- Hypertonia (HP:0001276): A condition in which there is increased muscle tone so that arms or legs, for example, are stiff and difficult to move. Evidence: IEA. (OMIM:601815)
- Spastic tetraplegia (HP:0002510): Spastic paralysis affecting all four limbs. Evidence: IEA. (OMIM:601815)
- 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: PCS. (OMIM:601815)
- 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: PCS. (OMIM:601815)
- Adducted thumb (HP:0001181): In the resting position, the tip of the thumb is on, or near, the palm, close to the base of the fourth or fifth finger. Evidence: IEA. (OMIM:601815)
- Reduced 3-phosphoglycerate dehydrogenase activity (HP:0034691): Diminished activity of the enzyme 3-phosphoglycerate dehydrogenase (PGDH), which catalyzes the first step in the pathway by converting D-3-phosphoglycerate (PGA), an intermediate in glycolysis, to phosphohydroxypyruvate concomitant with the reduction of NAD+. Evidence: TAS. (OMIM:601815)
- Nystagmus (HP:0000639): Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms. Evidence: IEA. (OMIM:601815)
- Primary microcephaly (HP:0011451): Head circumference below 2 standard deviations below the mean for age and gender at birth. Evidence: PCS. (OMIM:601815)
- Developmental cataract (HP:0000519): A cataract that occurs congenitally as the result of a developmental defect, in contrast to the majority of cataracts that occur in adulthood as the result of degenerative changes of the lens. Evidence: PCS. (OMIM:601815)
- Megaloblastic anemia (HP:0001889): Anemia characterized by the presence of erythroblasts that are larger than normal (megaloblasts). Evidence: IEA. (OMIM:601815)
- Cerebral dysmyelination (HP:0007266): Defective structure and function of myelin sheaths of the white matter of the brain. Evidence: PCS. (OMIM:601815)
- 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: IEA. (OMIM:601815)
- Decreased testicular size (HP:0008734): Reduced volume of the testicle (the male gonad). Evidence: PCS. (OMIM:601815)
- Growth delay (HP:0001510): A deficiency or slowing down of growth pre- and postnatally. Evidence: IEA. (OMIM:601815)
- Thrombocytopenia (HP:0001873): A reduction in the number of circulating thrombocytes. Evidence: IEA. (OMIM:601815)
- Intellectual disability (HP:0001249): The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence. Evidence: IEA. (OMIM:601815)
These phenotypes are associated with the disease PHGDH deficiency (OMIM:601815).