Medical Terms



  • agnosia: A loss of the ability to recognize objects, persons, sounds, shapes or smells without injury to the primary sensory organ or memory loss.
  • agrammatism: The presence of grammatical errors in speech, such as the omission or incorrect usage of articles (“cow jumped over moon”), prepositions (“dog walk bridge”) or verbs (“cat eated mouse”).
  • akinetic mutism: A state where a person can no longer move or talk due to damage to the base of the brain, but the person is awake (not comatose) and their eyes are open and can follow what is going on around them.
  • allele: One version of a gene at a given location on a chromosome.
  • amino acid: The basic building blocks of proteins. There are 20 amino acids.
  • amyloid: A clump of insoluble, fibrous protein that can accumulate in brain tissue because of a variety of different diseases. These deposits disrupt cell function and can lead to premature cell death. The aggregated protein will vary with the particular disease.
  • aphasia: A loss of the ability to produce and/or understand language due to injury to brain areas specialized for these functions.
  • apolipoprotein E (APOE) gene: A gene on chromosome 19 involved in making a protein that helps carry cholesterol and other types of fat in the bloodstream. The APOE ε4 allele is a major known risk-factor gene for late-onset Alzheimer’s disease.
  • apraxia: The loss of the ability to perform tasks that require remembering patterns or sequences of movements (like waving goodbye).
  • associative agnosia: A failure to assign meaning to an object, animal or building that is clearly perceived. For example, a patient with an associative visual agnosis might be able to draw a cow, but would not know what a cow was or did.
  • ataxia: Shaky movements, wobbliness, unsteady walk and clumsiness usually caused by damage to the cerebellum, a part of the brain which controls movement.
  • atrophy: Wasting away or shrinking. Neuronal atrophy is wasting away of neurons, a decrease in neuronal density.
  • autosomal: Refers to any of the 22 paired chromosomes, or the genes on them, that are not the X or Y sex-determining chromosomes.
  • autosomal dominant: Describes a trait or disorder which is expressed in those who have inherited only one copy of a particular gene mutation.


  • base pair: Each base pair forms a “rung of the DNA ladder.” They are the “letters” that spell out the genetic code; the molecules connecting the complementary strands of DNA or RNA.
  • biomarker: A biomarker, or “biological marker,” is something that can be objectively measured and provides information about the normal or abnormal function of the body or the state of a condition or disease.
  • BSE: Bovine spongiform encephalopathy or “mad cow disease.”


  • carrier: An individual who has a recessive, disease-causing gene mutation on one chromosome of a pair and a normal allele at the same spot on the other matching chromosome.
  • cellular inclusion: Any small entity found within a cell.
  • central nervous system: A general term used to describe the brain and spinal cord.
  • cerebellar ataxia: Shaky movements, wobbliness, unsteady walk and clumsiness usually caused by damage to the cerebellum, a part of the brain which controls movement.
  • cerebellar signs: Pertaining to the cerebellum, the part of the brain in the back of the head between the cerebrum and the brain stem; the cerebellum controls balance for walking and standing and other complex motor functions.
  • cerebrospinal fluid (CSF): A clear, watery liquid that bathes, cushions and protects the brain and spinal cord.
  • cerebrum: The largest part of the brain; it is responsible for learning and other conscious mental functions.
  • chorea: Irregular, spasmodic, involuntary movements of the limbs or facial muscles, often accompanied by hypotonia (decreased tone of skeletal muscles).
  • chromosome: Strands of DNA compressed and organized into a double helix structure. Humans typically have 23 pairs of chromosomes.
  • chromosome 17q21 (FTDP-17): The chromosome that contains the gene for making the protein tau.
  • codon: In DNA or RNA, a sequence of three nucleotides that codes for a certain amino acid or signals the termination of translation (stop or termination codon).
  • codon 129: The human prion protein (PrP) has a common polymorphism at codon 129 of the gene PRNP; this polymorphism has a strong influence on genetic susceptibility to prion diseases.
  • cortex: The outer portion of an organ. In the brain, the outer portion of the cerebrum is the cerebral cortex.
  • CT (computerized tomography): Pictures of structures within the body created by a computer that takes the data from multiple X-ray images and turns them in pictures. Using the same dosage of radiation as that of an ordinary X-ray machine, an entire slice of the body can be made visible with about 100 times more clarity with the CT scan.


