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Glossary
A | B | C | D | E | F | G | H | I-J | K | L | M | N | O | P | Q | R | S | T | U | V | W-Z

A

Acoustic neuroma: Benign tumor of the eighth cranial nerve (acoustic or hearing nerve) which causes hearing impairment (also called acoustic neurinoma or acoustic schwannoma).

Allele: Specific form of a gene. Each individual has two copies of every gene, one inherited from each parent. The particular form of the gene inherited from each parent is referred to as an allele. Neurofibromatosis is due to an alteration of one of the two alleles at the neurofibromatosis gene locus.

Amniocentesis: Method of prenatal diagnosis in which a small amount of amniotic fluid which bathes the fetus is removed for genetic study. Usually performed at 16 to 20 weeks of gestation.

Astrocytoma: A brain tumor containing cells derived from the glial cells (astrocytes or "star-shaped" cells) of the nervous system, which may be benign or malignant.

Axilla: The hollow area under the arm where it joins the body. Skin-fold freckles related to NF1 often develop in this area.

Autosomal dominant inheritance: Only one gene of a pair needs to be altered (mutated) for expression of a trait or disorder. A person who carries such a gene has a 50% chance of passing it on to any of his or her children. Neurofibromatosis is an autosomal dominant disorder.


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B

Biopsy: Surgical removal of tissue for examination for diagnostic purposes.

C

image: cafe-au-lait spot
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Café-au-lait spots: Light-brown flat skin spots, variable in shape and size, commonly present on people with NF1.

Cerebrospinal fluid (CSF): Fluid which bathes the brain and spinal cord.

Chemotherapy: Treatment of person with malignant tumor by chemical agents.

Chorionic villus sampling: Method of prenatal diagnosis in which a small piece of fetal placenta is removed for genetic study. Can be performed in the first third of pregnancy.

Chromosomes: Structures located in the cell nucleus which contain genes determining hereditary characteristics.

Congenital: Present at birth.

CT scan (for computerized tomogram, also called CAT scan for computerized axial tomography): Computer-processed image that allows structures inside the body, including soft tissues, to be visualized.


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D

DNA: The chemical substance that makes genes.

E

EEG: Electroencephalogram, used to examine electrical activity of the brain for diagnosis of seizures and other problems of brain function.

Expressivity: Degree to which a genetic trait is manifested.


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F

Fibroblast: Cell type that is found in connective tissue throughout the body and involved in the development of neurofibromas.

G

Gene: Basic unit of heredity.

Genetic testing: Tests to determine characteristics of genes done to establish a diagnosis or provide genetic counseling.

Genotype: A tiny biochemical structure in cells that transmits characteristics from one generation to the next.

Glaucoma: Increased pressure within the eyeball, which may occur in individuals with neurofibromatosis type 1 having a plexiform neurofibroma of the orbit.

Glioblastoma: A type of malignant brain tumor.

image: glioma
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Glioma: A tumor composed of connective tissue of the nervous system and affecting the brain or spinal cord. Sometimes found on the optic nerve of people with NF1.


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H

Heterozygote: Individual who possesses different alleles at a gene locus on each of a pair of homologous chromosomes.

Homozygote: Individual who possesses the same allele at a gene locus on each of a pair of homologous chromosomes.

Hormone: Chemical substances secreted by glands in the body which serve particular roles.

Hydrocephalus: Presence of increased spinal fluid pressure within the ventricles of the brain.

image: hypertrophy
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Hypertrophy: Increase in the size of a part of the body.

Hypothalamus: Part of brain responsible for control of hormone secretion, appetite, and other "automatic" functions.


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K

Kyphoscoliosis: Spinal deformity combining sideways curvature and hunching forward of the upper part of the spine.

L

Learning disability: A condition that either prevents or significantly hinders somebody from learning basic skills or information at the same rate as most people of the same age.

Leukemia: Malignancy involving white blood cells, found rarely in association with neurofibromatosis type 1.

Linkage analysis: Method of mapping genes in relation to one another along the chromosome.

Lisch nodules
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Lisch nodules: Small clumps of pigment on the iris of the eye, often seen in people with NF1.


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M

Macrocephaly: Enlargement of the head.

Mast cell: Type of cell that is widely distributed throughout the body and particularly prevalent in neurofibroma tissue. Mast cells secrete substances that may affect the behavior of other cells nearby, including those involved in the development of neurofibromas.

Megalencephaly: Enlargement of the head.

Meiosis: Process of cell division which occurs exclusively in germ cells and functions to reduce the chromosome number from 46 to 23 in this cell lineage.

Melanosome: Structure inside melanocytes which contains pigment. Giant melanosomes are seen within pigment cells in a café-au-lait spot.

Mitosis: Process of cell duplication.

MRI Scan
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MRI scan (magnetic resonance imaging): An imaging technique that use electromagnetic radiation to obtain images of the body's soft tissues.

Mutation: A random, permanent alteration in a gene that results in a new trait or characteristic that can be inherited by offspring.

Myelin: The substance that forms an "insulating" sheath around many nerve fibers.


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N

Neural crest: An embryonic structure which contains many of the cell types that tend to grow abnormally in neurofibromatosis.

