PWS Glossary

This is a(n incomplete) list of terms and abbreviations as they apply to Prader-Willi syndrome, with links as appropriate. Please feel free to Contact Ali and submit more entries!


AFO - ankle-foot orthosis - "orthoses or braces, usually plastic, encompassing the ankle joint and all or part of the foot. AFOs are externally applied, and are intended to control position and motion of the ankle, compensate for weakness, or correct deformities. They control the ankle directly, and can be designed to control the knee joint indirectly as well." (

aspiration (or pulmonary aspiration) - when food or liquid that enters the mouth goes into the trachea and lungs instead of into the esophagus. This can be common in young ones with PWS because low muscle tone sometimes makes the epiglottis (valve that seals off either the trachea or esophagus) weak. Thickening liquids and food can help with preventing aspiration. Aspiration is determined primarily through a swallow study.



CAI - see Central Adrenal Insufficiency.

carnitine - an amino acid used in fatty acid metabolism that many individuals with PWS take in supplement form (typically either carnitor/levocarnitine or carnitine fumarate).

central adrenal insufficiency - CAI. "a lack of secretion of corticotropin-releasing hormone (CRH) from the hypothalamus or of adrenocorticotropic hormone (ACTH) from the pituitary leads to hypofunction of the adrenal cortex." ( Basically, in times of extreme stress from illness, surgery, etc., the body does not properly respond to that stress and the result can be very serious, even death. It is thought that there is a higher incidence of CAI in persons with PWS. Treatment for this is a prophylactic dose of steroids. See for more information.

central sleep apnea - "In central sleep apnea, the basic neurological controls for breathing rate malfunction and fail to give the signal to inhale, causing the individual to miss one or more cycles of breathing. If the pause in breathing is long enough, the percentage of oxygen in the circulation will drop to a lower than normal level (hypoxaemia) and the concentration of carbon dioxide will build to a higher than normal level (hypercapnia). In turn, these conditions of hypoxia and hypercapnia will trigger additional effects on the body." ( Central sleep apnea can improve with GH therapy.

CoQ10 - Coenzyme Q10. A supplement used often with people with PWS. Reported benefits include increases in energy and alertness.

CPAP machine - Continuous Positive Airway Pressure machine. Used for the treatment of sleep apnea in some persons with PWS.


deletion - a subtype of PWS in which the PWS critical region on the paternal 15th chromosome is not present. Deletions vary in size. This subtype accounts for about 70% of cases of PWS.



failure-to-thrive - marks the beginning stage of PWS. "Infants or children who fail to thrive have a height, weight, and head circumference that do not match standard growth charts. The person's weight falls lower than 3rd percentile (as outlined in stand
ard growth charts) or 20% below the ideal weight for their height. Growing may have slowed or stopped after a previously established growth curve. The following are delayed or slow to develop: physical skills such as rolling over, sitting, standing and walking; mental and social skills; secondary sexual characteristics (delayed in adolescents)." (Google Health)

FISH test - fluorescence in-situ hybridization test. Performed to detect PWS by deletion. Does not diagnose other forms of PWS. (

FPWR - Foundation for Prader-Willi Research. See more information at


G-tube - gastrostomy tube. This is a feeding tube for more long-term feeding assistance and is required for many babies with PWS. The G-tube must be surgically placed, a routine procedure that requires general anesthesia.

Genotropin - a brand name of GH manufactured by the Pfizer company. One of the most popular brands of GH for PWS because it is the only brand that carries the FDA indication for use in PWS.

GH - growth hormone. Also known as hGH. Most people with PWS receive nightly (usually 6-7x/week) subcutaneous injections of GH to help with a variety of issues, including muscle mass, cognitive development, strength, and muscle tone.


hCG - human chorionic gonadotropin. In PWS, intramuscular injection rounds of hCG are administered in boys to descend testicles that are in the inguinal canal but have not fully dropped into the scrotum. If successful, surgery to descend the testes (orchiopexy) can possibly be avoided, or at least made more successful. A typical round of hCG injections is 2x/week for about five weeks. hCG in boys increases testosterone levels, thus its usefulness for the aforementioned purpose. There are frequently secondary benefits such as increase in strength, stamina, and muscle tone.

hGH - human growth hormone. See GH.

hippotherapy - therapeutic horse riding for people with PWS. Helps with balance and strength in the trunk.

