- Seizure (HP:0001250): A seizure is an intermittent abnormality of nervous system physiology characterized by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:95232)
- Thick cerebral cortex (HP:0006891). Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:95232)
- Infantile spasms (HP:0012469): Infantile spasms represent a subset of "epileptic spasms". Infantile Spasms are epileptic spasms starting in the first year of life (infancy). Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:95232)
- Progressive microcephaly (HP:0000253): Progressive microcephaly is diagnosed when the head circumference falls progressively behind age- and gender-dependent norms. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Abnormal corpus callosum morphology (HP:0001273): Abnormality of the corpus callosum. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Pachygyria (HP:0001302): Pachygyria is a malformation of cortical development with abnormally wide gyri with sulci 1,5-3 cm apart and abnormally thick cortex measuring more than 5 mm (radiological definition). See also neuropathological definitions for 2-, 3-, and 4-layered lissencephaly. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Hypoplasia of the corpus callosum (HP:0002079): Underdevelopment of the corpus callosum. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Ventriculomegaly (HP:0002119): An increase in size of the ventricular system of the brain. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Cavum septum pellucidum (HP:0002389): If the two laminae of the septum pellucidum are not fused then a fluid-filled space or cavum is present. The cavum septum pellucidum is present at birth but usually obliterates by the age of 3 to 6 months. It is up to 1cm in width and the walls are parallel. It is an enclosed space and is not part of the ventricular system or connected with the subarachnoid space. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Poor head control (HP:0002421): Difficulty to maintain correct position of the head while standing or sitting. Infant head lag is observed when the head seems to flop around or lags posteriorly behind the trunk. Several articles have maintained that head lag should be absent by age 3 to 4 months. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Tetraplegia (HP:0002445): Paralysis of all four limbs, and trunk of the body below the level of an associated injury to the spinal cord. The etiology of quadriplegia is similar to that of paraplegia except that the lesion is in the cervical spinal cord rather than in the thoracic or lumbar segments of the spinal cord. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Language impairment (HP:0002463): Language impairment is a deficit in comprehension or production of language that includes reduced vocabulary, limited sentence structure, or impairments in written or spoken communication. Language abilities are substantially and quantifiably below age expectations. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Impaired smooth pursuit (HP:0007772): An impairment of the ability to track objects with the ocular smooth pursuit system, a class of rather slow eye movements that minimizes retinal target motion. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Axial hypotonia (HP:0008936): Muscular hypotonia (abnormally low muscle tone) affecting the musculature of the trunk. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- EEG with spike-wave complexes (HP:0010850): Complexes of spikes (<70 ms) and sharp waves (70-200 ms), which are sharp transient waves that have a strong association with epilepsy, in cerebral electrical activity recorded along the scalp by electroencephalography (EEG). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Severe intellectual disability (HP:0010864): Severe intellectual disability (ID) is defined as a type of ID characterized by severely sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) the range of 20-34. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Feeding difficulties (HP:0011968): Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Dilation of Virchow-Robin spaces (HP:0012520): Increased dimensions of the Virchow-Robin spaces (also known as perivascular spaces), which surround the walls of vessels as they course from the subarachnoid space through the brain parenchyma. Perivascular spaces are commonly microscopic, and not visible on conventional neuroimaging. This term refers to an increase of size of these spaces such that they are visible on neuroimaging (usually magnetic resonance imaging). The dilatations are regular cavities that always contain a patent artery. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Neurodevelopmental delay (HP:0012758): Neurodevelopmental delay (NDD) refers to delays in the maturation of the brain and central nervous system; infants and young children with NDD may experience delays in the development of one or more skills including gross motor abilities, fine-motor coordination, language abilities and ability to solve increasingly complex problems. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Anterior predominant thick cortex pachygyria (HP:0020191): Pachygyria with cortical thickness greater than 10 mm and an anterior predominant severity gradient. The severity gradient is determined based on the gyral width, with gyri typically wider than 5mm over the more severely affected regions. Anterior predominant gradient indicates pachygyria more severe over the frontal and temporal lobes. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Delayed ability to sit (HP:0025336): A failure to achieve the ability to sit at an appropriate developmental stage. Most children sit with support at 6 months of age and sit steadily without support at 9 months of age. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Agyria (HP:0031882): A congenital abnormality of the cerebral hemisphere characterized by lack of gyrations (convolutions) of the cerebral cortex. Agyria is defined as cortical regions lacking gyration with sulci great than 3 cm apart and cerebral cortex thicker than 5 mm. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Dysgyria (HP:0032398): An abnormal gyral pattern characterized by abnormalities of sulcal depth or orientation. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Epileptic encephalopathy (HP:0200134): A condition in which epileptiform abnormalities are believed to contribute to the progressive disturbance in cerebral function. Epileptic encephalaopathy is characterized by (1) electrographic EEG paroxysmal activity that is often aggressive, (2) seizures that are usually multiform and intractable, (3) cognitive, behavioral and neurological deficits that may be relentless, and (4) sometimes early death. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:95232)
