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Term Definition
ADHD (Attention deficit hyperactivity disorder)

A behavior disorder originating in childhood in which the essential characteristics are developmentally inappropriate hyperactivity, inattention, and impulsivity. The disorder can end in late adolescence or may persist into adulthood.

Amino Acids

When proteins are digested in the diet, amino acids remain - amino acids are either essential (obtained through diet) or non-essential (made by the body from the essential amino acids). Amino acids are the building blocks of proteins, which are formed by linking amino acids together in chains. Amino acids are either essential (must be consumed through the diet) or nonessential (made by the body from the essential amino acids). There are eight essential amino acids and twelve non-essential amino acids.


A by-product of protein metabolism.

Anion Gap

The difference between the sum of cations and anions found in plasma or serum. The anion gap is used to aid in the differential diagnosis of metabolic acidosis. It is calculated by subtracting the chloride and bicarbonate levels from the sodium plus potassium levels.

Anxiety disorder

A psychological disorder characterized by a persistent and disabling feeling of apprehension or fear.


A non-essential amino acid produced in the normal urea cycle by the transfer of a nitrogen atom from aspartate to citrulline. Pharmaceutical-grade arginine supplementation is used in all the urea cycle disorders except arginase deficiency, which is characterized by high levels of arginine in the blood.

Argininosuccinate (ASL) lyase deficiency

A urea cycle disorder that results in defective cleavage of ASA, leading to an accumulation of ASA in cells and an excessive excretion of ASA in urine (arginosuccinic aciduria).

Argininosuccinate or Argininosuccinic Acid

Arginosuccinic acid (ASA) an acid formed as an intermediate during the urea cycle in a reaction involving aspartic acid and adenosine triphosphate.

Argininosuccinate synthetase deficiency

A urea cycle disorder that results in accumulation of excessive ammonia and citrulline. Also called Citrullinemia.


A non-essential amino acid.


An assessment of characteristics (as in weight, measure, or quality).


Showing no symptoms, as in asymptomatic carriers for OTC deficiency.

Autosomal Recessive Inherited Disorder

A characteristic or disorder occurring when an individual receives two copies of a gene for that condition, one from the mother and one from the father.

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