- Axial hypotonia (HP:0008936): Muscular hypotonia (abnormally low muscle tone) affecting the musculature of the trunk. Evidence: PCS. Frequency: 17/17. (PMID:24995870;OMIM:615905)
- Microcephaly (HP:0000252): Head circumference below 2 standard deviations below the mean for age and gender. Evidence: TAS. (OMIM:615905)
- Delayed eruption of teeth (HP:0000684): Delayed tooth eruption, which can be defined as tooth eruption more than 2 SD beyond the mean eruption age. Evidence: IEA. (OMIM:615905)
- Status epilepticus (HP:0002133): Status epilepticus is a type of prolonged seizure resulting either from the failure of the mechanisms responsible for seizure termination or from the initiation of mechanisms which lead to abnormally prolonged seizures (after time point t1). It is a condition that can have long-term consequences (after time point t2), including neuronal death, neuronal injury, and alteration of neuronal networks, depending on the type and duration of seizures. Evidence: PCS. Frequency: 5/6. (PMID:24995870)
- Absent speech (HP:0001344): Complete lack of development of speech and language abilities. Evidence: PCS. Frequency: 8/8. (PMID:24995870)
- Choreoathetosis (HP:0001266): Involuntary movements characterized by both athetosis (inability to sustain muscles in a fixed position) and chorea (widespread jerky arrhythmic movements). Evidence: PCS. Frequency: 2/8. (PMID:24995870)
- Dystonia (HP:0001332): An abnormally increased muscular tone that causes fixed abnormal postures. There is a slow, intermittent twisting motion that leads to exaggerated turning and posture of the extremities and trunk. Evidence: PCS. Frequency: 2/8. (PMID:24995870)
- Global developmental delay (HP:0001263): 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: 8/8. (PMID:24995870)
- Ataxia (HP:0001251): 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: TAS. (OMIM:615905)
- Delayed myelination (HP:0012448): Delayed myelination. Evidence: IEA. (OMIM:615905)
- Amelogenesis imperfecta (HP:0000705): A developmental dysplasia of the dental enamel. Evidence: IEA. (OMIM:615905)
- Reduced eye contact (HP:0000817): A reduced frequency or duration of eye contact. Evidence: PCS. Frequency: 2/8. (PMID:24995870)
- Multifocal seizures (HP:0031165): Seizures that start from several different areas of the brain (i.e., with multiple ictal onset locations). Evidence: TAS. (OMIM:615905)
- Limb hypertonia (HP:0002509). Evidence: PCS. Frequency: 5/7. (PMID:24995870)
- Hypodontia (HP:0000668): The absence of five or less teeth from the normal series by a failure to develop. Evidence: TAS. (OMIM:615905)
- Autosomal recessive inheritance (HP:0000007): 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:24995870)
- 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: PCS. Frequency: 8/8. (PMID:24995870)
- Spasticity (HP:0001257): A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes. Evidence: TAS. (OMIM:615905)
- Abnormal cerebral white matter morphology (HP:0002500): An abnormality of the cerebral white matter. Evidence: IEA. (OMIM:615905)
- Involuntary movements (HP:0004305): Involuntary contractions of muscle leading to involuntary movements of extremities, neck, trunk, or face. Evidence: IEA. (OMIM:615905)
- Neonatal onset (HP:0003623): Onset of signs or symptoms of disease within the first 28 days of life. Evidence: PCS. Frequency: 8/8. (PMID:24995870)
These phenotypes are associated with the disease developmental and epileptic encephalopathy, 25 (OMIM:615905).