NCI Dictionary of Genetics Terms

22 results found for: P

palmar pit: (PAL-mer ...); A small depression in the skin on the palm of the hand. Depressions may also be seen on the sole of the foot (plantar pits). They are usually pink or flesh-colored and range from 2 to 3 mm in diameter and 1 to 3 mm in depth. Palmar pits are often more visible after a brief soaking of the hands or feet. This condition is associated with basal cell nevus syndrome, which is a hereditary syndrome associated with the development of basal cell carcinoma.
pathogenic variant: (PA-thoh-JEH-nik VAYR-ee-unt); A genetic alteration that increases an individual’s susceptibility or predisposition to a certain disease or disorder. When such a variant (or mutation) is inherited, development of symptoms is more likely, but not certain. Also called deleterious mutation, disease-causing mutation, predisposing mutation, and susceptibility gene mutation.
pathognomonic: (PA-thog-noh-MAH-nik); Findings that are distinctive or characteristic of a particular disease or condition and can be used to make a diagnosis.
PCR: A common laboratory technique used during molecular genetic testing to produce many copies of a specific sequence of DNA . PCR allows these DNA sequences to be amplified so there is a sufficient quantity of DNA to be analyzed by molecular genetic tests. Also called polymerase chain reaction.
pedigree: (PEH-dih-gree); A diagram of family history that uses standardized symbols. A pedigree shows relationships between family members and indicates which individuals have certain genetic pathogenic variants, traits, and diseases within a family as well as vital status. A pedigree can be used to determine disease inheritance patterns within a family.
penetrance: (PEH-neh-trunts); Penetrance refers to the likelihood that a clinical condition will occur when a particular genotype is present. For adult-onset diseases, penetrance is usually described by the individual carrier's age, sex, and organ site. For example, the penetrance for breast cancer in female carriers of BRCA1 pathogenic variants is often quoted by age 50 years and by age 70 years.
phenocopy: (FEE-noh-KAH-pee); A phenotypic trait or disease that resembles the trait expressed by a particular genotype but in an individual who is not a carrier of that genotype.
phenotype: (FEE-noh-tipe); The observable characteristics or traits in an individual based on the expression of their genes. The phenotype is determined by the individual's genotype and possibly influenced by other factors, such as environmental factors or other genetic modifiers.
plantar pit: (PLAN-ter ...); A small depression in the skin on the sole of the foot. Depressions may also be seen on the palm of the hand (palmar pits). They are usually pink or flesh-colored and range from 2 to 3 mm in diameter and 1 to 3 mm in depth. Plantar pits are often more visible after a brief soaking of the hands or feet. This condition is associated with basal cell nevus syndrome, which is a hereditary syndrome associated with the development of basal cell carcinoma.
poikiloderma: (POY-kih-loh-DER-muh); Irregular patterns of reddish brown pigmentation of the skin associated with sun exposure, aging, or a genetic cause.
point mutation: (poynt myoo-TAY-shun); A genetic alteration caused by the substitution of a single nucleotide for another nucleotide. Also called point variant.
point variant: (poynt VAYR-ee-unt); A genetic alteration caused by the substitution of a single nucleotide for another nucleotide. Also called point mutation.
polygenic risk score: (PAH-lee-JEH-nik risk skor); An assessment of the risk of a specific condition based on the collective influence of many genetic variants. These can include variants associated with genes of known function and variants not known to be associated with genes relevant to the condition. Also called PRS.
polymerase chain reaction: (puh-LIH-meh-rays chayn ree-AK-shun); A common laboratory technique used during molecular genetic testing to produce many copies of a specific sequence of DNA . Polymerase chain reaction allows these DNA sequences to be amplified so there is a sufficient quantity of DNA to be analyzed by molecular genetic tests. Also called PCR.
polymorphism: (PAH-lee-MOR-fih-zum); A common variant in a specific sequence of DNA. “Common” is typically defined as an allele frequency of at least 1% in the general population.
positive predictive value: (PAH-zih-tiv preh-DIK-tiv VAL-yoo); The likelihood that an individual with a positive test result truly has the particular gene and/or disease in question. Also called PPV.
PPV: The likelihood that an individual with a positive test result truly has the particular gene and/or disease in question. Also called positive predictive value.
predisposing mutation: (PREE-dih-SPOH-zing myoo-TAY-shun); A genetic alteration that increases an individual’s susceptibility or predisposition to a certain disease or disorder. When such a variant (or mutation) is inherited, development of symptoms is more likely, but not certain. Also called deleterious mutation, disease-causing mutation, pathogenic variant, and susceptibility gene mutation.
presymptomatic testing: (PREE-simp-toh-MA-tik TES-ting); Genetic testing performed in an individual who does not show symptoms of the disorder, but who is at risk of developing the disorder.
proband: (PROH-band); The first individual in a family to be identified as possibly having a genetic disorder or condition.
PRS: An assessment of the risk of a specific condition based on the collective influence of many genetic variants. These can include variants associated with genes of known function and variants not known to be associated with genes relevant to the condition. Also called polygenic risk score.
pseudogene: (SOO-doh-jeen); A DNA sequence that resembles a gene but has been mutated into an inactive form over the course of evolution. It often lacks introns and other essential DNA sequences necessary for function. Though genetically similar to the original functional gene, pseudogenes do not result in functional proteins, although some may have regulatory effects.