People with Prader-Willi syndrome (PWS) experience symptoms such as metabolic abnormalities, obesity, behavioral problems, and bone damage.
The disorder is caused by genetic alterations that result in the loss of function of paternal genes located in chromosome 15. The altered genes control sleep, metabolism, appetite, growth, intellectual ability, and social behavior.
Weak muscle tone
More commonly noticed right after delivery, hypotonia or weak muscle tone can be present before birth, causing a fetus to move less and be abnormally positioned in the womb. As such, there is an increased risk of an assisted delivery for a woman giving birth to a child with PWS.
After birth, newborns with PWS are “floppy” when held. They have a weak cry, poor reaction to stimuli, and trouble sucking, which result in feeding difficulties and insufficient weight gain.
Hypotonia increases the risk of developing scoliosis, a sideways curvature of the spine.
Despite being mostly present in children and improving over time, hypotonia may be also present in some adults with PWS.
Physical features
Some of the facial features of PWS patients include almond-shaped eyes, a thin upper lip, a downturned, triangular-shaped mouth, a thinner nose bridge, a narrower forehead, and a disproportionately long and narrow head. Eye misalignment, or strabismus, and nearsightedness may also occur.
Some individuals may also have a lack of color — known as hypopigmentation — affecting the hair, eyes, and skin.
PWS leads to an insufficient secretion of growth hormone. As a result, children may be shorter than normal. Growth hormone deficiency also results in a decrease in muscle mass and an increase in fat.
Patients may also have smaller hands and feet, and hip malformation.
Increased appetite
Children with PWS typically develop an excessive and insatiable appetite, beginning between the ages of 1 and 4.
Because they require fewer calories than normal due to low muscle mass, and reduced metabolism and physical activity, they may experience rapid weight gain and morbid obesity if they are not treated with growth hormones.
Morbid obesity can potentially lead to other conditions, including heart and lung problems, diabetes, high blood pressure, and gastrointestinal complications.
Cognitive and behavioral symptoms
Most children with PWS may have cognitive impairments, including mild to moderate intellectual and learning disabilities, and a low intelligence quotient (IQ).
As a result, they are delayed in reaching important developmental milestones, such as sitting up and starting to walk. Speech and language development is often delayed, and short-term memory is usually weak.
Behavioral problems can occur frequently and include stubbornness, temper outbursts, and obsessive-compulsive activities such as skin picking.
Some patients experience psychosis, a set of psychological symptoms resulting in the loss of contact with reality, in late adolescence or young adulthood.
Sleep problems
Many children with PWS have problems sleeping. Sleep problems include disturbance of the normal sleep cycle, and central and/or obstructive sleep apnea, which occur when airflow is blocked during sleep. These issues cause excessive daytime sleepiness, which may worsen inactivity and obesity.
Underdeveloped sex organs
Hypogonadism is a common PWS symptom and occurs when sex organs — the testes in males and the ovaries in females — produce little or no sex hormones. Consequently, sex organs are underdeveloped and puberty is often incomplete or delayed. Infertility may also occur.
The underdevelopment of sex organs is evident at birth. Boys may have a small penis and small testicles that fail to descend.
Girls may have a small clitoris and no menstrual cycle when they reach the age of puberty. In some cases, menstruation may start at age 30 or older.
Central adrenal insufficiency
Central adrenal insufficiency is a condition characterized by a deficiency of adrenocorticotropic hormone and may occur in some individuals with PWS.
This hormone stimulates the adrenal glands (small, triangular-shaped glands located on top of the kidneys) to produce cortisol. Cortisol is the body’s stress hormone, which also helps regulate blood sugar levels.
The exact cause of central adrenal insufficiency in PWS syndromes is not clear.
Other symptoms
Some patients may have little production of saliva, which can be thick and sticky. Recurrent respiratory infections may also occur.
There is also a higher risk of developing other conditions, such as osteopenia (decreased bone density leading to fractures), swelling, and ulcers in the legs, mainly in obese adults.
Additional symptoms may include an underactive thyroid gland, high pain tolerance, and seizures.
Children are also highly tolerant of vomiting, meaning they can eat much larger amounts of food before they vomit.
Variability in symptoms
PWS includes a range of linked conditions, and symptoms differ in severity and occurrence between patients. Many symptoms are common to other diseases, and may develop slowly over time or may occur subtly. Some subtle differences in the severity of symptoms may be explained by genetic alterations.
Patients with a deletion in chromosome 15 (DEL15) genes may have lighter skin and hair than other family members. They are also more likely to have seizures and psychiatric symptoms.
Young adults with maternal uniparental disomy may also be at increased risk for mental illness.
Last updated: March 24, 2021
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