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Gale Encyclopedia of Genetic Disorder / Gale Encyclopedia of Genetic Disorders, Two Volume Set - Volume 2 - M-Z - I

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GENETIC TEST Testing of chromosomes and genes from an individual or unborn baby for a genetic condition. Genetic testing can only be done if the gene is known.

GENETICIST A specialist (M.D. or Ph.D.) who has training and certification in diagnosing, managing, and counseling individuals/families with genetic disorders. Genetic counselors hold a master’s degree in medical genetics, and provide many of the same services as geneticists.

GENETICS The study of hereditary traits passed on through the genes.

GENITAL TRACT The organs involved in reproduction. In a male, they include the penis, testicles, prostate, and various tubular structures to transport seminal fluid and sperm. In a female, they include the clitoris, vagina, cervix, uterus, fallopian tubes, and ovaries.

GENITALS The internal and external reproductive organs in males and females.

GENITOURINARY Related to the reproductive and urinary systems of the body.

GENOME All of the DNA in one cell.

GERM LINE MOSAICISM A rare event that occurs when one parent carries an altered gene mutation that affects his or her germ line cells (either the egg or sperm cells) but is not found in the somatic (body) cells.

GERM-LINE GENE THERAPY The introduction of genes into reproductive cells or embryos to correct inherited genetic disorders that can cause disease.

GESTATIONAL DIABETES Diabetes of pregnancy that can be insulinor non-insulin-dependent. Usually resolves following delivery, but may predispose to recurrent gestational diabetes and/or other forms of diabetes.

GILLBERG’S CRITERIA A six-item checklist for Asperger syndrome developed by Christopher Gillberg, a Swedish researcher. It is widely used as a diagnostic tool.

GLAUCOMA An increase in the fluid eye pressure, eventually leading to damage of the optic nerve and ongoing visual loss.

GLIOBLASTOMA MULTIFORME Tumor of the central nervous system consisting of undifferentiated glial cells.

GLOBIN One of the component protein molecules found in hemoglobin. Normal adult hemoglobin has a pair each of alpha-globin and beta-globin molecules.

GLOBOID CELLS Large cells containing excess toxic metabolic “waste” of galactosylceramide and psychosine.

GLOMERULI Tiny clusters of capillaries in the kidney.

GLOMERULUS A structure in the kidney composed of blood vessels that are actively involved in the filtration of the blood.

GLUCOCEREBROSIDE A cerebroside that contains glucose in the molecule.

GLUCOSE One of the two simple sugars, together with galactose, that makes up the protein, lactose, found in milk. Glucose is the form of sugar that is used by the body to generate energy.

GLUTEN A protein found in wheat, rye, barley, and oats.

GLYCOGEN The chemical substance used by muscles to store sugars and starches for later use. It is composed of repeating units of glucose.

GLYCOLYSIS The pathway in which a cell breaks down glucose into energy.

GLYCOPROTEIN A protein with at least one carbohydrate group.

GLYCOPROTEIN IIB/IIIA (GP IIB/IIIA) Sugar-proteins on the surface of platelets that bind to the fibrous protein, fibrinogin. These sugar-proteins are abnormal in Glanzmann’s thrombasthenia.

GLYCOSYLPHOSPHATIDYLINOSITOL (GPI) A fat that attaches proteins to the outside walls of blood cells.

GOITER An enlargement of the thyroid gland, causing tissue swelling that may be seen and/or felt in the front of the neck. May occur in people who have overactive production of thyroid hormones (hyperthyroidism), decreased production of thyroid hormones (hypothyroidism), or among people who have normal production of thyroid hormones.

GONAD The organ that will become either a testis (male reproductive organ) or ovary (female reproductive organ) during fetal development.

GONADOTROPHIN Hormones that stimulate the ovary and testicles.

GONIOSCOPE An instrument used to examine the trabecular meshwork; consists of a magnifier and a lens equipped with mirrors.

GRAFT-VERSUS-HOST DISEASE In bone marrow transplantation, the complication that occurs when the donor’s cells attack the recipient’s tissues, in part due to nonidentical donor-recipient HLA types.

GRAND MAL SEIZURE A seizure that causes a loss of consciousness, a loss of bladder control, generalized muscle contractions, and tongue biting.

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GRANULOCYTOPENIA A reduced number of white blood cells in the circulation.

GRAY MATTER Areas of the brain and spinal cord that are comprised mostly of unmyelinated nerves.

GREAT TOE The first and largest toe on the foot.

GRIEF REACTION The normal depression felt after a traumatic major life occurrence such as the loss of a loved one.

GROWTH HORMONE A hormone that eventually stimulates growth. Also called somatotropin.

GUSTATORY LACRIMATION Abnormal development of the tear ducts causing tears when chewing.

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HALLUCAL POLYDACTYLY The appearance of an extra great toe.

