Term Glossary

  • A
  • B
  • C
  • D
  • E
  • F
  • H
  • I
  • L
  • M
  • N
  • O
  • P
  • R
  • S
  • T
  • U
  • V
  • W
  • X

Abnormal: Differing from normal.

Accumulation: The process of acquiring more or the build-up of a substance.

Ammonia: A product of protein digestion.

Amino Acids: Amino acids combine to form proteins and when proteins are digested amino acids remain – amino acids are either essential (obtained through the diet) or non-essential (made by the body from the essential amino acids).

Amniocytes: Cells in the amniotic fluid surrounding the fetus before birth.

Amniotic Fluid: The fluid surrounding the fetus inside the uterus.

Analysis: Examination to discover characteristics or meanings.

Anorexia: Loss of appetite.

Arginine: Non-essential Amino Acid (made only by the urea cycle).

Argininosuccinate or Argininosuccinic Acid: A molecule made by the urea cycle.

Aspartate: Non-essential Amino Acid (made only by the urea cycle).

Assay: Assessment of characteristics (as weight, measure, or quality).

Athetosis: Repeated slow movements especially of the arms and legs due to brain dysfunction.

Autosomal Recessive Inherited Disorder: Two copies of an abnormal gene inherited from both parents that is capable of producing disease, specifically on one of 22 pairs of autosomes (non-sex linked).

Autosomes: Any of the non-sex determining chromosomes.

Biochemical Pathways: Systems in the body for processing molecules for useful purposes.

Biopsy: The removal of blood, tissue, or cells from the body for examination.

Bouts: An episode, an intermittent occurrence of an abnormal condition.

Carrier: Individuals with one abnormal gene in their gene pair. These individuals do not show evidence of the disorder.

Chronic (or Chronically): A situation or disease with a long duration.

Citrulline: An Amino Acid not used in protein made by the urea cycle.

Cofactor: Interaction between two substances that to bring about changes.

Collagen: A basic component of connective tissue.

Coma: Unconsciousness.

Concentrations: The level or amount of a substance.

Connective Tissue: Tissue that surrounds other tissues and organs in the body.

Conversion: A change from one state to another.

Crisis: A negative change in the physical and/or mental well-being of a person.

CVS: A procedure used in the first trimester of pregnancy to diagnose genetic diseases.

Cytoplasm: Area of the cell that most of the chemical actions occur.

Defects: An abnormality.

Deficiency: A lower amount than necessary for functioning.

Developmental Disabilities: A chronic mental or physical impairment that results in decreased ability of an individuals to reach appropriate age level developmental goals.

Disease: Deviation from a normal state of physical or mental health caused by the body’s response to the environment and/or infective substances.

Disorder: An abnormal physical or mental condition.

Elevation: An abnormal increase in a substance.

Enzyme: Proteins produced by cells in the body and assists the body’s processes.

Enzymatic Assay: Examination of the enzyme. (Also see: Assay)

Etiology: The origins of a disease.

Experimental: Information based on a scientific study.

Fibroblasts: A cell that is always present in connective tissue and active in making a secreting collagen.

Fibrosis: An increase of fibrous tissue, tissues that contain or resemble fibers.

Formation: The act of taking shape or form.


Hepatic: Pertaining to the liver.

Hepatocytes: Cells in the liver.

Homocitrullinuria or Homocitrulline: A chemical variant of Citrulline.

Hyperammonemia: Elevated levels of Ammonia in the blood.

Hyperornithinemia: A chemical variant of Ornithine.

Intellectual Development: The ability to gain knowledge.

Intramitochondrial: Within the cell, produces energy for the cell.

Investigation: An in-depth study.



Lethargy: Sleepiness.

Liver: A large vascular organ in the body that causes important changes in substances in the body in order for the body to use these substances.

Lysine: An essential Amino Acid.

Metabolic Pathway: The sequence by which the chemical changes in living cells provide energy for vital processes in the body, resulting in new material mitochondria – found inside the cell and produce energy for the cell.

Molecule: A combination of tiny, invisible particles in the body that are bonded together.

N-acetylglutamate: A coenzyme that assists in processing the first step of the urea cycle and activates carbamoyl phosphate synthetase I.

Nitrogen: An atmospheric gas that forms many compounds in the body (such as proteins) and is a component of all living cells.

Ornithine: Functions in the urea cycle and acts as a carrier by changing from Citrulline to Arginine.

Ornithine Translocase: A molecule that moves ornithine from one part of the cell to another.

Orotic Aciduria: A crystalline acid that is found in milk, a key to the growth of different microorganisms.

Partial Activity: Not completely active, may be missing vital components.

Plasma: Liquid part of the blood in which blood cells are suspended.

Prenatal: Before birth.

Primarily: Occurring first, of most importance.

Protein: Essential to all living cells, simplified by body processes to simple alpha-amino acids.


Rapid-onset: Beginning quickly without warning.

Red blood cells: A type of cell in the body that carries oxygen to the body’s tissues.

Rescued from crisis: Removed from harm or a dangerous situation.

Scavenger: Collects excess particles.

Seizures: A temporary change in brain performance due to abnormal electrical activity of a specific group of cells in the brain that either present with sudden muscle contractions, decreased level of consciousness, and several other symptoms.

Self-select: To determine on one’s own either consciously or subconsciously.

Spasticity: Continuous contraction of certain muscles.

Stressful: Having stress, irritation.

Supplementation: A substance added to counteract a deficiency or potential deficiency.

Switching Off: To turn off.

Tissue: A group of cells that have a similar structure and function.

Transcarbamylation: The addition of a carbon group.

Transaminases: The addition of an amine group.

Transport: To carry from one area to another.

Tremor Ataxia: Trembling or shaking and lack of control of voluntary muscles.

Trichorrhexis Nodosa: A node-like appearance of fragile hair.

Triggering Event: An episode that causes a reaction or illness.

Urea: A product of protein breakdown of Amino Acids, excreted in the urine.

Urea Cycle: A metabolic process in which waste (nitrogen) from the breakdown of proteins in the body is changed by the liver into a urea, excreted in the urine.

Ureagenesis: The transformation of proteins to a urea compound that can be excreted in the urine.

Voluntary muscles: Muscles of the body that a person can control.

Waste: unusable or excess material, lost by breaking down of the body’s tissues.

X-Chromosome: A sex chromosome in both males and females (males have one X-chromosome, XY=male, and females have two X-chromosomes, XX=females).