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Term Definition

Recurring or moving in cycles.


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

De novo mutation

A genetic change in the DNA that happens for the first time in a patient, i.e., the parents do not carry the change.


A lower amount than necessary for functioning.


Excessive loss of water from the body or from an organ or body part, as from illness or fluid deprivation.

Developmental Disabilities

A chronic mental or physical impairment that results in decreased ability of an individual to reach appropriate age-level developmental goals.


Deoxyribonucleic acid (DNA) is the chemical inside the nucleus of all cells that carries the genetic instructions for making living organisms.

DNA sequencing (genome sequencing)

A multistage process that includes cloning, physical mapping, subcloning, determination of the DNA sequence of the nucleotide bases and information analysis. Sometimes the entire gene is decoded and sometimes only the most important parts are. Different people can have slightly different sequences (variants) with little or no impact on how well the gene works. However, some errors in a gene's sequence can have serious consequences.

DTaP vaccine

An immunization against diphtheria, tetanus, and pertussis (whooping cough) that is one of the recommended childhood immunizations. Five DTaP vaccines are recommended, usually given to children at ages 2 months, 4 months, 6 months, 15-18 months, and 4-6 years.


Any of various ions, such as sodium or chloride, required by cells to regulate the electric charge and flow of water molecules across the cell membrane. The primary ions of electrolytes are sodium, potassium, calcium, magnesium, chloride, phosphate and bicarbonate.


Caused by an abnormal condition of the structure or function of the tissues in the brain, especially chronic, destructive or degenerative conditions such as hyperammonemia, metabolic or mitochondrial disorders.

Enzymatic Assay

laboratory methods for measuring enzymatic activity.


A protein molecule that helps other organic molecules enter into chemical reactions with one another but is itself unaffected by these reactions.


The origins of a disease.


A cell that is present in connective tissue and active in making and secreting collagen. Skin cells.

fMRI (Functional magnetic resonance imaging)

A diagnostic imaging technique used in brain mapping to measure the tiny metabolic changes that take place in an active part of healthy, diseased, or injured brains. During an fMRI examination, the patient will perform a particular task during the imaging process, causing increased metabolic activity in the area of the brain responsible for the task which is then recorded on MRI images.

Gastroesophageal reflux (GER)

A condition in which the muscle at the end of the esophagus does not close properly, allowing the contents of the stomach to leak back, or reflux, into the esophagus. This causes irritation such as a burning sensation in the chest or throat (heartburn) or the taste of stomach fluid in the back of the mouth (acid indigestion). Also known as acid reflux.

Gastroesophageal reflux disease (GERD)

Refers to the passage of gastric contents into the esophagus or oropharynx; with or without vomiting. GER can be a daily, normal physiological occurrence in infants, children and adolescents. Most episodes of GER in healthy individuals last less than 3 minutes, occur after eating, and cause few or no troublesome symptoms. Regurgitation or spitting up is the most obviously visible symptom to caregivers and pediatricians, particularly in the very young child, occurring daily in about 50% of infants less than 3 months of age. Regurgitation resolves spontaneously in most healthy infants by 12-14 months of age. Gastroesophageal reflux disease (GERD) refers to the symptoms and complications that may develop secondary to persistent GER. If left untreated, GERD can cause chronic inflammation of the esophagus and lungs, esophageal strictures (scars that narrow the esophagus), stomach ulcers, breathing problems, and an increased risk for esophageal cancer.

Gastrostomy Tube/gastric feeding tube (G-tube or "button")

A tube inserted through a small incision in the abdomen into the stomach and is usually used long term for administering nutrition and/or medications.


A gene is, in essence, a segment of DNA that has a particular purpose, i.e., that codes for (contains the chemical information necessary for the creation of) a specific enzyme or other protein.

Generalized anxiety disorder

A condition characterized by 6 months or more of chronic, exaggerated worry and tension that is unfounded or much more severe than the normal anxiety most people experience.


A nonessential amino acid; also a


Pertaining to the liver.


Liver cells.


An individual who has carries a gene with a particular characteristic (like OTC deficiency).

HiB vaccine

An immunization which prevents childhood Haemophilus influenzae B infections, which can cause severe and potentially deady illnesses that affect the brain, lungs, and bones or joints. It is administered as a series of four doses to children older than 6 weeks but younger than 5 years of age.


Abnormally high levels of ammonia in the blood; if untreated, causing severe agitation, vomiting, lethargy, coma and death.


Abnormally high levels of sodium in the blood.


Overproduction of the thyroid hormone by the thyroid gland.


A disorder that occurs when the thyroid gland produces too much thyroid hormone, causing nervousness, fatigue, difficulty sleeping, heat intolerance, rapid and irregular heartbeat, frequent bowel movements, weight loss, mood swings, and possibly a goiter (an enlarged thyroid that may cause the neck to look swollen).

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