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Medium chain acyl-CoA dehydrogenase deficiency is a fatty acid oxidation disorder in which people have problems breaking down fat into energy for the body. It is caused by an enzyme that does not work properly. MCADD occurs when an enzyme, called medium chain acyl-CoA dehydrogenase, is either missing or not working properly. This enzyme’s job is to break down certain fats in food into energy. It also breaks down fat already stored in the body. Energy from fat keeps us going whenever our bodies run low of their main source of energy, a type of sugar called glucose. Our bodies rely on fat when we don’t eat for a stretch of time – like when we miss a meal or when we sleep.When the medium chain acyl-CoA dehydrogenase enzyme is missing or not working well, the body cannot use certain types of fat for energy, and must rely solely on glucose. Although glucose is a good source of energy, there is a limited amount available. Once the glucose has been used up, the body tries to use fat without success. This leads to low blood sugar, called hypoglycemia, and to the build up of harmful substances in the blood, which can lead to metabolic crises. Symptoms often happen after having nothing to eat for more than a few hours. Hypoglycemia can occur, with or without other symptoms of metabolic crisis, just by going too long without food. Hypoglycemia can cause a person to feel weak, shaky, or dizzy, and to have clammy, cold skin. If not treated, hypoglycemia can lead to coma and even death.