Prader-Willi syndrome (PWS) is a rare genetic disorder that is predominantly caused by the absence of genetic material on the long arm of the chromosome 15 contributed by the father. However, PWS may also result when an individual is missing chromosome 15 from the father, and instead, has two chromosome 15s from the mother (uniparental disomy), or when there is a mutation on the paternal chromosome 15. PWS is estimated to occur in 1 in 12,000 to 1 in 15,000 live births. Though it is considered a rare disorder, it is the most common genetic cause of obesity. Males and females are affected equally and PWS occurs in all races.
Most cases of PWS are the result of new spontaneous genetic errors that occur some time around the point of conception. In approximately 2% of cases, however, there is a mutation that is passed down from the parent, causing PWS. In these cases, more than one child may be affected in the family.
Descriptions of individuals with PWS date as far back as the 17th century, however, in 1956, doctors A. Prader, H. Willi, and A. Labhart published a brief paper describing a syndrome which was characterized by obesity, short stature, lack of muscle tone in infancy, cryptorchism, and mental retardation. They later presented the disorder at the 8th International Pediatric Congress in Copenhagen, claiming the most distinctive feature to be hyperphagia, which leads to excessive obesity.
Features and Characteristics
The following characteristics are most often found in individuals with PWS and are considered diagnostic criteria for the syndrome (Holm et al, Pediatrics 91, 2, 1993):
Major Clinical Findings
- Neonatal and infantile central hypotonia, improving with age
- Feeding problems and poor weight gain in infancy
- Excessive or rapid weight gain between 1 and 6 years of age; central obesity in the absence of intervention
- Distinctive facial features - dolichocephaly in infants, narrow face/bifrontal diameter, almond-shaped eyes, small-appearing mouth with thin upper lip and down-turned corners of mouth
- Hypogonadism - genital hypoplasia, including undescended testes and small penis in males; delayed or incomplete gonadal maturation and delayed pubertal signs after age 16, including scant or no menses in women
- Global developmental delay before age 6; mild to moderate mental retardation or learning problems in older children
- Hyperphagia/food foraging/obsession with food
Minor Clinical Findings
- Decreased fetal movement, infantile lethargy, weak cry
- Characteristic behavior problems - temper tantrums, violent outbursts, obsessive/compulsive behavior; tendency to be argumentative, oppositional, rigid, manipulative, possessive, and stubborn; perseverating, stealing, lying
- Sleep disturbance or sleep apnea
- Short stature for genetic background by age 15
- Hypopigmentation - fair skin and hair compared with family
- Small hands and/or feet for height/age
- Narrow hands with straight ulnar border
- Eye abnormalities (esotropia, myopia)
- Thick, viscous saliva with crusting at corners of the mouth
- Speech articulation defects
- Skin picking
- High pain threshold
- Decreased vomiting
- Temperature instability in infancy or altered temperature sensitivity in older children and adults
- Scoliosis or kyphosis (curvature of the spine)
- Early adrenarche (pubic or axillary hair before age 8)
- Osteoporosis (demineralization, or thinning, of the bones)
- Unusual skill with jigsaw puzzles
- Normal neuromuscular studies
Hyperphagia (abnormal increased appetite)
The cause of hyperphagia in individuals with PWS is thought to be the result of a dysfunction in the hypothalamus. Compulsive eating begins before age 6. The urge to eat is physiological and totally overwhelming. The risk of obesity results not only because individuals with PWS have an insatiable appetite, but because they also burn less calories than others due to low muscle mass and inactivity. Unless their diet is carefully controlled, weight gain can be very rapid leading not only to obesity, but to disease and early death as well. Appetite suppressants have not been proven to be effective in individuals with PWS.
Motor skills are usually 1 to 2 years behind due to the hypotonia. Balance, strength, coordination and motor planning are often affected. Growth hormone treatment may increase motor skills by increasing muscle mass. Physical therapy and occupational therapy may be useful in promoting development in the affected areas. In addition, low tone may cause feeding problems due to an inability to suck, and could, therefore, result in the infant requiring a feeding tube for the first few days or weeks of life.
Speech articulation defects
Hypotonia can also lead to poor speech skills. The need for speech therapy should be addressed in early infancy. Speech problems can lead to frustration and sometimes aggressive behavior. Products to increase saliva may help articulation skills, however, other forms of communication may be necessary, such as sign language or communication boards. Though children with PWS have problems with articulation, verbal ability often becomes a strength for them.
