Unlike digestive disorders, which often are caused by lifestyle or develop over time, metabolic disorders are genetic. Such disorders occur due to rare mutations (changes) on various single genes. These genes all produce enzymes or proteins that assist in the metabolism of various substances. The gene affected determines the disorder. The kind of mutation and whether both parents have contributed identical genes determine its severity. They are not caused by chromosomal error, as is Down syndrome, or errors in fetal development, as is spina bifida. They are also not environmental or caused by a bacteria or virus and cannot be contracted later in life, though some do not appear until later in life. Mutations in each parent’s DNA are passed on to a child who then has these mutations present in every cell of his or her body.
Humans consume a wide variety of foods but they all break down into one of three substances in the body: glucose, amino acids, or fatty acids. There are disorders of glucose metabolism and amino acid metabolism as well as fat metabolism. They are all metabolic disorders. The moment a person takes a bite or a drink, the body starts breaking the substance down into its component parts, separating out the three fuels it can use from any water and bulk it cannot use. The digestive tract handles the excess water and bulk and the energy in any of its three forms, travels throughout the body in the blood for further metabolism in the organs, such as the liver, and in the mitochondria of the cells.
The most accessible fuel is glucose, which comes from carbohydrates. The glucose becomes immediately available following metabolism. This quick energy is not stored efficiently in the body and is gone within hours of consumption. Metabolic disorders in this process are called glycogen storage diseases (GSDs).
Protein disorders include phenylketonuria (PKU), one of the first genetic disorders to be tested in newborns. Proteins have many functions in the body but are not an efficient fuel for energy.
Fat or fatty acids play an important role in both energy storage and major organ health. Fatty acids also act as messengers, helping proteins do their work in the body. When any of the genes that control fat metabolism have errors, serious problem can result.