hyperphagia - uncontrolled, excessive hunger due to a malfunction in the hypothalamus in the brain. This is the hallmark issue of PWS and the reason why most people with PWS cannot live independently. External food controls are needed to prevent potentially lethal amount of food intake.

hypothalamus - "a small endocrine organ at the base of the brain that plays a crucial role in many bodily functions, including hunger and satiety, temperature and pain regulation, fluid balance, puberty, emotions, and fertility. Although hypothalamic dysfunction is believed to lead to the symptoms of PWS, it is unclear how the genetic abnormality causes hypothalamic dysfunction." (

hypotonia - low muscle tone. "state of low muscle tone (the amount of tension or resistance to movement in a muscle), often involving reduced muscle strength. Hypotonia is not a specific medical disorder, but a potential manifestation of many different diseases and disorders that affect motor nerve control by the brain or muscle strength." ( Hypotonia can be helped with early intervention, strengthening, physical therapy, and a variety of other interventions, but it often persists over time. Hypotonia ranges from mild to severe and affects all muscles in the body.

IEP - Individualized Education Plan. This is a legal document that states the present level of a child's performance, goals for various aspects of school, and the accommodations and services necessary to achieve those goals for the student with special needs. An "IEP meeting" is any meeting with a variety of teachers, therapists, administrators, and parents (sometimes others) to discuss/change/write an aspect of the IEP.

IGF-1 - insulin-like growth factor-1. For PWS purposes, all you need to know is that this is a measure of how well the body is using growth hormone (its own and whatever is injected). IGF-1 levels are used by many endocrinologists to determine ideal GH dosage along with other factors.

IM - intramuscular. Refers to the type of injection given. IM injections require a larger (longer and lower gauge) needle than do subcutaneous injections.

imprinting mutation - "in a very small percentage of cases, a small genetic mutation in the Prader-Willi region [of chromosome 15] causes the genetic material in that area to be the case of an imprinting mutation, Prader-Willi syndrome can recur within a family." (





muscle tone - "continuous and passive partial contraction of the muscles. It helps maintain posture, and it declines during REM sleep. It is not to be confused with the concept of toning in physical exercise." ( People with PWS often have *low* muscle tone, or hypotonia.


NG tube - nasogastric tube. This is a feeding tube that goes through one nostril, down the esophagus and into the stomach to assist with feeding. NG tubes can be easily taken in and out and do not require surgery to do either.


obstructive sleep apnea - OSA. "The muscle tone of the body ordinarily relaxes during sleep, and at the level of the throat the human airway is composed of collapsible walls of soft tissue which can obstruct breathing during sleep....chronic severe obstructive sleep apnea requires treatment to prevent low blood oxygen (hypoxemia), sleep deprivation, and other complications." ( GH therapy often helps central sleep apnea, but can worsen OSA due to the enlargement of tonsils & adenoids. Removal of partial/entire tonsils and/or adenoids can alleviate this condition.

orchiopexy - the surgery performed to descend undescended testicles in males with PWS.

OSA - see obstructive sleep apnea.

OT - occupational therapy. OT addresses mostly fine motor skills, sensory issues, and sometimes feeding in infancy.

polysomnography - see sleep study.

pulse ox (pulse oximeter) - a machine that measures the concentration of oxygen (O2) in the blood. A probe is wrapped around the foot or hand and measures the color of the patient's blood to determine percentage of cells carrying oxygen. The closer to 100%, the better. If the % is too low, supplemental oxygen is usually administered.

PWS - Prader-Willi syndrome. Also sometimes called Prader-Labhart-Willi syndrome.

PWS by deletion - see deletion.




sleep study - Also known as a polysomnogram. A test usually done in an overnight stay in a sleep lab. Leads are placed all over the body (mostly on the head) to measure a variety of factors while the patient is sleeping. In PWS, sleep studies are performed as needed to assess if sleep apnea (central or obstructive) is present. In many cases, a successful sleep study is required before beginning GH therapy.

SLP - speech/language pathologist. This professional is someone trained and licensed to assess and perform speech and language services. If someone says they are going to speech therapy, it is conducted by an SLP (might also hear someone call them a speech therapist).

subcutaneous injections - injections given just below the skin with a very small needle. GH is administered in this way.



UPD - uniparental disomy. Referring to one of the subtypes of PWS where the person inherited two of the maternal 15th chromosomes and none of the paternal 15th. This accounts for one way in which the critical region for PWS is absent. This subtype represents about 30% of cases of PWS.