Neurilemma: The thin membrane which spirally enwraps the myelin layers of myelinated nerves.

Neuro: Denotes relationship to a nerve or nerves, or to the nervous system.

image: neurofibroma
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Neurofibroma: A tumor of peripheral nerves caused by abnormal proliferation of Schwann cells and/or fibroblasts.

Neurofibromatosis 1 (NF1): A disorder characterized by developmental changes in the nervous system, skin, bones, and other tissues. Its most distinctive features are the occurrence of multiple benign soft tumors (neurofibromas) and patches of skin pigmentation (café-au-lait spots).

Neurofibromin: The protein product of the NF1 gene.

Neurofibrosarcoma: Malignant tumor of nerve sheath (also called malignant schwannoma).

Neurons: Electrically active cells of the nervous system responsible for controlling behavior and body functions.

Noonan syndrome: Dominantly inherited disorder characterized by short stature, congenital heart disease, and distinctive appearance. Features of Noonan syndrome have been found in a small proportion of individuals with neurofibromatosis type 1.


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O

image: optic glioma
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Optic glioma: A tumor affecting the optic nerve. Optic glioma may occur in NF1.

Optic nerve: The nerve that transmits visual information from the eye to the brain.

Orbit: The bony cavity of the skull where the eyeball lies.

Orbital dysplasia: A deformity in the orbit, the bony wall behind the eye, and/or the bone behind it, which may result in displacement of the eye.


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P

Penetrance: Proportion of individuals possessing a genetic trait who manifest specific features of the trait.

Peripheral: Situated away from the center or central nervous system.

PET scan (positron emission tomography): A specialized test that measures a region of the body's metabolic activity. The test may be helpful in distinguishing benign neurofibromas from other types of tumors.

Phenotype: Expression of a genetic trait.

Pheochromocytoma: Tumor of the adrenal gland which causes severe high blood pressure.

Pituitary gland: Gland located at the base of the brain which secretes hormones involved in growth, sexual function, and control of other endocrine glands.

image: plexiform
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Plexiform neuofibroma: A diffuse type of neurofibroma affecting a bundle or bundles of nerves.

Polymorphism: Genetic trait for which multiple alleles exist with appreciable frequency in the population.

Precocious puberty: Attainment of puberty abnormally early.

Prenatal diagnosis: The testing for the presence of a medical condition in an embryo or fetus.

Proteus syndrome: Recently described disorder that causes overgrowth of parts of the body, as well as abnormalities of skin and bone. It has been suggested that John Merrick, the "Elephant Man," actually had Proteus syndrome rather than neurofibromatosis.

Pseudoarthrosis: A false joint. May result from fracture within long bone that does not heal in some people with neurofibromatosis.


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R

Radiation therapy: A treatment of malignant tumors that involves killing tumor cells by exposing the affected area to radiation.

Recessive: Both members of a pair of genes need to be altered in order to have expression of the trait or disorder.

Recombination: Process whereby homologous chromosomes exchange segments during meiosis.

Rhabdomyosarcoma: Malignant tumor of muscle cells, found rarely in association with neurofibromatosis type 1.


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S

Sarcoma: Malignant soft-tissue tumor.

Schwann cell: The cell that wraps around a nerve fiber to form a protective myelin sheath.

Schwannoma: Type of tumor composed of Schwann cells and characteristic of NF2.

image: scoliosis
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Scoliosis: An excessive sideways curvature of the spine.

Segmental
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Segmental neurofibromatosis: The occurrence of features of NF1 confined to a specific part of the body. Segmental neurofibromatosis is thought to represent a mutation of the NF1 gene in some but not all cells of the body.

Seizure: Abnormal electrical discharge of brain tissue, often resulting in abnormal body movements or behaviors.

Skin-fold Freckles
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Skin-fold freckles: Freckles on areas of the skin not exposed to the sun. Often seen in people with NF1.

Slit lamp: Device used by ophthalmologists to examine the structures at the front of the eye. Necessary for proper examination for Lisch nodules.

Sphenoid
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Sphenoid: Skull bone that forms a portion of the back of the orbit. Sometimes the sphenoid is abnormally formed in people with NF1, resulting in deformity of the orbit.

Spinal fusion: A means of surgical treatment of scoliosis.

Spontaneous mutation: A mutation occurring without apparent external influence.

Sporadic trait: Occurring in a single individual in a family, with no prior family history.


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T

Tibia
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Tibia: The long bone in front of lower part of leg (shinbone), sometimes bowed in people with NF1.

Tibial dysplasia: A deformity involving excessive bowing or curvature of the tibia, also known as the shin bone.

Tumor: An abnormal uncontrolled growth or mass of body cells that has no physiological function and may be malignant or benign.

V

Ventricles: Cavities within the brain which are filled with cerebrospinal fluid.

Vertebra: Bone of the spinal column.

Vestibular nerve: Cranial nerve that conveys information about sense of balance to the brain. This nerve may be affected by complications of NF2 known as vestibular schawannomas.

von Recklinghausen neurofibromatosis: Another name for neurofibromatosis type 1, the peripheral form of neurofibromatosis.


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