Adrenarche Onset of pubic and axillary hair; normally occurs after age 8 years.

Adrenal glands Glands that sit on top of the kidneys and regulate stress reactions and some mineral balance.

Adrenocorticotropic hormone (ACTH): A hormone secreted by the pituitary that stimulates the adrenal glands; part of the stress response system.

Allele One of two or more alternative forms of a gene occupying corresponding sites (loci) on partner chromosomes.

Amenorrhea Lack of menstrual periods.

Amniocentesis A procedure in which a small amount of the amniotic fluid surrounding the fetus is drawn off and subjected to genetic and biochemical analysis.

Androgen Any one of several male hormones.

Angelman syndrome A rare syndrome reported in 1965 by Dr. H. Angelman and associated with a chromosome 15 deletion similar to that seen in PWS.
In AS, however, the deletion is seen on the chromosome contributed by the mother, whereas those with PWS lack certain genes from the father. The clinical problems and appearance of AS and PWS are distinctly different. These two syndromes represent the first examples in humans of genetic imprinting.

Autosome Any chromosome that is not a sex chromosome; in humans there are 22 pairs of autosomes and one pair of sex chromosomes.

Chromosome Package of genes that carries genetic information. Most cells have 46 chromosomes, which are found in the nucleus.

Chromosome abnormality Any variation from the normal chromosomal pattern. The common abnormalities found in Prader-Willi syndrome are:
 Deletion: a condition in which a piece of genetic material is lost or missing from a chromosome. Typically it is a small piece of the long arm of the 15th chromosome that is missing.
 Translocation: a transfer of a fragment of one chromosome to another chromosome.

Cocontraction The simultaneous contraction of all the muscles around a joint to stabilize it.

Cortisol A hormone secreted by the adrenal glands in response to stress.

Cryptorchidism Undescended testicles (testicles are not present in the scrotal sac).

DNA Deoxyribonucleic acid; the genetic code or chemical blueprint for the cell.

de novo New. Used in genetics to describe a structural alteration of the chromosomes that is present in a child but not in either parent.

Deletion A missing piece of chromosomal material. In PWS, the deletion is in the proximal long arm of chromosome 15.

Dominant Capable of expression when carried by only one of a pair of partner chromosomes in the cells of the body.

Down syndrome A syndrome resulting from three (instead of the usual two) copies of chromosome 21.

Dual-photon absorptiometry (DPA) A gamma radiation technique for measuring bone density.

Electrophoresis In genetics, the technique for separating materials via the movement of charged particles suspended in a gel under the influence of an applied electric field.

Failure to thrive Poor or inadequate weight gain during infancy.

FISH Fluorescence in situ hybridization. A test using a fluorescence-tagged segment of DNA that combines with the DNA present in the normal PWS critical region and allows determination by its presence or absence as to whether a 15q deletion is present.

Gene A unit of genetic information. Usually contains the genetic code for one protein.

Genetic imprinting Differential modification of the expression of genes depending upon whether they are inherited from the mother or the father. This affects only certain segments of the human genetic complement, including PWS and Angelman syndrome on chromosome 15q.

Genetic counseling Counseling that explains facts about genetics issues to parents/care providers. Emphasis is on clarification of information, possible recurrence risk, reproductive options, support to affected persons and their families, and follow-up services.

Glucocorticoid Hormones secreted by the adrenal glands regulating sugar and energy availability.

Gonadotropin A hormone from the pituitary gland that stimulates the genital organs to produce the sex hormones.

Growth hormone (GH) A pituitary-secreted hormone that aids in growth.

Gynecomastia Breast development — used in reference to male breast development.

Heredity The genetic transmission or passing of a particular quality or trait from parent to offspring.

Hyperphagia Consumption of more than a normal quantity of food.

Hypogenitalism The genital organs are undersized.

Hypogonadism A condition of abnormal decrease in the function of the ovaries and testes, causing retardation of growth and sexual development.

Hypogonadotropic  resulting from a decrease in hormones released by the pituitary.

Hypopigmentation Unusually lighter hair, eyes, and skin color in relation to other family members. This decreased pigmentation is common in PWS, particularly in individuals with partial deletion of the long arm of chromosome 15.

Hypothalamus The part of the brain that controls appetite, body temperature, hormones, and other vital functions.

Hypotonia Decreased muscle tone. Decreased muscle resistance to passive movement.

IGFBP-3 A binding protein for insulin-like growth factor (IGF) that carries it around the blood stream.

Imprinting center The portion of a chromosome that controls whether imprinted genes on that chromosome are expressed. If the imprinting center is missing or altered, genes that require imprinting will not function appropriately.

