HD Glossary

Note: Some words can have differing definitions depending on the context in which they are used. The definitions presented here are the ones that best apply to the words as they are used. HDSA is grateful to the Stanford Hopes website for their contribution and maintenance of this glossary.

 

 

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  • P53 - One of the transcription factors that requires the presence of CBP in order to bind to DNA. An inability of P53 to access and bind to the DNA can lead to abnormal gene transcription and expression, ultimately leading to cell death.
  • pancreas - A large gland that secretes digestive enzymes and the hormones insulin and glucagon.
  • parasite - Something that lives in, with, or on another organism and obtains benefits from the host, which it usually injures.
  • Parkinson's disease - A neurodegenerative disorder that primarily affects one's ability to perform smooth movements. The disease is associated with a loss of dopamine-producing nerve cells in the substantia nigra region of the brain.
  • parietal lobes - Sections of the brain that are involved with cognition, information processing, spatial orientation, and the perception of stimuli related to touch, pressure, temperature and pain.
  • paroxetine - A member of the class of drugs known as selective serotonin reuptake inhibitors (SSRIs). It is normally used to treat depression and severe anxiety, but may also be helpful in slowing the progression of HD.
  • partial seizure - A seizure that usually begins with electrical discharges in one part of the brain. Partial seizures may or may not result in a loss of consciousness.
  • paternally - From or related to the father of an individual. A disease that is paternally inherited is inherited from an individual’s father.
  • pathogen - A microorganism (such as a bacterium or virus) that causes disease.
  • pathogenesis - The origination and development of a disease.
  • pathology - The branch of medicine concerned with disease, especially the structure of pathogens and their functional effects on the body.
  • PCr - See phosphocreatine.
  • PDC - See pyruvate dehydrogenase complex.
  • PDC Kinases - A group of molecules that add a phosphate onto one of the enzymes in the pyruvate dehydrogenase complex (PDC), effectively turning the entire PDC off. These kinases are usually activated by acetyl-CoA.
  • pedigree - A family lineage, or a chart of a family lineage that follows the inheritance of a particular trait.
  • peptide - A description of two linked amino acids.
  • peptide bond - The actual link between two amino acids. More specifically, the new bond that forms between the carboxylic acid group (COOH) of one amino acid and the amine group (NH2) of another amino acid.
  • peripheral nervous system (PNS) - The part of the nervous system consisting of everything but the brain and spinal cord. The PNS includes spinal and cranial nerves, ganglia, and plexuses.
  • peripheral neurons - Neurons that are part of the nervous system but are not in the brain or spinal cord; usually associated with supplying sensation or motor messages to the skin and skeletal muscles.
  • peripheral neuropathy - Damage to the nerve cells that supply sensation to the arms and legs.
  • peristriatal - An area of the brain's occipital lobe that is concerned with vision.
  • permeability - The degree to which cells and other molecules can pass through the walls of a blood vessel.
  • peroxides - Chemicals capable of causing oxidative damage to cell membranes and other molecules.
  • petri dish - a shallow glass or plastic cylindrical dish that scientists use to grow cells. These cells can be from many different kinds of organisms, like bacteria, yeast, mouse, or human, and can be from different tissues, like muscle, the liver, or the brain.
  • PG1 and PG3 - Classes of prostaglandins that are known to have anti-inflammatory effects such as decreasing pain, increasing oxygen flow, dilating airways, and decreasing inflammation.
  • PG2 - A class of prostaglandins that is known to have pro-inflammatory effects such as increasing pain, decreasing oxygen flow, constricting airways, and increasing inflammation.
  • pH - A measure of how acidic or basic a solution is. Water has a pH of 7 and is neutral. Solutions with a pH below 7 are acidic, while solutions with a pH above 7 are basic.
  • pharmacodynamics - explain at what the drug does to the body. This looks at the dose-response relationship, and what effect the drug has on each of the major organs within the animal.
  • pharmacokinetics - indicate what the body does to the drug. It is characterized by the ADME, or absorption (how it gets into the body), distribution (how it spreads around the body), metabolism (how cells and tissues in the body utilize it, and change its composition), and excretion (how it gets removed from the body) of the compound.
  • pharmacological - pharmacological research involves studing how chemicals interact with living organisms. It involves looking at the composition and properties of drugs (also called pharmaceuticals), therapy, and medical applications
  • phase I clinical trial - The first in a series of studies that test the safety and efficacy of a new drug or treatment in human participants. This type of study usually involves a very small number of participants, tests for side effects of the treatment, and attempts to determine safe dosages.
  • phase II clinical trial - The second in a series of studies that test the safety and efficacy of a new drug or treatment in human participants and is only performed once the drug has successfully passed the phase I clinical trial. This study involves more participants and attempts to determine if the treatment has positive effects on the participants’ conditions. Side effects continue to be noted.
  • phase III clinical trial - The third in a series of studies that test the safety and efficacy of a new drug or treatment in human participants and is only performed once the drug has successfully passed the phase II clinical trial. This study involves large numbers of participants and may compare the efficacy of the new treatment with a standard treatment. It also assesses the safety of long-term use.
