What are the genetic changes related to lactate dehydrogenase deficiency ?
Mutations in the LDHA gene cause lactate dehydrogenase-A deficiency, and mutations in the LDHB gene cause lactate dehydrogenase-B deficiency. These genes provide instructions for making the lactate dehydrogenase-A and lactate dehydrogenase-B pieces (subunits) of the lactate dehydrogenase enzyme. This enzyme is found throughout the body and is important for creating energy for cells. There are five different forms of this enzyme, each made up of four protein subunits. Various combinations of the lactate dehydrogenase-A and lactate dehydrogenase-B subunits make up the different forms of the enzyme.  The version of lactate dehydrogenase made of four lactate dehydrogenase-A subunits is found primarily in skeletal muscles, which are muscles used for movement. Skeletal muscles need large amounts of energy during high-intensity physical activity when the body's oxygen intake is not sufficient for the amount of energy required (anaerobic exercise). During anaerobic exercise, the lactate dehydrogenase enzyme is involved in the breakdown of sugar stored in the muscles (in the form of glycogen) to create additional energy. During the final stage of glycogen breakdown, lactate dehydrogenase converts a molecule called pyruvate to a similar molecule called lactate.  Mutations in the LDHA gene result in the production of an abnormal lactate dehydrogenase-A subunit that cannot attach (bind) to other subunits to form the lactate dehydrogenase enzyme. A lack of functional subunit reduces the amount of enzyme that is formed, mostly affecting skeletal muscles. As a result, glycogen is not broken down efficiently, leading to decreased energy in muscle cells. When muscle cells do not get sufficient energy during exercise or strenuous activity, the muscles become weak and muscle tissue can break down, as experienced by people with lactate dehydrogenase-A deficiency.  The version of lactate dehydrogenase made of four lactate dehydrogenase-B subunits is found primarily in heart (cardiac) muscle. In cardiac muscle, lactate dehydrogenase converts lactate to pyruvate, which can participate in other chemical reactions to create energy. LDHB gene mutations lead to the production of an abnormal lactate dehydrogenase-B subunit that cannot form the lactate dehydrogenase enzyme. Even though lactate dehydrogenase activity is decreased in the cardiac muscle of people with lactate dehydrogenase-B deficiency, they do not appear to have any signs or symptoms related to their condition. It is unclear why this type of enzyme deficiency does not cause any health problems.