glossary

glossary of terms within deCODEme

A

• Absolute Risk (AR): is defined as the chance of a person developing a specific disease over a specified time-period. For example, a woman's lifetime absolute risk of breast cancer is one in nine. That is to say, one woman in every nine will develop breast cancer at some point in their lives. Absolute risk can also be expressed as a percentage (e.g. a woman's absolute risk of breast cancer can be written as 11 per cent instead of one in nine) or as a decimal (one in nine becomes 0.11).
• Allele: One of the variant forms of the DNA sequence at a particular locus, or location, on a chromosome. Different alleles can produce variation in inherited characteristics such as hair color or blood type. In an individual, one form of the allele (the dominant one) may be expressed more than another form (the recessive one). Other alleles may have no affect (are silent) but may tag genes or other nearby alles that are causative or contribute to a genetic characteristic, such as a disease or disease succeptibility.
• Autosomal: refers to the location on any chromosome other than a sex chromosome (X- or Y-chromosome). Humans have 22 pairs of autosomes.
• Arrhythmia: A disorder of the regular rhythmic beating of the heart. Also called Cardiac Arrhythmia.
• Autoimmune disease: An illness that occurs when the body's immune system attacks its own tissues. Patients with autoimmune diseases frequently have unusual antibodies circulating in their blood that target their own body tissues. The female hormone estrogen may predispose some women to autoimmune diseases; hence autoimmune diseases affect more women than men. Furthermore, the presence of one autoimmune disease increases the chance for developing another simultaneous autoimmune disease. A few examples of autoimmune diseases include Rheumatoid Arthritis, Multiple Sclerosis, and Type 1 Diabetes.

B

• Body Mass Index (BMI): A measure of weight that adjusts for differences in height. BMI is calculated as body weight in kilograms divided by height in meters squared. Calculate your BMI.

  C

• Central Obesity: Excessive fat accumulation around the waist and midsection, including the internal organs.
• Congenital: Present at birth. A congenital condition is a condition that one is born with.
• Colonoscopy: A medical procedure consisting of inserting a long, flexible, tubular instrument called the colonoscope into the colon via the anus, to view the entire inner lining of the colon (large intestine) and the rectum. If suspicious growths are observed, tiny biopsy forceps or brushes can be inserted through the colonoscope and tissue samples can be obtained.

D

• Dilated Eye Exam: An eye exam using eye drops to dilate or enlarge the pupil in order to obtain a better view of the internal surface of the eye (i.e. fundus) with an ophthalmoscope. Also called Dilated Fundus Examination (DFE).
• Dizygotic Twins: Twins derived from separate eggs independently fertilized by two different sperm cells. Twins derived from a single fertilized egg are Monozygotic twins.
• DNA (Deoxyribonucleic Acid): The chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.

  E

• Enzyme: An enzyme is a protein that catalyzes (accelerates) chemical reactions. The human body relies on many different enzymes to function properly. Enzymes are in general very specific, meaning that a given enzyme generally catalyzes only one reaction type and operates on only one type of substrate.

F

• Fecal Immunochemical Test (FIT): A newer type of FOBT (Fecal Occult Blood test) which is more specific than the FOBT (it produces fewer false-positive results), and certain types of fecal immunochemical tests may also be more sensitive (better able to detect cancers and advanced polyps).
• Fecal Occult Blood test (FOBT): A test to detect microscopic blood in the stool. Is a screening tool for colorectal cancer.
• First-degree relatives: Are parents, children, and full-siblings.
• Flexible Sigmoidoscopy: A procedure by which a doctor inserts either a flexible fiber-optic tube into the rectum to examine the lower portion of the large intestine (or bowel). In a colorectal cancer screening, the doctor is looking for polyps or tumors.

G

• Genetic Scan: Analysis of the genome by typing it for multiple sequence variations. The deCODEme Genetic Scan measures over one million genomic locations with single nucleotide variations (SNPs).
• Genetic Marker: A segment of DNA with a known and identifiable location on a chromosome and whose inheritance can be followed. A marker can be any section of DNA (up to a whole gene) with known or unknown function. Because DNA segments that are close to each other on a chromosome tend to be inherited together, markers are often used to track patterns of inheritance of genes that have not yet been identified, but whose approximate locations are known.
• Genetic Variant or Variation: An alteration or change in the genetic sequence. Only well established risk variants are used in deCODEme.
• Genome: All the DNA contained in an organism or a cell, which includes both the chromosomes within the nucleus and the DNA in mitochondria.
• Genome Scan: Analysis of the genome by typing it for multiple sequence variations. The deCODEme Scan measures over one million genomic locations with single nucleotide variations (SNPs).
• Genotype: The genetic makeup of an individual person. The term refers to a specific sequence composition or alleles.
• Genotyping: The process of determining the genotype of an individual. Single nucleotide polymorphisms (SNP) are the most common type of genetic variation.
• Gestational Diabetes: Glucose intolerance during pregnancy. It is a form of diabetes which affects pregnant women who have never had diabetes before. There is no known specific cause, but it's believed that the hormones produced during pregnancy reduce a woman's receptivity to insulin resulting in high blood sugar.