  • dementia: A deterioration of intellectual faculties, such as memory, concentration and judgment, resulting from an organic disease or disorder of the brain. It is sometimes accompanied by emotional disturbance and personality changes.
  • DNA (deoxyribonucleic acid): The complex molecule that holds the “blueprint” for your body to make proteins.
  • dysesthesia: Painful sensory symptoms, distortion/impairment of any sense (especially the sense of touch), a condition in which an unpleasant sensation is produced by ordinary stimuli.
  • dysphagia: Difficulty in swallowing due to problems in nerve or muscle control.
  • dystonia: Involuntary, sustained muscle contractions that frequently cause twisting body motions, tremor, and abnormal posture (these movements may involve the entire body or only an isolated area).


  • episodic memory: The memory of events, times, places, associated emotions and other conception-based knowledge in relation to an experience.
  • electroencephalogram (EEG): An EEG is a recording of the electrical activity of your brain. Flat metal discs (electrodes) placed on your scalp detect and record the patterns of electrical activity generated by your brain.
  • encephalopathy: Any disease in which the functioning of the brain is affected.
  • extrapyramidal signs: The extrapyramidal system regulates subconscious control of erratic motions, muscle tone and truncal stability through the basal ganglia; injuries to this system can cause movement disorders, inability to initiate movement and/or inability to remain motionless.


  • frontal lobe: The part of each hemisphere of the brain located behind the forehead that serves to regulate and mediate the higher intellectual functions. The frontal lobes have intricate connections to other areas of the brain. In the frontal lobes, we meld emotions, cognition, error detection, volition, a sense of self, and more to create our social brain.
  • frontotemporal dementia (FTD): The umbrella term for the clinical syndromes of behavioral variant frontotemporal dementia (bvFTD), semantic variant primary progressive aphasia (svPPA) and non-fluent variant primary progressive aphasia (nfvPPA). These syndromes share involvement of the frontal and temporal lobes of the brain. This term is sometimes used to refer specifically to bvFTD.
  • frontotemporal lobar degeneration (FTLD): The term that describes the specific pathological diseases that result in FTD syndromes. Subtyping is based on the specific proteins found within neuronal inclusions.


  • gait: How a person walks.
  • gene: A basic unit of DNA that codes for a specific protein. Genes direct a cell to make proteins and guide almost every aspect of a cell’s construction, operation and repair.
  • gene therapy: Experimental treatment of a genetic disorder by replacing, supplementing, or manipulating the expression of abnormal genes with normally functioning genes.
  • genetic mutation: A permanent change in a gene that can be passed on to children.
  • genetic predisposition or susceptibility: Increased susceptibility to a particular disease due to the presence of one or more gene mutations associated with an increased risk for the disease and/or a family history that indicates an increased risk for the disease.
  • genetic risk factor: A change in a gene that increases a person’s risk of developing a disease.
  • genetic variant: A change in a gene that may or may not increase or decrease a person’s risk of developing a disease.
  • genome: The complete DNA sequence, containing all genetic information and supporting proteins, in the chromosomes of an individual or species.
  • genome-wide association study (GWAS): A research method that involves rapidly scanning the genomes of many individuals to find genetic variations associated with a particular disease.
  • gliosis: A process leading to scars in the central nervous system that involves the production of a dense fibrous network of neuroglia (supporting cells) in areas of damage. Gliosis is a prominent feature of many diseases of the central nervous system, including frontotemporal dementia, Alzheimer’s disease, multiple sclerosis and stroke. After a stroke, neurons die and disappear with replacement gliosis.
  • gray matter: The cortex of the brain which contains nerve cell bodies. The gray matter is in contrast to the white matter, the part of the brain that contains myelinated nerve fibers. The gray matter is so named because it appears gray.


  • hyperreflexia: An abnormal, increased action of the reflexes; a reaction of the autonomic (involuntary) nervous system to over-stimulation.


  • iatrogenic: Disease acquired as the result of accidental transmission from one patient to another by medical or surgical procedures.


  • MRI (magnetic resonance imaging): A radiology technique that uses magnetism, radio waves and a computer to produce non-invasive, high-quality images of internal structures of the body. An MRI is painless, does not use x-ray radiation and is a powerful tool for delineating brain structure.
  • microtubules: A key structural element of the scaffolding structure of a cell or cytoskeleton.
  • mutation: A permanent change in the DNA or RNA - the molecular "blueprints" that direct the building of proteins. Mutations can be helpful, neutral or harmful and can be caused randomly or by environmental factors.
  • myoclonus: Sudden, involuntary jerking or twitching of a muscle or group of muscles.


  • neurofibrillary tangle: Pathological clusters of the protein tau that are found within neurons.
  • neuronal inclusion: Any small intracellular body found within a neuron (nerve or brain cell).
  • nonsense mutation: A single base pair substitution that prematurely codes for a stop in amino acid translation (stop codon).


