Mitochondrial encephalopathy, lactic acidosis and stroke syndrome (MELAS), occurs when mitochondrial deoxyribonucleic acid (DNA) undergoes a mutation, causing insufficient energy production in cells. Patients can acquire the syndrome, but the disorder often passes from the mother. Age of onset varies, with patients exhibiting symptoms as early as three months of age, while others do not experience problems until past the age of 60. Most individuals having the syndrome do exhibit symptoms before the age of 20, however. As all bodily cells contain mitochondria, symptoms secondary to the syndrome may occur anywhere in the body, but are generally multi-system problems.
Cells typically contain hundreds to thousands of organelles known as mitochondria. The structures produce energy through an electron transport chain, which synthesizes proteins into adenosine triphosphate (ATP). DNA mutations occurring in the mitochondria disrupt different components of this chain, inhibiting ATP formation. Patients diagnosed with mitochondrial encephalopathy commonly have mitochondria containing normal DNA and others with mutated DNA. In an attempt to compensate for insufficient energy production, the abnormal mitochondria replicate into more mitochondria, which also contain the genetic mutation.
Mitochondrial cytopathy also triggers compensation for insufficient energy production by using other metabolic processes. The body generally synthesizes glucose into pyruvate and lactic acid during exercise, but in mitochondrial encephalopathy, these processes occur at rest, causing lactic acidosis. The lack of sufficient cellular energy combined with the by-products of metabolic processes produce an accumulation of toxins, which leads to cellular damage and destruction. Researchers have also discovered that patients display an abnormal amount of intracellular calcium, causing increased cellular membrane excitability.
The organs and systems most affected by the syndrome are those requiring the greatest amount of energy. Patients generally experience symptoms that affect the central nervous system, cardiac and skeletal muscles. The pancreas, liver, and kidneys can be affected as well.
Central nervous system symptoms associated with mitochondrial encephalopathy include dementia, seizures, and stroke-like abnormalities which occur as the result of lesions forming in the brain. The syndrome may also affect sensory nerves, causing blindness or deafness. Neural and muscular tissue damage, or destruction, commonly produces loss of muscle tone, spasticity, and abnormal body movements. Affected cells in the heart may cause conduction disruptions, leading to an irregular heart rate. Pancreatic involvement often leads to diabetes.
Leigh syndrome, a variety of mitochondrial myopathy that is also known as subacute necrotizing encephalomyelopathy, affects children aged 3 to 12 months and often materializes after a viral infection. In addition to affecting the central nervous system and muscular tissue, the disorder commonly involves the cardiac and respiratory systems. Young children having the disease often die by the age of three from cardiac or respiratory failure.
Specialists diagnose mitochondrial encephalopathy using imaging studies, blood and spinal fluid tests, and cellular studies. Magnetic resonance imaging (MRI) usually reveals infarct type lesions, or dead tissue, not associated with vascular structures. The lesions usually develop more frequently in the rear portion of the brain. Abnormalities in the blood and spinal fluid generally include increased levels of the amino acid alanine and lactic acid. Cells taken from muscles reveal red, ragged looking fibers.
Cell samples obtained from inside the mouth and the skin generally contain mitochondria with faulty DNA. Physicians typically treat patients on an individual basis because the symptoms vary from patient to patient and affect different body systems. Physicians often prescribe a regimen of antioxidants, amino acids, and vitamins.
