Prader-Willi Syndrome (PWS) is a rare genetic disorder. It causes poor muscle tone, low levels of sex hormones and a constant feeling of hunger. The part of the brain that controls feelings of fullness or hunger does not work properly in people with PWS. They overeat, leading to obesity.

Babies with PWS are usually floppy, with poor muscle tone, and have trouble sucking. Boys may have undescended testicles. Later, other signs appear. These include

• Short stature
• Poor motor skills
• Weight gain
• Underdeveloped sex organs
• Mild intellectual and learning disabilities

There is no cure for PWS. Growth hormone, exercise, and dietary supervision can help build muscle mass and control weight. Other treatments may include sex hormones and behavior therapy. Most people with PWS will need specialized care and supervision throughout their lives.

The term PWS refers to a genetic disorder that affects many parts of the body. Genetic testing can successfully diagnose nearly all infants with PWS.

The syndrome usually results from deletions or partial deletions on chromosome 15 that affect the regulation of gene expression, or how genes turn on and off. Andrea Prader and Heinrich Willi first described the syndrome in the 1950s.

One of the main symptoms of PWS is the inability to control eating. In fact, PWS is the leading genetic cause of life-threatening obesity. Other symptoms include low muscle tone and poor feeding as an infant, delays in intellectual development, and difficulty controlling emotions.

There is no cure for PWS, but people with the disorder can benefit from a variety of treatments to improve their symptoms. These treatments depend on the individual's needs, but they often include strict dietary supervision, physical therapy, behavioral therapy, and treatment with growth hormone, among others. As adults, people with PWS usually do best in special group homes for people with this disorder. Some can work in sheltered environments.

Scientists do not know what increases the risk for Prader-Willi syndrome. The genetic error that leads to Prader-Willi syndrome occurs randomly, usually very early in fetal development. The syndrome is usually not hereditary.

Prader-Willi syndrome is caused by genetic changes on an "unstable" region of chromosome 15 that affects the regulation of gene expression, or how genes turn on and off. This part of the chromosome is called unstable because it is prone to being shuffled around by the cell's genetic machinery before the chromosome is passed on from parent to child.

The genetic changes that cause Prader-Willi syndrome occur in a portion of the chromosome, referred to as the Prader-Willi critical region (PWCR), around the time of conception or during early fetal development. This region was identified in 1990 using genetic DNA probes. Although Prader-Willi syndrome is genetic, it usually is not inherited and generally develops due to deletions or partial deletions on chromosome 15.

Specific changes to the chromosome can include the following:

• Deletions. A section of a chromosome may be lost or deleted, along with the functions that this section supported. A majority of PWS cases result from a deletion in one region of the father's chromosome 15 that leads to a loss of function of several genes. The corresponding mother's genes on chromosome 15 are always inactive and thus cannot make up for the deletion on the father's chromosome 15. The missing paternal genes normally play a fundamental role in regulating hunger and fullness.
• Maternal uniparental disomy (pronounced yoo-nuh-puh-REN-tl DAHY-soh-mee). A cell usually contains one set of chromosomes from the father and another set from the mother. In ordinary cases, a child has two chromosome 15s, one from each parent. In around one-fourth of PWS cases, the child has two copies of chromosome 15 from the mother and none from the father. Because genes located in the PWCR are normally inactive in the chromosome that comes from the mother, the child's lack of active genes in this region leads to PWS.
• An imprinting center defect. Genes in the PWCR on the chromosome that came from the mother are normally inactivated, due to a process known as "imprinting" that affects whether the cell is able to "read" a gene or not. In a small percentage of PWS cases, the chromosome 15 inherited from the father is imprinted in the same way as the mother's. This can be caused by a small deletion in a region of the father's chromosome that controls the imprinting process, called the imprinting center. In these cases, both of the child's copies of chromosome 15 have inactive PWCRs, leading to Prader-Willi syndrome.

Normal Function

The OCA2 gene (formerly called the P gene) provides instructions for making a protein called the P protein. This protein is located in melanocytes, which are specialized cells that produce a pigment called melanin. Melanin is the substance that gives skin, hair, and eyes their color. Melanin is also found in the light-sensitive tissue at the back of the eye (the retina), where it plays a role in normal vision.