HALLUCINATION A sensory experience of something that does not exist outside the mind. A person can experience a hallucination in any of the five senses. Auditory hallucinations are a common symptom of schizophrenia.

HALLUX The great toe.

HAMARTOMA An overgrowth of normal tissue.

HAPLOID Means “half the number;” the number of chromosomes in a sex cell.

HAPLOINSUFFICIENCY The lack of one of the two normal copies of a gene. Haploinsufficiency can result in a genetic disorder if normal function requires both copies of the gene and is one explanation for a dominant pattern of inheritance.

HAPLOTYPE A set of alleles that are inherited together as a unit on a single chromosome because of their close proximity.

HEAD TURN Habitual head position that has been adopted to compensate for abnormal eye movements.

HEARING THRESHOLD The minimum sound level at which a particular individual can hear. This is also called the hearing level (HL) of that person.

HEART VALVE One of four structures found within the heart that prevents backwards flow of blood into the previous chamber.

HEIMLICH MANEUVER An action designed to expel an obstructing piece of food from the throat. It is performed by placing the fist on the abdomen, underneath the breastbone, grasping the fist with the other hand (from behind), and thrusting it inward and upward.

HELICOBACTER PYLORI (H. PYLORI) Bacterium that infects humans and may be associated with an increased risk of gastric cancer.

HELLER’S SYNDROME Another name for Childhood Disintegrative Disorder (CDD). It is also sometimes called dementia infantilis.

HELPER T-CELL Specialized white blood cell that assists in humoral and cellular immunity.

HEMANGIOBLASTOMA A tumor of the brain or spinal cord arising in the blood vessels of the meninges or brain.

HEMANGIOMA Benign tumor made up of clusters of newly formed blood vessels.

HEMATIN A drug administered intravenously to halt an acute porphyria attack. It causes heme biosynthesis to decrease, preventing the further accumulation of heme precursors.

HEMATOMA An accumulation of blood, often clotted, in a body tissue or organ, usually caused by a break or tear in a blood vessel.

HEMATOPOETIC GROWTH FACTORS Substances that assist in the formation of blood cells.

HEMATURIA The presence of blood in the urine.

HEME The iron-containing molecule in hemoglobin that serves as the site for oxygen binding.

HEMIFACIAL MICROSOMIA Term used to describe when one side of the face is smaller than the other.

HEMIHYPERPLASIA A condition in which overdevelopment or excessive growth of one half of a specific organ or body part on only one side of the body occurs.

HEMIHYPERTROPHY Asymmetric overgrowth in which there is an increase in size of existing cells.

HEMIPLEGIA Paralysis of one side of the body.

HEMIVERTEBRA A disorder in which one side or half of a vertebra fails to form.

HEMIZYGOUS Having only one copy of a gene or chromosome.

HEMOCHROMATOSIS Accumulation of large amounts of iron in the tissues of the body.

HEMOGLOBIN Protein-iron compound in the blood that carries oxygen to the cells and carries carbon dioxide away from the cells.

HEMOGLOBIN A Normal adult hemoglobin that contains a heme molecule, two alpha-globin molecules, and two beta-globin molecules.

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HEMOGLOBIN A1C TEST A screening test for diabetes.

HEMOGLOBIN ELECTROPHORESIS A laboratory test that separates molecules based on their size, shape, or electrical charge.

HEMOGLOBIN S Hemoglobin produced in association with the sickle cell trait; the beta-globin molecules of hemoglobin S are abnormal.

HEMOLYTIC Refers to the type of anemia caused by the breakdown of red blood cells, as opposed to anemia due to decreased production, for example.

HEMOLYTIC ANEMIA Anemia that results from premature destruction and decreased numbers of red blood cells.

HEMORRHAGE Very severe, massive bleeding that is difficult to control. Hemorrhage can occur in hemophiliacs after what would be a relatively minor injury to a person with normal clotting factors.

HEMOSTASIS The arrest of bleeding by blood coagulation.

HEPATIC Referring to the liver.

HEPATITIS A viral disease characterized by inflammation of the liver cells (hepatocytes). People infected with hepatitis B or hepatitis C virus are at an increased risk for developing liver cancer.

HEPATOMEGALY An abnormally large liver.

HEPATOSPLENOMEGALY Enlargement of the liver and spleen.

HEREDITARY ANGIONEUROTIC EDEMA Abbreviated HANE, or HAE, this is an inherited kind of angioneurotic edema. Type I HANE is caused by a deficiency of C1INH. Type II HANE is caused by a malformation of the C1-INH protein.

HEREDITARY NON-POLYPOSIS COLON CANCER (HNPCC) A genetic syndrome causing increased cancer risks, most notably colon cancer. Also called Lynch syndrome.

HERITABILITY The proportion of causative factors for a disease that can be attributed to genetics.

HERMANSKY-PUDLAK SYNDROME (HPS) A rare form of albinism, most common in the Puerto Rican community, which can cause pigment changes, lung disease, intestinal disorders, and blood disorders.

