| Term | Meaning |
| Ataxia | Poor balance and lack of muscle co-ordination due to problems with the nervous system. |
| Chorionic villus sampling (CVS) | A procedure done early in pregnancy to obtain a small sample of cells from the placenta. These cells are similar to those of the developing baby (fetus). The genetic make up of the cells is analyzed to identify errors (called mutations). |
| Echocardiogram (ECHO) | An ultrasound scan to examine the heart. |
| Electroencephalogram (EEG) | A test to check the electrical activity of the brain and detect seizures. |
| Forearm exercise test | An exercise test that involves blood tests during exercise and rest to measure ammonia and lactate levels. Also called forearm ischemic test. |
| Hypotonia | Decreased muscle tone. Babies with hypotonia seem floppy, like a rag doll, when held. |
| Lumbar puncture | A diagnostic test to measure the pressure in the spinal column and take a sample of the fluid that surrounds the brain and spinal cord (cerebrospinal fluid or CSF). Also called a spinal tap. |
| Magnetic resonance imaging and scanning (MRI and MRS) | A diagnostic test using a powerful magnet and radio waves to see inside the body. This test can detect signs of Mitochondrial disease in the brain. |
| Metabolism | The chemical reactions in the body that make energy. As mitochondria make 90% of the energy needed by the body, they are an important part of metabolism. As Mitochondrial disease affects metabolism, it is called a metabolic disease. |
| Mitochondria | Tiny structures inside every cells of the body (except red blood cells) where energy is produced. Almost all of the energy the body needs for life and growth comes from mitochondria. A single one is called a mitochondrion. |
| Muscle biopsy | A procedure to obtain a tiny sample of muscle for testing. |
| Mutation | A specific change or error in a gene. |
| Pulmonary function test (PFT) | A group of tests that measure how well the lungs are working. Tests measure how well the lungs take in and exhale air and how efficiently they transfer oxygen from air into the blood. |
| Urine organic acids | A urine test to check for metabolic disorders present at birth (called inborn errors of metabolism). |
| VO2 MAX | The amount (volume) of oxygen (O2) used when a person is exercising as much as possible (maximum capacity). The VO2MAX indicates a person’s fitness level. People with Mitochondrial disease have a low VO2MAX, even lower than that of people with inactive (sedentary) lives. |
