Definitions


A  |  B  |  C  |  D  |  E  |  F  |  G  |  H  |  I  |  J  |  K  |  L  |  M
N  |  O  |  P  |  Q  |  R  |  S  |  T  |  U  |  V  |  W  |  X  |  Y  |  Z


A

Alzheimer's disease - a type of progressive dementia in which individuals exhibit severe memory loss and abnormal behaviors. Alzheimer's disease is more common in people with Down syndrome than in the general population.

Anal Atresia - incomplete development of the end of the intestinal tract (anus). Also called imperforate anus. Anal atresia is more common in Down syndrome population than in the general population.

Anal Stenosis - a narrowing of the anal opening, which makes it difficult for stool contents to pass through easily. Similar to imperforate anus. An anal stenosis is a malformation more common in Down syndrome population than the general population.

Annular Pancreas - a ring of pancreatic tissue encircling the small intestine resulting in intestinal blockage. Annular pancreas is more common in people with Down syndrome than in the general population.

Apnea - literally means "without breath", and is the term used when someone stops breathing for very short periods of time, usually 10 to 20 seconds. "Obstructive Apnea" is the term used when respiratory efforts continue, such as movements of the chest. Apnea causes decreased oxygenation of the blood. Symptoms of Obstructive Sleep Apnea (OSA) are: snoring, restless/disturbed sleep, frequent partial or total awakenings and daytime mouth breathing. Some children with OSA have odd sleep positions, often with their neck bent backwards, or even in a sitting position. Some children with OSA sweat profusely during sleep. In adults, there is an association of obesity, but that's not a common association in children. People with Down syndrome have a higher risk for apnea, between 45 and 57% of people with Down syndrome suffer from apnea.

Atresia - a condition in which a body orifice or passage in the body is abnormally closed or absent.

Atrial Septal Defect (ASD) - an opening between the two atria, the upper chambers of the heart.
There are several types of ASD. The main types of ASD are:

1. Ostium primum, (ASD1°), opening between the two atria in the lower part of the septum often involving mitral valve abnormalities. This endocardial cushion type of ASD is a partial form of AVSD.
2. Ostium secundum (ASD2°). This is often difficult to distinguish from a PFO.
3. Other types of ASDs (e.g.,single atrium).

Atrioventricular Septal Defect (AVSD) - a variety of defects (or malformations) of the muscular septa that separate the two atria and the two ventricles of the heart and the adjacent parts of the mitral and triscupid valves. Can be partial or complete. May also be called AV Canal (AVC), complete AV canal (CAVC), partial AV canal, endocardial cushion defect (ECD), common atrioventricular opening, common AV valve.

Complete AVSD has both an ostium primum-type atrial septal defect (ASD1°) and a particular type of ventricular septal defect or VSD (inlet, inflow VSD).
Partial AVSD can be either:

1. an ostium primum-type atrial septal defect (ASD1°) without a VSD. The ASD1° is often accompanied by a cleft mitral valve (aka bicuspid valve, the valve between the left atrium and left ventricle. Common atrium is also an ASD1°.
- OR -
2. a VSD of the AVSD type.

AV Canal - see Atrioventricular Septal Defect

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B

Behavioral Audiogram - A special hearing test that should be given at 1 year of age. Children with Down syndrome have a 50% to 70% risk for developing ear problems, a health professional should regularly inspect his or her ears for signs of fluid behind the ear drum (otitis media with effusion).

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C

Chromosomal Trisomy - having three copies of a particular chromosome instead of the normal two copies.

Chromosome - a grouping of coiled strands of DNA, containing many genes. Most multicellular organisms have several chromosomes, which together comprise the genome. Sexually reproducing organisms (humans, most animals and plants) have two copies of each chromosome, one from the each parent. Every chromosome contains specific genes that carry hereditary information.

Chromosome Number - the usually constant number of chromosomes characteristic of a particular kind of animal or plant.

Common Atrioventricular Opening - see Atrioventricular Septal Defect

Common AV Canal - see Atrioventricular Septal Defect

Common AV Valve - see Atrioventricular Septal Defect

Complete AV Canal - see Atrioventricular Septal Defect

Congenital - A congenital disorder, or congenital disease, is a condition existing at birth and often before birth, or that develops during the first month of life (neonatal disease), regardless of causation.

