Tyrosinemia—Metabolic Disorders

Metabolism is the process your body uses to get or make energy from the food you eat. Food is made up of proteins, carbohydrates, and fats. Chemicals in your digestive system break the food parts down into sugars and acids, your body’s fuel. Your body can use this fuel right away, or it can store the energy in your body tissues, such as your liver, muscles, and body fat.

A metabolic disorder occurs when abnormal chemical reactions in your body disrupt this process. When this happens, you might have too much of some substances or too little of other ones that you need to stay healthy. There are different groups of disorders. Some affect the breakdown of amino acids, carbohydrates, or lipids. Another group, mitochondrial diseases, affects the parts of the cells that produce the energy.

You can develop a metabolic disorder when some organs, such as your liver or pancreas, become diseased or do not function normally. Diabetes is an example.

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Tyrosinemia is a genetic disorder characterized by disruptions in the multistep process that breaks down the amino acid tyrosine, a building block of most proteins. If untreated, tyrosine and its byproducts build up in tissues and organs, which can lead to serious health problems.There are three types of tyrosinemia, which are each distinguished by their symptoms and genetic cause. Tyrosinemia type I, the most severe form of this disorder, is characterized by signs and symptoms that begin in the first few months of life. Affected infants fail to gain weight and grow at the expected rate (failure to thrive) due to poor food tolerance because high-protein foods lead to diarrhea and vomiting. Affected infants may also have yellowing of the skin and whites of the eyes (jaundice), a cabbage-like odor, and an increased tendency to bleed (particularly nosebleeds). Tyrosinemia type I can lead to liver and kidney failure, softening and weakening of the bones (rickets), and an increased risk of liver cancer (hepatocellular carcinoma). Some affected children have repeated neurologic crises that consist of changes in mental state, reduced sensation in the arms and legs (peripheral neuropathy), abdominal pain, and respiratory failure. These crises can last from 1 to 7 days. Untreated, children with tyrosinemia type I often do not survive past the age of 10.Tyrosinemia type II can affect the eyes, skin, and mental development. Signs and symptoms often begin in early childhood and include eye pain and redness, excessive tearing, abnormal sensitivity to light (photophobia), and thick, painful skin on the palms of their hands and soles of their feet (palmoplantar hyperkeratosis). About 50 percent of individuals with tyrosinemia type II have some degree of intellectual disability.Tyrosinemia type III is the rarest of the three types. The characteristic features of this type include intellectual disability, seizures, and periodic loss of balance and coordination (intermittent ataxia).About 10 percent of newborns have temporarily elevated levels of tyrosine (transient tyrosinemia). In these cases, the cause is not genetic. The most likely causes are vitamin C deficiency or immature liver enzymes due to premature birth.