Mitochondrial diseases are very rare, estimated to affect about 200,000 individuals per year in the US. They are very interesting because they are genetic diseases—or caused by mutations—and yet differ from other types of genetic diseases. Mitochondrial dysfunction has been linked with acquired conditions such as diabetes, Huntington's disease, cancer, Alzheimer's disease, Parkinson's disease, bipolar, schizophrenia, anxiety disorders, cardiovascular disease, and sarcopenia. Mitochondrial diseases may be more severe when the defective mitochondria are present in the cerebrum or nerve cells or in muscle cells since these cells consume more energy than most other cells in the body. Brain cells are said to use twice as much energy as most body cells and three times as much energy as muscle cells. Currently, mitochondrial DNA is an extremely active area of research.