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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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MEDIAL RECTUS MUSCLE The muscle that turns the eye inward toward the nose (adduction).

MEDIUM CHAIN ACYL-COA DEHYDROGENASE

Abbreviated MCAD, this is the enzyme responsible for the breakdown of medium chain fatty acids in humans. People affected with MCAD deficiency produce a form of MCAD that is not as efficient as the normal form of MCAD.

MEDIUM CHAIN FATTY ACIDS Fatty acids containing between four and 14 carbon atoms.

MEDULLARY CAVITY The marrow-filled cavity inside of a long bone (such as the femur).

MEDULLOBLASTOMA Tumor of the central nervous system derived from undifferentiated cells of the primitive medullary tube.

MEGACOLON Dilation of the colon.

MEIOSIS The process in which a cell in the testes or ovaries undergoes chromosome separation and cell division to produce sperm or eggs.

MELANIN Pigments normally produced by the body that give color to the skin and hair.

MELANOCYTES A cell that can produce melanin.

MELANOMA Tumor, usually of the skin.

MELANOSOMES Granules of pigment within melanocytes that synthesize melanin.

MELATONIN A sleep-inducing hormone secreted by the pineal gland.

MEMORY CELLS B-cells whose antibodies recognized antigens from a previous infection; able to mount a quick, efficient response upon a second infection by the same organism.

MENDEL, GREGOR Austrian monk who discovered the basic principals of heredity.

MENINGES The two-layered membrane that covers the brain and spinal cord.

MENINGITIS An infection of the covering of the brain.

MENOPAUSE Cessation of menstruation in the human female, usually occurring between the ages of 46 and 50.

MENSTRUATION Discharge of blood and fragments of the uterine wall from the vagina in a monthly cycle in the absence of pregnancy.

MENTAL RETARDATION Significant impairment in intellectual function and adaptation in society. Usually associated with an intelligence quotient (IQ) below 70.

MERMAID SYNDROME Alternate name for sirenomelia, often used in older references.

MESOMELIA Shortness of the portion of arm connecting the elbow to the wrist or forearm.

MESOMELIC The anatomical term used to describe the middle of a limb. The bones that constitute the middle of the arm are the radius and ulna, and mesomelic bones of the leg are the tibia and fibula.

METABOLIC ACIDOSIS High acidity (low pH) in the body due to abnormal metabolism, excessive acid intake, or retention in the kidneys.

METABOLIC DISORDER A disorder that affects the metabolism of the body.

METABOLIC MYOPATHIES A broad group of muscle diseases whose cause is a metabolic disturbance of some type.

METABOLIC PATHWAY A sequence of chemical reactions that lead from some precursor to a product, where the product of each step in the series is the starting material for the next step.

METABOLISM The total combination of all of the chemical processes that occur within cells and tissues of a living body.

METACARPAL A hand bone extending from the wrist to a finger or thumb.

METACENTRIC When a chromosome has the centromere in the middle of the chromosome it is called a metacentric chromosome.

METACHRONOUS Occurring at separate time intervals.

METAFEMALE An out of date term for XXX females; also called triple X syndrome.

METAPHYSEAL FLARING A characteristic found only by x rays. If present, it means that the ends of the bone are wider than normal.

METAPHYSES The growth zone of the long bones located between the ends (epiphyses) and the shaft (diaphysis) of the bone.

METAPHYSIS An area of softer bone and cartilage in long bones between the diaphysis (shaft) and epiphysis (end).

METASTASIS The spreading of cancer from the original site to other locations in the body.

METASTATIC CANCER A cancer that has spread to an organ or tissue from a primary cancer located elsewhere in the body.

METATARSAL A foot bone extending from the ankle to a toe.

METHYLATION TESTING DNA testing that detects if a gene is active or if it is imprinted.

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METHYLMALONIC ACID An intermediate product formed when certain substances are broken down in order to create usable energy for the body.

METHYLMALONIC COA MUTASE (MCM) The enzyme responsible for converting methylmalonic acid to succinic acid, in the pathway to convert certain substances to usable energy.

METHYLMALONICACIDEMIA The build-up of high levels of methylmalonic acid in the bloodstream due to an inborn abnormality in an enzyme.

METHYLMALONICACIDURIA The buildup of high levels of methylmalonic acid in the urine due to an inborn defect in an enzyme.

MICRO-DELETION SYNDROME A collection of signs and symptoms caused by a deletion of a gene or genes that is too small to be seen through the microscope.

MICROARRAY An ordered arrangement of many different genes on a glass slide or silicon chip. Microarrays allow researchers to study large numbers of genes simultaneously in determining different levels of gene activity in such complex processes as the body’s response to alcohol.

MICROCEPHALIC Having an abnormally small head.

MICROCEPHALIC PRIMORDIAL DWARFISM SYNDROMES A group of disorders characterized by profound growth delay and small head size.

