsions involving one half the body, hemiconvulsions, or forced eye deviation or head turning are common. Younger patients typically experience symptoms similar to migraine with nausea and headache, and older patients typically complain of more visual symptoms. The EEG in BOEC shows spikes recorded from the occipital (back of head) regions. The EEG and genetic pattern suggest an autosomal dominant transmission as described by Ruben Kuzniecky, et al. Lately, a group of epilepsies termed Panayiotopoulos syndrome that share some clinical features of BOEC but have a wider variety of EEG findings are classified by some as BOEC.

The hallmark characteristic of PCDH19 gene-related epilepsy is early-onset cluster seizures that often cause cyanotic spells, which start in infancy or early childhood. The onset of the first cluster of seizures usually coincides with a fever (febrile seizures), however subsequent seizures may be febrile or afebrile. The seizure clusters are generally brief seizures, lasting 1–5 minutes, often accompanied by fearful screaming observed in 63% of girls. These cluster seizures can occur more than 10 times a day over several days, with varying amounts of time between seizure clusters.

Over time, children with PCDH19 gene-related epilepsy tend to exhibit multiple seizure types, including focal, generalized tonic-clonic, tonic, atonic, myclonus, and absence seizures. In a small study of 35 female patients with PCDH19 gene-related epilepsy, rare episodes of status epilepticus occurred in about 30% of patients in the early course of the disorder.

In PCDH19 gene-related epilepsy, the seizures are often refractory to treatment, especially in infancy and childhood. Additionally, seizures are usually characterized by persistence of cluster seizures, with variable frequency. In a study of 35 female patients with PCDH19 gene-related epilepsy, approximately 30% had become seizure free in the girl's childhood (mean age of 12 years), yet some continued into adulthood. In the same study, a few patients still had recurrent cluster seizures that evolved into status epilepticus in childhood or early adolescence.

Childhood absence epilepsy (CAE) is an idiopathic generalized epilepsy that affects children between the ages of 4 and 12 years of age, although peak onset is around five to six years old. These patients have recurrent absence seizures, brief episodes of unresponsive staring, sometimes with minor motor features such as eye blinking or subtle chewing. The EEG finding in CAE is generalized 3 Hz spike and wave discharges. Some go on to develop generalized tonic-clonic seizures. This condition carries a good prognosis because children do not usually show cognitive decline or neurological deficits, and the seizures in the majority cease spontaneously with ongoing maturation.

Beyond early-onset and treatment-resistant cluster seizures, PCDH19 gene-related epilepsy is usually, but not always, associated with cognitive and sensory impairment of varying degrees, and psychiatric and behavioral problems. It is estimated that up to 60 to 75% of the females have cognitive deficits, ranging from mild to severe intellectual disability, which do not appear to be related to frequency or severity of seizures. Development over the course of a female patients’ childhood can follow one of three courses: delays from birth that persist into adulthood, normal development and then regression, or normal intellectual development. It is not yet clear why some people experience delayed intellectual growth and others regress with epilepsy.

From the University of Melbourne study, two-thirds of PCDH19 gene-related epilepsy patients have borderline intellectual functioning or intellectual disability, while one third have normal intelligence. A connection to depression, autism, obsessive and aggressive behaviors and other disorders has been observed in PCDH19 gene-related epilepsy. Approximately 40-60% of girls diagnosed with a PCDH19 mutation are on the autism spectrum.

Many of those with PCDH19 gene mutations also exhibit behavioral and psychological problems – including ADHD, aggression, obsessive-compulsive disorder, and anxiety. Other neurological abnormalities may present, including sleep disturbances, ictal apnea, motor deficits, hypotonia, language delay, sensory integration problems and dysautonomia.

The epileptic seizures which can be observed in infants with West syndrome fall into three categories, collectively known as infantile spasms. Typically, the following triad of attack types appears; while the three types usually appear simultaneously, they also can occur independently of each other:

- "Lightning attacks": Sudden, severe myoclonic convulsions of the entire body or several parts of the body in split seconds, and the legs in particular are bent (flexor muscle convulsions here are generally more severe than extensor ones).

- "Nodding attacks": Convulsions of the throat and neck flexor muscles, during which the chin is fitfully jerked towards the breast or the head is drawn inward.