Although the exact function of the P protein is unknown, it is essential for normal pigmentation and is likely involved in the production of melanin. Within melanocytes, the P protein may transport molecules into and out of structures called melanosomes (where melanin is produced). Researchers believe that this protein may also help regulate the relative acidity (pH) of melanosomes. Tight control of pH is necessary for most biological processes.

Health Conditions Related to Genetic Changes

Angelman syndrome

The OCA2 gene is located in a region of chromosome 15 that is often deleted in individuals with Angelman syndrome. A loss of this gene does not cause the characteristic neurologic features of Angelman syndrome; however, people with this condition who are missing one copy of the OCA2 gene tend to have unusually light-colored hair and fair skin. Cells with only one copy of the OCA2 gene make a reduced amount of P protein compared with cells with two functional copies of this gene, which affects the coloring of the hair and skin.

A small percentage of people with Angelman syndrome also have oculocutaneous albinism type 2. This condition occurs when people have two nonfunctional copies of the OCA2 gene in each cell. In addition to a deletion in chromosome 15 that removes one copy of the OCA2 gene, these individuals have a variant (also known as a mutation) in the OCA2 gene on the other copy of chromosome 15. As a result, cells make little or no functional P protein. A lack of P protein disrupts the production of melanin, leading to the characteristic features of albinism.

Oculocutaneous albinism

More than 80 variants in the OCA2 gene have been identified in people with oculocutaneous albinism type 2. People with this form of albinism often have light yellow, blond, or light brown hair; creamy white skin; light-colored eyes; and problems with vision. The most common OCA2 variant is a large deletion in the gene, which is found in many affected individuals of sub-Saharan African heritage. Other OCA2 gene variants, including changes in single DNA building blocks (base pairs) and small deletions, are more common in other populations. Variants in the OCA2 gene disrupt the normal production of melanin, which reduces coloring of the hair, skin, and eyes and affects vision.

Prader-Willi syndrome

The region of chromosome 15 containing the OCA2 gene is often deleted in individuals with Prader-Willi syndrome. A loss of this gene does not cause intellectual disability and the other characteristic features of Prader-Willi syndrome; however, people with this condition who are missing one copy of the OCA2 gene tend to have unusually light-colored hair and fair skin. Cells missing a copy of the OCA2 gene make less P protein than cells with two functional copies of the gene, which affects the coloring of the hair and skin.

Oculocutaneous albinism type 2 also occurs in a small number of people with Prader-Willi syndrome. This condition occurs when people have two nonfunctional copies of the OCA2 gene in each cell. In addition to a deletion in chromosome 15 that removes one copy of the OCA2 gene, these individuals have a variant in the OCA2 gene on the other copy of chromosome 15. As a result, cells make little or no functional P protein. A lack of P protein disrupts the production of melanin, leading to the characteristic features of albinism.

Melanoma

MedlinePlus Genetics provides information about Melanoma

Other Names for This Gene

• BOCA
• Melanocyte-specific transporter protein
• oculocutaneous albinism II
• oculocutaneous albinism II (pink-eye dilution homolog, mouse)
• P gene
• P_HUMAN
• PED
• Pink-eyed dilution protein homolog

Genomic Location

Chromosome 15 spans more than 102 million DNA building blocks (base pairs) and represents more than 3 percent of the total DNA in cells. Chromosome 15 likely contains 600 to 700 genes that provide instructions for making proteins. These proteins perform a variety of different roles in the body.

The following chromosomal conditions are associated with changes in the structure or number of copies of chromosome 15.

15q11-q13 duplication syndrome

Duplication of a region of the long (q) arm of chromosome 15 can result in 15q11-q13 duplication syndrome (dup15q syndrome), a condition whose features can include weak muscle tone (hypotonia), intellectual disability, recurrent seizures (epilepsy), characteristics of autism spectrum disorder affecting communication and social interaction, and other behavioral problems.

Dup15q syndrome is caused by the presence of at least one extra copy of a region of chromosome 15 called 15q11.2-q13.1. This region is also called the Prader-Willi/Angelman critical region (PWACR) because genetic changes in it are also involved in conditions called Prader-Willi syndrome and Angelman syndrome (described below). Dup15q syndrome arises only if the chromosome abnormality occurs on the copy of the chromosome inherited from the mother (the maternal copy). People normally inherit one copy of chromosome 15 from each parent. However, some genes on this chromosome, including some of those in the 15q11.2-q13.1 region, are turned on (active) only on the maternal copy. This parent-specific gene activation results from a phenomenon called genomic imprinting.

