MedGen

KCNQ2-related disorders represent a continuum of overlapping neonatal epileptic phenotypes ranging from self-limited familial neonatal epilepsy (SLFNE) at the mild end to neonatal-onset developmental and epileptic encephalopathy (NEO-DEE) at the severe end. Additional, less common phenotypes consisting of neonatal encephalopathy with non-epileptic myoclonus, infantile or childhood-onset developmental and epileptic encephalopathy (DEE), and isolated intellectual disability (ID) without epilepsy have also been described. KCNQ2-SLFNE is characterized by seizures that start in otherwise healthy infants between two and eight days after term birth and spontaneously disappear between the first and the sixth to 12th month of life. There is always a seizure-free interval between birth and the onset of seizures. Seizures are characterized by sudden onset with prominent motor involvement, often accompanied by apnea and cyanosis; video EEG identifies seizures as focal onset with tonic stiffening of limb(s) and some migration during each seizure's evolution. About 30% of individuals with KCNQ2-SLFNE develop epileptic seizures later in life. KCNQ2-NEO-DEE is characterized by multiple daily seizures beginning in the first week of life that are mostly tonic, with associated focal motor and autonomic features. Seizures generally cease between ages nine months and four years. At onset, EEG shows a burst-suppression pattern or multifocal epileptiform activity; early brain MRI can show basal ganglia hyperdensities and later MRIs may show white matter or general volume loss. Moderate-to-profound developmental impairment is present. [from GeneReviews]

KCNQ3-related disorders include self-limited familial neonatal epilepsy (SLFNE) and self-limited familial infantile epilepsy (SLFIE), seizure disorders that occur in children who typically have normal psychomotor development. An additional KCNQ3-related neurodevelopmental disorder (NDD) with and without epilepsy has also been described. In KCNQ3-SLFNE, seizures begin in an otherwise healthy infant between age days two and eight of life and spontaneously disappear within the first year of life. Seizures are generally brief, lasting one to two minutes. Seizure types include tonic or apneic episodes and focal clonic activity, with or without autonomic changes. Motor activity may be confined to one body part, migrate to other regions, or generalize. Infants are normal between seizures and feed normally. In KCNQ3-SLFIE, seizures start in the first year of life beyond the neonatal period and disappear after age one to two years. Seizures are generally brief, lasting two minutes; they appear as daily repeated clusters. Seizure types are usually focal, but can also include generalized, causing diffuse hypertonia with jerks of the limbs, head deviation, or motor arrest with unconsciousness and cyanosis. Infants are normal between seizures and psychomotor development is usually normal. In KCNQ3-NDD, individuals present with intellectual disability with or without seizures and/or cortical visual impairment. As little clinical information on these individuals is available, the clinical presentation of KCNQ3-NDD remains to be defined. [from GeneReviews]

Multiple congenital anomalies-hypotonia-seizures syndrome-2 (MCAHS2) is an X-linked recessive neurodevelopmental disorder characterized by dysmorphic features, neonatal hypotonia, early-onset myoclonic seizures, and variable congenital anomalies involving the central nervous, cardiac, and urinary systems. Some affected individuals die in infancy (summary by Johnston et al., 2012). The phenotype shows clinical variability with regard to severity and extraneurologic features. However, most patients present in infancy with early-onset epileptic encephalopathy associated with developmental arrest and subsequent severe neurologic disability; these features are consistent with a form of developmental and epileptic encephalopathy (DEE) (summary by Belet et al., 2014, Kato et al., 2014). The disorder is caused by a defect in glycosylphosphatidylinositol (GPI) biosynthesis. For a discussion of genetic heterogeneity of MCAHS, see MCAHS1 (614080). For a discussion of nomenclature and genetic heterogeneity of DEE, see 308350. For a discussion of genetic heterogeneity of GPI biosynthesis defects, see GPIBD1 (610293). [from OMIM]

KCNT1-related epilepsy is most often associated with two phenotypes: epilepsy of infancy with migrating focal seizures (EIMFS) and autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). EIMFS is characterized by seizures, typically focal and asynchronous, beginning in the first six months of life with associated developmental plateau or regression. Autonomic manifestations (e.g., perioral cyanosis, flushing, apnea) are common. Seizures are intractable to multiple anticonvulsants and progress to become nearly continuous by age six to nine months. ADNFLE is characterized by clusters of nocturnal motor seizures that vary from simple arousals to hyperkinetic events with tonic or dystonic features. Individuals with KCNT1-related ADNFLE are more likely to develop seizures at a younger age, have cognitive comorbidity, and display psychiatric and behavioral problems than individuals with ADNFLE resulting from other causes. Less common seizure phenotypes in individuals with KCNT1-related epilepsy include West syndrome, Ohtahara syndrome, early myoclonic encephalopathy, leukodystrophy and/or leukoencephalopathy, focal epilepsy, and multifocal epilepsy. Additional neurologic features include hypotonia, microcephaly developing by age 12 months, strabismus, profound developmental delay, and additional movement disorders. Other systemic manifestations including pulmonary hemorrhage caused by prominent systemic-to-pulmonary collateral arteries or cardiac arrhythmia have been reported. [from GeneReviews]

D-glyceric aciduria is a rare autosomal recessive metabolic disorder with a highly variable phenotype. Some patients have an encephalopathic presentation, with severely impaired intellectual development, seizures, microcephaly, and sometimes early death, whereas others have a mild phenotype with only mild speech delay or even normal development (summary by Sass et al., 2010). [from OMIM]