- "Salaam or jackknife attacks": a flexor spasm with rapid bending of the head and torso forward and simultaneous raising and bending of the arms while partially drawing the hands together in front of the chest and/or flailing. If one imagined this act in slow motion, it would appear similar to the Muslim ceremonial greeting (Salaam), from which this type of attack derives its name.

Epileptic spasms, also known as infantile spasms, juvenile spasms, or West syndrome is an uncommon-to-rare epileptic disorder in infants, children and adults. It is named after the English physician, William James West (1793–1848), who first described it in an article published in The Lancet in 1841. The original case actually described his own son, James Edwin West (1840–1860). Other names for it are "generalized flexion epilepsy", "infantile epileptic encephalopathy", "infantile myoclonic encephalopathy", "jackknife convulsions", "massive myoclonia" and "Salaam spasms". The term "infantile spasms" can be used to describe the specific seizure manifestation in the syndrome, but is also used as a synonym for the syndrome itself. West syndrome in modern usage is the triad of infantile spasms, a pathognomonic EEG pattern (called hypsarrhythmia), and developmental regression – although the international definition requires only two out of these three elements.

The syndrome is age-related, generally occurring between the third and the twelfth month, generally manifesting around the fifth month. There are various causes. The syndrome is often caused by an organic brain dysfunction whose origins may be prenatal, perinatal (caused during birth) or postnatal.

Lennox–Gastaut syndrome (LGS) is a childhood-onset epilepsy that most often appears between the second and sixth year of life. LGS is characterized by a triad of signs including frequent seizures of multiple types, an abnormal EEG pattern of less than 2.5 Hz slow spike wave activity, and moderate to severe intellectual impairment.

Myoclonic jerks that are not epileptic may be due to a nervous system disorder or other metabolic abnormalities that may arise in renal (e.g. hyperuraemia) and liver failure (e.g. high ammonia states).

FIRES seizures are non-focal - there is no specified starting or stopping point - making brain surgery impossible. These seizures damage cognitive abilities of the brain such as memory or sensory abilities. This can result in learning disabilities, behavioral disorders, memory issues, sensory changes, inability to move, and death. Children continue to have seizures throughout their lives.

Benign familial infantile epilepsy (BFIE), also known as benign familial infantile seizures (BFIS) or benign familial infantile convulsions (BFIC) is an epilepsy syndrome. Affected children, who have no other health or developmental problems, develop seizures during infancy. These seizures have focal origin within the brain but may then spread to become generalised seizures. The seizures may occur several times a day, often grouped in clusters over one to three days followed by a gap of one to three months. Treatment with anticonvulsant drugs is not necessary but they are often prescribed and are effective at controlling the seizures. This form of epilepsy resolves after one or two years, and appears to be completely benign. The EEG of these children, between seizures, is normal. The brain appears normal on MRI scan.

A family history of epilepsy in infancy distinguishes this syndrome from the non-familial classification (see benign infantile epilepsy), though the latter may be simply sporadic cases of the same genetic mutations. The condition is inherited with an autosomal dominant transmission. There are several genes responsible for this syndrome, on chromosomes 2, 16 and 19. It is generally described as idiopathic, meaning that no other neurological condition is associated with it or causes it. However, there are some forms that are linked to neurological conditions. One variant known as infantile convulsions and choreoathetosis (ICCA) forms an association between BFIE and paroxysmal kinesigenic choreoathetosis and has been linked to the PRRT2 gene on chromosome 16. An association with some forms of familial hemiplegic migraine (FHM) has also been found. Benign familial infantile epilepsy is not genetically related to benign familial neonatal epilepsy (BFNE), which occurs in neonates. However, a variation with seizure onset between two days and seven months called "benign familial neonatal–infantile seizures" (BFNIS) has been described, which is due to a mutation in the SCN2A gene.

Lennox–Gastaut syndrome is often associated with intellectual deficits as well as a lack of response to anti-epileptic drugs. It usually begins in the first years of life.

Reticular reflex myoclonus is a generalized form of epilepsy originating from the brain stem. Jerks associated with the disorder can affect all muscles on the body or be selective in certain areas. Jerks can be triggered by voluntary movement or be stimulus-selective.

