Allele Alleles are different forms of the same gene – meaning, they have a slightly different DNA sequence. Humans have 2 forms of every gene that code for the same trait—the difference is how they are expressed. For example, eye color. Blue, green, hazel, and brown eyes are each encoded by unique alleles of the same gene. Alleles play a big role in determining our inherited traits, along with DNA and other genes.
Autoimmune disease An abnormal immune response is when a foreign invader is able to trigger your immune system to attack your own body tissues. There are many types of autoimmune diseases, celiac disease is one of them.
Autosomes Any chromosome that is not a sex chromosome, numbers 1 to 22. Autosomes control our inherited characteristics, except those that are sex-linked.
Celiac disease (CD) Celiac disease or CD is an autoimmune disorder that is triggered by an abnormal reaction to dietary gluten protein. This reaction can be mild to severe, causing injury to the small intestine and other organs in people who consume dietary gluten. About 1 in 3 people who become sensitive to gluten are at risk for CD due to the celiac-associated genes they inherit—CD runs in families.
Carrier In genetics, a person who carries a recessive allele for a certain trait or disease but does not express that trait or have the disease— but, can pass on the trait or disease to offspring.
Chromosomal Disorder Abnormalities that occur as the result of an extra or missing chromosome or a section of chromosome has been altered or deleted. Down’s syndrome is an example.
Chromosome 6 Chromosomes are DNA and RNA protein structures within your cell nuclei that carry genetic information inherited from both of your parents. This genetic information can sometimes be passed on to your children. Chromosome 6 carries the HLA celiac-associated genes.
De Novo Mutation A genetic variation or mutation that is present for the first time in a family member.
DNA DNA (deoxyribonucleic acid) is a molecule that contains your unique genetic code. All living things have DNA within their cells. DNA is important for growth, reproduction and our health. Your DNA is packaged in chromosomes and resides within the nucleus of your cells. You inherit half of your nuclear DNA from your mother, and the other half from your father.
DNA Nucleotide DNA is a double-stranded helix that is intertwined with each other. Its structure is composed of a backbone made of alternating sugar (deoxyribose) and phosphate groups. Each sugar in the strand is attached 1 of 4 nucleotides or nucleotide bases, adenine (A), cytosine (C), guanine (G), and thymine (T) that are held together by bonds between the bases; adenine always bonds to thymine and cytosine to guanine. DNA nucelotides form a unique DNA sequence that instructs the protein and RNA assembly.
DNA Sequencing DNA sequencing means determining the order of nucleotides in a DNA strand. Sequencing allows laboratory professionals to read and learn your genetic code. It also allows them to find changes or variations in a gene that may cause a disease, like Celiac.
Dominant & Recessive You have 2 alleles for each gene, the allele that is dominant of the 2, will be expressed. The allele not expressed is said to be recessive. It’s there but has no job unless both alleles are recessive. Take eye color again, bb is termed homozygous recessive and indicates blue eyes—both the alleles are the same (homozygous) and both are the usually recessive allele. If both alleles were dominant BB, it would be termed homozygous dominant.
DQ Locus The DQ locus is a specific location of a gene or DNA sequence on a chromosome, like a street address. The DQ locus, on chromosome 6, contains 2 linked MHC Class II genes, DQA1 and DQB1. This is the location associated with DQ gene variants associated with celiac disease.
Environmental Factors These factors include things like diet, obesity, physical activity, tobacco smoking, alcohol consumption, environmental pollutants and psychological stress.
Epigenetics Epigenetics is the study of how your lifestyle and environment can cause change and affect the way your genes work. It refers to non-genetic factors that can cause change without actually changing your DNA. See Environmental Factors in this Glossary for examples.
Gene A gene is a unit of hereditary information. Two copies of each gene are located at a specific location on a chromosome—one copy is inherited from each parent.
Gene or Allele? Where a gene is a section of DNA that encodes for a certain trait, an allele is a variant form of a gene or a mutated form of a gene.
Gene Mutation When a gene is damaged or changed in a permanent way that alters its genetic code or function, it is said to be mutated. It is a permanent change to the DNA sequence. This becomes known as a gene variant. Gene variants do not always cause disease and can be inherited or occur during one’s lifetime due to environmental factors or occur during cell division. Non-inherited gene variants are not passed on to the next generation.
Genetic Risk Genetic risk is the chance or likelihood a certain health event may happen based on your genetic-makeup—because of your genes. Your chances may be increased because you have inherited genes that increase your susceptibility to a specific health condition.
Genetic Health Risk Testing Tests that can detect genetic variants which may increase your risk of developing certain health conditions. Particular variants are linked to a higher risk for a condition but do not necessarily mean you will develop the condition.
Genotype Your genotype refers to your entire set of genes inherited from your parents.
Gluten Proteins found in wheat, barley, and rye products which can produce a mild to severe immune response in people who have a celiac genetic risk.
HLA Every person, you, have a unique combination of self-identification molecules called “receptors” located on the surface of your white blood cells. These receptors are called human leukocyte antigens (HLA) or, just HLAs and their function is to regulate your immune system.