HERNIA A rupture in the wall of a body cavity, through which an organ may protrude.

HETEROCHROMIA IRIDES A medical term for individuals with different-colored eyes.

HETEROGENEOUS A set of symptoms or a disorder caused by several different gene mutations.

HETEROPLASMY When all copies of mitochondrial DNA are not the same, and a mix of normal and mutated mitochondrial DNA is present.

HETEROTOPIA Small nodules of gray matter that are present outside the cortex.

HETEROZYGOTE/HETEROZYGOUS Having two different versions of the same gene.

HIGH DENSITY LIPOPROTEIN (HDL) A cholesterol carrying substance that helps remove cholesterol from the cells of the body and deliver it to the liver where it is digested and removed from the body.

HIGH-FUNCTIONING AUTISM (HFA) A subcategory of autistic disorder consisting of children diagnosed with IQs of 70 or higher.

HIGHLY AEROBIC TISSUES Tissue that requires the greatest amount of oxygen to thrive.

HIRSCHPRUNG DISEASE A deformation in which the colon becomes enlarged (megacolon), caused by abnormal nerve control of that portion of the large intestine.

HIRSUITISM The presence of coarse hair on the face, chest, upper back, or abdomen in a female as a result of excessive androgen production.

HISTAMINE A substance released by immune system cells in response to the presence of an allergen; stimulates widening of blood vessels and increased porousness of blood vessel walls so that fluid and protein leaks out from blood to surrounding tissue, causing inflammation of local tissues.

HISTOLOGIC Pertaining to histology, the study of cells and tissues at the microscopic level.

HLA TYPE Refers to the unique set of proteins called human leukocyte antigens. These proteins are present on each individual’s cell and allow the immune system to recognize ‘self’ from ‘non-self’. HLA type is particularly important in organ and tissue transplantation.

HLA-B27 Stands for a specific form of human leukocyte antigen, the proteins involved in immune system function. Strongly associated with ankylosing spondylitis.

HMLH1 AND HMSH2 Genes known to control mismatch repair of genes.

HOLT-ORAM SYNDROME Inherited disorder characterized by congenital heart defects and abnormalities of the arms and hands; may be associated with Duane retraction syndrome.

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HOMEOPATHIC A holistic and natural approach to health care.

HOMEOSTASIS A state of physiological balance.

HOMEOTIC GENES Developmental control genes active in the embryo.

HOMOCYSTEINE An amino acid that is not used to produce proteins in the human body.

HOMOGENTISATE 1,2-DIOXYGENASE (HGD) Homogentisic acid oxidase, the fourth enzyme in the metabolic pathway for the breakdown of phenylalanine.

HOMOGENTISIC ACID (HGA) 2,5-Dihydroxypheny- lacetic acid, the third intermediate in the metabolic pathway for the breakdown of phenylalanine.

HOMOLOGOUS CHROMOSOMES Homologous chromosomes are two chromosomes of a doublet set that are identical, particularly for the genes that are on them.

HOMOLOGUES Chromosomes or chromosome parts identical with respect to their construction and genetic content (i.e. the two chromosome 1s are homologous, as are the two #2s, #3s, etc . . . ).

HOMOPLASMY When all copies of mitochondrial DNA are the same, or have the same mutation.

HOMOZYGOTE/HOMOZYGOUS Having two identical copies of a gene or chromosome.

HORMONE A chemical messenger produced by the body that is involved in regulating specific bodily functions such as growth, development, and reproduction.

HORMONE THERAPY Treatment of cancer by changing the hormonal environment, such as testosterone and estrogen.

HUMAN GENOME PROJECT An international collaborative project among scientists to map the genetic sequence of all the chromosomes. This project is funded by the National Institute of Health in the United States.

HUMAN LEUKOCYTE ANTIGENS (HLA) Proteins that help the immune system function, in part by helping it to distinguish ‘self’ from ‘non-self’.

HUMORAL IMMUNITY A type of acquired immunity mediated by B-cells and their secreted antibodies; important in fighting bacterial and some viral infections.

HUNTINGTON DISEASE A midlife-onset inherited disorder characterized by progressive dementia and loss of control over voluntary movements. It is sometimes called Huntington’s chorea.

HUNTINGTON’S CHOREA A hereditary disease that typically appears in midlife, marked by gradual loss of

brain function and voluntary movement. Some of its symptoms resemble those of schizophrenia.

HYALINE A clear substance that occurs in cell deterioration.

HYDRAMNIOS A condition in which there is too much amniotic fluid in the womb during pregnancy.

HYDROCEPHALUS The excess accumulation of cerebrospinal fluid around the brain, often causing enlargement of the head.

HYDROLASE Enzyme that uses water to break down substances.

HYDROMETROCOLPOS An abnormal accumulation of fluids in the uterus and vagina.

