Genetics Northern California

Glossary

TermDescription
p53

A gene that normally regulates the cell cycle and protects cells from damage to its genome. If a mutation occurs in this gene, cells can develop cancer. Individuals with Li-Fraumeni cancer syndrome have a defect in their p53 gene.

Paracentric inversion

An inversion of genetic material( in a chromosome)that does not include the centromere (see inversion). ( When a crossover occurs a dicentric and acentric fragment are formed that are considered unstable and in humans would likely result in a miscarriage if conceived.)

PCR

Polymerase chain reaction is a quick, inexpensive technique for making an unlimited copy of any piece of DNA sequences and is used often in gene testing techniques.

Pedigree

A diagram of genetic relationships and medical history in a family (also called family history).

Penetrance

In relation to autosomal inheritance, a term referring to the chance that a carrier of a mutant gene will manifest effects of that gene. When the penetrance is reduced, not everyone who inherits the gene will develop detectable features.

Pericentric inversion

An inversion of a chromosome that includes the centromere (see inversion). Individuals who carry an inversion are at increased risk for to have a duplication or deletion of the genetic material occur which would lead to an abnormal individual.

Phenotype

Observable traits or characteristics of an organism produced by the individual's genes interacting with the environment(ie. Hair color, height, weight, presence or absence of disease). The physical appearance or makeup of an individual.

Phenylketonuria (PKU)A disorder that affects the way the body processes protein in the food we eat. Individuals with PKU cannot process a specific part of protein called phenylalanine, because they are missing an enzyme in the liver. Without treatment, phenylalanine builds up in the body, and over time, causes damage to the brain and central nervous system. Untreated PKU leads to mental retardation and other symptoms such as seizures and behavior problems. The treatment for PKU is a special diet that is restricted in phenylalanine. When the diet is started early and followed carefully, children with PKU can expect normal growth and development.
Philadelphia chromosome

A structural abnormality of chromosome 22 typically occurring in a proportion of bone marrow cells in patients with CML (chronic myelogenous leukemia) whereby a reciprocal translocation occurs between chromosomes 9 and 22.

Polydactyly

Abnormality where an individual is born with more than the normal number of fingers and/or toes.

Polymorphism

Naturally occurring variations in DNA sequence. ( They are useful as they act as genetic markers to allow researchers to track the DNA of different origins.)

Polyploid

Any multiple of the basic haploid (n=23 chromosomes) other than 2n which is referred to as diploid (ie. 3n, 4n.

Polyunsaturated fatsThese fats are usually liquid at room temperature and are vegetable in origin, such as safflower, sunflower, and corn oils. They are felt to lower cholesterol when used in place of saturated fats.
Population riskThe risk of a condition or trait to occur in the general population.
PreconceptionBefore pregnancy. Preconception counseling refers to counseling that takes place prior to a couple beginning a pregnancy. Includes an assessment of personal and family medical history, risk factors (including age and lifestyle factors), as well as certain screening blood tests, such as ethnicity-based screening tests.
PredispositionA latent susceptibility to disease, which may be activated under certain conditions, as by stress (Dorland's 27th edition).
Pre-eclampsia (toxemia)

A condition of late pregnancy characterized by the mother having elevated blood pressure, protein spilling in her urine and swelling of her tissues. If not treated successfully it can lead to eclampsia or toxemia which can cause seizures and have severe consequences to the mother and baby (ie. Stroke, death).

Pregnancy-associated plasma protein-A

Pregnancy-associated plasma protein-A (PAPP-A) is a protein that is produced by the early embryonic cells that form into the placenta. PAPP-A can be detected in the mother's blood. The first trimester level of PAPP-A may be lower than average in pregnancies with Down syndrome and other chromosome abnormalities like trisomy 18 and trisomy 13.

Premature labor

A mother going into labor prior to 38 weeks gestation from last menstrual period.

PremutationsThe first mutation in a multi-step process leading to disease. (e.g. In Fragile X syndrome, individuals with 55-200 CGG repeats in the FMR1 gene are considered to be premutation carriers (normal is <30). They are not affected by the disease, but in passing on that gene to their offspring, the premutation may expand to a full mutation, leading to disease.)
PrenatalExisting or occurring before birth (i.e., prenatal care is provided to a mother by OB/GYN prior to the baby's birth. )
Primary cancer

The site of the cancer that first invaded the individual and now may have metastasized to other organs but originated in the first organ (ie. Breast cancer that metastases to brain or lung).

Primary congenital hypothyroidism

This condition occurs when there is not enough thyroid hormone to meet the body's needs for growth and development. This can happen if the thyroid gland, a small, bow-shaped gland in the front of the neck, is missing, not working, or in the wrong place. Without treatment, primary congenital hypothyroidism can cause mental retardation, growth failure, neurologic problems, and low metabolic rate. Primary congenital hypothyroidism is treated by giving thyroid hormone pills everyday. With proper treatment, children with hypothyroidism grow and develop normally.

Proband

The family member through whom the family history is ascertained.

Prognosis

A forecast of the probable course and outcome of an attack of disease and the prospects of recovery as indicated by the nature of the disease and symptoms of the individual.

PROM

Premature rupture of membranes. A term used to describe the amnion and chorion (bag of waters around the baby) rupturing prior to 40 weeks of pregnancy.

Propionic acidemiaPropionic acidemia (PPA) is a condition that occurs when the body is missing one of the enzymes needed to break down (metabolize) protein. Without this enzyme, parts of the protein build up in the body causing damage to the nervous system, especially the brain. If left untreated, PPA can result in vomiting, anorexia, cardiac problems, blood disorders, failure to thrive, develomental delays, mental retardation, and even death.

The way propionic acidemia is inherited is called autosomal recessive.

Protein

A large complex molecule made up of one or more chains of amino acids. Proteins perform a wide variety of activities in the cell.

Pseudoachondroplasia

An inactive gene within a gene family derived by mutation of an ancestral active gene.

PUBS

Percutaneous umbilical blood sampling which obtains blood from the umbilical vein of the fetus to get a rapid chromosome analysis or a specific blood analysis.

Pyloric stenosis

A narrowing of the pylorus of the stomach causing projectile vomiting. This can be life threatening if not surgically corrected as the infant cannot take in nourishment until the defect is repaired.