MICROCEPHALY An abnormally small head.

MICROCORNEA Abnormal smallness of the cornea.

MICRODONTIA Small teeth.

MICROGNATHIA A term used to describe small, underdeveloped lower jaw and chin.

MICROGNATHY Having a very small and receding jaw.

MICROMELIA The state of having extremely short limbs.

MICROPHTHALMIA Small or underdeveloped eyes.

MICROTIA Small or underdeveloped ears.

MIDLINE DEFECTS Disorders involving organs along the center of the body such as the lips, penis, and corpus callosum.

MIDLINE ORGANS Organs found along the center of the body such as the lips, penis, and corpus callosum.

MINIATURIZATION The process of shortening and thinning of the hair shafts that is found in androgenetic alopecia. It is caused by the effects of DHT on the hair follicle.

MINOXIDIL A topical medication sold under the trade name Rogaine for the treatment of male pattern hair loss. It is applied to the scalp as a 2% or 5% solution.

MISCARRIAGE Spontaneous pregnancy loss.

MISMATCH REPAIR Repair of gene alterations due to mismatching.

MITOCHONDRIA Organelles within the cell responsible for energy production.

MITOCHONDRIAL INHERITANCE Inheritance associated with the mitochondrial genome, which is inherited exclusively from the mother.

MITOCHONDRIAL MYOPATHIES Diseases of the muscle accompanied by abnormal changes in the cell mitochondria that results in excessive accumulation of lipids.

MITOSIS The process by which a somatic cell—a cell not destined to become a sperm or egg—duplicates its chromosomes and divides to produce two new cells.

MITRAL VALVE The heart valve that prevents blood from flowing backwards from the left ventricle into the left atrium. Also known as bicuspid valve.

MITRAL VALVE PROLAPSE A heart abnormality in which one of the valves of the heart (which normally controls blood flow) becomes floppy. Mitral valve prolapse may be detected as a heart murmur but there are usually no symptoms.

MIXED TYPE HEARING LOSS Hearing loss that involves both conductive and sensorineural losses.

MONOSOMY Missing an entire copy of a chromosome or a piece of one copy of a chromosome.

MONOZYGOTIC From one zygote, as in identical twins. The zygote is the first cell formed by the union of sperm and egg.

MORPHEA The most common form of localized scleroderma.

MOSAIC A term referring to a genetic situation in which an individual’s cells do not have the exact same composition of chromosomes. In Down syndrome, this may mean that some of the individual’s cells have a normal 46 chromosomes, while other cells have an abnormal 47 chromosomes.

MOSAICISM A genetic condition resulting from a mutation, crossing over, or nondisjunction of chromosomes during cell division, causing a variation in the number of chromosomes in the cells.

MOTOR FUNCTION The ability to produce body movement by complex interaction of the brain, nerves, and muscles.

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MOTOR NEURONS Class of neurons that specifically control and stimulate voluntary muscles.

MOTOR SKILLS DISORDER A disorder that affects motor coordination or its development, and the control of particular groups of muscles that perform activities.

MOTOR UNITS Functional connection with a single motor neuron and muscle.

MOTTLED RETINA Changes in the retina of the eye causing a loss of visual acuity.

MUCOCILIARY ESCALATOR The coordinated action of tiny projections on the surfaces of cells lining the respiratory tract, which moves mucus up and out of the lungs.

MUCOLIPID Lipid that accumulates in cells in mucolipidosis disorders.

MUCOLIPIN-1 Protein in the cell membrane, probably a calcium ion channel, involved in recycling membrane lipids and is deficient in mucolipidosis IV.

MUCOLYTIC An agent that dissolves or destroys mucin, the chief component of mucus.

MUCOPOLYSACCHARIDE A complex molecule made of smaller sugar molecules strung together to form a chain. Found in mucous secretions and intercellular spaces.

MUCOPOLYSACCHARIDOSIS I H (MPS I H) Another name for Hurler syndrome.

MUCORMYCOSIS An organism that commonly infects individuals with diabetes following ketosis events.

MUCOUS MEMBRANE Thin, mucous covered layer of tissue that lines organs such as the intestinal tract.

MULLERIAN DUCTS Structures in the embryo that develop into the fallopian tubes, the uterus, the cervix, and the upper vagina in females.

MULTI-INFARCT DEMENTIA Dementia caused by damage to brain tissue resulting from a series of blood clots or clogs in the blood vessels. It is also called vascular dementia.

MULTIFACTORIAL Describes a disease that is the product of the interaction of multiple genetic and environmental factors.

MULTIFACTORIAL INHERITANCE A type of inheritance pattern where many factors, both genetic and environmental, contribute to the cause.

MULTIFOCAL BREAST CANCER Multiple primary cancers in the same breast.