HYDRONEPHROSIS Obstruction of the tube that carries urine from the kidney into the bladder causing the pelvis and kidney duct to become swollen with excess urine.

HYDROPS FETALIS A condition characterized by massive edema in a fetus or newborn.

HYDROXYAPATITE A mineral that gives bone its rigid structure and strength. It is primarily composed of calcium and phosphate.

HYDROXYUREA A drug that has been shown to induce production of fetal hemoglobin. Fetal hemoglobin has a pair of gamma-globin molecules in place of the typical beta-globins of adult hemoglobin. Higher-than-nor- mal levels of fetal hemoglobin can ameliorate some of the symptoms of thalassemia.

HYPERAMMONEMIA An excess of ammonia in the blood.

HYPERCALCEMIA High levels of calcium in the blood.

HYPEREXTENSIBILITY The ability to extend a joint beyond the normal range.

HYPERHIDROSIS Excessive perspiration that may be either general or localized to a specific area.

HYPERKERATOSIS Thickening of the skin.

HYPERLORDOSIS An exaggerated curve in the lower (lumbar) portion of the back.

HYPERMOBILITY Unusual flexibility of the joints, allowing them to be bent or moved beyond their normal range of motion.

HYPERPHAGIA Over-eating.

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HYPERPIGMENTATION An abnormal condition characterized by an excess of melanin in localized areas of the skin, which produces areas that are much darker than the surrounding unaffected skin.

HYPERSENSITIVE A process or reaction that occurs at above normal levels; overreaction to a stimulus.

HYPERTELORISM A wider-than-normal space between the eyes.

HYPERTHERMIA Body temperature that is much higher than normal (i.e. higher than 98.6°F).

HYPERTONIA Excessive muscle tone or tension, causing resistance of muscle to being stretched.

HYPERTRICHOSIS Growth of hair in excess of the normal. Also called hirsutism.

HYPERTROPHIC CARDIOMYOPATHY A condition in which the muscle of the heart is abnormally excessively thickened. In microscopic examination, normal alignment of muscle cells is absent (myocardial disarray).

HYPERTROPHY Increase in the size of a tissue or organ brought on by the enlargement of its cells rather than cell multiplication.

HYPNAGOGIC HALLUCINATIONS Dream-like auditory or visual hallucinations that occur while falling asleep.

HYPOCHONDROPLASIA An autosomal dominant form of dwarfism whose physical features are similar to those of achondroplasia but milder. Affected individuals have mild short stature and a normal facial appearance.

HYPOGLYCEMIA An abnormally low glucose (blood sugar) concentration in the blood.

HYPOGONADISM Small testes in men and scarce or irregular mentruation for females.

HYPOHIDROSIS Insufficient perspiration or absent perspiration which may be either general or localized to a specific area.

HYPOKETOSIS Decreased levels of ketone bodies.

HYPOMYELINATION The death of myelin on a nerve or nerves.

HYPOPHOSPHATEMIA The state of having abnormally low levels of phosphate in the bloodstream.

HYPOPIGMENTATION Decreased or absent color (pigment) in a tissue.

HYPOPLASIA/HYPOPLASTIC Incomplete or underdevelopment of a tissue or organ. Hypoplastic left heart syndrome is the most serious type of congenital heart disease.

HYPOSPADIAS An abnormality of the penis in which the urethral opening is located on the underside of the penis rather than at its tip.

HYPOTHALAMUS A part of the forebrain that controls heartbeat, body temperature, thirst, hunger, body temperature and pressure, blood sugar levels, and other functions.

HYPOTHYROID Deficiency in thyroid gland activity or thyroid hormone levels.

HYPOTONIA Reduced or diminished muscle tone.

I I

IATROGENIC Caused by (-genic) doctor (iatro-). An iatrogenic condition is a condition that is caused by the diagnosis or treatment administered by medical professionals. Iatrogenic conditions may be caused by any number of things, including: unsterile medical instruments or devices, contaminated blood or implantations, or contaminated air within the medical facility.

ICHTHYOSIS Rough, dry, scaly skin that forms as a result of an abnormality in skin formation.

IDIOPATHIC Of unknown origin.

IgE An antibody composed of protein; specific forms of IgE produced by cells of immune system in response to different antigens that contact the body; major factor that stimulates the allergic response.

ILIAC ARTERIES Arteries that supply blood to the lower body including the pelvis and legs.

IMMUNE SYSTEM A major system of the body that produces specialized cells and substances that interact with and destroy foreign antigens that invade the body.

IMMUNODEFICIENCY A disorder in the immune system that leaves an individual vulnerable to infection.

IMMUNOGLOBULIN A protein molecule formed by mature B cells in response to foreign proteins in the body; the building blocks for antibodies.

IMMUNOLOGIC Related to immunology, the study of how the body’s immune system fights disease. Many immunologic disorders are characterized by the body’s use of antibodies.