Congenital Cataracts - A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light. Congenital cataracts are present at birth. Cataracts are more common in people with Down syndrome than in the general population.

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D

Diagnosis - the act of identifying a disease from its signs and symptoms, or investigation or analysis of the cause or nature of a condition or medical problem.

Disease - an impairment of health or a condition of irregular functioning; abnormal condition of the body or mind that causes discomfort, dysfunction, or distress to the person.

DNA (Deoxyribonucleic Acid) - The long, spiraling molecule that orchestrates the cell's daily operations and provides the genetic blueprint for the physical characteristics of all living organisms. When made up of two strands, the strands intertwine like a spiral staircase to form a structure called a double helix. Subunits, called bases (A,C,G,T), are the rungs of the staircase. In most organisms, DNA is organized on chromosomes located in the nucleus of the cell.

Double-Outlet Right Ventricle (DORV) - both the pulmonary artery and the aorta arise from the right ventricle. Often accompanied by VSD and other defects.

Down syndrome (DS) - Down syndrome is caused by an extra chromosome 21 in the majority of cells of an individual, sometimes called trisomy 21. The extra chromosome is present from before or shortly after conception. Individuals with Down syndrome have mental retardation, characteristic facial features, low muscle tone, and, in some cases, birth defects including heart abnormalities. 95% of Down syndrome is due to an extra, free-standing chromosome 21. This type of trisomy 21 is not "inherited". It is due to a spontaneous error that occurs during the formation of either the egg or the sperm, or, in rare cases, during the first cell divisions after fertilization {see Mosaic Down syndrome}. In the other 5% of Down syndrome, the extra chromosome 21 is present because it is attached to another chromosome. This is called a translocation and it can be inherited.

Duodenal Atresia - a condition in which the duodenum (the first part of the small intestine) has not developed properly. It is completely blocked and cannot allow the passage of stomach contents. Duodenal atresia is more common in people with Down syndrome than in the general population.

Duodenal Stenosis - a block of the first part of the small intestine (the duodenum). Stenosis refers to a partial block. Duodenal stenosis is more common in people with Down syndrome than in the general population.

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E

Endocardial Cushion Defect - see Atrioventricular Septal Defect

Esophageal Atresia - incomplete development of the esophagus, where the esophagus usually ends in a blind pouch before reaching the stomach. In over 85% of esophageal Atresia, there is an accompanying tracheoesophageal fistula. The disorder is usually detected shortly after birth when feeding is attempted and the baby coughs, chokes, and turns blue. Immediate surgical repair of this disorder is required so that the lungs are not damaged and the baby can be fed. Babies with Down syndrome have increased risk of Esophageal Atresia.

Esophagus - the tube that connects the mouth to the stomach.

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F

Fistula - abnormal passage from a body organ to the body surface or between two internal body organs.

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G

Gastrointestinal Defects - structural defects that can occur at any point along the gastrointestinal tract, which is made up of the esophagus, stomach, small and large intestines, rectum, and anus. The incomplete or abnormal development of any of these organs can cause obstructions or blockages that can lead to swallowing difficulties, vomiting, and problems with bowel movements.

Gastroschisis - A birth defect in which there is a separation in the abdominal wall. Through this opening protrudes part of the intestines which are not covered by peritoneum (the membrane that normally lines the inside of the abdomen). Babies with Down syndrome appear to have a reduced risk for gastroschisis.

Genes - units of heredity passed from one generation to the next. Genes are segments of DNA on a chromosome containing instructions essential for the physical development and behavior of an organism. Often one gene may determine one physical characteristic such as eye color. Sometimes multiple genes may be involved, such as in height determination.

Genetics - a branch of biology that deals with the heredity and variation of organisms.

Genome - an organism's total genetic information contained in the full DNA sequence of one set of chromosomes. The normal human genome consists of 3 billion base pairs of DNA in each set of 23 chromosomes inherited from each parent.

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H

Hematological Neoplasms - - types of cancer that affect blood, bone marrow and lymph nodes. Cancers in this classification include leukemias, lymphomas, and myelomas.

Hirschsprung's Disease (Congenital Aganglionic Megacolon) - Disorder of the large intestine caused by the absence of certain nerve cells in the bowel wall. A section of the large intestine is missing the nerves that control its contractions, resulting in severe constipation and sometimes bowel obstruction. Hirschsprung’s Disease is more common in people with Down syndrome than in the general population.

