What are the signs and symptoms of Mitochondrial complex IV deficiency? There are currently 4 known forms of COX deficiency. The range and severity of signs and symptoms can vary widely from case to case. In one form, referred to as the benign infantile mitochondrial myopathy type, symptoms may be limited to the skeletal muscles. Episodes of lactic acidosis may occur and can cause life-threatening complications if left untreated. However, with appropriate treatment, individuals with this form of the condition may spontaneously recover within the first few years of life. In the second form of the disorder, referred to as the infantile mitochondrial myopathy type, the skeletal muscles as well as several other tissues (such as the heart, kidney, liver, brain, and/or connective tissue) are affected. Symptoms associated with this form typically begin within the first few weeks of life and may include muscle weakness; heart problems; kidney dysfunction; failure to thrive; difficulties sucking, swallowing, and/or breathing; and/or hypotonia. Affected infants may also have episodes of lactic acidosis. The third form of COX deficiency is thought to be a systemic form of the condition and is referred to as Leigh's disease. This form is characterized by progressive degeneration of the brain as well as dysfunction of several other organs including the heart, kidneys, muscles, and/or liver. Symptoms of this form, which predominantly involve the central nervous system, may begin between three months and two years of age and may include loss of previously acquired motor skills and/or head control; poor sucking ability; loss of appetite; vomiting; irritability; and possible seizures. Intellectual disability may also occur. In the fourth form of COX deficiency, the French-Canadian type, the brain (as in Leigh's disease) and liver are particularly affected in addition to the skeletal muscles and connective tissues. However, in this form, the kidneys and heart appear to have near-normal enzyme activity. Individuals with this form may have developmental delay; hypotonia; slight facial abnormalities; Leigh's disease; strabismus; ataxia; liver degeneration; and/or episodes of lactic acidosis. Although some mildly affected individuals survive into adolescence or adulthood, this condition is often fatal in childhood. The Human Phenotype Ontology provides the following list of signs and symptoms for Mitochondrial complex IV deficiency. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Aminoaciduria - Anemia - Ataxia - Autosomal recessive inheritance - Decreased activity of cytochrome C oxidase in muscle tissue - Decreased liver function - Exercise intolerance - Exertional dyspnea - Failure to thrive - Glycosuria - Hepatomegaly - Hyperphosphaturia - Hypertrophic cardiomyopathy - Increased CSF lactate - Increased hepatocellular lipid droplets - Increased intramyocellular lipid droplets - Increased serum lactate - Intellectual disability - Lactic acidosis - Mitochondrial inheritance - Motor delay - Muscular hypotonia - Optic atrophy - Pigmentary retinopathy - Proteinuria - Ptosis - Renal Fanconi syndrome - Renal tubular dysfunction - Respiratory difficulties - Respiratory insufficiency due to muscle weakness - Seizures - Sensorineural hearing impairment - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.