IMMUNOTHERAPY Treatment of cancer by stimulating the body’s immune defense system.

IMPAIRED GLUCOSE TOLERANCE (IGT) May be a precursor to diabetes; marked by blood glucose levels that are not quite elevated to the level seen in nephrogenic diabetes insipidus.

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IMPERFORATE ANUS Also known as anal atresia. A birth defect in which the opening of the anus is absent or obstructed.

IMPOTENCE The inability to have a penile erection, which can be due to tissue damage resulting from sickling within the penis (priapism).

IMPRINTING Process that silences a gene or group of genes. The genes are silenced depending on if they are inherited through the egg or the sperm.

IN UTERO While in the uterus; before birth.

IN VITRO FERTILIZATION Process by which a woman has her eggs surgically removed and fertilized in the laboratory. The developing embryos can then be transferred to her uterus to hopefully achieve a pregnancy.

INCLUSION BODY Abnormal storage compartment inside a cell.

INDUCTION Process where one tissue (the prechordal plate, for example) changes another tissue (for example, changes tissue into neural tissue).

INFANTILE SPASMS The form of grand mal or focal seizures experienced by infants prior to the development of many voluntary muscular controls.

INFECTIVE ENDOCARDITIS An infection of the endothelium, the tissue lining the walls of the heart.

INFERTILITY Inability in a woman to become pregnant.

INFLAMMATION Swelling and reddening of tissue; usually caused by the immune system’s response to the body’s contact with an allergen.

INFORMED CONSENT Provision of complete information to a competent individual regarding a treatment or test. Part of informed consent is to ensure a patient’s understanding of the pros and cons of a procedure and to get their voluntary authorization to perform the procedure.

INGUINAL HERNIA A condition in which part of the intestines protrudes through a tear in the muscles of the abdomen.

INHERITANCE PATTERN The way in which a genetic disease is passed on in a family.

INHERITED GIANT PLATELET DISORDER (IGPD) A group of hereditary conditions that cause abnormal blood clotting and other conditions.

INSOMNIA An inability to either fall or stay asleep, particularly at a time of day when sleep is expected. A number of medications are available and may be used for treatment.

INSULIN A hormone produced by the pancreas that is secreted into the bloodstream and regulates blood sugar levels.

INSULIN RECEPTOR GENE The gene responsible for the production of insulin receptor sites on cell surfaces. Without properly functioning insulin receptor sites, cells cannot attach insulin from the blood for cellular use.

INSULIN RESISTANCE An inability to respond normally to insulin in the bloodstream.

INSULIN-DEPENDENT DIABETES MELLITUS (IDDM)

Synonymous with type I diabetes, the more serious form of diabetes that tends to affect people at a younger age.

INSULIN-LIKE GROWTH FACTOR I A hormone released by the liver in response to high levels of growth hormone in the blood. This growth factor is very similar to insulin in chemical composition; and, like insulin, it is able to cause cell growth by causing cells to undergo mitosis (cell division).

INTERPERSONAL THERAPIES Also called “talking therapy,” this type of psychological counseling is focused on determining how dysfunctional interpersonal relationships of the affected individual may be causing or influencing symptoms of depression.

INTRACRANIAL HEMORRHAGE Abnormal bleeding within the space of the skull and brain.

INTRACRANIAL PRESSURE The pressure of the fluid between the brain and skull.

INTRAGENIC Occuring within a single gene.

INTRAUTERINE Situated or occurring in the uterus.

INTRAUTERINE GROWTH RETARDATION A form of growth retardation occurring in the womb that is not caused by premature birth or a shortened gestation time. Individuals affected with this condition are of lower than normal birth weight and lower than normal length after a complete gestation period.

INTRAVENOUS A route for administration of fluids, nutrients, blood products, or medications. A small, flexible plastic tube is inserted into a vein by way of a needle to establish this route.

INTRAVENOUS PYELOGRAM An x ray assessment of kidney function.

INTRON Portion of the DNA sequence of a gene that is not directly involved in the formation of the chemical that the gene codes for.

INTUSSUSCEPTION One piece of bowel inside another, causing obstruction.

INVERSION A type of chromosomal disorder in which a broken segment of a chromosome attaches to the same chromosome, but in reverse position.

ION CHANNEL Cell membrane proteins that control the movement of ions into and out of a cell.

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IONIZING RADIATION High-energy radiation such as that produced by x rays.

IQ Abbreviation for Intelligence Quotient. Compares an individual’s mental age to his/her true or chronological age and multiplies that ratio by 100.

IRIS The colored part of the eye, containing pigment and muscle cells that contract and dilate the pupil.

IRON OVERLOAD A side effect of frequent blood transfusions in which the body accumulates abnormally high levels of iron. Iron deposits can form in organs, particularly the heart, and cause life-threatening damage.