Hypothyroidism - - the thyroid gland does not make enough thyroid hormone. It is the most common thyroid problem associated with Down syndrome. Also known as an under-active thyroid, hypothyroidism may cause a variety of symptoms and may affect all body functions. Hypothyroidism can be a serious problem if left untreated so it is important that children with Down syndrome be tested at birth and then each year to insure that the thyroid is working correctly. Untreated, hypothyroidism can lead to slow growth, skin disorders, blood disorders, sleep problems, lethargy, learning problems, and feeding problems.

Hypotonia - lack of muscle tone. Hypotonia is a common clinical feature of Down syndrome.

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I

Imperforate Anus - see anal atresia.

Inferior Vena Cava - the inferior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the legs and lower torso feed into the inferior vena cava, which empties into the right atrium of the heart.

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K

Karyotypes - an organized profile of a person's chromosomes. In a karyotype, chromosomes are arranged and numbered by size, from largest to smallest. This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder. The normal karyotype of the human female contains 23 pairs of homologous chromosomes: 22 pairs of autosomes and 1 pair of X chromosomes. The normal karyotype of the human male contains the same 22 pairs of autosomes, plus one X chromosome and one Y chromosome.

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L

Left Atrium - one of four chambers (two atria and two ventricles) in the human heart. The left atrium receives oxygenated blood from the lungs through the pulmonary vein. As the contraction triggered by the sinoatrial node progresses through the atria, the blood passes through the mitral valve into the left ventricle.

Left Ventricle - one of four chambers (two atria and two ventricles) in the human heart. The left ventricle receives oxygenated blood as the left atrium contracts. When the left ventricle contracts, blood is pumped to the body.

Leukemia - a cancer of the blood or bone marrow characterized by an abnormal proliferation of blood cells, usually white blood cells (leukocytes). It is part of the broad group of diseases called hematological neoplasms. Leukemia is more common in people with Down syndrome than in the general population.

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M

Mitral Valve - the mitral valve separates the left atrium from the left ventricle. It opens to allow the oxygenated blood collected in the left atrium to flow into the left ventricle. It closes as the left ventricle contracts, preventing blood from returning to the left atrium; thereby, forcing it to exit to the body.

Mosaicism - a condition where an individual has two or more cell populations that differ in genetic makeup. This situation can affect any type of cell, including blood cells, gametes (egg and sperm cells), and skin.

Mosaic Down syndrome - an individual is said to have mosaic Down syndrome when their body is composed of a mixture of cells with and without an extra chromosome 21 (see mosaicism). Mosaic Down syndrome occurs when the initial zygote had three copies of chromosome 21, which normally would result in simple trisomy 21, but during the course of cell division one or more cell lines lost one of the chromosomes 21, or when the initial zygote had two chromosomes 21, but during the course of cell division one of them was duplicated.

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O

Obstructive Sleep Apnea (OSA) - see Apnea.

Omphalocele - a defect in the abdominal wall allowing the intestine and other abdominal organs to protrude outside the abdomen. This defect must be repaired by surgery. Omphalocele and gastroschisis make up most of the major defects of the abdominal wall. Babies with Down syndrome appear to have a reduced risk for omphalocele.

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P

Papillary Muscles - Small muscles within the heart that anchor the heart valves. The papillary muscles attach to the lower portion of the interior wall of the ventricles. They connect to the chordae tendineae, which attach to the tricuspid valve in the right ventricle and the mitral valve in the left ventricle. The contraction of the papillary muscles opens these valves. When the papillary muscles relax, the valves close.

Partial AV Canal - see Atrioventricular Septal Defect

Patent (Persistent) Ductus Arteriosus (PDA) - a congenital heart condition that exists when the ductus does not close. The ductus arteriosus is a passageway which normally is present in every baby until a few days after birth. It is a communication between the two major arteries coming out of the heart. When this passageway does not close, the too much blood is allowed to flow to the lungs.

Patent Foramen Ovale (PFO) - an opening between the two atria (upper chambers). Like the PDA, it is important during fetal life and closes after birth. Its purpose is to shunt blood from the right to the left atrium bypassing the not-yet-functioning fetal lungs.

Pulmonary Artery - the pulmonary artery is the vessel transporting de-oxygenated blood from the right ventricle to the lungs.