Early myoclonic encephalopathy (EME) is an epilepsy syndrome where myoclonic seizures develop in the neonatal period. After several months, the seizure pattern may develop to infantile spasms (West syndrome). Various genetic and metabolic disorders are responsible. The seizures are resistant to treatment. The neurology is very abnormal and patients often do not live beyond one year.

Panayiotopoulos syndrome occurs exclusively in otherwise normal children and manifests mainly with infrequent autonomic epileptic seizures and autonomic status epilepticus. Onset of seizures is from age 1 to 14 years with 76% starting between 3–6 years. Autonomic seizures consist of episodes of disturbed autonomic function with nausea, retching and vomiting as predominant symptoms. Other autonomic manifestations include pallor (or, less often, flushing or cyanosis), mydriasis (or, less often, miosis), cardiorespiratory and thermoregulatory alterations, incontinence of urine and/or feces, hypersalivation, and modifications of intestinal motility. In approximately one fifth of the seizures the child becomes unresponsive and flaccid (syncope-like epileptic seizures or ictal syncope) before or often without convulsions. Syncope-like epileptic seizures (ictal syncope) with the child becoming "completely unresponsive and flaccid like a rag doll" occur in one fifth of the seizures. More-conventional seizure symptoms often appear after the onset of autonomic manifestations. The child, who was initially fully conscious, becomes confused and unresponsive. Eyes turn to one side or gaze widely open. Only half of the seizures end with brief hemiconvulsions or generalized convulsions. Autonomic symptoms may be the only features of the seizures. None of the above symptoms alone is a prerequisite for diagnosis. Recurrent seizures may not be stereotyped. The same child may have brief or prolonged seizures and autonomic manifestations may be severe or inconspicuous. The full emetic triad (nausea, retching, vomiting) culminates in vomiting in 74% of the seizures; in others only nausea or retching occur, and in a few, none of the emetic symptoms are apparent.

Most of the seizures are prolonged and half of them last more than 30 minutes thus constituting autonomic status epilepticus, which is the more common nonconvulsive status epilepticus in normal children. Characteristically, even after the most severe seizures and autonomic status epilepticus, the child is normal after a few hours of sleep, which is both diagnostic and reassuring. However, it has been recently reported that sometime after status epilepticus in children with Panayiotopoulos syndrome a. growth of the frontal and prefrontal lobes is slightly decreased and b.the scores on the neuropsychological tests is decreased.

Focal onset hemiconvulsions or generalised convulsions occur in nearly half of the seizures. These are usually shorter than the preceding autonomic manifestations but in a few cases a. they may be prolonged constituting convulsive status epilepticus or b. the preceding autonomic manifestations are brief and not apparent

Seizures can occur at any time but they are more common during sleep.

The cause of FIRES is not known. It does not happen twice in the same family, but the medical community does not know if it is genetic. It happens in boys more than girls. After the initial status, life expectancy is not affected directly. Issues such as overdose of medications or infections at a food tube site are examples of things that would be secondary to the status.

Epilepsy is most commonly recognised by involuntary movements of the head and limbs, however other characteristics include salivation, lack of and anxiety. Animals often lose consciousness and are not aware of their surroundings.

The specific and familial association of BIFE and PKC defines a novel clinical entity : the infantile convulsions and choreoathetosis syndrome. The first observation was made in four families where children were affected with nonfebrile convulsions at age 3–12 months.Partial epileptic seizures started with a psychomotor arrest and a deviation of the head and eyes to one side, followed inconstantly by unilateral jerks.In some cases, seizures generalized secondarily. None of the interictal electroencephalograms showed epileptiform abnormalities, and magnetic-resonance imaging were normal. These convulsions had a favorable outcome. At 5–8 years of age affected children developed abnormal movements. They presented with twisting movements of the hands of a reptilian type when stressed or embarrassed. They also developed jerky movements of the legs after running. Initially, abnormal movements were intermediate in speed between quick and slow, typical of paroxysmal choreoathetosis. Combinations of abnormal movements involving the arms, legs, trunk and occasionally the head were observed. The attacks lasted only a few minutes, occurring with a frequency of 5-30 episodes per day and were not accompanied by unconsciousness. In all patients, abnormal movements disappeared at 25–30 years of age without any treatment. Since the first report similar clinical presentations have been published which confirm the specificity of the ICCA syndrome.