The most common chromosome abnormality that leads to 15q11.2-q13.1 duplication, occurring in about 80 percent of people with dup15q syndrome, is called an isodicentric chromosome 15. An isodicentric chromosome contains mirror-image segments of genetic material and has two constriction points (centromeres), rather than one centromere as in normal chromosomes. In people with an isodicentric chromosome 15, cells have the usual two copies of chromosome 15 plus the two duplicated copies of the segment of genetic material in the isodicentric chromosome, for a total of four copies of the duplicated segment.

In about 20 percent of cases of dup15q syndrome, the duplication occurs on the long (q) arm of one of the two copies of chromosome 15 in each cell; this situation is called an interstitial duplication. In these cases, cells have two copies of chromosome 15, one of which has an extra copy of the segment of genetic material, for a total of three copies of the duplicated segment.

In all cases of dup15q syndrome, the duplicated genetic material results in extra copies of certain genes involved in development. This extra genetic material disrupts normal development, causing the characteristic features of this disorder. People with dup15q syndrome resulting from an interstitial duplication often have milder signs and symptoms than those in whom the disorder results from an isodicentric chromosome 15.

15q13.3 microdeletion

15q13.3 microdeletion is a chromosomal change in which a small piece of chromosome 15 is deleted in each cell. The deletion occurs on the q arm of the chromosome at a position designated q13.3. Most people with a 15q13.3 microdeletion are missing a sequence of about 2 million DNA base pairs, also written as 2 megabases (Mb). The exact size of the deleted region varies, but it typically contains at least six genes. It is unclear how a loss of these genes increases the risk of intellectual disability, seizures, behavioral problems, and psychiatric disorders in some individuals with a 15q13.3 microdeletion.

Other people with a 15q13.3 microdeletion have no obvious signs or symptoms related to the chromosomal change. In these individuals, the microdeletion is often detected when they undergo genetic testing because they have an affected relative. It is unknown why 15q13.3 microdeletion causes cognitive and behavioral problems in some individuals but few or no health problems in others. Researchers believe that additional genetic or environmental factors may be involved.

15q24 microdeletion

15q24 microdeletion is a chromosomal change in which a small piece of chromosome 15 is deleted in each cell. Specifically, affected individuals are missing between 1.7 Mb and 6.1 Mb of DNA at position q24 on chromosome 15. The exact size of the deletion varies, but all individuals are missing the same 1.2 Mb region. This region contains several genes that are thought to be important for normal development. It is unclear how a loss of these genes leads to intellectual disability, distinctive facial features, and other abnormalities often seen in people with a 15q24 microdeletion.

Acute promyelocytic leukemia

A type of blood cancer known as acute promyelocytic leukemia is caused by a rearrangement (translocation) of genetic material between chromosomes 15 and 17. This translocation, written as t(15;17), fuses part of the PML gene from chromosome 15 with part of the RARA gene from chromosome 17. This mutation is acquired during a person's lifetime and is present only in certain cells. This type of genetic change, called a somatic mutation, is not inherited. The t(15;17) translocation is called a balanced reciprocal translocation because the pieces of chromosome are exchanged with each other (reciprocal) and no genetic material is gained or lost (balanced). The protein produced from this fused gene is known as PML-RARα.

The PML-RARα protein functions differently than the protein products from the normal PML and RARA genes. The PML gene on chromosome 15 provides instructions for a protein that acts as a tumor suppressor, which means it prevents cells from growing and dividing too rapidly or in an uncontrolled way. The PML protein blocks cell growth and division (proliferation) and induces self-destruction (apoptosis) in combination with other proteins. The RARA gene on chromosome 17 provides instructions for making a transcription factor called the retinoic acid receptor alpha (RARα). A transcription factor is a protein that attaches (binds) to specific regions of DNA and helps control the activity of particular genes. Normally, the RARα protein controls the activity (transcription) of genes important for the maturation (differentiation) of immature white blood cells beyond a particular stage called the promyelocyte. The PML-RARα protein interferes with the normal function of both the PML and the RARα proteins. As a result, blood cells are stuck at the promyelocyte stage, and they proliferate abnormally. Excess promyelocytes accumulate in the bone marrow and normal white blood cells cannot form, leading to acute promyelocytic leukemia.

