Disorders of metabolism principally involve an imbalance in nucleic acids, proteins, lipids, or carbohydrates. They are usually associated with either a deficiency or excess resulting in an imbalance in a particular metabolic pathway. All metabolic disorders have a genetic background, and some of them are expressed as specific genetic diseases. Metabolic processes throughout life are strongly influenced by the genetic component of aging, by diet, and by various types of environmental injury, including infectious agents (bacteria, viruses, fungi, and parasites), physical agents such as radiation and temperature, and chemical agents in the environment.