Glossary

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A

Abnormality - a health problem or feature not normally present in a healthy individual

Amplification - the production of many copies of a region of DNA

Angelman syndrome - a combination of birth defects caused by inheriting both copies of a section of the #15 chromosome from the father

Anomaly - a health problem or feature not normally present in a healthy individual; a deviation from the normal

Autosomal dominant inheritance - a gene on one of the first 22 pairs of chromosomes, which, when present in one copy, causes a trait or disease to be expressed

Autosomal recessive inheritance - a gene on one of the first 22 pairs of chromosomes, which, when present in two copies, causes a trait or disease to be expressed

Autosome - one of the first 22 pairs of chromosomes

B

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Biochemical genetic testing - a test to study specific enzymes in the body

Birth defect - a health problem present at birth

C

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Carrier testing - testing performed to determine whether a person carries one copy of an altered gene for a particular recessive disease

Centromere - the center part of a chromosome that appears pinched between the p and q arms

Chromosome - a structure in the nucleus of cells which contains genes

Chromosomal microarray analysis - a new laboratory test used to detect chromosomal imbalance at a higher resolution than current standard chromosome or FISH techniques

Codon - a triplet of three letters (base pairs) of the DNA alphabet

Congenital - present at birth

Congenital anomaly - a health problem present at birth (not necessarily genetic)

Congenital varicella syndrome - a combination of birth defects caused by contracting chickenpox during the first 20 weeks of pregnancy

Cri du Chat syndrome - a rare combination of birth defects caused by a deletion of chromosome 5p

Cystic fibrosis - an inherited autosomal recessive condition that causes the secretion of abnormal mucus in the lungs and problems with pancreas function and food absorption

Cytogenetics - the study of chromosomal material

D

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De novo - new, not present previously

Deletion - when a part of a chromosome is missing, or part of the DNA code is missing

Diagnostic testing - used to identify or confirm the diagnosis of a disease or a condition in a person or a family

Direct DNA studies - studies which look directly at the gene in question for an error

DNA - deoxyribosenucleic acid, the chemical which makes up our genes

Down syndrome - a combination of birth defects caused by the presence of an extra No. 21 chromosome

Duplication - when a part of a chromosome is present in two copies

E

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Enzyme replacement therapy (ERT) - replacing the enzyme which is missing or defective in a genetic disease

Extended banding chromosome study - when the chromosomes are studied at a higher resolution than a standard chromosome study, allowing you to see smaller pieces of the chromosome material

F

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Fetal alcohol syndrome - a combination of birth defects caused by the mother's consumption of alcohol during pregnancy

Fetal hydantoin syndrome - a combination of birth defects caused by the mother's use of phenytoin, an anti-seizure medication, during the first trimester of pregnancy

First-degree relative - a relative that you share 1/2 of your genes with - such as your parents, children, and siblings

Fluorescence in situ hybridization (FISH) - a laboratory technique used to determine how many copies of a specific segment of DNA are present or absent in a cell

Folic acid - a nutrient found in some green leafy vegetables, nuts, beans, citrus fruits, fortified breakfast cereals, and some vitamin supplements, helping to reduce the risk of birth defects of the brain and spinal cord

Fragile-X syndrome - a combination of health problems caused by an abnormally high number of trinucleotide repeats in the FMR-1 gene

G

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Galactosemia - an inherited recessive disorder which is a disease tested for by newborn screening. Dietary treatment is available for this disorder

Gene - a segment of DNA that produces a protein product; genes determine traits

Gene therapy - inserting the normal gene into a person, to replace a non-working or missing gene

Genetic - determined by genes or chromosomes

Genetic counseling - providing an assessment of inheritable risk factors and information to patients and their relatives concerning the consequences of a disorder, the probability of developing or transmitting it and ways in which it can be prevented, treated and managed

H

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Hemophilia A - a blood clotting disorder caused by a gene on the X chromosome

Human Genome Project - a government funded project to sequence and map all of the human genes (25,000) on the 46 chromosomes (23 pairs)

Hypothyroidism - a treatable disorder which is a disease tested for by many newborn screening programs. Low thyroid levels in a newborn can cause major problems if left untreated

I

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Inborn error of metabolism - a disorder caused by an inherited defect in an enzyme pathway which affects the body's metabolism

Incontinentia pigmenti (IP) - an inherited X-linked dominant condition that causes skin abnormalities and many other health problems

Indirect DNA studies - studies that look at markers around the gene in question, due to an inability to study the gene itself; also called linkage studies

Inheritance - used to describe a trait or gene passed from one generation to the next

Inversion - when a chromosome breaks and the piece of the chromosome turns upside down and reattaches itself. Inversions may or may not cause birth defects depending upon their exact structure

Isolated - refers to an individual who is the only affected member of his/her family, either by chance or through a new mutation, of a birth defect

K

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Karyotype - a picture of the 46 chromosomes, lined up into 23 pairs