Insulin A hormone secreted by the pancreas that regulates sugar in the body.

Insulin-like growth factor I and II (IGF-I, IGF-II) Factors that act upon body tissues to stimulate growth.

Karyotype The collection of chromosomes from the nucleus of a cell arranged according to established guidelines; the photomicrograph of chromosomes.

Klinefelter’s syndrome XXY syndrome A chromosome abnormality in which a male has an extra X chromosome.

Lability Marked fluctuations in mood or disposition.

Learning disabled A term applied to low-achieving children whose performance is inconsistent with overall intelligence. These children may be part of an identifiable group who are limited in their ability to process written or spoken language, which may result in limited capacity to master some basic academic tasks.

Loci Sites on chromosomes occupied by genes.

Luteinizing hormone (LH) One of the pituitary hormones acting upon the genital organs.

Maternal Referring to the mother.

Melatonin A hormone secreted by the pineal gland in the brain.

Mental age A measured level of cognitive function established by a test of intelligence.

Metabolism Pertaining to the body’s process of absorbing nourishment from food and turning it into energy or stored fat.

Methylation DNA methylation analysis. A form of genetic testing used to determine the parent of origin of chromosome 15q, which is always maternal in Prader-Willi syndrome.

Motor planning The ability of the brain to conceive of, organize, and carry out a sequence of unfamiliar activities. Also known as “praxis.”

Mutation A sudden change in the genetic material that can be passed to an offspring.

Narrow bifrontal diameter A narrow forehead.

Normalization The effort to make available activities and patterns of everyday life that are as close as possible to the habits of normal, mainstream individuals.

Obesity A condition in which body weight is considerably (more than two standard deviations) above the range that is normal for body height.

Orchiopexy Surgical lowering of the testicles into the scrotum.

Osteoporosis Demineralization (thinning) of the bones.

Oxandrolone An anabolic (mass-building) steroid.

Paternal Referring to the father.

Pedigree Diagram showing family members, their relationships, and presence or absence of a particular trait or traits.

Phenotype The clinical expression; often used when talking about a genetic condition.

Pituitary A gland at the base of the brain, stimulated by a portion of the brain called the hypothalamus, that secretes hormones that work elsewhere in the body (e.g., ACTH, FSH, LH, TSH, prolactin).

Polymerase chain reaction

(PCR) A genetic laboratory technique used to copy and amplify a portion of a gene or DNA sequence (for example, SNRPN gene). The sizes or alterations of the PCR amplified portion of the gene identified may be useful in diagnosing certain genetic conditions.

Polymorphism Normal variation in genetic information. Used to describe minor variation in chromosome shape and normal or abnormal variation in molecular structure or content of genes.

Praxis The capacity of the brain to integrate and carry out unfamiliar motor activities. Also known as motor planning.

Prolactin A pituitary-secreted hormone acting upon the genital organs and breasts.

Proximal musculature The muscles of the trunk, shoulder girdle, and hip girdle.

Rehabilitation A dynamic process of continuing evaluation of disabled individuals in order to meet their need and develop realistic methods of coping. This “process” acknowledges that one individual may have more than just one problem to confront and that the individual’s ability to function cannot be separated from environmental concerns.

Restriction endonuclease An enzyme-produced bacteria which cleaves or cuts DNA into fragments at specific sites.

Sheltered workshop A controlled work-oriented rehabilitation setting that utilizes work experiences and related services to assist disabled individuals in making the maximum progress possible toward vocational productivity and normal living.

Southern blotting The process of transferring DNA fragments from the electrophoresis gel onto filter paper; named after Dr. E. Southern.

Strabismus A lack of coordinated eye muscle movement, observed as either “crossed-eye” or “wall eye.”

Syndrome A term used to describe a symptom complex characterized by many medical signs. In many syndromes, not all affected individuals will have every diagnostic sign.

System advocacy Refers to actions taken by individuals or groups to influence policy making.

Tanner stages A five-step staging of pubertal development: 1 = prepuberty; 5 = full adult breast (females), pubic hair, or genital development.

Thyroid-releasing hormone (TRH) A hypothalamic hormone that stimulates the release of TSH from the pitutary.

Thyroid-stimulating hormone (TSH) A pituitary hormone that stimulates the thyroid, leading to increases in metabolism and heart rate.

Turner syndrome A syndrome with only one sex chromosome (XO) but phenotypical appearance of a female.

Uniparental disomy A situation in which both members of a chromosome pair are derived from a single parent. In about one-fourth of people with PWS, both chromosome 15s are maternal in origin, and no paternal chromosome 15 is present in the affected individual.

X-linked Genes on the X chromosome or traits determined by such genes.