MULTIPLE CARBOXYLASE DEFICIENCY A type of propionic acidemia characterized by an inability to metabolize biotin.

MULTIPLE SCLEROSIS (MS) A progressive degeneration of nerve cells that causes episodes of muscle weakness, dizziness, and visual disturbances, followed by periods of remission.

MURMUR A noise, heard with the aid of a stethoscope, made by abnormal patterns of blood flow within the heart or blood vessels.

MUSCULAR DYSTROPHY A group of inherited diseases characterized by progressive wasting of the muscles.

MUTAGEN An environmental influence that causes changes in DNA.

MUTANT A change in the genetic material that may alter a trait or characteristic of an individual or manifest as disease.

MUTATION A permanent change in the genetic material that may alter a trait or characteristic of an individual, or manifest as disease, and can be transmitted to offspring.

MYELIN A fatty sheath surrounding nerves in the peripheral nervous system, which help them conduct impulses more quickly.

MYELODYSPLASIA A bone marrow disorder that can develop into aplastic anemia requiring bone marrow or stem cell transplantation.

MYELOMENINGOCELE A sac that protrudes through an abnormal opening in the spinal column.

MYOCLONUS Twitching or spasms of a muscle or an interrelated group of muscles.

MYOGLOBINURIA The abnormal presence of myoglobin, a product of muscle disintegration, in the urine. Results in dark-colored urine.

MYOPATHY Any abnormal condition or disease of the muscle.

MYOPIA Nearsightedness. Difficulty seeing objects that are far away.

MYOTONIA The inability to normally relax a muscle after contracting or tightening it.

MYOTONIC DYSTROPHY A form of muscular dystrophy, also known as Steinert’s condition, characterized by delay in the ability to relax muscles after forceful contraction, wasting of muscles, as well as other abnormalities.

MYXEDEMA Swelling of the face, hands, feet, and genitals due to hypothyroidism.

MYXOID Resembling mucus.

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N-ACETYLGLUCOSAMINE-1-PHOSPHOTRANSFERASE (GNPTA) Enzyme that attaches a signal to other enzymes and directs those enzymes to the lysosome; deficient in mucolipidoses II and III.

NALTREXONE A medication originally developed to treat addiction to heroin or morphine that is also used to treat alcoholism. It works by reducing the craving for alcohol rather than by producing vomiting or other unpleasant reactions.

NANISM Short stature.

NARCOTICS Strong, prescription medication that can be effective in treating pain, but has the potential to be habit-forming if their use is not supervised correctly.

NASOGASTRIC TUBE A long flexible tube inserted through the nasal passageways, down the throat, and into the stomach. Used to drain the contents of the stomach.

NATURAL IMMUNITY First line immune response that is non-specific. Includes action of phagocytes, natural killer cells, and complement cells.

NATURAL KILLER CELLS Specialized white blood cells involved in natural immunity. Can kill some viruses and cancer cells.

NECROSIS Death of a portion of tissue differentially affected by disease or injury.

NECROTIZING ENCEPHALOMYELOPATHY A progressive degeneration of the brain and central nervous system. This condition is fatal in nearly all individuals affected with type A pyruvate carboxylase deficiency.

NEGATIVE SYMPTOMS Symptoms of schizophrenia characterized by the absence or elimination of certain behaviors. DSM-IV specifies three negative symptoms: affective flattening, poverty of speech, and loss of will or initiative.

NEONATAL Neonatal refers to the first 28 days after birth.

NEONATOLOGIST A physician (pediatrician) who has special training in the care of newborns (neonates).

NEPHRONS Microscopic-size tubes that filter the water that flows into the kidneys.

NEPHROPATHY Kidney disease.

NEPHROSIS A non-inflammatory disease of the kidneys.

NERVE CONDUCTION TESTING Procedure that measures the speed at which impulses move through the nerves.

NERVOUS SYSTEM The complete network of nerves, sense organs, and brain in the body.

NEUCHAL TRANSLUCENCY A pocket of fluid at the back of an embryo’s neck visible via ultrasound that, when thickened, may indicate the infant will be born with a congenital heart defect.

NEURAL Regarding any tissue with nerves, including the brain, the spinal cord, and other nerves.

NEURAL CREST CELLS A group of cells in the early embryo, located on either side of the area that will eventually develop into the spinal cord. The cells migrate (move) away from the area and give rise to various body structures, including melanocytes (pigment producing cells), certain structures of the face and head, and parts of the nervous system.

NEURAL TUBE DEFECT A group of severe birth disorders in which the brain and spinal cord are malformed and lack the protective skeletal and soft tissue encasement.

NEUROCRISTOPATHY A disorder that results from abnormal development and/or migration of the neural crest cells in the embryo.

NEURODEGENERATIVE Relating to degeneration of nerve tissues.

NEUROFIBROMA A soft tumor usually located on a nerve.