  • pathology: The study and diagnosis of disease through examination of organs, tissues, bodily fluids or whole bodies.
  • PCR (polymerase chain reaction): A key technique in molecular genetics to rapidly copy a short section of DNA or RNA for analysis without having to clone it.
  • pedigree: A diagram of the genetic relationships and medical history of a family using standard symbols and terminology.
  • phenotype: The observable physical and/or biochemical characteristics of the expression of a gene; the clinical presentation of an individual with a particular genotype.
  • phonemic paraphasias: Errors involving the incorrect phoneme (“ped” instead of “bed”) or transposition of a phoneme (“efelant” for “elephant”).
  • Pick bodies: A specific type of cellular inclusion made up of the protein tau and seen in some people with FTD.
  • Pick’s disease: Another name for behavioral variant frontotemporal dementia (bvFTD), also called frontotemporal dementia (FTD).
  • polymorphism: Natural variations in a gene, DNA sequence, protein or chromosome that do not affect the functioning of the gene or cause disease and occur with fairly high frequency in the general population; some polymorphisms can change your susceptibility or resistance to disease.
  • PPA (primary progressive aphasia): A neurodegenerative disease marked by the progressive decline of language functions. PPA has now been split into three subgroups: semantic dementia (SD), progressive nonfluent aphasia (PNFA) and logopenic progressive aphasia (LPA).
  • presenile degenerative dementia: Dementia that starts in people before 65 years of age.
  • presenting symptom: The first change noticed by the patient or caregiver; the change that brings them into the doctor’s office.
  • prion: An infectious agent made up of abnormally folded protein and no genetic material. A disease-causing agent that is neither bacterial nor fungal nor viral and contains no genetic material. The prion protein occurs normally in a harmless form. By folding into an aberrant shape, the normal prion protein turns into a rogue agent. It then co-opts other normal prions to become rogue prions.
  • prodromal symptoms: Any symptom affecting a system other than the nervous system preceding the first neurologic symptom or sign.
  • protein: A substance that determines the physical and chemical characteristics of a cell and, therefore, of an organism. Proteins are essential to all cell functions and are created using genetic information.
  • pulvinar sign: Symmetrically increased signal intensity in the pulvinar region (posterior part of the thalamus) relative to the signal intensity in other deep and cortical gray matter areas on an MRI; the presence of this MRI feature may suggest a vCJD diagnosis in the appropriate clinical context.
  • pyramidal signs: The pyramidal system controls all of our voluntary movements; it is made up of two systems: upper motor neurons in the primary motor cortex and lower motor neurons in the anterior horn of the spinal cord; the axons of the corticospinal tract the condense to form the pyramids – giving the system its name; injuries to this system can cause paralysis.


  • rapidly progressive dementia: A form of dementia in which the time course from the first symptom to dementia is less than two years and often less than one year.


  • semantic memory: The memory of meanings, understandings and other concept-based knowledge. Remembering that a robin is a bird with a red breast is one example of semantic knowledge.
  • semantic paraphasia: The substitution of a word that is closely related to the target word, as in “cat” for “dog.”
  • sign: A sign is an indication that something is not right in the body; defined as things that can be seen by a doctor, nurse or other health care professional; fever, rapid breathing rate and abnormal breathing sounds heard through a stethoscope may be signs of pneumonia.
  • symptom: An indication of disease, illness, injury or that something is not right in the body; symptoms are felt or noticed by a person, but may not easily be noticed by anyone else; chills, weakness, shortness of breath, and a cough may be symptoms of pneumonia.


  • tau: A protein in the body that aids in the cellular structure (cytoskeleton) and cellular transportation.
  • temporal lobe: The lobe of the cerebral hemisphere located down on the side of the brain near the ears. The temporal lobe contains the auditory cortex which is responsible for hearing, language comprehension and memory.
  • transcription: The synthesis of RNA from DNA.
  • translation: The synthesis of protein from RNA.


  • vacuolation: A neuropathologic term that replaces the older terminology of “spongiform change.” This term describes the fluid-filled vesicles (vacuoles) that are seen at dendrite terminals in the neuropil (the network of nerve fibers, neuroglial cells and synapses in the gray matter). Brain damage characterized by a spongy appearance of brain tissue seen under a microscope. This is considered to be a classic neuropathologic feature of prion diseases.


  • white matter: The part of the brain that contains myelinated nerve fibers. The white matter is white because it is the color of myelin, the insulation covering the nerve fibers. The white matter is as opposed to the gray matter (the cortex of the brain which contains nerve cell bodies).