Angelman syndrome

Angelman syndrome results from a loss of gene activity (expression) in a specific part of chromosome 15 in each cell. This region is located on the q arm of the chromosome and is designated 15q11-q13. This region contains a gene called UBE3A that, when mutated or absent, likely causes the characteristic neurologic features of Angelman syndrome.

People normally inherit one copy of the UBE3A gene from each parent, and both copies of this gene are active in many of the body's tissues. In certain areas of the brain, however, only the copy inherited from a person's mother (the maternal copy) is active. This parent-specific gene activation results from a phenomenon called genomic imprinting. If the maternal copy is lost because of a chromosomal change or a gene mutation, a person will have no working copies of the UBE3A gene in some parts of the brain.

In most cases (about 70 percent), Angelman syndrome results from a deletion in the maternal copy of chromosome 15. This chromosomal change deletes the region of chromosome 15 that includes the UBE3A gene. Because the copy of the UBE3A gene inherited from a person's father (the paternal copy) is normally inactive in certain parts of the brain, a deletion in the maternal chromosome 15 leaves no active copies of the UBE3A gene in these brain regions.

In 3 percent to 7 percent of cases of Angelman syndrome, the condition results when a person inherits two copies of chromosome 15 from his or her father instead of one copy from each parent. This phenomenon is called paternal uniparental disomy (UPD). People with paternal UPD for chromosome 15 have two copies of the UBE3A gene, but they are both inherited from the father and are therefore inactive in the brain.

About 10 percent of cases of Angelman syndrome are caused by a mutation in the UBE3A gene, and another 3 percent results from a defect in the DNA region that controls the activation of the UBE3A gene and other genes on the maternal copy of chromosome 15. In a small percentage of cases, Angelman syndrome is caused by a chromosomal rearrangement (translocation) or by a mutation in a gene other than UBE3A. These genetic changes abnormally inactivate the UBE3A gene.

Prader-Willi syndrome

Prader-Willi syndrome is caused by a loss of active genes in a region of chromosome 15. This region is located on the q arm of the chromosome and is designated 15q11-q13. It is the same part of chromosome 15 that is usually affected in people with Angelman syndrome, although different genes are associated with the two disorders. People can have either Prader-Willi syndrome or Angelman syndrome, but they typically cannot have both.

People normally inherit one copy of chromosome 15 from each parent. Some genes on this chromosome are turned on (active) only on the copy inherited from a person's father (the paternal copy). This parent-specific gene activation results from a phenomenon called genomic imprinting.

In about 70 percent of cases, Prader-Willi syndrome occurs when the 15q11-q13 region of the paternal chromosome 15 is deleted in each cell. A person with this chromosomal change will be missing certain critical genes in this region because the genes on the paternal copy have been deleted, and the genes on the maternal copy are turned off (inactive). Researchers are working to identify which missing genes are associated with the characteristic features of Prader-Willi syndrome.

In about 25 percent of cases, people with Prader-Willi syndrome inherit two copies of chromosome 15 from their mother instead of one copy from each parent. This phenomenon is called maternal UPD. A person with two maternal copies of chromosome 15 will have no active copies of certain genes in the 15q11-q13 region.

In a small percentage of cases, Prader-Willi syndrome is caused by a chromosomal rearrangement called a translocation. Rarely, the condition results from a mutation or other defect that abnormally inactivates genes on the paternal copy of chromosome 15.

Sensorineural deafness and male infertility

Sensorineural deafness and male infertility is caused by a deletion of genetic material on the q arm of chromosome 15. The symptoms of sensorineural deafness and male infertility are related to the loss of multiple genes in this region. The size of the deletion varies among affected individuals. Researchers have determined that the loss of a particular gene on chromosome 15, STRC, is responsible for hearing loss in affected individuals. The loss of another gene, CATSPER2, in the same region of chromosome 15 is responsible for sperm abnormalities, which lead to an inability to father children (infertility) in affected males. Researchers are working to determine how the loss of additional genes in the deleted region affects people with sensorineural deafness and male infertility.

