MedGen

Episodic ataxia type 9 (EA9) is a neurologic disorder characterized by onset of ataxic episodes in the first years of life. Features may include difficulty walking, dizziness, slurred speech, headache, vomiting, and pain. The ataxic episodes vary in frequency and duration; most tend to occur every few weeks or months and last minutes to hours. Prior to the EA, most patients have neonatal- or infantile-onset tonic or generalized tonic-clonic (GTC) seizures that may be severe and refractory to medication, but remit later in infancy or early childhood, either spontaneously or concurrently with medication. Some patients have mildly delayed development with speech delay and/or autistic features or mildly impaired intellectual development. However, others show normal psychomotor development. Treatment of the ataxic episodes with acetazolamide is effective in about 50% of patients (summary by Schwarz et al., 2019). For a phenotypic description and discussion of genetic heterogeneity of episodic ataxia, see EA1 (160120). [from OMIM]

Some people with GEFS+ have seizure disorders of intermediate severity that may not fit into the classical diagnosis of simple febrile seizures, FS+, or Dravet syndrome.

Family members with GEFS+ may have different combinations of febrile seizures and epilepsy. For example, one affected family member may have only febrile seizures, while another also has myoclonic epilepsy. While GEFS+ is usually diagnosed in families, it can occur in individuals with no history of the condition in their family.

A condition called Dravet syndrome (also known as severe myoclonic epilepsy of infancy or SMEI) is often considered part of the GEFS+ spectrum and is the most severe disorder in this group. Affected infants typically have prolonged seizures lasting several minutes (status epilepticus), which are triggered by fever. Other seizure types, including afebrile seizures, begin in early childhood. These types can include myoclonic or absence seizures. In Dravet syndrome, these seizures are difficult to control with medication, and they can worsen over time. A decline in brain function is also common in Dravet syndrome. Affected individuals usually develop normally in the first year of life, but then development stalls, and some affected children lose already-acquired skills (developmental regression). Many people with Dravet syndrome have difficulty coordinating movements (ataxia) and intellectual disability.

The most common and mildest feature of the GEFS+ spectrum is simple febrile seizures, which begin in infancy and usually stop by age 5. When the febrile seizures continue after age 5 or other types of seizure develop, the condition is called febrile seizures plus (FS+). Seizures in FS+ usually end in early adolescence.

Genetic epilepsy with febrile seizures plus (GEFS+) is a spectrum of seizure disorders of varying severity. GEFS+ is usually diagnosed in families whose members have a combination of febrile seizures, which are triggered by a high fever, and recurrent seizures (epilepsy) of other types, including seizures that are not related to fevers (afebrile seizures). The additional seizure types usually involve both sides of the brain (generalized seizures); however, seizures that involve only one side of the brain (partial seizures) occur in some affected individuals. The most common types of seizure in people with GEFS+ include myoclonic seizures, which cause involuntary muscle twitches; atonic seizures, which involve sudden episodes of weak muscle tone; and absence seizures, which cause loss of consciousness for short periods that appear as staring spells. [from MedlinePlus Genetics]

Developmental and epileptic encephalopathy-11 (DEE11) is a neurologic disorder characterized by onset of seizures in the first days, weeks, or months of life. Some patients may have later onset. Seizures comprise multiple types, including tonic, generalized, and myoclonic, and tend to be refractory to medication. However, some patients with onset of seizures before 3 months of age may respond to sodium channel blockers, particularly phenytoin. About half of patients become seizure-free in childhood. Affected individuals have global developmental delay, usually with severely impaired intellectual development, although some may be less severely affected and show autism spectrum disorder. Additional common features include microcephaly, hypotonia, and abnormal movements, such as dystonia, dyskinesias, and choreoathetotic movements. Brain imaging may show white matter defects. The phenotype is highly variable, even in patients with the same mutation (summary by Ogiwara et al., 2009; Howell et al., 2015; Wolff et al., 2017). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Benign familial neonatal-infantile seizures is an autosomal dominant disorder in which afebrile seizures occur in clusters during the first year of life, without neurologic sequelae (Shevell et al., 1986). For a general phenotypic description and a discussion of genetic heterogeneity of benign familial infantile seizures, see BFIS1 (601764). [from OMIM]