HLA-DQA1 and HLA-DQB1 Genes / HLA-DQ2 and DQ8 Inheriting certain gene haplotype variants associated with the HLA-DQA1 and HLA-DQB1 genes can increase your risk for developing celiac disease. HLA-DQA1 and HLA-DQB1 are genes that provide instructions for making the specific immune cell receptors, HLA-DQ2 and HLA-DQ8 that recognize gluten proteins. HLA-DQ2 and DQ8 play important roles in the development of celiac disease; though, only about 1% of those people who have DQ2 and DQ8 actually will develop celiac disease. For those who go on to develop celiac disease, about 90% will have DQ2 and about 20%, DQ8.
HLA Haplotype An HLA haplotype is a group of genes inherited together from one of your parents—your genetic makeup includes HLA haplotypes from both of your parents. Human leukocyte antigen (HLA) genes located in close proximity on chromosome 6; these genes are linked and inherited together as a group. This is why knowing your heredity is important in a celiac diagnosis.
Homozygous Means that you have 2 identical alleles of a particular gene or genes. Example, your eye color, BB or bb means you have 2 identical alleles, one each contributed from each parent, BB for brown eyes and bb for blue eyes.
Heterozygous Means that have inherited 2 different alleles of a particular gene or genes. Same above example, Bb which is still brown eye color as B is the dominant expressed allele.
Karyotype A karyotype is a visual and numerical inspection of your chromosomes in a cell using a laboratory technique that produces an image of your chromosomes.
Linkage Two or more genes virtually always inherited together from the same parent.
Levels of Evidence (LOE) Clinical study data are rated on several levels as to the quality of the information they actually provide – just how good is the evidence and does it apply to the group of people for whom it's intended. “Levels of evidence” are assigned based on the design of the clinical trial, the validity of the results, and their applicability to patient care, in this case, you. These decisions apply a "grade (or strength) of recommendation" from grade level I to VII with I being the highest and best LOE. This is also called hierarchy of evidence since the strength of the evidence can range from high to low, with high giving you the most confidence in the strength of the data.
Locus (Loci) A locus (one) or loci (multiple) indicate a specific “street address” for a specific section of DNA on a gene or chromosome.
Mendelian Disorder Gregor Mendel and Austrian Monk are considered the fathers of Genetics and determined key principles of inheritance, known as Mendelian Inheritance. Today, these are called alleles – for every trait, 2 alleles determine how that trait is expressed, automsomal dominant or recessive, or x-linked (sex chromosomes). A Mendelian disorder occurs as a result of a single gene alteration or mutation of a single gene which is more uncommon. Cystic fibrosis is an example.
MHC Major Histocompatibility Complex is a large group of genes that code for proteins located on cell surfaces that play an important role in immune response. Their function is the ability to recognize foreign molecules and initiate protective and defensive immune responses.
Multifactorial disease Multifactorial is a complex way to say there are multiple factors and reasons that contribute to a disease, it's not caused by just one thing. In genetics, it means the multiple genes in combination with lifestyle or environmental factors influence disease development.
Negative Predictive Value (NPV) Negative predictive value is the percent chance (%) that you might develop a specific disease when your test results are negative.
Non-Celiac Genetics Your test results will indicate “non-celiac genetics” if no celiac-risk-associated GlutenID® haplotypes were detected in your sample. A “non-celiac genetics” test result has a negative predictive value (NPV) of 99% or, in other words, you would have less than a 1% chance of developing celiac disease.
Nucleotide There are four different types of DNA nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C). Each nucleotide, in turn, is made up of a nitrogen base, a pentose sugar, and a phosphate. The functions of nucleic acids have to do with the storage and expression of genetic information. Deoxyribonucleic acid (DNA) encodes the information the cell needs to make proteins.
Phenotype Your phenotype is the physical expression of your genotype, what you look like, your physical traits. It’s all in your genes.
Polymorphism In genetics, this refers to the presence of multiple alleles at a gene locus (the same DNA address). For example again, the many variations in eye color, each caused by a unique allele. Genetic polymorphism in our human population or any other for that matter, is why we have such diversity in physical traits. Polymorphisms are not mutations but rather, one of more variations in a DNA sequence common to a population. SNPs are the most common of the DNA polymorphisms. See SNP Genotyping in this glossary.
Tag SNP See SNP Genotyping below. This mutation occurs at a specific location in the DNA sequencing called a Tag – it’s the DNA address where the SNP has occurred and can be found by using a laboratory technique called DNA sequencing.
Sex Chromosomes Type of chromosome that determines the sex of a person or animal. Each of us inherit one from our mother and one from our father—XX (female) or XY (male).
SNP Genotyping A single nucleotide polymorphism or SNP, pronounced “snip”, is a variation at only one position in the chain of a DNA sequence. SNPs are one of the most common types of genetic variation and can be used to identify changes in the DNA sequence that may be associated with certain diseases, like celiac disease.
Syndrome A syndrome is characterized by a specific group of symptoms which occur consistently together.
Trait A distinguishing feature or characteristic of a person.
X-linked Refers to trait arising from a gene located on the X sex chromosome. More common in men than women. Example, male baldness which is usually inherited from the mother’s father’s side of the family.