Genetic terms used in Creutzfeldt-Jakob disease (CJD)

• 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
• 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
• 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
• chromosome: Physical structure consisting of a large DNA molecule organized into genes and supported by proteins called chromatin
• 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
• de novo mutation: An alteration in a gene that is present for the first time in one family member as a result of a mutation in a germ cell (egg or sperm) of one of the parents or in the fertilized egg itself
• diagnostic testing: Testing designed to confirm or exclude a known or suspected genetic disorder in a symptomatic individual or, prenatally in a fetus, at risk for a certain genetic condition
• DNA: (deoxyribonucleic acid) The molecule that encodes the genes responsible for the structure and function of an organism and allows for transmission of genetic information from one generation to the next
• duplication: The presence of an extra segment of DNA, resulting in redundant copies of a portion of a gene, an entire gene, or a series of genes, usually caused by unequal crossing-over during gene replication when gametes are formed in meiosis
• false negative result: A test result which indicates that an individual is unaffected and/or does not have a particular gene mutation when he or she is actually affected and/or does have a gene mutation; i.e., a negative test result in an affected individual
• false positive result: A test result which indicates that an individual is affected and/or has a certain gene mutation when he or she is actually unaffected and/or does not have the mutation; i.e., a positive test result in a truly unaffected individual
• gene therapy: Experimental treatment of a genetic disorder by replacing, supplementing, or manipulating the expression of abnormal genes with normally functioning genes
• 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
• genome: The complete DNA sequence, containing all genetic information and supporting proteins, in the chromosomes of an individual or species
• mutation: Any alteration in a gene from its natural state; may be disease-causing or a benign, normal variant
• nonsense mutation: A single base pair substitution that prematurely codes for a stop in amino acid translation (stop codon)
• novel mutation: A distinct gene alteration that has been newly discovered; not the same as a "new" or "de novo" mutation
• 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
• 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
• predictive testing: Testing offered to asymptomatic individuals with a family history of a genetic disorder and a potential risk of eventually developing the disorder
• presymptomatic testing: Testing of an asymptomatic individual in whom the discovery of a gene mutation indicates certain development of findings related to a specific diagnosis at some future point; a negative result excludes the diagnosis
• RNA: (ribonucleic acid) The molecule synthesized from the DNA template; contains the sugar ribose instead of deoxyribose, which is present in DNA; three types of RNA exist, messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)
• transcription: The synthesis of RNA from DNA
• translation: The synthesis of protein from RNA