  • PHD - A person with Huntington’s disease.
  • phenotype - The physical characteristics displayed by an organism; results from interaction between the genotype and the environment.
  • phosphate - One of the molecular components of a nucleotide; a small molecule made up of phosphorus and oxygen.
  • phosphocreatine (PCr) - A phosphorylated form of creatine. Phosphocreatine is a molecule that stores high-energy bonds in the body.
  • phospholipase A2 (PLA2) - A key enzyme involved in the release of arachidonic acid (AA) from the cell membrane. Inhibition of PLA2 by lipocortins results in a decrease in inflammation.
  • phospholipid - An important constituent of cell membranes that is composed mainly of fatty acids.
  • phosphorylation - The process of adding on a phosphate group to a molecule. Often used in cell signaling to turn molecules on or off.
  • photoreceptor - A cell or group of cells that can sense and receive light.
  • physical therapy - Treatment of injury or disease by physical therapeutic means instead of by medical, surgical, or radiologic measures. Physical therapy can include massage, patient education, and water therapy. Also referred to as physiotherapy.
  • physiological - Pertaining to physiology, the science of how living organisms function. A treatment with physiological effects influences the way that the body functions.
  • physiotherapy - Another term for physical therapy.
  • phytoalexin - A type of compound produced by some plants in response to fungal infection or injury. Resveratrol is one example of a phytoalexin.
  • pipetting - Using a pipette (a syringe-like instrument) to measure and transfer liquids from one container to another.
  • PLA2 - An abbreviation for Phospholipase A2.
  • placebo - Any intentionally ineffective medical treatment, such as a sugar pill, used to replace medication. In clinical trials, placebos are given to control groups to compare the results of people who receive the placebo with the results of those who receive the experimental drug. The experimental treatment must produce better results than the placebo in order to be considered effective.
  • plasmid - A small, independently replicating piece of DNA that can be taken from one organism and inserted into another.
  • plastic - Able to be shaped or changed.
  • platelet-activating factor (PAF) - A compound that reduces inflammation by increasing permeability of blood vessels and contracting various involuntary muscles such as those in airways.
  • platelets - Cells that aid in blood clotting.
  • plexus - A network or interweaving of nerves and blood vessels. (Plural form: plexuses.)
  • plexuses - Plural form of plexus.
  • pluripotent - The ability to give rise to most of the cells required to produce an organism, excluding the placenta and other supporting tissues.
  • pneumonia - An inflammation of the lungs that can be caused by infection or other environmental irritants.
  • PNS - See peripheral nervous system.
  • point mutation - A mutation in which a single base pair in the DNA strand is replaced by a different base pair.
  • poly(ADP-ribose) polymerase (PARP1) - An enzyme involved in a number of cellular processes including DNA repair and apoptosis.
  • polyglutamine diseases - Diseases that arise from extra copies of the CAG codon in certain segments of the DNA. The CAG codon codes for the amino acid glutamine. Also referred to as polyglutamine expansion disorders.
  • polyglutamine expansion disorders - Another term for polyglutamine diseases.
  • polymer - A large molecule made up of repeating subunits, called monomers. Polymers made up of proteins are called polypeptides.
  • polymerase chain reaction (PCR) - A technique used to produce millions of copies of a particular stretch of DNA.
  • polymerase slippage - During replication, the slipping of DNA polymerase III from the DNA template strand at the repeat region and the subsequent reattachment at a more distant site. Polymerase slippage can cause the newly created DNA strand to contain an expanded section of DNA.
  • polymerase slippage model - A possible model for how expansions occur. This model suggests that polymerase slippage is the cause of increased repeat regions.
  • polymerization - The process of single molecules coming together to bind into a variety of three dimensional shapes, including a chain.
  • polymorphism - Multiple alleles (versions) of a gene within a population, usually expressing different phenotypes.
  • polypeptide - A chain of multiple amino acids.
  • polyunsaturated fat - A type of unsaturated fat in which there are many double bonds.
  • pons - Region of the brain that acts as a relay station between the cerebellum and the cerebrum. The pons is part of the brain stem, and it also aids the medulla in the control of breathing.
  • pool therapy - A type of physiotherapy in which the individual does exercises while submerged in warm water. The temperature of the water is soothing for muscles, and the buoyancy of the water makes movement easier.
  • population genetics - Field of study that investigates the fate of genes within populations.
  • postmortem - Pertaining to the period after death. The word can also be used in reference to the medical examination of a body after death.
  • postsynaptic - Literally “after the synapse;” a structure or event that occurs after small gaps between nerve cells. This word is often used to describe the nerve cell that receives the message (i.e. neurotransmitter) sent by a presynaptic cell.
  • postsynaptic cell - cell that receives a neurotransmitter signal
  • PPAR-gamma - Proteins that inhibit the expression of genes that code for proteins involved in inflammation.
  • PPAR-gamma activators - Compounds that activate PPAR-gamma proteins, leading to a decrease in the inflammatory response. NSAIDs are said to be PPAR-gamma activators.
