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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)

A tube that is 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.

Gene dosage

The number of copies of a given gene present in the cell of an organism. An increase in gene dosage can result in higher levels of gene product formation.  See Dosage sensitive

Gene environment interaction

An influence on the expression of a trait that results from the interplay between genes and the environment. Some traits are strongly influenced by genes, while other traits are strongly influenced by the environment. Most traits, however, are influenced by one or more genes interacting in complex ways with the environment.


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.

Genetic counseling

The professional interaction between a healthcare provider with specialized knowledge of genetics and an individual or family. The genetic counselor determines whether a condition in the family may be genetic and estimates the chances that another relative may be affected. Genetic counselors also offer and interpret genetic tests that may help to estimate risk of disease. The genetic counselor conveys information in an effort to address concerns of the client and provides psychological counseling to help families adapt to their condition or risk.


Genetic counselor

Professionals who have special training to help people and families cope with and understand genetic conditions. They are also trained to provide counseling and support for people and families with genetic conditions.


Genetic discrimination

Prejudice directed against people who have or may have a genetic disease. Genetic discrimination can involve being denied employment or health insurance. In a healthcare context, it can refer to people being treated based on their genetic status rather than by some more relevant criterion.


Geneticist/Clinical Geneticist

Medical doctors with special training in genetics. In addition to educating families about genetic conditions, they perform clinical exams and order lab tests to diagnose the causes of birth defects and other genetic conditions. They can explain how a genetic condition may affect a person and give advice about treatment options and recurrence risks for future pregnancies.


Genetic predisposition

A susceptibility, or higher risk, for a disease due to genetic factors.


Genetic screening

Testing a group of people to identify individuals at high risk of having or passing on a specific genetic disorder.


Genetic testing

The use of a laboratory test to look for genetic variations associated with a disease. The results of a genetic test can be used to confirm or rule out a suspected genetic disease or to determine the likelihood of a person passing on a mutation to their offspring. Genetic testing may be performed prenatally or after birth. Ideally, a person who undergoes a genetic test will discuss the meaning of the test and its results with a genetic counselor.


Genetic Variation

Refers to diversity in gene frequencies. Genetic variation can refer to differences between individuals or to differences between populations. Mutation is the ultimate source of genetic variation, but mechanisms such as sexual reproduction and genetic drift contribute to it as well.



The study of heredity, when a parent passes certain genes on to their children.



All the genetic material in the chromosomes of a particular organism; its size is generally given as its total number of base pairs.



The genetic constitution of an organism, as distinguished from its physical appearance (its phenotype). The designation of two alleles at a particular locus is a genotype.



See The Genetic Information Nondiscrimination Act


Pertaining to the liver.


Liver cells.


An individual who 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.

High-risk Pregnancy

A high-risk pregnancy is one of greater risk to the mother or her fetus than an uncomplicated pregnancy. Pregnancy places additional physical and emotional stress on a woman’s body. Health problems that occur before a woman becomes pregnant or during pregnancy may also increase the likelihood for a high-risk pregnancy.



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).


A condition marked by an abnormal increase in muscle tension and a reduced ability of a muscle to stretch, caused by disease, or conditions such as dystonia (prolonged muscle contractions that cause twisting and repetitive movements or abnormal posture), rigidity, or a combination of factors. Severe cases can also make joint movement impossible.


An abnormally low blood calcium level.



Low blood sugar


A condition characterized by below normal or absent reflexes and generally associated with a lower motor neuron deficit.


A birth defect in boys in which the urethra (the tube that carries urine from the bladder to outside the body) does not end at the tip of the penis. Instead, it ends on the underside. In more severe cases, the urethra opens at the middle or bottom of the penis, or in or behind the scrotum.



Abnormally low body temperature below 95 degrees F, causing heart and respiration slowing and paleness.


Insufficient production of the thyroid hormone by the thyroid gland.


A disorder that occurs when the thyroid gland does not produce enough thyroid hormone, causing sensitivity to cold temperatures, depression, fatigue, constipation, joint or muscle pain, unintentional weight gain, and eventual slow speech, hoarseness, and decrease in taste and smell.

Hypotonia (low tone)

A condition in which there is diminution or loss of muscular tonicity, resulting in stretching of the muscles beyond their normal limits. Decreased muscle tone that may be a sign of a problem with the brain, spinal cord, nerves, or muscles. Infants with hypotonia seem floppy and feel like a "rag doll" when held.


See Intellectual and Developmental Disabilities


A personality trait characterized by the inclination of an individual to initiate behavior without adequate forethought as to the consequences of their actions, referred to as "acting on the spur of the moment." While it a normal behavior which contributes to adaptive functioning, abnormal patterns of impulsivity may be related to neurodegenerative diseases, traumatic brain injury, or neuropsychiatric disorders such as ADHD, substance abuse disorders, and bipolar disorder.

In situ hybridization

Use of a DNA or RNA probe to detect the presence of the complementary DNA sequence in cloned bacterial or cultured eukaryotic cells.


In vivo

Occurring in a living organism. In vivo experiments are therefore performed on living organisms.

Inborn error of metabolism

Genetic disorders in which an inherited defect (usually a missing or inadequate enzyme) results in an abnormality in the body.

Informed Consent

An individual willingly agrees to participate in an activity after first being advised of the risks and benefits.



In genetics, to receive genetic material from parents through biological processes.



An inherited trait is one that is genetically determined. Inherited traits are passed from parent to offspring according to the rules of Mendelian genetics. Most traits are not strictly determined by genes, but rather are influenced by both genes and environment.


Intellectual and Developmental Disabilities

Disorders that are usually present at birth and that negatively affect the trajectory of the individual’s physical, intellectual, and/or emotional development. Many of these conditions affect multiple body parts or systems. Also known as IDDs


Intellectual Development

The ability to gain knowledge.

Intellectual disability

A disability (sometimes referred to as cognitive disabilities or mental retardation) in which a person has certain limitations in mental functioning and in skills such as communicating, taking care of him or herself, and social skills. Children with intellectual disabilities learn and develop more slowly than a typical child and may take longer to speak, walk, and learn to take care of their personal needs such as dressing or eating.


Within the cell, produces energy for the cell.

Intravenous (IV)

Delivery of a substance (such as medication) into the bloodstream.


A branched chain essential amino acid found in proteins. One of the restricted amino acids for patients with propionic acidemia.


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