Panayiotopoulos syndrome is now the formally approved nomenclature for this syndrome in the new International League against Epilepsy report on classification, which abandoned a number of previously used descriptive terms such as early onset benign childhood epilepsy with occipital paroxysms, early onset benign childhood occipital epilepsy, nocturnal childhood occipital epilepsy. The reason for this is that these descriptive terms were criticized as incorrect because in Panayiotopoulos syndrome:

“An autonomic seizure is an epileptic seizure characterized by altered autonomic function of any type at seizure onset or in which manifestations consistent with altered autonomic function are prominent (quantitatively dominant or clinically important) even if not present at seizure onset. The altered autonomic function may be objective or subjective or both.”

“Autonomic status epilepticus is an autonomic seizure which lasts for more than 30 minutes, or a series of such seizures over a 30 minute period without full recovery between seizures.”

There are six main types of generalized seizures: tonic-clonic, tonic, clonic, myoclonic, absence, and atonic seizures. They all involve a loss of consciousness and typically happen without warning.

- Tonic-clonic seizures present with a contraction of the limbs followed by their extension, along with arching of the back for 10–30 seconds. A cry may be heard due to contraction of the chest muscles. The limbs then begin to shake in unison. After the shaking has stopped it may take 10–30 minutes for the person to return to normal.

- Tonic seizures produce constant contractions of the muscles. The person may turn blue if breathing is impaired.

- Clonic seizures involve shaking of the limbs in unison.

- Myoclonic seizures involve spasms of muscles in either a few areas or generalized through the body.

- Absence seizures can be subtle, with only a slight turn of the head or eye blinking. The person often does not fall over and may return to normal right after the seizure ends, though there may also be a period of post-ictal disorientation.

- Atonic seizures involve the loss of muscle activity for greater than one second. This typically occurs bilaterally (on both sides of the body).

Patients diagnosed with porencephaly display a variety of symptoms, from mild to severe effects on the patient. Patients with severe cases of porencephaly suffer epileptic seizures and developmental delays, whereas patients with a mild case of porencephaly display little to no seizures and healthy neurodevelopment. Infants with extensive defects show symptoms of the disorder shortly after birth, and the diagnosis is usually made before the age of 1.

The following text lists out common signs and symptoms of porencephaly in affected individuals along with a short description of certain terminologies.

Focal seizures are often preceded by certain experiences, known as an aura. These may include: sensory, visual, psychic, autonomic, olfactory or motor phenomena.

In a complex partial seizure a person may appear confused or dazed and can not respond to questions or direction. Focal seizure may become generalized.

Jerking activity may start in a specific muscle group and spread to surrounding muscle groups—known as a "Jacksonian march". Unusual activities that are not consciously created may occur. These are known as automatisms and include simple activities like smacking of the lips or more complex activities such as attempts to pick something up.

Onset of symptoms usually occur in early adulthood and is characterized by intention tremor, progressive ataxia, convulsions, and myoclonic epileptic jerks.

Tremors usually affect one extremity, primarily the upper limb, and eventually involve the entire voluntary motor system. Overall, the lower extremity is usually disturbed less often than the upper extremity.

Additional features of the syndrome include: an unsteady gait, seizures, muscular hypotonia, reduced muscular coordination, asthenia, adiadochokinesia and errors with estimating range, direction, and force of voluntary movements. Mental deterioration can occur, however it is rare.

Watching an animal have a seizure can be quite frightening. There is not much that can be done during a seizure except to remain calm and not leave the animal alone. If your pet is having a seizure it is important to make sure they are laying down on the floor away from any water, stairs or other animals. When an animal has a seizure, do not try to grab their tongue or clear their mouth as there is a high chance you will be bitten; contrary to popular myth, neither humans nor animals can "swallow their tongue" during a seizure so it is safest to stay well away from their mouth during one. Timing seizures is also crucial. Take notes of seizures - what time they occur, how often and any other specific information which can be passed onto the vet or emergency animal clinic.