L

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Lebers Hereditary Optic Neuropathy (LHON) - a disorder of central vision loss caused by a gene inherited from the mother's mitochondria

M

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Marfan syndrome - a connective tissue disorder associated with autosomal dominant inheritance

Markers - known DNA sequences used to track a gene in a family

Meiosis - the cell division process that eggs and sperm go through which halves the chromosome number from 46 to 23

Mendel - an Austrian monk who performed experiments on garden peas to understand inheritance patterns

Metabolism - a term used to describe how the body converts food to energy, and then gets rid of waste products

Mitochondrial inheritance - when a gene from the mitochondria is passed through a family (always the mother) that results in a trait or disease

Mitosis - the cell division process that other cells, besides eggs and sperm, go through

Monosomy - having a single copy of a chromosome, rather than the usual pair

Mosaicism - the presence of two or more chromosome patterns in the cells of a person, resulting in two or more cell lines (e.g., some with 46 chromosomes, others with 47)

Multifactorial - an inheritance pattern involving both genetic and environmental factors

Mutations - changes in the DNA that codes for a gene, which may or may not cause a normal working gene to become a non-working gene

N

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Newborn screening - a test done on every baby born in the United States within the first few days of life, to look for inherited, treatable, metabolic disorders

Nondisjunction - an error in cell division where the chromosomes fail to disjoin, so that both pass to the same daughter cell

O

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Open neural tube defects (ONTDs) - defects in the primitive spine, called the neural tube, such as spina bifida (open spine) and anencephaly (open skull)

P

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"P" arm - the top half, or shorter arm of a chromosome

Pallister Killian - a combination of birth defects caused by a duplication of the No. 12 chromosome material

Pedigree - a diagram of a family tree indicating the family members and their relationship to the person with an inherited disorder

Phenylketonuria (PKU) - an inherited recessive disorder which is a disease tested for by newborn screening and often treatable by diet

Prader-Willi syndrome - A combination of birth defects caused by inheriting both copies of a section on the No. 15 chromosome from the mother or by inheriting a deletion of a region of chromosome No. 15 from the father

Preconception visit - a pre-pregnancy examination performed by your physician before you become pregnant to assess overall health and identify potential risk factors that may complicate a pregnancy

Predictive genetic testing - determines the chances that a healthy individual with or without a family history of a certain disease might develop that disease

Preimplantation studies - used following in vitro fertilization to diagnose a genetic disease or condition in an embryo before it is implanted into the mother's uterus

Prenatal diagnosis - used to diagnose a genetic disease or condition in the developing fetus

Presymptomatic genetic testing - used to determine whether persons who have a family history of a disease but no current symptoms have the gene alteration associated with the disease

Q

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"Q" arm - the bottom half, or longer arm, of a chromosome

R

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Red-green color blindness - a gene on the X chromosome which causes difficulty with distinguishing shades of red and green

Ring chromosome - a chromosome whose ends stick together to form a circle or ring

S

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Second-degree relative - a relative that you share 1/4 of your genes with such as your aunts, uncles, nieces, nephews and grandparents

Sex chromosomes - the 23rd pair of human chromosomes which determine gender; females have two X chromosomes; males have one X and one Y chromosome

Sibling - brother or sister

Sickle cell disease - an inherited autosomal recessive condition that causes abnormal hemoglobin in blood cells, leading to infections and organ damage

Syndrome - a collection of traits, health problems, and/or birth defects in an individual which usually has a single underlying cause

T

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Tay Sachs disease - an inherited autosomal recessive condition that causes a progressive degeneration of the central nervous system which is fatal (usually by age 5)

Teratogen - an agent that has the potential to cause birth defects if exposure to a fetus occurs at a critical time in pregnancy

Third-degree relative - a relative that you share 1/8 of your genes, such first cousins

Threshold - a term used to describe the level of liability genes and environmental triggers needed to cause expression of a disorder in multifactorial inheritance; the level may differ between males and females

Translocation - when the location of specific chromosome material moves to another chromosome

Trinucleotide repeats - several triplets of the DNA alphabet in a row

Trisomy - having three copies of one chromosome, rather than two copies

Trisomy 13 - the presence of three No. 13 chromosomes, also known as Patau syndrome

Trisomy 18 - the presence of three No. 18 chromosomes, also known as Edwards syndrome

Trisomy 21 - the presence of three No. 21 chromosomes, also known as Down syndrome

Turner syndrome - a combination of health problems caused by the absence of one sex chromosome, leaving a single X chromosome or 45 total

U

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Uniparental disomy - when two copies of a chromosome come from one parent, rather than one copy from the mother, and one copy from the father

V

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Varicella - the virus which causes chickenpox

Vitamin therapy - using nutrition to decrease the incidence of disease or symptoms

VZIG - varicella-zoster immune globulin, a vaccine for chickenpox

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X-linked inheritance - a gene on the X chromosome passed through a family, resulting in a specific trait or disease to be seen more commonly in males than females