PWS research and clinical trial terms can sometimes feel like a different language altogether. This glossary has been created to help make those terms clearer and easier to understand.
We’re always looking to improve and expand this resource, so if you have suggestions for terms we should include, please get in touch at info@fpwr.org.uk.
Abstract
A short summary of a research study, usually found at the beginning of a scientific paper.
Adrenarche
A stage of development when the adrenal glands begin producing hormones, usually before puberty. This process may occur differently in individuals with PWS.
Adverse Event
Any unwanted or unexpected side effect experienced during a clinical trial or treatment.
Amniocentesis
A test performed before a baby is born where a small sample of amniotic fluid is taken to check for genetic conditions. This isn’t routinely done to check for PWS but may be offered to pregnant women if PWS is suspected or to women who have had a child with a genetic condition like PWS before.
BDNF (Brain-Derived Neurotrophic Factor)
A protein in the brain that helps nerve cells grow and communicate. It also plays a role in appetite and energy balance. Researchers are studying how BDNF may be involved in the hunger difficulties seen in PWS.
Behavioural Challenges
Difficulties such as anxiety, rigidity, emotional outbursts, or obsessive behaviours often seen in individuals with PWS.
Bias
A tendency to favour one outcome or perspective, which can affect the fairness of research results.
Biomarker
A measurable sign in the body (such as a blood test or hormone level) that can show how a condition is progressing or how well a treatment is working.
Blind Study
A study where participants do not know whether they are receiving the treatment or a placebo. A Double-Blind study is where the participants nor the Researchers are aware.
Body Composition
The proportion of fat, muscle, and other tissues in the body. People with PWS often have higher body fat and lower muscle mass.
Bright Light Therapy
A treatment that involves exposure to bright light at specific times of day to help regulate sleep and wake patterns. It may support people with PWS who experience sleep difficulties.
Case Study
A detailed report about an individual patient or a small group, often used to share insights or unusual findings. They can highlight real-life experiences, though results may not apply to everyone.
CCK (Cholecystokinin)
A hormone that helps signal fullness after eating. In PWS, this signal may not work as expected, contributing to ongoing hunger.
Chromosome
Structures in our cells that carry genetic information (DNA). Humans typically have 23 pairs.
Chromosome 15
The chromosome affected in Prader-Willi syndrome. Changes in the q11-13 region of this chromosome cause PWS.
Clinical Trial
A research study involving people that tests new treatments, interventions, or ways to manage a condition.
Confabulation
When someone fills in gaps in memory with information that isn’t accurate — without meaning to mislead. In PWS, this can sometimes be mistaken for lying, but it is part of how the brain processes information.
Cortisol
A hormone produced by the adrenal glands that helps the body respond to stress and regulate energy.
CRISPR
A research tool that allows scientists to make very precise changes to DNA — like editing a specific instruction in the body’s genetic code. For Prader-Willi syndrome, scientists are exploring whether CRISPR could one day help “switch on” important genes that are turned off.
Cryptorchidism
A condition where one or both testicles do not descend into the scrotum, common in males with PWS.
Deletion
A type of genetic change where a small piece of chromosome 15 is missing. This is the most common cause of PWS
De Novo
A genetic change that is new in an individual and not inherited from their parents. The vast majority of PWS cases are De Novo.
Developmental Delay
When a child reaches milestones (such as sitting, walking, or talking) later than expected
Dissemination
The process of sharing research findings with others, including families, clinicians, and the wider community.
Double-Blind Study
A Double-Blind study is where neither the participants nor the researchers know who is receiving the treatment or placebo
Efficacy
A measure of how well a treatment works under controlled conditions (such as in a clinical trial).
Eligibility Criteria
The set of rules that determine who can take part in a clinical trial (for example, age, medical history, or symptoms).
EMA (European Medicines Agency)
The organisation responsible for evaluating and approving medicines for use across Europe. Like the FDA and MHRA, it assesses whether treatments are safe and effective.
Endpoint
The main result that a clinical trial is designed to measure (such as reduction in hunger or improvement in behaviour). This is also sometimes referred to as the Primary Endpoint. Trials also sometimes have a Secondary Endpoint which are additional things that are being measured, e.g. hyperphagia might be the Primary Endpoint but researchers also might be monitoring behavioural changes as a Secondary Endpoint.
Epigenetics
Changes in how genes are switched on or off, without changing the DNA itself. Imprinting is an example of epigenetics.
Excessive Daytime Sleepiness
Feeling very tired during the day, even after a full night’s sleep. This is common in PWS and can affect attention, learning, and daily activities.
Exclusion Criteria
The set of rules that determine who cannot take part in a research study, usually to keep participants safe or ensure accurate results.
Failure to Thrive
When a baby or child does not gain weight or grow as expected. Common in infants with PWS due to feeding difficulties.
