- Congenital onset (HP:0003577): A phenotypic abnormality that is present at birth. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Pulmonary hypoplasia (HP:0002089). Evidence: PCS. Frequency: 2/2. (PMID:21549344)
- Staring gaze (HP:0025401): An abnormality in which the eyes are held permanently wide open. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Infantile onset (HP:0003593): Onset of signs or symptoms of disease between 28 days to one year of life. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Motor delay (HP:0001270): A type of Developmental delay characterized by a delay in acquiring motor skills. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Reduced left ventricular ejection fraction (HP:0012664): A diminution of the volumetric fraction of blood pumped out of the ventricle with each cardiac cycle. Evidence: PCS. Frequency: 2/2. (PMID:21549344)
- Failure to thrive (HP:0001508): Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm. Evidence: PCS. Frequency: 2/2. (PMID:21549344)
- Death in infancy (HP:0001522): Death within the first 24 months of life. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Metabolic acidosis (HP:0001942): Metabolic acidosis (MA) is characterized by a fall in blood pH due to a reduction of serum bicarbonate concentration. This can occur as a result of either the accumulation of acids (high anion gap MA) or the loss of bicarbonate from the gastrointestinal tract or the kidney (hyperchloremic MA). By definition, MA is not due to a respirary cause. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Cytochrome C oxidase-negative muscle fibers (HP:0003688): An abnormally reduced activity of the enzyme cytochrome C oxidase in muscle tissue. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Lactic acidosis (HP:0003128): An abnormal buildup of lactic acid in the body, leading to acidification of the blood and other bodily fluids. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Hyporeflexia (HP:0001265): Reduction of neurologic reflexes such as the knee-jerk reaction. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Generalized muscle weakness (HP:0003324): Generalized weakness or decreased strength of the muscles, affecting both distal and proximal musculature. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- 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: PCS. Frequency: 2/2. (PMID:21549344)
- Cardiomegaly (HP:0001640): Increased size of the heart, clinically defined as an increased transverse diameter of the cardiac silhouette that is greater than or equal to 50% of the transverse diameter of the chest (increased cardiothoracic ratio) on a posterior-anterior projection of a chest radiograph or a computed tomography. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Feeding difficulties (HP:0011968): Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Increased circulating lactate concentration (HP:0002151): Abnormally increased level of blood lactate (2-hydroxypropanoic acid). Lactate is produced from pyruvate by lactate dehydrogenase during normal metabolism. The terms lactate and lactic acid are often used interchangeably but lactate (the component measured in blood) is strictly a weak base whereas lactic acid is the corresponding acid. Lactic acidosis is often used clinically to describe elevated lactate but should be reserved for cases where there is a corresponding acidosis (pH below 7.35). Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Decreased activity of mitochondrial complex I (HP:0011923): A reduction in the activity of the mitochondrial respiratory chain complex I, which is part of the electron transport chain in mitochondria. Evidence: PCS. Frequency: 2/2. (PMID:21549344)
- Death in childhood (HP:0003819): Death in during childhood, defined here as between the ages of 2 and 10 years. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Hypertrophic cardiomyopathy (HP:0001639): Hypertrophic cardiomyopathy (HCM) is defined by the presence of increased ventricular wall thickness or mass in the absence of loading conditions (hypertension, valve disease) sufficient to cause the observed abnormality. Evidence: PCS. Frequency: 2/2. (PMID:21549344)
- Congestive heart failure (HP:0001635): The presence of an abnormality of cardiac function that is responsible for the failure of the heart to pump blood at a rate that is commensurate with the needs of the tissues or a state in which abnormally elevated filling pressures are required for the heart to do so. Heart failure is frequently related to a defect in myocardial contraction. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- 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:21549344)
- Decreased activity of mitochondrial complex IV (HP:0008347): A reduction in the activity of the mitochondrial respiratory chain complex IV, which is part of the electron transport chain in mitochondria. Evidence: PCS. Frequency: 2/2. (PMID:21549344)
- Neonatal death (HP:0003811): Death within the first 28 days of life. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
- Increased variability in muscle fiber diameter (HP:0003557): An abnormally high degree of muscle fiber size variation. This phenotypic feature can be observed upon muscle biopsy. Evidence: PCS. Frequency: 1/2. (PMID:21549344)
These phenotypes are associated with the disease combined oxidative phosphorylation defect type 8 (OMIM:614096).