Pulmonary Atresia - see Pulmonary Valve Stenosis

Pulmonary Valve - the pulmonary valve separates the right ventricle from the pulmonary artery.

Pulmonary Vein - the pulmonary vein is the vessel transporting oxygen-rich blood from the lungs to the left atrium.

Pulmonary Valve Stenosis/ Pulmonic Stenosis (PS) - A narrowing of the outflow from the right ventricle of the heart to the lungs. De- oxygenated blood is pumped through the Pulmonary Valve to the lungs to pick up oxygen. Normally the Pulmonary Valve has three leaflets. If these leaflets are malformed, the valve may become narrowed (stenotic) or leaky (insufficient).

Pyloric Stenosis - a condition in which the muscular wall of the passage carrying food from the stomach to the small intestine is abnormally thick and the passage narrow, forcing food back out through the esophagus (vomiting). Symptoms other than vomiting include constipation, change in stools (smaller and fewer stools or stools that have mucus in them), failure to gain weight or weight loss, and lethargy. As the condition worsens, babies are at risk for developing fluid and salt abnormalities and becoming dehydrated. Pyloric stenosis is fairly common, as it affects about three out of 1,000 babies in the United States. It does not occur at an increased rate among babies with Down syndrome.

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R

Right Atrium - one of four chambers (two atria and two ventricles) in the human heart, the right atrium receives de-oxygenated blood from the body through the superior vena cava (head and upper body) and inferior vena cava (legs and lower torso).

Right Ventricle - one of four chambers (two atria and two ventricles) in the human heart.The right ventricle receives de-oxygenated blood as the right atrium contracts.

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S

Stenosis - narrowing of a duct, passage, or opening in the body (i.e. aortic valve stenosis - an abnormal narrowing of the aortic valve).

Strabismus - crossed or wandering eyes. It is normal for newborn babies to have eyes that cross or wander sometimes, especially when they are tired. However, if a child's eyes cross or wander to the side after 3 months of age, he/she may have Strabismus. When the eye turn occurs all of the time, it is called constant strabismus. When the eye turn occurs only some of the time, it is called intermittent strabismus. With intermittent strabismus, the eye turn might be observed only occasionally, such as during stressful situations or when the person is ill.

Superior Vena Cava - the superior vena cava is one of the two main veins bringing de-oxygenated blood from the body to the heart. Veins from the head and upper body feed into the superior vena cava, which empties into the right atrium of the heart.

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T

Tracheoesophageal Fistula (TE-Fistula) - a birth defect in which the trachea (or windpipe) is connected to the esophagus. The trachea carries air to the lungs. The esophagus carries food to the stomach. Sometimes during development, these two tubes do not separate completely, but remain connected by a short passage. A TE-fistula must be surgically repaired. TE-Fistula may be accompanied by esophageal atresia.

Tetralogy of Fallot (TOF) - may also be called TOF or TET. A heart defect with four key features:

1. VSD (a hole between the ventricles),
2. narrowing (stenosis) of or beneath the pulmonary valve which leads from the right ventricle to the lungs,
3. right ventricular hypertrophy (thickening of the wall of the right ventricle),
4. overriding aorta (the aorta is directly over the VSD and so it receives blood from both ventricles.)

Trisomy 21 - the presence of three chromosomes 21, also known as Down syndrome. We normally have 23 pairs of chromosomes, each chromosome containing many genes. During the formation of the egg or the sperm, one chromosome of each of the 23 pairs is transmitted to a woman’s eggs or a man’s sperm. In most cases of Trisomy 21, the chromosome 21 pair did not separate properly and both chromosomes were transmitted into the egg or sperm. When the egg or sperm with two copies of chromosome 21 is joined with the contribution from the other parent (either egg or sperm that contains one copy of chromosome 21), the embryo will have three copies of chromosome 21, instead of the normal two. This type of error (called a nondisjunction error) is the cause of Down syndrome in approximately 95% of all cases.

Tricuspid Valve - the tricuspid valve separates the right atrium from the right ventricle in the heart. It opens to allow the de-oxygenated blood collected in the right atrium to flow into the right ventricle. It closes as the right ventricle contracts, preventing blood from returning to the right atrium.

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V

Ventricular Septal Defect (VSD) - an opening between the two ventricles, the lower chambers of the heart. There are several types of VSDs, notably, an "inlet" VSD is a type of partial AVSD.

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