FDA (Food and Drug Administration)
The government agency in the United States that decides whether new medicines are safe and effective enough to be approved for use. Many PWS treatments are first reviewed by the FDA.
FISH Test (Fluorescence In Situ Hybridisation)
A laboratory test used to detect missing or abnormal pieces of chromosomes. This can be used to diagnose PWS, but will only pick up cases caused by Deletion and not Uniparental Disomy or Imprinting.
Focus Group
A small group of people brought together to discuss their experiences or views on a topic.
Food Security
Steps taken to limit or control access to food in a safe and supportive way. In PWS, this may include locking food cupboards or having clear routines, to help manage constant hunger and keep the person safe.
Food-Seeking Behaviour
Actions driven by constant hunger, such as searching for food, hoarding, or asking repeatedly for meals or snacks.
Gene
A segment of DNA that provides instructions for how the body grows and functions.
Genetics
The study of genes and how traits or conditions are passed down or occur.
Ghrelin
A hormone that signals hunger to the brain. Levels are often higher than normal in people with PWS.
Global PWS Registry
An international database where individuals with PWS and their families can share information about health, behaviour, and treatments. This helps researchers better understand PWS and develop new therapies. You can visit it at https://pwsregistry.net
GLP-1 (Glucagon-Like Peptide-1)
A hormone that helps control appetite and blood sugar. Some medicines that act like GLP-1 are being explored to help reduce hunger and manage weight in PWS.
Growth Hormone Therapy (GH)
A common treatment in PWS that helps improve height, muscle tone, strength, and body composition.
Hereditary
A condition or trait that is passed from parents to children through genes.
Hyperphagia
A chronic, overwhelming drive to eat that is not relieved by food.
Hyperphagia Questionnaire (HQ-CT)
A questionnaire used in clinical trials to measure hunger-related behaviours in people with PWS. It helps researchers understand whether a treatment is improving appetite control. It is often filled in by the caregiver.
Hypogonadism
A condition where the body produces low levels of sex hormones.
Hypopigmentation
Lighter skin, hair, or eye colouring due to reduced pigment.
Hypothalamus
A part of the brain that controls hunger, temperature, hormones, and other essential functions. It does not work typically in PWS.
Hypotonia
Low muscle tone, often noticeable in babies with PWS, leading to feeding difficulties and delayed development. Hypotonia is often lifelong with PWS and can cause fatigue as muscles work harder to perform tasks.
IGF-1 (Insulin-like Growth Factor 1)
A hormone linked to growth that is influenced by growth hormone treatment. An Endocrinologist will often use this to monitor the effectiveness of growth hormone therapy. Readings are obtained from a blood test.
Imprinting Defect
Some important genes only work if they come from the father — the mother’s copy is naturally switched off. (Or vice versa with other conditions). In Prader-Willi syndrome, the father’s copy is sometimes switched off (rather than missing, as in deletion). This means neither the father’s nor the mother’s copy is working, which leads to PWS.
Inclusion Criteria
The set of rules that determine who can take part in a research study or clinical trial (for example, age range or diagnosis).
Leptin
A hormone that helps signal when we feel full. In PWS, the body’s hunger system does not respond to these signals in the usual way, which contributes to ongoing feelings of hunger.
MAGEL2
A gene normally inherited from the father that plays an important role in brain function, sleep, and behaviour. In PWS, this gene is not active, which may contribute to some of the condition’s features.
Methylation DNA Analysis
A test used to diagnose PWS by detecting whether the normal genetic “imprinting” pattern is missing. This test has a more than 99% accuracy rate for confirming PWS.
MHRA (Medicines and Healthcare products Regulatory Agency)
The UK regulator responsible for approving medicines and ensuring they are safe and effective.
Multidisciplinary Care
Care provided by a team of healthcare professionals, such as doctors, dietitians, psychologists, and therapists.
Mutation
A change in DNA that can affect how a gene works.
Neurons
Special cells in the brain and nervous system that send messages around the body. In PWS, some of these brain signals don’t work as expected, affecting appetite, behaviour, and hormones.
NICE (National Institute for Health and Care Excellence)
The organisation that decides whether treatments should be available on the NHS in England and Wales.
Nutritional Management
Careful planning of diet, usually with lower calorie intake and structured meals, to support healthy weight in PWS.
Open-Label Extension or OLE
A continuation after study where participants receive the actual treatment even if they were on the placebo in the actual study.
Open-Label Study
A type of study where both researchers and participants know which treatment is being given.
Orphan Drug
A medication developed specifically to treat a rare condition like PWS.
Orphan Drug Status / Orphan Drug Designation
A special status given to medicines being developed for rare conditions like PWS. It provides support and incentives to help companies develop treatments that might otherwise not be financially viable.
