- Bilateral tonic-clonic seizure (HP:0002069): A bilateral tonic-clonic seizure is a seizure defined by a tonic (bilateral increased tone, lasting seconds to minutes) and then a clonic (bilateral sustained rhythmic jerking) phase. Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Hypermelanotic macule (HP:0001034): A hyperpigmented circumscribed area of change in normal skin color without elevation or depression of any size. Evidence: TAS. (OMIM:609056)
- Hearing impairment (HP:0000365): A decreased magnitude of the sensory perception of sound. Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:609056)
- Global brain atrophy (HP:0002283): Unlocalized atrophy of the brain with decreased total brain matter volume and increased ventricular size. Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Hypotonia (HP:0001252): 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: 8/8. (PMID:15502825)
- Infantile onset (HP:0003593): Onset of signs or symptoms of disease between 28 days to one year of life. Evidence: PCS. (PMID:15502825)
- Multifocal epileptiform discharges (HP:0010841): An abnormality in cerebral electrical activity recorded along the scalp by electroencephalography (EEG) and being identified at multiple locations (foci). Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Failure to thrive (HP:0001508): Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm. Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Cerebral visual impairment (HP:0100704): A form of loss of vision caused by damage to the visual cortex rather than a defect in the eye. Evidence: PCS. (PMID:15502825)
- Irritability (HP:0000737): An emotional state characterized by negative feelings of heightened frustration, annoyance, or feeling upset, often triggered by internal factors (e.g., fatigue, hunger, unfulfilled desires) or external factors (e.g., social or environmental challenges). Irritability may be unpredictable, and is accompanied by a lowered threshold for emotional reactivity and observable features (speech, facial expressions, or psychomotor activity). Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Feeding difficulties in infancy (HP:0008872): Impaired feeding performance of an infant as manifested by difficulties such as weak and ineffective sucking, brief bursts of sucking, and falling asleep during sucking. There may be difficulties with chewing or maintaining attention. Evidence: PCS. Frequency: 6/8. (PMID:15502825)
- Hyporeflexia of upper limbs (HP:0012391): Reduced intensity of muscle tendon reflexes in the upper limbs. Reflexes are elicited by stretching the tendon of a muscle, e.g., by tapping. Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Neonatal onset (HP:0003623): Onset of signs or symptoms of disease within the first 28 days of life. Evidence: PCS. (PMID:15502825)
- Developmental stagnation at onset of seizures (HP:0006834): A cessation of the development of a child in the areas of motor skills, speech and language, cognitive skills, and social and/or emotional skills, following the onset of epilepsy. Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Visual loss (HP:0000572): Loss of visual acuity (implying that vision was better at a certain time point in life). Otherwise the term reduced visual acuity should be used (or a subclass of that). Evidence: IEA. (OMIM:609056)
- Microcephaly (HP:0000252): Head circumference below 2 standard deviations below the mean for age and gender. Evidence: TAS. Frequency: Occasional (HP:0040283). (OMIM:609056)
- Absent speech (HP:0001344): Complete lack of development of speech and language abilities. Evidence: IEA. (OMIM:609056)
- 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: TAS. (OMIM:609056)
- 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. (PMID:15502825)
- Developmental regression (HP:0002376): Loss of developmental skills, as manifested by loss of developmental milestones. Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Vomiting (HP:0002013): Forceful ejection of the contents of the stomach through the mouth by means of a series of involuntary spasmic contractions. Evidence: PCS. Frequency: 8/8. (PMID:15502825)
- Lower limb hyperreflexia (HP:0002395): Increased intensity of the a reflex in the leg. Evidence: PCS. (PMID:15502825)
- 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:15502825)
- 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:15502825)
- Optic atrophy (HP:0000648): Atrophy of the optic nerve. Optic atrophy results from the death of the retinal ganglion cell axons that comprise the optic nerve and manifesting as a pale optic nerve on fundoscopy. Evidence: IEA. (OMIM:609056)
- Myoclonus (HP:0001336): Very brief, involuntary random muscular contractions occurring at rest, in response to sensory stimuli, or accompanying voluntary movements. Evidence: IEA. (OMIM:609056)
These phenotypes are associated with the disease GM3 synthase deficiency (OMIM:609056).