H

• Heterozygous: When an individual has two different forms of a particular gene, one inherited from each parent.
• Homozygous: When an individual has two identical forms of a particular gene, one inherited from each parent.

  I

• Incidence: The number of new cases of a disease that develop within a specified population over a specified period of time.
• Impaired Glucose Tolerance (IGT): According to the criteria of the World Health Organization and the American Diabetes Association, impaired glucose tolerance is defined as two-hour glucose levels of 140 to 199 mg per dL (7.8 to 11.0 mmol) on a 75-g oral glucose tolerance test. A patient is said to be under the condition of IGT when he/she has an intermediately raised glucose level after 2 hours, but less than would qualify for type 2 diabetes mellitus. The fasting glucose may be either normal or mildly elevated.

J

K

L

• Locus: A position on a chromosome where a gene, or some other sequence, is located (pleural: loci).

M

• Malabsorption: Disturbed or inadequate absorption of nutrients from the intestinal tract.
• Marker (Genetic Marker): A segment of DNA with a known and identifiable location on a chromosome and whose inheritance can be followed. A marker can be any section of DNA (up to a whole gene) with known or unknown function. Because DNA segments that are close to each other on a chromosome tend to be inherited together, markers are often used to track patterns of inheritance of genes that have not yet been identified, but whose approximate locations are known.
• Mendel, Gregor Johann: Austrian priest and scientist (1822-1884), also known as the father of modern genetics. His controlled experiments with breeding peas in the monastery garden showed that the inheritance of traits follows certain predictable patterns, determined by heritable units we now call genes.
• Mendelian Trait: A characteristic or condition which follows the simple patterns of inheritance proposed by Gregor J. Mendel or a trait produced by a single gene.
• Mitochondria: The organelles that generate energy for the cell and have their own genetic material
• Modeling Genetic Risks: The calculations performed by deCODEme usually assume that the relative risks of different genetic variants multiply. This is a parsimonious model that usually fits the data of complex traits reasonably well. When judged to be well supported by data, more complex models will be implemented by deCODEme.
• Monozygotic Twins: Twins derived from a single fertilized egg. Twins derived from separate eggs independently fertilized by two different sperm cells are dizygotic twins.
• Mutations: Changes to the base pair sequence of the genetic material. Gene mutations have varying effects on health depending on where they occur and whether they alter the function of the genes and their products, the essential proteins.

N

• Nuclear Family: A family consisting of parents (a biological father and mother) and their children.

O

• Oral Glucose Tolerance Test: A test involving giving an individual a glucose challenge, which is performed by giving a glucose drink and then drawing a blood sample one hour later and measuring the level of blood glucose present.

P

• Periodic Limb Movements (PLM): Repetitive limb movements, most often leg movements associated with Restless Legs Syndrome and some sleep disorders. "Periodic" refers to the fact that the movements are repetitive and rhythmic, occurring about every 20-40 seconds.
• Phenotype: The observable traits or characteristics of an individual, for example hair color, weight, or the presence or absence of a disease.
• Polyps: A smooth, rounded or oval mass projecting from a membrane-covered surface. They are usually an overgrowth of normal tissue, but sometimes polyps are true tumors or masses of new tissue separate from the supporting membrane. Although usually benign, they may lead to complications or eventually become malignant.
• Prevalence: A proportion of a population that has the disease or condition at a specific point in time.

Q

R

• Relative Risk (RR): RR is used to compare risks associating with two variants or the risks of two different groups of people. For example, it can be used to compare a group of people with a certain genotype with another group having a different genotype. For a disease, a relative risk of 2 means that one group has twice the chance of developing a disease as the other group.
• Risk: risk is measured by looking at very large numbers of people, rather than at a particular individual. Risk is often presented in terms of Absolute Risk and Relative Risk. Read more.
• Risk relative to the population. Risk presented is usually the relative risk for a person, or a specific genotype of a person, compared to the population with matched gender and ethnicity. Risks of two individuals of the same gender and ethnicity could be compared in a simple manner. For example, if, compared to the population, the first individual has relative risk 1.5 and the second has relative risk 0.5, then the risk of the first individual compared to the second individual is 1.5/0.5 = 3.

S

• Second-degree Relatives: Are grandparents, half-siblings, and grandchildren
• Single Nucleotide Polymorphism (SNP): Pronounced "snip". A SNP is a genetic marker resulting from variation in sequence at a particular position within a DNA sequence. These variations happen when a single nucleotide or base (A, T, G or C) in the genome sequence is changed. A person's unique DNA profile is determined by the set of SNPs the person has.
• Sex chromosome/X or Y chromosome: One of the two chromosomes that specify an organism's genetic sex. Humans have two kinds of sex chromosomes, one called X and the other Y. Normal females have two X chromosomes and normal males one X and one Y.

T

• Twin Studies: Studies that assess identical (monozygotic) twins for medical, genetic, or psychological characteristics to try to isolate genetic influence from environmental influence.

U

V

• Variant or Variation: An alteration or change in the genetic sequence. Only well established risk variants are used in deCODEme.

W

X

Y

Z

For more on definitions see for example:

• Genetics Home Reference from the National Library of Medicine and a
  
• Glossary of Genetic Terms from the National Human Genome Research Institute
• Medical Dictionary from the National Library of Medicine.

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