ISCHEMIC ATTACK A period of decreased or no blood flow.

ISCHOPAGUS Conjoined twins who are attached at the lower half of the body.

ISOMERISM Refers to the organs that typically come in pairs, but where the right organ is structurally different from the left organ. In a condition like asplenia, however, the organs are identical.

ISOMERS Two chemicals identical in chemical composition (contain the same atoms in the same amounts) that have differing structures. The normal prion protein and the infectious prion protein are conformational isomers of one another. They have the same chemical structures, but for some reason, assume different shapes.

ISOTOPE Any of two or more species of atoms of a chemical element with the same atomic number and nearly identical chemical behavior, but with differing atomic mass and physical properties.

ISOZYME/ISOENZYME A group of enzymes that perform the same function, but are different from one another in their structure or how they move.

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JAUNDICE Yellowing of the skin or eyes due to an excess of bilirubin in the blood.

JOINT CONTRACTURES Stiffness of the joints that prevents full extension.

JOINT DISLOCATION The displacement of a bone from its socket or normal position.

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KABUKI Traditional Japanese popular drama performed with highly stylized singing and dancing using special makeup and cultural clothing.

KALLIKREIN A protein necessary for the activation of chemicals that cause dilation of blood vessels to allow increased blood flow to an area that requires more blood than normal. It is also capable of cleaving the complement, C5, into C5a, a much more robust and active form of this complement molecule.

KANNER’S SYNDROME Another name for autism.

KARYOTYPE A standard arrangement of photographic or computer-generated images of chromosome pairs from a cell in ascending numerical order, from largest to smallest.

KARYOTYPING A laboratory procedure in which chromosomes are separated from cells, stained, and arranged so that their structure can be studied under the microscope.

KERATIN A tough, non-water-soluble protein found in the nails, hair, and the outermost layer of skin. Human hair is made up largely of keratin.

KERATINOCYTES Skin cells.

KERATOACANTHOMA A firm nodule on the skin typically found in areas of sun exposure.

KERATOLYTIC An agent that dissolves or breaks down the outer layer of skin (keratins).

KERATOSIS A raised thickening of the outer horny layer of the skin.

KETOACIDOSIS A condition that results when organic compounds (such as propionic acid, ketones, and fatty acids) build up in the blood and urine.

KETOLACTIC ACIDOSIS The overproduction of ketones and lactic acid.

KETONE BODIES Products of fatty acid metabolism in the liver that can be used by the brain and muscles as an energy source.

KETONES “Fuel” molecules that can accumulate and cause the potentially life-threatening complication of ketosis.

KETONURIA The presence of excess ketone bodies (organic carbohydrate-related compounds) in the urine.

KETOSIS An abnormal build-up of chemicals called ketones in the blood. This condition usually indicates a problem with blood sugar regulation.

KIDNEY Either of two organs in the lumbar region that filter the blood, excreting the end products of the body’s metabolism in the form of urine and regulating the concentrations of hydrogen, sodium, potassium, phosphate, and other ions in the body.

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KIDNEY TUBULES A portion of the kidneys that causes water to be excreted as urine or reabsorbed into the body.

KLINEFELTER SYNDROME A syndrome that occurs in XXY males; characterized by sterility and small testes; normal intelligence.

KNOCKOUT EXPERIMENT A type of genetic experiment in which researchers are able to deactivate, or knock out, a gene that may influence a particular trait, such as vulnerability to alcohol.

KYPHOSCOLIOSIS Abnormal front-to-back and side- to-side curvature of the spine.

KYPHOSIS An abnormal outward curvature of the spine, with a hump at the upper back.

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L-CARNITINE A substance made in the body that carries wastes from the body’s cells into the urine.

LABIA Lips of the female genitals.

LACRIMAL DUCTS Tear ducts.

LACTIC ACID The major by-product of anaerobic (without oxygen) metabolism.

LACTIC ACIDOSIS A condition characterized by the accumulation of lactic acid in bodily tissues. The cells of the body make lactic acid when they use sugar as energy. If too much of this acid is produced, the person starts feeling ill with symptoms such as stomach pain, vomiting, and rapid breathing.

LACTOSE A sugar made up of of glucose and galactose. It is the primary sugar in milk.

LAPAROSCOPY A diagnostic procedure in which a small incision is made in the abdomen and a slender, hollow, lighted instrument is passed through it. The doctor can view the ovaries more closely through the laparoscope, and if necessary, obtain tissue samples for biopsy.

LAPAROTOMY An operation in which the abdominal cavity is opened up.

LARYNX The voice box, or organ that contains the vocal cords.

LASER-ASSISTED IN-SITU KERATOMILEUSIS (LASIK) A procedure that uses a cutting tool and a laser to modify the cornea and correct moderate to high levels of myopia.

LATERAL RECTUS MUSCLE The muscle that turns the eye outward toward the ear (abduction).