Other chromosomal conditions

Other changes in the number or structure of chromosome 15 can cause intellectual disability, delayed growth and development, hypotonia, and characteristic facial features. These changes include an extra copy of part of chromosome 15 in each cell (partial trisomy 15), a missing segment of the chromosome in each cell (partial monosomy 15), and a circular structure called ring chromosome 15. A ring chromosome occurs when a chromosome breaks in two places and the ends of the chromosome arms fuse together to form a circular structure.

Scientists think that the symptoms of PWS may be caused by a problem in a portion of the brain called the hypothalamus (pronounced hahy-puh-THAL-uh-muhs). The hypothalamus lies in the base of the brain. When it works normally, it controls hunger or thirst, body temperature, pain, and when it is time to awaken and to sleep. Problems with the hypothalamus can affect various body functions and pathways, leading to a variety of symptoms.

Individuals with PWS may have mild to severe symptoms, which often include:

Feeding and Metabolic Symptoms

An important early symptom of PWS is an infant's inability to suck, which affects the ability to feed. Nearly all infants with PWS need help with feeding. Infants may require feeding support for several months. Without assistance, they will not grow. Nursing systems with one-way valves and manual sucking assistive devices, similar to those used with cleft palate (such as bottles with special nipples for babies who do not have the sucking reflex), often are needed. Occasionally, feeding tubes are required, but generally for no more than the first 6 months after birth. The infants may need fewer calories because of the reduced metabolism associated with PWS and may not demand feeding on their own. Frequent weight checks will help in adjusting the infant's diet to maintain a suitable weight gain.

As the infants grow into toddlers and children, compulsive overeating replaces the need for feeding support. Because the metabolic rate of individuals with PWS is lower than normal, their caloric intake must be restricted to maintain a healthy weight, often to 60% of the caloric requirement of comparably sized children without the syndrome.

Feeding and metabolic symptoms persist into adulthood. Unless individuals with PWS live in environments that limit access to food (such as locked cabinets and a locked refrigerator), they will eat uncontrollably, even food that is rotten or sitting in the garbage. Uncontrollable eating can cause choking, a ruptured esophagus, and blockages in the digestive system. It can also lead to extreme weight gain and morbid obesity. Because of their inability to stop eating, people with PWS are at increased risk for diabetes, trouble breathing during sleep, and other health risks. For these reasons, people with PWS need to be monitored by a health care professional their entire lives.

Physical Symptoms

Many physical symptoms of PWS arise from poor regulation of various hormones, including growth hormone, thyroid hormone, and possibly adrenalin. Individuals with PWS grow slowly and experience delays in reaching physical activity milestones (e.g., standing, walking).

Children with PWS tend to be substantially shorter than other children of similar age. They may have small hands and feet and a curvature of the back, called scoliosis (pronounced skoh-lee-OH-sis). In addition, they frequently have difficulty making their eyes work together to focus, a condition called strabismus (pronounced struh-BIZ-muhs).

Infants with PWS are often born with underdeveloped sex organs, including a small penis and scrotum or a small clitoris and vaginal lips. Most individuals with PWS are infertile.

Intellectual Symptoms

Individuals with PWS have varying levels of intellectual disabilities. Learning disabilities are common, as are delays in starting to talk and in the development of language.

Behavioral and Psychiatric Symptoms

Imbalances in hormone levels may contribute to behavioral and psychiatric problems. Behavioral problems may include temper tantrums, extreme stubbornness, obsessive-compulsive symptoms, picking the skin, and general trouble in controlling emotions. The individual will often repeat questions or statements. Sleep disturbances may include excessive daytime sleepiness and disruptions of sleep. Many individuals with PWS have a high pain threshold.