NEUROFIBROMATOSIS Progressive genetic condition often including multiple café-au-lait spots, multiple raised nodules on the skin known as neurofibromas, developmental delays, slightly larger head sizes, and freckling of the armpits, groin area, and iris.

NEUROLEPTIC Another name for the older type of antipsychotic medications given to schizophrenic patients.

NEUROLOGIC Relating to the brain and central nervous system.

NEUROLOGIST A physician who specializes in disorders of the nervous system, including the brain, spine, and nerves.

NEUROMETABOLIC DISORDER Any disorder or condition that affects both the central nervous system (CNS) and the metabolism of the body.

NEUROMUSCULAR Involving both the muscles and the nerves that control them.

NEUROMUSCULAR JUNCTION The site at which nerve impulses are transmitted to muscles.

NEURON The fundamental nerve cell that conducts impulses across the cell membrane.

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NEURONAL CEROID LIPOFUSCINOSES A family of four progressive neurological disorders.

NEUROPATHY A condition caused by nerve damage. Major symptoms include weakness, numbness, paralysis, or pain in the affected area.

NEUROTRANSMITTER Chemical in the brain that transmits information from one nerve cell to another.

NEUTROPENIA A condition in which the number of leukocytes (a type of white or colorless blood cell) is abnormally low, mainly in neutrophils (a type of blood cell).

NEUTROPHIL The primary type of white blood cell involved in inflammation. Neutrophils are a type of granulocyte, also known as a polymorphonuclear leukocyte.

NEVI Plural of nevus.

NEVUS Any anomaly of the skin present at birth, including moles and various types of birthmarks.

NEVUS FLAMMEUS A flat blood vessel tumor present at birth; also known as a “port wine stain.”

NEWBORN SCREENING The act of testing all infants for a specific disease shortly after birth for the purpose of preventing disease progression through prompt medical treatment.

NITRATES/NITRITES Chemical compounds found in certain foods and water that, when consumed, may increase the risk of gastric cancer.

NITROGEN A gaseous element that makes up the base pairs in DNA.

NON-INSULIN-DEPENDENT DIABETES MELLITUS (NIDDM) Synonymous with type II diabetes, the most common form of diabetes that tends to be highly influenced by lifestyle factors and typically occurs in adulthood.

NON-SYNDROMIC HEARING LOSS Hearing loss that is not accompanied by other symptoms characteristic of a larger genetic syndrome.

NONDISJUNCTION Non-separation of a chromosome pair, during either meiosis or mitosis.

NONSPHEROCYTIC Literally means not sphereshaped. Refers to the shape of red blood cells in nonspherocytic hemolytic anemia.

NONVERBAL LEARNING DISABILITY (NLD) A learning disability syndrome identified in 1989 that may overlap with some of the symptoms of Asperger syndrome.

NOONAN SYNDROME A genetic syndrome that possesses some characteristics similar to cardiofaciocutanous syndrome. It is unclear whether the two syndromes are different or two manifestations of the same disorder.

NUCLEAR INHERITANCE Inheritance associated with the nuclear genome (the 23 pairs of chromosomes). This inheritance follows the rules of segregation developed by Gregor Mendel and is alternately termed Mendelian inheritance.

NUCLEIC ACID A type of chemical used as a component for building DNA. The nucleic acids found in DNA are adenine, thymine, guanine, and cytosine.

NUCLEOTIDES Building blocks of genes, which are arranged in specific order and quantity.

NUCLEUS The central part of a cell that contains most of its genetic material, including chromosomes and DNA.

NYSTAGMUS Involuntary, rhythmic movement of the eye.

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OBLIGATE CARRIER An individual who, based on pedigree analysis, must carry a genetic mutation for a particular genetic disease. Parents of a child with an autosomal recessive disorder are obligate carriers.

OBSESSIVE COMPULSIVE DISORDER (OCD) Disorder characterized by persistent, intrusive, and senseless thoughts (obsessions) or compulsions to perform repetitive behaviors that interfere with normal functioning.

OCCIPITAL LOBE An anatomical subdivision, located at the back of the brain, that contains the visual cortex.

OCHRONOSIS A condition marked by pigment deposits in cartilage, ligaments, and tendons.

OCULAR A broad term that refers to structure and function of the eye.

OCULAR ALBINISM A type of albinism that affects the vision.

OCULO Related to the eye.

OCULO-DIGITAL REFLEX A reflex causing an individual to press on their eyes with their fingers or fists.

OCULOCUTANEOUS ALBINISM Inherited loss of pigment in the skin, eyes, and hair.

OCULOMOTOR NERVE Cranial nerve III; the nerve that extends from the midbrain to several of the muscles that control eye movement.

OCULOPHARYNGEAL MUSCULAR DYSTROPHY (OPMD) Form of muscular dystrophy affecting adults of both sexes and causing weakness in the eye muscles and throat.