LEBERS HEREDITARY OPTIC ATROPHY OR LEBERS HEREDITARY OPTIC NEUROPATHY (LHON) Discovered in 1871 by Theodore Leber, the painless loss of central

vision in both eyes, usually occurring in the second or third decade of life, caused by a mutation in mitochondrial DNA. Other neurological problems such as tremors or loss of ankle reflexes may also be present.

LEFT VENTRICULAR ENLARGEMENT Abnormal enlargement of the left lower chamber of the heart.

LENS The transparent, elastic, curved structure behind the iris (colored part of the eye) that helps focus light on the retina.

LENTIGENE A dark colored spot on the skin.

LEPROSY A chronic, contagious skin and nervous system disease that leads, in the more serious form, to numbness, muscle weakness, and paralysis. Leprosy is sometimes referred to as Hansen’s disease.

LEPTOMENINGEAL ANGIOMA A swelling of the tissue or membrane surrounding the brain and spinal cord, which can enlarge with time.

LESION An abnormal or injured section or region of the brain (or other body organ).

LEUCOPENIA A decrease in white blood cells.

LEUKEMIA Cancer of the blood forming organs that results in an overproduction of white blood cells.

LEUKOCYTE A white blood cell. The neutrophils are a type of leukocyte.

LEUKOCYTOSIS An increase in the number of leukocytes in the blood.

LEUKODYSTROPHY A disease that affects the white matter called myelin in the CNS.

LEUKOENCEPHALOPATHY Any of various diseases, including leukodystrophies, affecting the brain’s white matter.

LEVOTHYROXINE A form of thyroxine (T4) for replacement of thyroid hormones in hypothryoidism.

LEWY BODIES Areas of injury found on damaged nerve cells in certain parts of the brain associated with dementia.

LI-FRAUMENI SYNDROME Inherited syndrome known to cause increased risk of different cancers, most notably sarcomas.

LIFETIME RISK A risk that exists over a person’s lifetime; a lifetime risk to develop disease means that the chance is present until the time of death.

LIGAMENT A type of connective tissue that connects bones or cartilage and provides support and strength to joints.

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LIMB DYSTONIA Involuntary cramp or spasm that affects the hands. Also known as writer’s cramp.

LIMB GIRDLES Areas around the shoulders and hips.

LIMB-GIRDLE MUSCULAR DYSTROPHY (LGMD) Form of muscular dystrophy that begins in late childhood to early adulthood and affects both men and women, causing weakness in the muscles around the hips and shoulders.

LIMITED SCLERODERMA A subtype of systemic scleroderma with limited skin involvement. It is sometimes called the CREST form of scleroderma, after the initials of its five major symptoms.

LINKAGE The association between separate DNA sequences (genes) located on the same chromosome.

LINKAGE ANALYSIS A method of finding mutations based on their proximity to previously identified genetic landmarks.

LIPASE A digestive enzyme found in pancreatic fluid that breaks down fats.

LIPID Large, complex biomolecule, such as a fatty acid, that will not dissolve in water. A major constituent of membranes.

LIPOMA A benign tumor composed of well-differen- tiated fat cells.

LIPOPIGMENTS Substances made up of fats and proteins found in the body’s tissues.

LIPOPROTEIN A lipid and protein chemically bound together, which aids in transfer of the lipid in and out of cells, across the wall of the intestine, and through the blood stream.

LIPOSOME Fat molecule made up of layers of lipids.

LISSENCEPHALY A condition in which the brain has a smooth appearance because the normal convolutions (gyri) failed to develop.

LOCALIZED SCLERODERMA Thickening of the skin from overproduction of collagen.

LOCI The physical location of a gene on a chromosome.

LONGITUDINAL STUDY A type of research project in which the same subjects are interviewed repeatedly at intervals over a period of time.

LORICIN One of the proteins that give skin cells their structure.

LOW DENSITY LIPOPROTEINS (LDL) A cholesterol carrying substance that can remain in the blood stream for a long period of time.

LUMBAR LORDOSIS Abnormal inward curvature of the spine.

LUPUS ERYTHEMATOSUS A chronic inflammatory disease that affects many tissues and parts of the body including the skin.

LUTENIZING HORMONE (LH) A hormone secreted by the pituitary gland that regulates the menstrual cycle and triggers ovulation in females. In males it stimulates the testes to produce testosterone.

LYMPH NODE A bean-sized mass of tissue that is part of the immune system and is found in different areas of the body.

LYMPHATIC SYSTEM Lymph nodes and lympatic vessels that transport infection fighting cells to the body.

LYMPHEDEMA DISTICHIASIS Autosomal dominant condition with abnormal or absent lymph vessels. Common signs include a double row of eyelashes (distichiasis) and edema of the limbs beginning around puberty.

LYMPHOCYTES Also called white blood cells, lymphocytes mature in the bone marrow to form B cells, which fight infection.

