TACO1-related conditions are inherited in an autosomal recessive manner. A positive result means that a pathogenic (disease-causing) or likely pathogenic variant was found in both copies of the TACO1 gene. A carrier result means that a pathogenic or likely pathogenic variant was found in one copy of the TACO1 gene. Carriers for TACO1-related conditions usually have no symptoms of the condition.
Variants in the TACO1 gene are associated with mitochondrial complex 4 deficiency (also called cytochrome c oxidase deficiency).
Features of TACO1-related conditions may vary from person to person. Cases of mitochondrial complex 4 deficiency due to changes in the TACO1 gene are rare. Information provided below also includes features of mitochondrial complex 4 deficiency related to changes in other genes.
Mitochondrial complex 4 deficiency is a condition caused by problems with the mitochondria (the structures that provide energy in the body’s cells). Features of mitochondrial complex 4 deficiency can vary widely between affected individuals. Commonly affected parts of the body include the skeletal muscles, the heart, the brain and the liver. The severity of mitochondrial complex 4 deficiency may depend on which tissues in the body are affected with this deficiency. In some individuals, deficiency of mitochondrial complex 4 is isolated to the skeletal muscles. These individuals experience muscle weakness (myopathy), low muscle tone (hypotonia) and typically no other symptoms.
When deficiency of mitochondrial complex 4 affects the whole body it can cause severe brain issues (encephalopathy), weakened heart muscle (hypertrophic cardiomyopathy), an enlarged liver (hepatomegaly) and an increase in lactic acid in the blood (lactic acidosis) which can cause kidney disease. Renal tubular disease is often reported.
Some individuals with mitochondrial complex 4 deficiency have a specific group of features known as Leigh syndrome, a severe form of mitochondrial complex 4 deficiency characterized by progressive degeneration of the brain and dysfunction of other organs of the body including the heart, kidneys, muscles, and/or liver. In individuals with Leigh syndrome, symptoms typically appear in the first year of life and death often occurs within 2-3 years.