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OKIHIRO SYNDROME Inherited disorder characterized by abnormalities of the hands and arms and hearing loss; may be associated with Duane retraction syndrome.

OLIGODACTYLY The absence of one or more fingers or toes.

OLIGODONITA The absence of one or more teeth.

OLIGOHYDRAMNIOS Reduced amount of amniotic fluid. Causes include non-functioning kidneys and premature rupture of membranes. Without amniotic fluid to breathe, a baby will have underdeveloped and immature lungs.

OLIGOSACCHARIDE Several monosaccharide (sugar) groups joined by glycosidic bonds.

OLLIER DISEASE Also termed multiple enchondromatosis. Excessive cartilage growth within the bone extremities that result in benign cartilaginous tumors arising in the bone cavity.

OMPHALOCELE A birth defect where the bowel and sometimes the liver, protrudes through an opening in the baby’s abdomen near the umbilical cord.

OMPHALOPAGUS Conjoined twins who are attached at the abdomen.

ONYCHOGRYPHOSIS Overgrowth of the fingernails and toenails.

OPHTHALMOLOGIST A physician specializing in the medical and surgical treatment of eye disorders.

OPHTHALMOLOGY The medical specialty of vision and the eye.

OPHTHALMOSCOPE An instrument, with special lighting, designed to view structures in the back of the eye.

OPISTHOTONOS An arched position of the body in which only the head and feet touch the floor or bed when the patient is lying on their back.

OPTIC DISC The region where the optic nerve joins the eye, also refered to as the blind spot.

OPTIC NERVE A bundle of nerve fibers that carries visual messages from the retina in the form of electrical signals to the brain.

OPTOMETRIST A medical professional who examines and tests the eyes for disease and treats visual disorders by prescribing corrective lenses and/or vision therapy. In many states, optometrists are licensed to use diagnostic and therapeutic drugs to treat certain ocular diseases.

ORAL LOADING TEST A procedure in which cystine is administered orally to a patient and plasma levels of cystine are measured. Under normal circumstances, amino

acids are absorbed by the intestine and result in an increase in plasma amino acid levels. However, in cystinuria, there is a problem in the absorption process and blood levels of amino acids do not rise or rise slowly after eating.

ORBITAL CYSTS Small fluid-filled sacs that abnormally develop inside the bony cavity of the skull that holds the eyeball.

ORGANELLE Small, sub-cellular structures that carry out different functions necessary for cellular survival and proper cellular functioning.

ORGANIC ACIDURIA The condition of having organic acid in the urine.

ORTHODONTIST Dentist who specializes in the correction of misaligned teeth.

ORTHOKERATOLOGY A method of reshaping the cornea using a contact lens. It is not considered a permanent method to reduce myopia.

ORTHOPEDIST A doctor specializing in treatment of the skeletal system and its associated muscles and joints.

ORTHOSTATIC HYPOTENSION A sudden decrease in blood pressure upon sitting up or standing. May be a side effect of several types of drugs.

OSMOLARITY The concentration of an osmotic solution, especially when measured in osmols or milliosmols per liter of solution.

OSMOTICALLY Referring to the movement of a solvent through a semipermeable membrane (as of a living cell) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.

OSSICLES Any of the three bones of the middle ear, including the malleus, incus, and stapes.

OSSIFICATION The process of the formation of bone from its precursor, a cartilage matrix.

OSTEOARTHRITIS A degenerative joint disease that causes pain and stiffness.

OSTEOCHONDROMATOSIS Another name for hereditary multiple exostoses, meaning a growth of bone and cartilage.

OSTEOMA A benign bone tumor.

OSTEOMALACIA The adult form of rickets, a lack of proper mineralization of bone.

OSTEOPENIA Abnormal bone mineralization, usually resulting from a failure of the rate of bone matrix formation to compensate for the rate of bone decomposition.

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OSTEOPENIC Bone density that is somewhat low, but not osteoporotic.

OSTEOPOROSIS Loss of bone density that can increase the risk of fractures.

OTITIS MEDIA Inflammation of the middle ear, often due to fluid accumulation secondary to an infection.

OTOLARYNGOLOGIST Physician who specializes in the care of the ear, nose, and throat and their associated structures.

OTOSCLEROSIS The main type of non-syndromic progressive conductive hearing loss seen in humans. In very advanced cases, otosclerosis can become of mixed type.

OVA Another name for the egg cells that are located in the ovaries.

OVARY The female reproductive organ that produces the reproductive cell (ovum) and female hormones.

OVULATION The monthly process by which an ovarian follicle or cyst ruptures, releasing a mature egg cell.

OXYGENATED BLOOD Blood carrying oxygen through the body.

OXYTOCIN A hormone that stimulates the uterus to contract during child birth and the breasts to release milk.

