- 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: 1/1. (PMID:23934111)
- Developmental regression (HP:0002376, a Human Phenotype Ontology term): Loss of developmental skills, as manifested by loss of developmental milestones. Evidence: PCS. Frequency: 1/1. Onset: Childhood onset (HP:0011463, a Human Phenotype Ontology term). (PMID:23934111)
- Hypoplasia of the corpus callosum (HP:0002079, a Human Phenotype Ontology term): Underdevelopment of the corpus callosum. Evidence: PCS. Frequency: 1/1. (PMID:23934111)
- 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: 1/1. (PMID:23934111)
- Cerebral visual impairment (HP:0100704, a Human Phenotype Ontology term): A form of loss of vision caused by damage to the visual cortex rather than a defect in the eye. Evidence: PCS. Frequency: 1/1. (PMID:23934111)
- 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: 1/1. (PMID:23934111)
- Hypotonia (HP:0001252, a Human Phenotype Ontology term): Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist. Evidence: PCS. Frequency: 1/1. (PMID:23934111)
- 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: 1/1. (PMID:23934111)
- Ataxia (HP:0001251, a Human Phenotype Ontology term): Ataxia refers to impaired coordination of voluntary muscle movement. Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- or overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly). Evidence: PCS. Frequency: 1/1. (PMID:23934111)
- 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: 1/1. (PMID:23934111)
- Autosomal dominant inheritance (HP:0000006, 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 heterozygotes. In the context of medical genetics, an autosomal dominant disorder is caused when a single copy of the mutant allele is present. Males and females are affected equally, and can both transmit the disorder with a risk of 50% for each child of inheriting the mutant allele. Evidence: PCS. (PMID:23934111)
These phenotypes are associated with the disease developmental and epileptic encephalopathy, 45 (OMIM:617153, an entry in Online Mendelian Inheritance in Man).