Prader-Willi Syndrome (PWS)
Understand PWS: what it is, how it occurs, symptoms, phases and treatment
Prader-Willi Syndrome (PWS) is a rare neurogenetic disorder caused by loss of function of paternally-inherited genes on the 15q11-q13 region of chromosome 15. It is considered the leading genetic cause of obesity and affects boys and girls of all ethnic backgrounds equally.
PWS affects approximately 1 in every 15,000 to 30,000 live births worldwide. It is a genetic error that occurs at conception — it is not inherited in most cases and is not related to any parental action during pregnancy.
First described in 1956, PWS has a distinct clinical evolution in phases, starting with severe hypotonia (muscle weakness) in the newborn and progressing — between ages 2 and 8 — to hyperphagia (insatiable hunger) that can lead to morbid obesity if uncontrolled.
Other names for Prader-Willi Syndrome
Prader-Willi Syndrome is known by several names in medical and popular literature:
- •PWS - Prader-Willi Syndrome
- •SPW (Portuguese and Spanish acronym)
- •Prader-Labhart-Willi Syndrome (original full name)
- •Prader Willi (without hyphen, popular form)
All terms refer to the same rare genetic condition first described in 1956 by Swiss physicians Andrea Prader, Alexis Labhart and Heinrich Willi.
How it occurs genetically
About 70% of cases result from paternal deletion: a segment of the paternally-inherited chromosome 15 is missing in every cell. Around 25% of cases involve maternal uniparental disomy (UPDmat), where the person inherits two maternal copies of chromosome 15. The remaining ~5% involve imprinting defects, point mutations, or translocations.
Some genes in the 15q11-q13 region are active only when inherited from the father — a phenomenon called genomic imprinting. When these paternal genes don't function, PWS manifests. This distinguishes PWS from Angelman Syndrome, which results from loss of maternal genes in the same chromosomal region.
Definitive genetic diagnosis is made by DNA methylation testing, which identifies 99% of PWS cases regardless of the underlying mechanism. SPW Brasil, in partnership with IFF/FIOCRUZ, offers this test free of charge to patients with clinical suspicion in Brazil.
Prevalence and epidemiology
Prader-Willi Syndrome is classified as a rare disease. Its global incidence is estimated at 1 case per 15,000-30,000 live births.
PWS affects boys and girls equally and occurs in all ethnic groups and geographic regions. With appropriate multidisciplinary care and strict nutritional control, life expectancy approaches that of the general population.
PWS symptoms: from pregnancy to childhood
During pregnancy, babies with PWS show decreased fetal movement. The mother may notice reduced activity compared to usual. In some cases there is polyhydramnios (excess amniotic fluid) because the fetus cannot swallow normally.
At birth, the baby has severe hypotonia (very floppy), weak cry and significant difficulty sucking. Breastfeeding usually fails and many babies temporarily require a nasogastric tube. This neonatal hypotonia phase is a key indicator for referral to genetic diagnosis.
Hypotonia progressively improves from 6-8 months onward, but motor developmental delay persists. Between ages 2-8, hyperphagia emerges — an exaggerated appetite that, if uncontrolled, leads to severe obesity. This is the most classic and recognizable phase of the syndrome.
Main clinical features
PWS manifestations vary in intensity, but certain clinical features are common to most people with the syndrome. They appear progressively across life phases.
Neuropsychomotor development
- •Motor developmental delay
- •Speech articulation difficulty (dysarthria)
- •Learning difficulties and mild to moderate intellectual disability
- •Concrete thinking, difficulty with abstraction
- •Obsessive-compulsive traits and difficulty with routine changes
Eating and hyperphagia
- •Constant intense sensation of hunger
- •Compulsive interest in food (hyperphagia)
- •Lack of satiety after meals
- •Obesity, mainly abdominal, if uncontrolled
- •Increased risk of type 2 diabetes
Physical features
- •Short stature (usually below 25th percentile)
- •Small hands and feet (acromicria)
- •Skin lighter than that of family members
- •Small mouth with thin upper lip and downturned corners
- •Narrow forehead and almond-shaped eyes
- •Hypogonadism: delayed or incomplete puberty
Other manifestations
- •Decreased pain sensitivity
- •Strabismus (common)
- •Sleep disorders, obstructive apnea
- •Thick saliva, difficulty with dry foods
- •Unstable body temperature
Physical features and appearance
People with PWS share a recognizable set of physical traits, though not all are present in every patient. The face tends to be elongated with a narrow forehead, almond-shaped eyes, a small mouth with thin upper lip and downturned corners.
Hands and feet are notably small in proportion to the body (acromicria), an important clinical diagnostic feature. Skin is often lighter than family members', and hair may also be lighter. Short stature is common and can be mitigated with early growth hormone (GH) treatment.
Clinical phases of Prader-Willi Syndrome
Phase 1 — Neonatal hypotonia and early life
Characterized by severe hypotonia, feeding difficulties (weak sucking, tube feeding needs), weak cry, and motor developmental delay. This is the phase when clinical suspicion typically arises. Early interventions: physiotherapy, speech therapy and referral for genetic diagnosis.
Phase 2 — Transition and weight gain
Between ages 2 and 4, weight gain begins before overt hyperphagia, even without proportional increase in caloric intake. This is a critical transition phase to initiate strict dietary control and nutritional monitoring.
Phase 3 — Hyperphagia (from around age 8)
The classic PWS phase: development of insatiable appetite, compulsive food-seeking behavior and complete absence of satiety. Without strict environmental control of food access, morbid obesity and cardiovascular complications are a high risk. This is the most recognizable phase of the syndrome.
Recent studies show PWS is a multi-stage syndrome, with up to 7 sub-phases described in the literature, including variations in adolescence and adulthood. See the Phases page for details.
Treating Prader-Willi Syndrome
PWS treatment is multidisciplinary and should begin as early as possible. There is no cure, but with appropriate interventions life expectancy and quality of life approach those of the general population. Interventions aim to prevent obesity and its complications (diabetes, hypertension, apnea), which are the leading causes of death in these patients.
The typical multidisciplinary team includes: geneticist, pediatric endocrinologist, nutritionist, physiotherapist, speech-language pathologist, occupational therapist, psychologist, and — in more advanced phases — psychiatrist. Environmental control of food access (locked pantries, constant mealtime supervision) is an essential part of treatment from phase 3 onward.
Growth hormone (GH) treatment
Recombinant human growth hormone (GH) therapy is the most effective pharmacological intervention for PWS and is approved worldwide for this indication. It improves final height, body composition (more lean mass, less fat), muscle tone, motor and cognitive development.
Studies show that the earlier GH is started — ideally in the first year of life — the greater the functional and developmental gains. Therapy is long-term and requires regular endocrinological follow-up with cardiac and respiratory evaluation.
Free diagnosis in Brazil
SPW Brasil, in partnership with IFF/FIOCRUZ, offers DNA methylation testing free of charge to patients with clinical suspicion. Referral is made by a physician and samples can be sent from anywhere in Brazil.
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