Developmental Delay/Learning Disabilities
IQS of individuals with PWS range from 40 to 105, with an average of 70. Those who do have an IQ in the "normal" range typically have learning disabilities and the spread of their abilities is mixed. Areas in which the child may have difficulties are with attention, short-term auditory memory, and abstract thinking. However, they do exhibit strengths in the areas of long-term memory, reading ability, and receptive language.
There are several diagnostic studies used to test for PWS. Methylation analysis is a test that can detect virtually all cases of PWS, however, the test is not available everywhere. Therefore, FISH (for deletion cases) and PCR (for UPD cases) testing may be used. Together, these two tests will identify 99% of the cases. With the latest molecular testing available, patients who tested negative with older tests should be retested. In addition to genetic testing, diagnostic criteria for clinical recognition of PWS (as shown above) has also been made available.
There is no cure for PWS nor is there a drug that is universally prescribed to treat all symptoms. However, there are methods of managing some of the symptoms. For example, synthetic growth hormones can be used to treat children who are determined to be growth hormone deficient. In terms of the obesity factor, during the pre-school years (ages 2-5 years) a restrictive diet can be maintained to prevent extreme weight gain and an exercise program should begin as early as possible. And, for some individuals, pyschotropic drugs may be used to help with some of the behaviors commonly seen in individuals with PWS (although positive behavior management is a preferred alternative).
In regards to education, children with PWS typically start their formal education in a mainstream setting with various forms of support. Some, however, may attend a special education program in schools that are equipped for children with moderate to severe learning disabilities. In the primary school years, teachers may have difficulty with several problems that children with PWS may have. For example, children with PWS tend to have difficulty with change and prefer to stick with a routine. Strategies for coping with change should be taught in the early years. Children with PWS may also have poor short-term memories, therefore, requiring the teacher to continually reiterate the topics until they are fully grasped. Also, children with PWS may have difficulty working in groups and may need extra support and guidance from the teacher. Many times, when the child is not receiving enough attention, the child can become frustrated, which can then lead to tantrums. Last, school parties become a concern for teachers in that cakes and candy can be very distressful to the child with PWS who is on a restricted diet.
In the secondary school years, another set of concerns arise. Some of these concerns may include:
- being around easily accessible food;
- being exposed to unsafe laboratories or workshops;
- having privacy in changing rooms, especially for boys who are not as physically developed as their peers;
- dealing with name calling and other hurtful comments;
- having the opportunity to compete in team games; and
- having the opportunity to make close friends, which is particularly important for teenagers.
These issues should be addressed prior to choosing a school for the child with PWS. It is important that whatever type of school is chosen (public vs. private, special vs. mainstream), the quality is there. The staff should be supportive and educated in terms of working with children who have PWS. The atmosphere should be calm, with little opportunities for peer conflict and harassment.
What to Expect
With proper guidance, individuals with PWS can accomplish many of the same things as their peers. They can complete school, become employed, and live independently. They do, however, need lifelong diet supervision to avoid obesity and other serious health problems. Therefore, if the individual is not able to live alone and instead lives in a group home, it is best to be in a home that has specifically been designed for individuals with PWS, where access to food can be properly restricted. In the past, individuals died in their teens or early adult years, however, if weight is controlled, individuals can expect to live a normal life span. There have been several reported cases of individuals with PWS in their 60's, and the oldest recorded person died at the age of 71 years.
Puberty is often delayed and sexual development is immature in both men and women. In males, undescended testicles are common and there is sparse growth of facial and body hair. In women, breast development may not be complete and menstruation may be delayed (as late as 25-35 years of age) or non-existent. There are no definite reports of either men or women with PWS having a child.
If you are interested in meeting other parents and individuals who are involved in raising a child with Prader-Willi syndrome, the following listserv is available:
Prader-Willi List - click here to register: http://www.onelist.com/subscribe.cgi/Prader-Willi
For more information on Prader-Willi, visit these helpful sites:
- The Prader-Willi Syndrome Association (USA) http://www.pwsausa.org/
- The Prader-Willi Syndrome Association (UK) http://www.pwsa-uk.demon.co.uk/
- Pediatric Database (PEDBASE) http://www.icondata.com/health/pedbase/files/PRADER-W.HTM
- National Center for Biotechnology Center http://www3.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?176270
The Disorder Zone has been created for educational purposes only and is not intended to serve as medical advice. The information provided in The Zone should not be used for diagnosing or treating a health problem or disease. It is not a substitute for professional care. If your child has any health concerns, please consult your health care provider.
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