Oxytocin
A natural hormone often called the “social” or “bonding” hormone. It helps with connection, emotions, and social behaviours. Researchers are studying whether oxytocin may help improve social and emotional challenges in PWS.
Perseverance
A tendency to become “stuck” on a particular thought, activity, or topic, even when it is no longer appropriate or relevant. In people with PWS, perseverance may show as repeatedly returning to the same idea, wanting to finish a task exactly as started, or finding it difficult to shift attention to something new. This is linked to differences in cognitive flexibility and can make transitions or changes in routine challenging.
Pharmaceutical Company
A company that researches, develops, and manufactures medicines. Many pharmaceutical companies work on developing new treatments for rare conditions like PWS, often through clinical trials.
Phase 1 (Clinical Trial)
The first stage of testing a new treatment in people. It focuses mainly on safety and finding the right dose. Sometimes this is done in healthy volunteers, but for conditions like PWS, it may involve people with PWS so researchers can safely study how the treatment works in the condition.
Phase 2 (Clinical Trial)
The stage where researchers begin to look at whether the treatment actually works, while continuing to monitor safety.
Phase 3 (Clinical Trial)
A larger study to confirm that a treatment is effective and safe, often comparing it to existing treatments or a placebo.
Phase 4 (Clinical Trial)
Research that takes place after a treatment is approved and in wider use, to monitor long-term safety and benefits.
Phenotype
The observable characteristics of a person — what we can see or notice — such as their physical features, behaviours, and medical traits. In Prader-Willi syndrome, the “phenotype” refers to the typical pattern of features and behaviours associated with the condition, such as low muscle tone, increased appetite, learning differences, and certain physical characteristics.
Placebo
An inactive treatment designed to look like the real treatment but contains no active ingredient. Often used in trials to compare whether a new treatment truly works.
Postnatal
The period after a baby is born. In PWS, early postnatal signs can include low muscle tone and feeding difficulties.
Preclinical Research
Early-stage research carried out in laboratories or animal studies before testing in humans begins.
Proof of Concept
Early evidence from research showing that a treatment has the potential to work.
Protocol (Clinical Trial)
The detailed plan for how a research study will be carried out, including what will happen, how participants will be monitored, and what researchers are measuring.
Qualitative Research
Research that focuses on understanding experiences, feelings, or behaviours, often using interviews or discussions.
Quality of Life (QoL)
A measure of overall wellbeing, including physical health, emotional state, and daily functioning.
Quantitative Research
Research that involves numbers and measurements, such as clinical trial results or surveys
Randomised Trial
A study in which participants are assigned by chance to different treatment groups.
Repetitive Questioning
The frequent asking of the same or very similar questions, often within a short period of time, even when the question has already been answered. In individuals with PWS, repetitive questioning is usually not intentional but reflects anxiety, a need for reassurance, or difficulty processing and retaining information. It can increase during times of uncertainty, change, or anticipation (for example, around food, routines, or upcoming events).
Satiety
The feeling of fullness after eating. In PWS, this signal is reduced or absent, which contributes to ongoing hunger.
SMC (Scottish Medicines Consortium)
An organisation in Scotland that reviews new medicines and decides whether they should be available on the NHS in Scotland.
Skin Picking
A common behaviour in PWS where a person repeatedly picks at their skin, which can lead to sores or infections. It is not done on purpose to cause harm and can be difficult to control.
Sleep Apnoea
A condition where breathing briefly stops and starts during sleep. It is more common in people with Prader-Willi syndrome (PWS) and can lead to poor sleep and daytime tiredness.
There are two main types:
- Obstructive sleep apnoea – when the airway becomes partly or fully blocked during sleep, making it hard for air to flow in and out.
- Central sleep apnoea – when the brain does not send the proper signals to control breathing for short periods.
Both types can affect sleep quality and overall health, and some people with PWS may experience one or both.
Sleep Disorders
Problems with sleep, such as sleep apnoea or excessive daytime sleepiness, are commonly seen in people with PWS.
snoRNAs (Small Nucleolar RNAs)
Tiny pieces of genetic material that help control how other genes work. In PWS, some of these are missing or not working properly, which may affect how the brain develops and functions. SNORD genes are a specific group of snoRNAs that play an important role in PWS. Missing or inactive SNORD genes are thought to be a key reason why PWS develops.
Strabismus
A condition where the eyes do not align properly (sometimes called a squint). This can be common in PWS.
Targeted Therapy
A treatment that is designed to work on a very specific part of the body that is causing the problem.
Uniparental Disomy (UPD)
A genetic cause of PWS where both copies of chromosome 15 are inherited from the mother instead of one from each parent.
Vagus Nerve Stimulation (VNS)
A treatment that involves sending gentle electrical signals to a nerve that connects the brain to many parts of the body. Researchers are exploring whether this could help with appetite, mood, or behaviour in PWS.