  • pre-clinical development - The testing of a lead compound before clinical trials start. This includes testing the drug in at least two animal models to determine safe doses, to understand side effects, and know more about long-term toxicity
  • predictive testing - Predictive testing determines whether the genetic sequence that causes HD is present or absent (also called genetic testing).
  • Prednisolone - Similar to prednisone in its high glucocorticoid activity. Most commonly used glucocorticoid because of its high glucocorticoid activity. Prednisone is transformed by the liver into prednisolone. Prednisolone may be administered in tablet form or produced by the body from prednisone. These medications are considered to be interchangeable.
  • Prednisone - Most commonly used glucocorticoid because of its high glucocorticoid activity, which reduces the risk of dangerous side effects caused by mineralocorticoids. Prednisone is transformed by the liver into prednisolone. The two medications are considered to be interchangeable.
  • pre-implantation genetic diagnosis (PGD) - The procedure by which a single cell is removed from an embryo to test it for genetic disease. It is done in combination with in-vitro fertilization.
  • pre-symptomatic - The state of health prior to the clinical appearance of the signs and symptoms of a disease.
  • presynaptic - Literally “before the synapse;” a structure or event that occurs before small gaps between nerve cells. This word is often used to describe the nerve cell that transmits the message (i.e. neurotransmitter) to another receiving cell.
  • presynaptic cell - cell that releases a neurotransmitter signal
  • pre-synaptic terminal - The region of the neuron at the end of the axon where neurotransmitters are stored. When an action potential reaches the pre-synaptic terminal, neurotransmitters are released into the synapse.
  • pretest counseling - Counseling offered to help individuals make informed decisions as to whether or not they should be genetically tested for HD. For more on genetic testing, click here
  • prevalence - The proportion of individuals in a population having a given disease.
  • primate - Any member of the order of animals including monkeys, apes, and humans.
  • primordial germ cells - The most primitive sex cells; will eventually give rise to sperm or eggs.
  • prion [A protein particle similar to a virus but lacking nucleic acid (any of a group of complex compounds - such as DNA and RNA] that are found in living cells and viruses and control cellular function and heredity). Prions are thought to be the infectious agent responsible for certain degenerative diseases of the nervous system.
  • pro-inflammatory cytokines - Cytokines produced predominantly by activated immune cells such as microglia and are involved in the amplification of inflammatory reactions. These include IL-1, IL-6, TNF-a, and TGF-ß.
  • proline - One of 20 amino acids essential for human life.
  • promoter - See promoter region.
  • promoter region - A DNA sequence that is recognized and bound by an RNA polymerase (enzyme) during the initiation of transcription.
  • prostaglandins - Short-lived, hormone-like chemicals that regulate cellular activities on a moment-to-moment basis and are produced in most tissues of the body.
  • protease - An enzyme that breaks down proteins.
  • proteasome - An enzyme that destroys abnormal proteins (which are flagged by ubiquitin).
  • protein - An important kind of molecule in the human body, consisting of a sequence of amino acids. The shape of a protein depends on the number and sequence of amino acids that make it.
  • protein aggregate - A misfolded, rigid protein grouping. In HD, protein aggregates result from excess glutamines.
  • protein aggregation - the process of forming protein aggregates.
  • protein chaperones - Molecules that discriminate between slowly-folding and misfolded proteins and localize with aggregates to inhibit their formation.
  • protein complex - a group of two or more associated proteins that function together to perform a specific task or make a certain structure.
  • protofibrils - Intermediate fibrils formed early in the protein aggregation process.
  • proton gradient - The product of the electron transport chain. A higher concentration of protons outside the inner membrane of the mitochondria than inside the membrane is the driving force behind ATP synthesis.
  • proximal - Near the center of the body.
  • psychiatric - related to a set of mental, emotional, or behavioral disorders
  • psychopathy - A condition characterized by the inability to connect to other people normally. Psychopathic individuals often show lack of empathy or conscience and poor inhibition. Specific psychopathic symptoms can include lack of restraint, touchiness, conflict making, evil mindedness, manipulative behaviors and aggressiveness.
  • psychosocial - A term used to describe the interaction between psychological and social aspects of one’s life.
  • psychostimulants - A group of drugs that lead to increased motor activity and decreased fatigue as well as an induced euphoric state.
  • Purkinje cells - A specific type of nerve cell that carries each and every piece of information sent out by the cerebellum. These cells possess a great deal of control over the refinement of motor activities.
  • putamen - Part of the basal ganglia in the brain. The putamen acts with the caudate to influence motor activity.
  • pyramidal nerve cells - Nerve cells projecting from the motor cortex to other parts of the brain and spinal cord. The pyramidal nerve cells play a key role in performing highly skilled movements.
  • pyruvate - This product of glycolysis is used and synthesized by many metabolic pathways. In energy generation, it can be either converted to lactate under anaerobic conditions, or broken down to water and carbon dioxide in the presence of oxygen, generating large amounts of ATP.
  • pyruvate dehydrogenase complex - A critical group of enzymes involved in energy metabolism.
  • pyruvate oxidation - The process in cellular metabolism where pyruvate is turned into acetyl-coA.