- Hypsarrhythmia (HP:0002521, a Human Phenotype Ontology term): 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: PCS. Frequency: 3/3. Onset: Infantile onset (HP:0003593, a Human Phenotype Ontology term). (PMID:29394991)
- Spastic tetraplegia (HP:0002510, a Human Phenotype Ontology term): Spastic paralysis affecting all four limbs. Evidence: PCS. Frequency: 2/3. (PMID:29394991)
- Inability to walk (HP:0002540, a Human Phenotype Ontology term): Incapability to ambulate. Evidence: PCS. Frequency: 3/3. (PMID:29394991)
- Seizure (HP:0001250, a Human Phenotype Ontology term): 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: PCS. Frequency: 3/3. Onset: Infantile onset (HP:0003593, a Human Phenotype Ontology term). (PMID:29394991)
- Focal impaired awareness seizure (HP:0002384, a Human Phenotype Ontology term): 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: PCS. Frequency: 2/3. (PMID:29394991)
- Profound intellectual disability (HP:0002187, a Human Phenotype Ontology term): 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: PCS. Frequency: 3/3. (PMID:29394991)
- Global brain atrophy (HP:0002283, a Human Phenotype Ontology term): Unlocalized atrophy of the brain with decreased total brain matter volume and increased ventricular size. Evidence: PCS. Frequency: 3/3. (PMID:29394991)
- Global developmental delay (HP:0001263, a Human Phenotype Ontology term): A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age. Evidence: PCS. Frequency: 3/3. (PMID:29394991)
- Infantile onset (HP:0003593, a Human Phenotype Ontology term): Onset of signs or symptoms of disease between 28 days to one year of life. Evidence: PCS. Frequency: 3/3. (PMID:29394991)
- Myoclonic seizure (HP:0032794, a Human Phenotype Ontology term): A myoclonic seizure is a type of motor seizure characterized by 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: PCS. Frequency: 2/3. (PMID:29394991)
- EEG with burst suppression (HP:0010851, a Human Phenotype Ontology term): The burst suppression pattern in electroencephalography refers to a characteristic periodic pattern of low voltage (<10 microvolts) suppressed background and a relatively shorter pattern of higher amplitude slow, sharp, and spiking complexes. Evidence: PCS. Frequency: 1/3. Onset: Infantile onset (HP:0003593, a Human Phenotype Ontology term). (PMID:29394991)
- Epileptic spasm (HP:0011097, a Human Phenotype Ontology term): A sudden flexion, extension, or mixed extension-flexion of predominantly proximal and truncal muscles that is usually more sustained than a myoclonic movement but not as sustained as a tonic seizure. Limited forms may occur: Grimacing, head nodding, or subtle eye movements. Epileptic spasms frequently occur in clusters. Infantile spasms are the best known form, but spasms can occur at all ages. Evidence: PCS. Frequency: 3/3. (PMID:29394991)
- Hippocampal malrotation (HP:0034396, a Human Phenotype Ontology term): Hippocampal malrotation, also termed incomplete inversion of the hippocampus or hippocampal malformation, is an increasingly recognized neuroimaging finding of undetermined clinical significance. It is characterized by features including (i) Round or pyramidal shape instead of ovoid shape; (ii) Medial position of the hippocampus on the hippocampal sulcus; (iii) The collateral sulcus is excessively deep or verticalized; (iv) Fimbria located medial to the hippocampus; (v) Small or displaced fornix; (vi) Enlarged temporal horn and empty choroid fissure; (vii) Thickened subiculum; (viii) Reduced upper horizontal portion of the parahippocampal gyrus. Evidence: PCS. Frequency: 3/3. (PMID:29394991)
- Tonic seizure (HP:0032792, a Human Phenotype Ontology term): A tonic seizure is a type of motor seizure characterized by unilateral or bilateral limb stiffening or elevation, often with neck stiffening. Evidence: PCS. Frequency: 1/3. (PMID:29394991)
- Autosomal recessive inheritance (HP:0000007, a Human Phenotype Ontology term): A mode of inheritance that is observed for traits related to a gene encoded on one of the autosomes (i.e., the human chromosomes 1-22) in which a trait manifests in individuals with two pathogenic alleles, either homozygotes (two copies of the same mutant allele) or compound heterozygotes (whereby each copy of a gene has a distinct mutant allele). Evidence: PCS. (PMID:29394991)
- Epileptic encephalopathy (HP:0200134, a Human Phenotype Ontology term): 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: PCS. Frequency: 3/3. (PMID:29394991)
These phenotypes are associated with the disease developmental and epileptic encephalopathy, 60 (OMIM:617929, an entry in Online Mendelian Inheritance in Man).