- 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: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- 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: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- Encephalopathy (HP:0001298): Encephalopathy is a term that means brain disease, damage, or malfunction. In general, encephalopathy is manifested by an altered mental state. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- Hepatic failure (HP:0001399). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- EEG abnormality (HP:0002353): Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- Lactic acidosis (HP:0003128): An abnormal buildup of lactic acid in the body, leading to acidification of the blood and other bodily fluids. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- 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: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- Axial hypotonia (HP:0008936): Muscular hypotonia (abnormally low muscle tone) affecting the musculature of the trunk. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- Decreased activity of mitochondrial respiratory chain (HP:0008972): Decreased activity of the mitochondrial respiratory chain. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:137681)
- Hypospadias (HP:0000047): Abnormal position of urethral meatus on the ventral penile shaft (underside) characterized by displacement of the urethral meatus from the tip of the glans penis to the ventral surface of the penis, scrotum, or perineum. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Microcephaly (HP:0000252): Head circumference below 2 standard deviations below the mean for age and gender. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- 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. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- 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: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Intrauterine growth retardation (HP:0001511): An abnormal restriction of fetal growth with fetal weight below the tenth percentile for gestational age. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Premature birth (HP:0001622): The birth of a baby of less than 37 weeks of gestational age. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Hypoglycemia (HP:0001943): A decreased concentration of glucose in the blood. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Ventriculomegaly (HP:0002119): An increase in size of the ventricular system of the brain. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Hepatomegaly (HP:0002240): Abnormally increased size of the liver. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Elevated circulating hepatic transaminase concentration (HP:0002910): Elevations of the levels of SGOT and SGPT in the serum. SGOT (serum glutamic oxaloacetic transaminase) and SGPT (serum glutamic pyruvic transaminase) are transaminases primarily found in the liver and heart and are released into the bloodstream as the result of liver or heart damage. SGOT and SGPT are used clinically mainly as markers of liver damage. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Hypoalbuminemia (HP:0003073): The concentration of albumin in the blood circulation is below the lower limit of normal. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
- Thin corpus callosum (HP:0033725): An abnormally thin corpus callous, due to atrophy, hypoplasia or agenesis. This term is intended to be used in situations where it is not known if thinning of the corpus callosum (for instance, as visualized by magnetic resonance tomography) is due to abnormal development (e.g. a leukodystrophy) or atrophy following normal development (e.g. neurodegeneration). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:137681)
These phenotypes are associated with the disease Hepatoencephalopathy due to combined oxidative phosphorylation defect type 1 (ORPHA:137681).