Medical Genetics Glossary

	Glossary
	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
	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 the #15 chromosome from the father. anomaly - A health problem or feature not normally present in a healthy individual. autosome - One of the first 22 pairs of chromosomes. 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.
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	B
	biochemical genetic testing - A test to study specific enzymes in the body. birth defect - A health problem present at birth.
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	C
	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', in-between the p and q arms. chromosome - A structure in the nucleus of cells which contains genes. 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.
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	D
	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 #21 chromosome. duplication - When a part of a chromosome is present in two copies.
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	E
	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.
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	F
	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. fluorescent 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 B vitamin which is known to decrease the occurrence of some birth defects such as open neural tube defects. fragile-X syndrome - A combination of health problems caused by an abnormally high number of trinucleotide repeats in the FMR-1 gene.
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	G
	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 heritable 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.
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	H
	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 (70,000) on the 46 chromosomes. 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.
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	I
	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.
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	J
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	K
	karyotype - A picture of the 46 chromosomes, lined up into 23 pairs.
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	L
	Lebers Hereditary Optic Neuropathy (LHON) - A disorder of central vision loss caused by a gene inherited from the mother's mitochondria.
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	M
	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 (i.e., some with 46 chromosomes, others with 47). myotonic dystrophy - An inherited autosomal dominant disorder that causes muscle weakness and myotonia (inability of muscles to relax after use), which becomes more severe over time. 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.
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	N
	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.
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	O
	open neural tube defects (ONTDs) - Defects in the primitive spine, called the neural tube, such as spina bifida (open spine) and anencephaly (open skull).
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	P
	Pallister Killian - A combination of birth defects caused by a duplication of the #12 chromosome material. "p" arm - The top half, or shorter arm of a chromosome. 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 the #15 chromosome from the mother or by inheriting a deletion of a region of chromosome #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.
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	Q
	"q" arm - The bottom half, or longer arm, of a chromosome.
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	R
	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.
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	S
	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 anemia - 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.
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	T
	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 with such as your 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 #13 chromosomes, also known as Patau syndrome. trisomy 18 - The presence of three #18 chromosomes, also known as Edwards syndrome. trisomy 21 - The presence of three #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.
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	U
	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.
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	V
	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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	W
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	X
	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.
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	Y
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	Z
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