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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.

Biochemical Pathway

Systems in the body that process molecules for useful purposes.


A vitamin Cofactor for carboxylase enzymes. Essential for metabolism of proteins, carbohydrates and fats.

Bipolar disease/manic depression

A psychiatric disorder marked by mood swings that range from of the lows of depression to the highs of mania, seen at the same time in some cases. Depression brings feelings of sadness, hopelessness and loss of interest in the activities that once brought pleasure. Mania brings a feeing of euphoria and energy, a time of great productivity. Mood shifts may only occur only a few times a year, or as often as several times a day. Sometimes referred to as manic-depressive disorder.

Branched Chain Amino Acid (BCAA)

L-Leucine, L-Isoleucine, L-Valine are essential amino acids because humans cannot survive unless they are present in the diet. They are easily converted to ATP, critical to energy and muscle metabolism. They aid in hemoglobin formation, which helps to stabilize blood sugar and lower elevated blood sugar levels. L-Leucine decreases blood sugar and boosts tissue healing, including bone. L-isoleucine is essential for hemoglobin formation and regulates blood sugar and energy levels. L-Valine acts as a natural stimulant and is involved in tissue regeneration and nitrogen balance. In urea cycle disorders, low levels of BCAA can trigger hyperammonemia.

Carbamyl phosphate synthetase deficiency

Also called CPS1 deficiency. A urea cycle disorder resulting from an enzyme deficiency of carbamyl phosphate synthetase. Caused by a mutation in the CPS1 gene.


Cardiomyopathy is a group of chronic disorders affecting the muscle of the heart resulting in impairment of the pumping function of the heart.


This essential fatty acid metabolism cofactor helps to move the fatty acid to the mitochondria from the cytoplasm of the cell.


Individuals carrying an abnormal gene that can be transmitted to their offspring. These individuals do not show evidence of the disorder.


The breakdown of lean muscle mass to obtain amino acids (for growth and development) and energy, resulting from inadequate supply in the diet. Results in excess production of ammonia. Any metabolic process by which organisms convert substances into excreted compounds

Cerebral edema

Accumulation of fluid in the tissues of the brain, ultimately causing coma.


A situation or disease with a long duration.


An amino acid produced from ornithine during the normal urea cycle and subsequently transformed to arginine by the transfer of a nitrogen atom from aspartate. L-citrulline is sometimes used in place of arginine supplementation in OTC deficiency.


A urea cycle disorder which leads to excessive accumulation of ammonia and other toxins in the blood. Also known as argininosuccinate synthetase deficiency.


A Cofactor is any substance that needs to be present in addition to an enzyme to catalyze a certain reaction.

Conduct disorder

A disorder of childhood and adolescence that involves chronic behavioral and emotional problems, characterized by defiant, impulsive, or antisocial behavior.


Difficult, incomplete, or infrequent evacuation of dry hardened feces from the bowels. Can cause elevation of ammonia in UCD and PA.

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