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PACHYDERMA An abnormal skin condition in which excess skin is produced that appears similar to that of an elephant (pachyderm).

PACHYGYRIA The presence of a few broad gyri (folds) and shallow sulci (grooves) in the cerebral cortex.

PALATE The roof of the mouth.

PALLIATIVE Treatment done for relief of symptoms rather than a cure.

PALMOPLANTAR KERATODERMA Group of mostly hereditary disorders characterized by thickening of the corneous layer of skin (hyperkeratosis) on the palms and soles as a result of excessive keratin formation (protein in the skin, hair, and nails).

PALMOPLANTAR KERATOSIS A raised thickening of the outer horney layer of the skin on the palms of the hand and the soles of the feet.

PALPEBRAL FISSURES The opening between the upper and lower eyelids.

PALPITATION An irregular heartbeat.

PALSY Uncontrollable tremors.

PANCREAS An organ located in the abdomen that secretes pancreatic juices for digestion and hormones for maintaining blood sugar levels.

PANCREATIC INSUFFICIENCY Reduction or absence of pancreatic secretions into the digestive system due to scarring and blockage of the pancreatic duct.

PANCREATIC ISLET CELL Cells located in the pancreas that serve to make certain types of hormones.

PANCREATITIS Inflammation of the pancreas.

PANCYTOPENIA An abnormal reduction in the number of erythrocytes (red blood cells), leukocytes (a type of white or colorless blood cell), and blood platelets (a type of cell that aids in blood clotting) in the blood.

PANHYPOPITUITARISM Generalized decrease of all of the anterior pituitary hormones.

PAPILLOMA Any benign localized growth of the skin and the linings of the respiratory and digestive tracts. The most common papilloma is the wart.

PAPILLOMATOUS PAPULES Skin-colored, raised bumps (not warts) found on the skin. Most of these growths are benign (non-cancerous) and rarely become malignant (cancerous).

PARAPAGUS Conjoined twins who are joined at the side of their lower bodies.

PARAPLEGIA Loss of voluntary movement and sensation of both lower extremities.

PARASITIC TWINS Occurs when one smaller, malformed twin is dependent on the larger, stronger twin for survival.

PARASYMPATHETIC GANGLION CELL Type of nerve cell normally found in the wall of the colon.

PARATHYROID GLANDS A pair of glands adjacent to the thyroid gland that primarily regulate blood calcium levels.

PARESTHESIA An abnormal sensation resembling burning, pricking, tickling, or tingling.

PARKINSON DISEASE A disease of the nervous system most common in people over 60, characterized by a shuffling gait, trembling of the fingers and hands, and muscle stiffness. It may be related in some way to Lewy body dementia.

PARKINSONISM A set of symptoms originally associated with Parkinson disease that can occur as side effects of neuroleptic medications. The symptoms include trembling of the fingers or hands, a shuffling gait, and tight or rigid muscles.

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PATAU SYNDROME A syndrome caused by trisomy 13; characterized by cleft palate, severe mental retardation, and many other physical abnormalities; usually lethal by age one.

PATELLA The kneecap.

PATERNAL Relating to one’s father.

PATHOLOGIST A physician who specializes in the diagnosis of disease by looking at living tissues with a microscope.

PECTORALIS MUSCLES Major muscles of the chest wall.

PECTUS CARINATUM An abnormality of the chest in which the sternum (breastbone) is pushed outward. It is sometimes called “pigeon breast.”

PECTUS EXCAVATUM An abnormality of the chest in which the sternum (breastbone) sinks inward; sometimes called “funnel chest.”

PEDIGREE ANALYSIS Analysis of a family tree, or pedigree, in an attempt to identify the possible inheritance pattern of a trait seen in this family.

PELVIC EXAMINATION Physical examination performed by a physician, often associated with a Pap smear. The physician inserts his/her finger into a woman’s vagina, attempting to feel the ovaries directly.

PENDRIN A protein encoded by the PDS (Pendred syndrome) gene located on chromosome 7q31. Pendrin protein is believed to transport iodide and chloride within the thyroid and the inner ear.

PENETRANCE The degree to which individuals possessing a particular genetic mutation express the trait that this mutation causes. One hundred percent penetrance is expected to be observed in truly dominant traits.

PEPTIC ULCER A wound in the bowel that can be caused by stomach acid or a bacterium called Helicobacter pylori.

PEPTIDE A molecular compound made of two or more amino acids.

PERCHLORATE DISCHARGE TEST A test used to check for Pendred syndrome by measuring the amount of iodine stored inside the thyroid gland. Individuals with Pendred syndrome usually have more iodine stored than normal, and thus their thyroid will release a large amount of iodine into the bloodstream when they are exposed to a chemical called perchlorate.

PERICARDIAL CAVITY Space occupied by the heart.