LYMPHOMA A malignant tumor of the lymph nodes.

LYNCH SYNDROME A genetic syndrome causing increased cancer risks, most notably colon cancer. Also called hereditary non-polyposis colon cancer (HNPCC).

LYSINE A crystalline basic amino acid essential to nutrition.

LYSIS Area of destruction.

LYSOSOMAL Pertaining to the lysosomes, special parts (organelles) of cells that contain a number of enzymes important in the breakdown of large molecules such as proteins and fats.

LYSOSOMAL STORAGE DISEASE A category of disorders that includes mannosidosis.

LYSOSOME Membrane-enclosed compartment in cells containing many hydrolytic enzymes; where large molecules and cellular components are broken down.

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MACROCEPHALY A head that is larger than normal.

MACROGLOSSIA A large tongue.

MACROMOLECULES A large molecule composed of thousands of atoms.

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MACROPHAGE Specialized white blood cells that play a role in breaking down old or abnormal red blood cells.

MACROSOMIA Overall large size due to overgrowth.

MACROSTOMIA A mouth that is larger or wider than normal.

MACULA A small spot located in the back of the eye that provides central vision and allows people to see colors and fine visual details.

MACULE A flat, discolored spot or patch on the skin.

MADAROSIS The medical term for loss of hair from the eyebrows or eyelashes. Madarosis may be associated with a form of alopecia areata called alopecia totalis. It may also result from such diseases as leprosy and syphilis, or from trauma.

MADELUNG’S DEFORMITY A forearm bone malformation characterized by a short forearm, arched or bow shaped radius, and dislocation of the ulna.

MAFFUCCI DISEASE A manifestation of Ollier disease (multiple enchondromatosis) with hemangiomas, which present as soft tissue masses.

MAGNETIC RESONANCE IMAGING (MRI) A technique that employs magnetic fields and radio waves to create detailed images of internal body structures and organs, including the brain.

MAJOR DEPRESSION A psychological condition in which the patient experiences one or more disabling attacks of depression that lasts two or more weeks.

MAJOR HISTOCOMPATIBILITY COMPLEX (MHC)

Includes HLA, as well as other components of the immune system. Helps the immune system function, in part by helping it to distinguish ‘self’ from ‘non-self’.

MALAR HYPOLPLASIA Small or underdeveloped cheekbones.

MALE-LETHAL X-LINKED DOMINANCE An inheritance pattern in which affected male children die from the characteristics of the trait. This death is typically either embryonic, fetal, or neonatal.

MALIGNANT A tumor growth that spreads to another part of the body; usually cancerous.

MALIGNANT HYPERTHERMIA A condition brought on by anesthesia during surgery.

MALROTATION An abnormality that occurs during the normal rotation of an organ or organ system.

MAMMOGRAM A procedure in which both breasts are compressed/flattened and exposed to low doses of x rays, in an attempt to visualize the inner breast tissue.

MAMMOGRAPHY X rays of the breasts; used to screen for breast cancer.

MANDIBLE Lower jaw bone.

MANDIBULAR HYPOPLASIA Underdevelopment of the lower jaw.

MANNOSE A type of sugar that forms long chains in the body.

MANOMETRY A balloon study of internal anal sphincter pressure and relaxation.

MAO-B INHIBITORS Inhibitors of the enzyme monoamine oxidase B. MAO-B helps break down dopamine; inhibiting it prolongs the action of dopamine in the brain. Selegiline is an MAO-B inhibitor.

MAORI A native New Zealand ethnic group.

MARFANOID Term for body type that is similar to people with Marfan syndrome. Characterized by a tall, lean body with long arms and long fingers.

MARFANOID HABITUS An abnormally low weight to height ratio that is sometimes seen in extremely tall and thin people.

MASCULINIZATION Development of excess body and facial hair, deepening of the voice, and increase in muscle bulk in a female due to a hormone disorder.

MASSETER SPASM Stiffening of the jaw muscles. Often one of the first symptoms of malignant hyperthermia susceptibility that occurs after exposure to a trigger drug.

MATERNAL Relating to the mother.

MATERNAL SERUM SCREENING A blood test offered to pregnant women usually under the age of 35, which measures analytes in the mother’s blood that are present only during pregnancy, to screen for Down syndrome, trisomy 18, and neural tube disorders.

MATERNAL UNIPARENTAL DISOMY Chromosome abnormality in which both chromosomes in a pair are inherited from the mother.

MATURITY-ONSET DIABETES OF THE YOUNG (MODY)

A dominantly-inherited subtype of NIDDM with clear genetic inheritance. Onset tends to be earlier than in NIDDM.

MAXIALLARY HYPOPLASIA Underdevelopment of the upper jaw.

MAXILLA One of the bones of the face.

MECONIUM The first waste products to be discharged from the body in a newborn infant, usually greenish in color and consisting of mucus, bile, and so forth.

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