Stages of PWS Symptoms

The appearance of PWS symptoms occurs in two recognized stages:

Stage 1 (Infancy to age 2 years)

• "Floppiness" and poor muscle tone
• Weak cries and a weak sucking reflex
• Inability to breastfeed, which may require feeding support, such as tube feeding
• Developmental delays
• Small genital organs

Stage 2 (Ages 2 to 8)

• Unable to feel satisfied with normal intake of food
• Inability to control eating, which can lead to overeating if not monitored
• Food-seeking behaviors
• Low metabolism
• Weight gain and obesity
• Daytime sleepiness and sleep problems
• Intellectual disabilities
• Small hands and feet
• Short stature
• Curvature of the spine (scoliosis)
• High pain threshold
• Behavioral problems, including the display of obsessive-compulsive symptoms, picking the skin, and difficulty controlling emotions
• Small genitals, often resulting in infertility in later life

Several other disorders and conditions are associated with PWS:

• Obesity and secondary problems due to extreme obesity
  • Diabetes
  • Sleep apnea
• Obsessive-compulsive disorder
• Infertility
• Autism-spectrum disorders

Until recently, experts believed that people with PWS were infertile. However, because several pregnancies have occurred in women with PWS, birth control should be considered.

In many cases of Prader-Willi syndrome, diagnosis is prompted by physical symptoms in the newborn.

If a newborn is unable to suck or feed for a few days and has a "floppy" body and weak muscle tone, a health care provider may conduct genetic testing for Prader-Willi syndrome. Formal diagnostic criteria for recognizing Prader-Willi syndrome depend on the age of the individual-specifically, whether the third birthday has been reached. Before age 3, the most important symptom is extremely poor muscle tone, called hypotonia (pronounced HAHY-poh-toh-nee-uh), which makes infants feel floppy. In affected children 3 years of age and older, other symptoms become apparent, such as obesity, intellectual delays, learning disabilities, or behavior problems, especially connected with food and eating.

• Children younger than 3 years must have at least four major criteria and at least one minor criterion for a Prader-Willi syndrome diagnosis.
• Those older than 3 years must have at least five major criteria and at least three minor criteria for a diagnosis of Prader-Willi syndrome.

Major Clinical Criteria of Prader-Willi Syndrome

• Extremely weak muscles in the body's torso
• Difficulty sucking, which improves after the first few months
• Feeding difficulties and/or failure to grow, requiring feeding assistance, such as feeding tubes or special nipples to aid in sucking
• Beginning of rapid weight gain, between ages 1 and 6, resulting in severe obesity
• Excessive, uncontrollable overeating
• Specific facial features, including narrow forehead and downturned mouth
• Reduced development of the genital organs, including small genitalia (vaginal lips and clitoris in females and small scrotum and penis in males); incomplete and delayed puberty; infertility
• Developmental delays, mild-to-moderate intellectual disability, multiple learning disabilities

Minor Clinical Criteria of Prader-Willi Syndrome

• Decreased movement and noticeable fatigue during infancy
• Behavioral problems-specifically, temper tantrums, obsessive-compulsive behavior, stubbornness, rigidity, stealing, and lying (especially related to food)
• Sleep problems, including daytime sleepiness and sleep disruption
• Short stature, compared with other members of the family, noticeable by age 15
• Light color of skin, eyes, and hair
• Small hands and feet in comparison to standards for height and age
• Narrow hands
• Nearsightedness and/or difficulty focusing both eyes at the same time
• Thick saliva
• Poor pronunciation
• Picking of the skin

Additional Findings

• High pain threshold
• Inability to vomit
• Curvature of the spine (scoliosis)
• Earlier-than-usual activity in the adrenal glands, which can lead to early puberty
• Especially brittle bones (called osteoporosis, pronounced os-tee-oh-puh-ROH-sis)

Genetic testing must confirm the Prader-Willi syndrome diagnosis. Almost all individuals with Prader-Willi syndrome have an abnormality within a specific area of chromosome 15. Early diagnosis is best because it enables affected individuals to begin early intervention/special needs programs and treatment specifically for Prader-Willi symptoms.

Genetic testing can confirm the chance that a sibling might be born with Prader-Willi syndrome. Prenatal diagnosis also is available for at-risk pregnancies-that is, pregnancies among women with a family history of Prader-Willi syndrome abnormalities.

Genetic Counseling and Testing of At-risk Relatives

Genetic counseling and testing provide individuals and families with information about the nature, inheritance, and implications of genetic disorders so that they can make informed medical and personal decisions about having children. Genetic counseling helps people understand their risks. The risk of occurrence in siblings of patients with Prader-Willi syndrome depends on what caused the disorder to occur.

