Overview of amino acid metabolism disorders

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Amino acid metabolism disorders are hereditary metabolic disorders. Hereditary disorders occur when parents pass the defective genes that cause these disorders on to their children. In most hereditary metabolic disorders, both parents of the affected child carry a copy of the abnormal gene. Because usually two copies of the abnormal gene are necessary for the disorder to occur, usually neither parent has the disorder. Some hereditary metabolic disorders are X-linked, which means only one copy of the abnormal gene can cause the disorder in boys.
Amino acids are the building blocks of proteins and have many functions in the body. Hereditary disorders of amino acid processing (metabolism) can result from defects either in the breakdown of amino acids or in the body’s ability to get amino acids into cells. Because these disorders cause symptoms early in life, newborns are routinely screened for several common amino acid disorders. In the United States, newborns are commonly screened for

Homocystinuria
Maple syrup urine disease
Phenylketonuria
Tyrosinemia

Newborns also are screened for a number of other inherited disorders, but screening varies from state to state.