- Mild intellectual disability (HP:0001256): Mild intellectual disability (ID) is defined as a type of ID characterized by mildly sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) the range of 50-69. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Neonatal hypotonia (HP:0001319): Muscular hypotonia (abnormally low muscle tone) manifesting in the neonatal period. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Polyhydramnios (HP:0001561): The presence of excess amniotic fluid in the uterus during pregnancy. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Generalized myoclonic seizure (HP:0002123): A generalized myoclonic seizure is a type of generalized motor seizure characterized by bilateral, sudden, brief (<100 ms) involuntary single or multiple contraction of muscles or muscle groups of variable topography (axial, proximal limb, distal). Myoclonus is less regularly repetitive and less sustained than is clonus. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Opisthotonus (HP:0002179): Opisthotonus is defined as a dramatic abnormal posture due to spastic contraction of the extensor muscles of the neck, trunk, and lower extremities that produces a severe backward arching from neck to heel. In most cases, the trunk is elevated off the ground by a few inches. It is usually sudden in onset and can be sustained or repetitive. It can be considered a variant of decerebrate posturing involving a hyperextension of the neck, back, and limbs. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Profound intellectual disability (HP:0002187): Profound intellectual disability (ID) is defined as a type of ID characterized by profoundly sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) below 20. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Developmental regression (HP:0002376): Loss of developmental skills, as manifested by loss of developmental milestones. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Focal impaired awareness seizure (HP:0002384): Focal impaired awareness seizure (or focal seizure with impaired or lost awareness) is a type of focal-onset seizure characterized by some degree (which may be partial) of impairment of the person's awareness of themselves or their surroundings at any point during the seizure. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Hypsarrhythmia (HP:0002521): Hypsarrhythmia is abnormal interictal high amplitude waves and a background of irregular spikes. There is continuous (during wakefulness), high-amplitude (>200 Hz), generalized polymorphic slowing with no organized background and multifocal spikes demonstrated by electroencephalography (EEG). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Neonatal hyperbilirubinemia (HP:0003265): A type of hyperbilirubinemia with neonatal onset. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Atypical absence seizure (HP:0007270): An atypical absence seizure is a type of generalized non-motor (absence) seizure characterized by interruption of ongoing activities and reduced responsiveness. In comparison to a typical absence seizure, changes in tone may be more pronounced, onset and/or cessation may be less abrupt, and the duration of the ictus and post-ictal recovery may be longer. Although not always available, an EEG often demonstrates slow (<3 Hz), irregular, generalized spike-wave activity. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Generalized tonic seizure (HP:0010818): A generalized tonic seizure is a type of generalized motor seizure characterized by bilateral limb stiffening or elevation, often with neck stiffening without a subsequent clonic phase. The tonic activity can be a sustained abnormal posture, either in extension or flexion, sometimes accompanied by tremor of the extremities. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Atonic seizure (HP:0010819): Atonic seizure is a type of motor seizure characterized by a sudden loss or diminution of muscle tone without apparent preceding myoclonic or tonic event lasting about 1 to 2 seconds, involving head, trunk, jaw, or limb musculature. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Focal motor seizure (HP:0011153): A type of focal-onset seizure characterized by a motor sign as its initial semiological manifestation. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- EEG with changes in voltage (HP:0011201): EEG with abnormal amplitude. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Aspiration pneumonia (HP:0011951): Pneumonia due to the aspiration (breathing in) of food, liquid, or gastric contents into the upper respiratory tract. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Posterior predominant thick cortex pachygyria (HP:0020189): Pachygyria with cortical thickness above 10 mm with and a posterior predominant severity gradient. The severity gradient is determined based on the gyral width, with gyri typically wider than 5mm over the more severely affected regions. Posterior predominant gradient indicates pachygyria more severe other the occipital lobes but also includes a rare perisylvian-predominant pachygyria and a temporal predominant pachygyria. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:95232)
- Cerebellar vermis hypoplasia (HP:0001320): Underdevelopment of the vermis of cerebellum. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:95232)
- Progressive spastic quadriplegia (HP:0002478). Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:95232)
- Scoliosis (HP:0002650): The presence of an abnormal lateral curvature of the spine. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:95232)
These phenotypes are associated with the disease Lissencephaly due to LIS1 mutation (ORPHA:95232).