Developmental and epileptic encephalopathy-28 (DEE28) is an autosomal recessive severe neurologic disorder characterized by the onset of refractory seizures in the first months of life. Affected individuals have severe axial hypotonia and profoundly impaired psychomotor development. More severely affected patients have acquired microcephaly, poor or absent visual contact, and retinal degeneration; early death may occur (summary by Mignot et al., 2015). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Diencephalic-mesencephalic junction dysplasia syndrome-1 (DMJDS1) is an autosomal recessive neurodevelopmental disorder characterized by progressive microcephaly, severely delayed or even absent psychomotor development with profound intellectual disability, and spasticity or dystonia. Some patients may have seizures and/or visual impairment. Brain imaging shows a characteristic developmental malformation of the midbrain; subtle intracranial calcifications may also be present (summary by Aran et al., 2016 and Guemez-Gamboa et al., 2018). Genetic Heterogeneity of Diencephalic-Mesencephalic Junction Dysplasia Syndrome See also DMJDS2 (618646), caused by mutation in the GSX2 gene (616253) on chromosome 4q12. [from OMIM]

Developmental and epileptic encephalopathy-59 (DEE59) is characterized by severe global developmental delay apparent in infancy with onset of various types of seizures in the first months of life (range 3 to 11 months). The seizures are usually refractory and are often associated with hypsarrhythmia on EEG, although brain imaging is usually normal. More severely affected individuals may be unable to speak or walk, have poor interaction, and require a feeding tube (summary by the EuroEPINOMICS-RES Consortium et al., 2014). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Developmental and epileptic encephalopathy-81 (DEE81) is an autosomal recessive neurodevelopmental disorder typically characterized by onset of severe refractory seizures soon after birth or in the first months of life. Affected individuals show little developmental progress with no eye contact and no motor or cognitive development. Other features may include facial dysmorphism, such as hypotonic facies and epicanthal folds, as well as sensorineural hearing loss and peripheral neuropathy. Brain imaging shows cerebral atrophy, impaired myelination, thin corpus callosum, and progressive leukoencephalopathy (summary by Esposito et al., 2019; Maddirevula et al., 2019). For a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Autosomal dominant epilepsy with auditory features (ADEAF) is an uncommon form of epilepsy that runs in families. People with this condition typically hear sounds (auditory features), such as buzzing, humming, or ringing, during seizures. Some people hear more complex sounds, like specific voices or music, or changes in the volume of sounds. Some people with ADEAF suddenly become unable to understand language before losing consciousness during a seizure. This inability to understand speech is known as receptive aphasia. Less commonly, seizures may cause visual hallucinations, a disturbance in the sense of smell, a feeling of dizziness or spinning (vertigo), or other symptoms that affect the senses.

ADEAF is called a focal epilepsy because the seizures start in one part of the brain, rather than involving the entire brain from the beginning. Most people with ADEAF have focal aware seizures, which do not cause a loss of consciousness. These seizures are thought to begin in a part of the brain called the lateral temporal lobe. In some people, seizure activity may spread from the lateral temporal lobe to affect other regions of the brain. If seizure activity spreads to the entire brain, it causes a loss of consciousness, muscle stiffening, and rhythmic jerking. Episodes that begin as focal seizures and spread throughout the brain are known as secondarily generalized seizures.

Seizures associated with ADEAF usually begin in adolescence or young adulthood. They may be triggered by specific sounds, such as a ringing telephone or speech, but in most cases the seizures do not have any recognized triggers. In most affected people, seizures are infrequent and effectively controlled with medication. [from MedlinePlus Genetics]

Developmental and epileptic encephalopathy-66 (DEE66) is a neurologic disorder characterized by the onset of various types of seizures in the first days or weeks of life. Most seizures have focal origins; secondary generalization is common. Seizure control is difficult at first, but may become easier with time. Affected individuals show global developmental delay with hypotonia, behavioral abnormalities, and dysmorphic features or ophthalmologic defects. Brain imaging often shows cerebellar dysgenesis. A subset of patients have extraneurologic manifestations, including hematologic and distal limb abnormalities (summary by Olson et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Developmental and epileptic encephalopathy-61 (DEE61) is an autosomal recessive neurologic disorder characterized by the onset of refractory seizures in the first months or years of life. There is profound global developmental delay with intellectual disability, inability to walk, poor voluntary movements, spasticity, microcephaly, cerebral atrophy, and dysmorphic facial features (summary by Muona et al., 2016). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Facial dysmorphism, hypertrichosis, epilepsy, intellectual/developmental delay, and gingival overgrowth syndrome (FHEIG) is a neurodevelopmental disorder characterized by these cardinal features. The distinctive facial gestalt includes bushy eyebrows, long eyelashes, short philtrum, thin and everted upper lip, and prominent upper and lower vermilion. Hypertrichosis is significant and generalized, and gingival overgrowth varies in severity. Developmental delay is variable, and seizures or EEG anomalies are present (Bauer et al., 2018). [from OMIM]

Developmental and epileptic encephalopathy-106 (DEE106) is an autosomal recessive disorder characterized by the onset of various types of frequent, often refractory, seizures within the first year of life. Affected individuals demonstrate profound global developmental delay with limited ability to move and severely impaired intellectual development with absent speech. Nonspecific brain abnormalities may be observed on MRI (Ni et al., 2021). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

Developmental and epileptic encephalopathy-116 (DEE116) is an autosomal dominant disorder characterized by severe developmental delay, seizures, and white matter abnormalities but normal plasma and cerebrospinal fluid biochemistry (Jones et al., 2024). For general phenotypic information and a discussion of genetic heterogeneity of DEE, see 308350. [from OMIM]

A focal clonic seizure is a type of focal motor seizure characterized by sustained rhythmic jerking, that is regularly repetitive. [from HPO]