Parents can enroll infants with PWS in early intervention programs. However, even if a PWS diagnosis is delayed, treatments are valuable at any age.

The types of treatment depend on the individual’s symptoms. The health care provider may recommend the following:

• Use of special nipples or tubes for feeding difficulties. Difficulty in sucking is one of the most common symptoms of newborns with Prader-Willi syndrome. Special nipples or tubes are used for several months to feed newborns and infants who are unable to suck properly, to make sure that the infant is fed adequately and grows. To ensure that the child is growing properly, the health care provider will monitor height, weight, and body mass index (BMI) monthly during infancy.
• Strict supervision of daily food intake.Once overeating starts between ages 2 and 4 years, supervision will help to minimize food hoarding and stealing and prevent rapid weight gain and severe obesity. Parents should lock refrigerators and all cabinets containing food. No medications have proven beneficial in reducing food-seeking behavior.
  
  A well-balanced, low-calorie diet and regular exercise are essential and must be maintained for the rest of the individual's life. People with PWS rarely need more than 1,000 to 1,200 calories per day. Height, weight, and BMI should be monitored every 6 months during the first 10 years of life after infancy and once a year after age 10 for the rest of the person's life to make sure he or she is maintaining a healthy weight. Ongoing consultation with a dietitian to guarantee adequate vitamin and mineral intake, including calcium and vitamin D, might be needed.
• Growth Hormone (GH) therapy. GH therapy has been demonstrated to increase height, lean body mass, and mobility; decrease fat mass; and improve movement and flexibility in individuals with PWS from infancy through adulthood. When given early in life, it also may prevent or reduce behavioral difficulties. Additionally, GH therapy can help improve speech, improve abstract reasoning, and often allow information to be processed more quickly. It also has been shown to improve sleep quality and resting energy expenditure. GH therapy usually is started during infancy or at diagnosis with PWS. This therapy often continues during adulthood at 20% to 25% of the recommended dose for children.
• Treatment of eye problems by a pediatric ophthalmologist.Many infants have trouble getting their eyes to focus together. These infants should be referred to a pediatric ophthalmologist who has expertise in working with infants with disabilities.
• Treatment of curvature of the spine by an orthopedist. An orthopedist should evaluate and treat, if necessary, curvature of the spine (scoliosis). Treatment will be the same as that for people with scoliosis who do not have PWS.
• Sleep studies and treatment. Sleep disorders are common with PWS. Treating a sleep disorder can help improve the quality of sleep. The same treatments that health care providers use with the general population can apply to individuals with PWS.
• Physical therapy. Muscle weakness is a serious problem among individuals with PWS. For children younger than age 3, physical therapy may increase muscular strength and help such children achieve developmental milestones. For older children, daily exercise will help build lean body mass.
• Behavioral therapy. People with PWS have difficulty controlling their emotions. Using behavioral therapy can help. Stubbornness, anger, and obsessive-compulsive behavior, including obsession with food, should be handled with behavioral management programs using firm limit-setting strategies. Structure and routines also are advised.
• Medications.Medications, especially serotonin reuptake inhibitors (SRIs), may reduce obsessive-compulsive symptoms. SRIs also may help manage psychosis.
• Early interventions/Special needs programs. Individuals with PWS have varying degrees of intellectual difficulty and learning disabilities. Early intervention programs, including speech therapy for delays in acquiring language and for difficulties with pronunciation, should begin as early as possible and continue throughout childhood.
  
  Special education is almost always necessary for school-age children. Groups that offer training in social skills may also prove beneficial. An individual aide is often useful in helping PWS children focus on schoolwork.
• Sex hormone treatments and/or corrective surgery.These treatments are used to treat small genitals (penis, scrotum, clitoris).
• Replacement of sex hormones. Replacement of sex hormones during puberty may result in development of adequate secondary sex characteristics (e.g., breasts, pubic hair, a deeper voice).
• Placement in group homes during adulthood. Group homes offer necessary structure and supervision for adults with PWS, helping them avoid compulsive eating, severe obesity, and other health problems.

Prader-Willi syndrome has no cure. However, early diagnosis and treatment may help prevent or reduce the number of challenges that individuals with Prader-Willi syndrome may experience, and which may be more of a problem if diagnosis or treatment is delayed.