PERICARDITIS Inflammation of the pericardium, the membrane surrounding the heart.

PERINATOLOGIST A physician (obstetrician) who has special training in managing difficult pregnancies. Some prenatal tests, such as chorionic villus sampling and level II ultrasound, are performed primarily by perinatologists.

PERIOD OF SUSCEPTIBILITY The time when teratogens can cause harm to the developing fetus.

PERIODONTITIS Inflammatory reaction of the tissues surrounding and supporting the teeth that can progress to bone destruction and abscess formation, and eventual tooth loss.

PERIOSTEAL Relating to the periosteum, which is the connective tissue that covers all human bones.

PERIPHERAL NERVES Nerves throughout the body that carry information to and from the spinal cord.

PERIPHERAL NEUROPATHY Any disease of the nerves outside of the spinal cord, usually resulting in weakness and/or numbness.

PERIPHERAL VISION The ability to see objects that are not located directly in front of the eye. Peripheral vision allows people to see objects located on the side or edge of their field of vision.

PERITONITIS Inflammation of the peritoneum, the membrane surrounding the abdominal contents.

PERNICIOUS ANEMIA A blood condition with decreased numbers of red blood cells related to poor vitamin B12 absorption.

PEROXISOME A cellular organelle containing different enzymes responsible for the breakdown of waste or other products.

PERVASIVE DEVELOPMENTAL DISORDER (PDD) The term used by the American Psychiatric Association for individuals who meet some but not all of the criteria for autism.

PES PLANUS Flat feet.

PEUTZ-JEGHERS SYNDROME Inherited syndrome causing polyps of the digestive tract and spots on the mouth as well as increased risk of cancer.

PHAGOCYTE White blood cells capable of engulfing and destroying foreign antigen or organisms in the fluids of the body.

PHALANGES Long bones of the fingers and toes divided by cartilage around the knuckles.

PHALILALIA Involuntary echoing of the last word, phrase, sentence, or sound vocalized by oneself.

PHENOTYPE The physical expression of an individuals genes.

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PHENYLALANINE An essential amino acid that must be obtained from food since the human body cannot manufacture it.

PHENYLKETORNURIA (PKU) An inborn error of metabolism that causes build-up of the amino acid, phenylalanine, in the body. The first disease to be used for newborn screening.

PHEOCHROMOCYTOMA A small vascular tumor of the inner region of the adrenal gland. The tumor causes uncontrolled and irregular secretion of certain hormones.

PHILTRUM The center part of the face between the nose and lips that is usually depressed.

PHLEBOTOMY The taking of blood from the body through an incision in the vein, usually in the treatment of disease.

PHOBIA An exaggerated fear.

PHOSPHATE A substance composed of the elements phosphorus and oxygen that contributes to the hydroxyapatite crystals found in normal bones.

PHOSPHORYLATION The addition of phosphoric acid to another compound.

PHOTOPHOBIA An extreme sensitivity to light.

PHOTORECEPTORS Specialized cells lining the innermost layer of the eye that convert light into electrical messages so that the brain can perceive the environment. There are two types of photoreceptor cells: rod cells and cone cells. The rod cells allow for peripheral and night vision. Cone cells are responsible for perceiving color and for central vision.

PHOTOREFRACTIVE KERATECTOMY (PRK) A procedure that uses an excimer laser to make modifications to the cornea and permanently correct myopia. As of early 1998, only two lasers have been approved by the FDA for this purpose.

PHYTANIC ACID A substance found in various foods that, if allowed to accumulate, is toxic to various tissues. It is metabolized in the peroxisome by phytanic acid hydroxylase.

PHYTANIC ACID HYDROXYLASE A peroxisomal enzyme responsible for processing phytanic acid. It is abnormal in Refsum disease.

PICK’S DISEASE A rare type of primary dementia that affects the frontal lobes of the brain. It is characterized by a progressive loss of social skills, language, and memory, leading to personality changes and sometimes loss of moral judgment.

PITUITARY GLAND A small gland at the base of the brain responsible for releasing many hormones, includ-

ing luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

PLACENTA The organ responsible for oxygen and nutrition exchange between a pregnant mother and her developing baby.

PLAQUES Abnormally deposited proteins that interfere with normal cell growth and functioning and usually progresses to cell death.

PLASMA The liquid part of the blood and lymphatic fluid that contains antibodies and other proteins.

PLASMA CELLS Antibody-secreting B-cells.

PLASMALOGENS Fat molecules that are important components of cells and of the myelin sheath that protects nerve cells.

PLASMAPHERESIS A procedure in which the fluid component of blood is removed from the bloodstream and sometimes replaced with other fluids or plasma.

PLASMIN The blood protein responsible for dissolving blood clots.

PLATELETS Small disc-shaped structures that circulate in the bloodstream and participate in blood clotting.

PLEURAL CAVITY Area of the chest occupied by the lungs.

PLEURITIS Inflammation of the pleura, the membrane surrounding the lungs.

PNEUMONIA An infection of the lungs.

PODIATRIST A physician who specializes in disorders of the feet.

POIKILODERMA A condition characterized by skin atrophy, widening of the small blood vessels (telangiectasia), and pigment changes giving a mottled appearance.

POLYDACTYLY The presence of extra fingers or toes.

POLYGENIC A trait, characteristic, condition, etc. that depends on the activity of more than one gene for its emergence or expression.

POLYHYDRAMNIOS A condition in which there is too much fluid around the fetus in the amniotic sac.

POLYMER A very large molecule, formed from many smaller, identical molecules.

POLYMORPHIC Describes a gene for which there exist multiple forms, or alleles.

POLYMORPHISM A change in the base pair sequence of DNA that may or may not be associated with a disease.

POLYMYOSITIS An inflammation of many muscles.

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POLYP A mass of tissue bulging out from the normal surface of a mucous membrane.

POLYPECTOMY Surgical removal of polyps.

POLYPLOIDY A condition in which a cell receives more than two complete sets of chromosomes.

POLYPOSIS A descriptive term indicating that hundreds to thousands of polyps have developed in an organ.

POLYSACCHARIDE Linear or branched macromolecule composed of numerous monosaccharide (sugar) units linked by glycosidic bonds.

POLYSYNDACTYLY Having both extra digits (toes, fingers) as well as webbing (syndactyly) between the digits.

POOR MUSCLE TONE Muscles that are weak and floppy.

PORPHYRIN A large molecule shaped like a four-leaf clover. Combined with an iron atom, it forms a heme molecule.

PORT-WINE STAIN Dark-red birthmarks seen on the skin, named after the color of the dessert wine.

POSITIONAL CLONING Cloning a gene simply on the basis of its position in the genome, without having any idea of the function of the gene.

POSITIVE PREDICTIVE VALUE (PPV) The probability that a person with a positive test result has, or will get, the disease.

POSITIVE SYMPTOMS Symptoms of schizophrenia that are characterized by the production or presence of behaviors that are grossly abnormal or excessive, including hallucinations and thought-process disorder. DSMIV subdivides positive symptoms into psychotic and disorganized.

POST-AXIAL POLYDACTYLY An extra finger or toe on the outside of the hand or foot.

POST-ICTAL STATE A period of lethargy, confusion, and deep breathing following a grand mal seizure that may last from a few minutes to several hours.

POSTERIOR FOSSA Area at the base of the skull attached to the spinal cord.

POVERTY OF SPEECH A negative symptom of schizophrenia, characterized by brief and empty replies to questions. It should not be confused with shyness or reluctance to talk.

PRADER-WILLI SYNDROME A syndrome caused by a deletion in the paternally inherited chromosome 15 or by uniparental disomy of the maternal chromosome 15.

PRE-AXIAL POLYDACTYLY An extra finger or toe on the inside of the hand or foot.

PREAURICULAR PITS Small pits in the skin on the outside of the ear.

PRECOCIOUS PUBERTY An abnormal condition in which a person undergoes puberty at a very young age. This condition causes the growth spurt associated with puberty to occur before the systems of the body are ready, which causes these individuals to not attain normal adult heights.

PREMUTATION A change in a gene that precedes a mutation; this change does not alter the function of the gene.

PRENATAL DIAGNOSIS The determination of whether a fetus possesses a disease or disorder while it is still in the womb.

PRENATAL TESTING Testing for a disease, such as a genetic condition, in an unborn baby.

PRIMARY ATRIAL SEPTATION An improper division of the atria of the heart, or a “hole in the heart,” which results in the formation of a common atrium rather than the normal two-chambered atrium.

PRIMARY CANCER The first or original cancer site, before any metastasis.

PRIMARY CRANIOSYNOSTOSIS Abnormal closure of the cranial sutures caused by an abnormality in the sutures themselves.

PRIMARY DYSTONIA Dystonia that has no connection to disease or injury. Often hereditary.

PRIMARY IMMUNODEFICIENCY DISEASE (PID) A group of approximately 70 conditions that affect the normal functioning of the immune system.

PRIMARY POSITION, PRIMARY GAZE When both eyes are looking straight ahead.

PRIMARY TUMOR The organ or tissue where the tumor began.

PRION A term coined to mean “proteinaceous infectious particle.” Prior to the 1982 discovery of prions, it was not believed that proteins could serve as infectious agents.

PROBAND The person in the family who is affected by a genetic disorder and who brings the family to the attention of a health care provider.

PROGERIA Genetic abnormality that presents initially as premature aging and failure to thrive in children.

PROGNATHISM A protruding lower jaw.

PROLACTIN A hormone that helps the breast prepare for milk production during pregnancy.

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