| Prader Willi Syndrome is a genetic condition that is usually caused by a microdeletion (meaning a small piece of the chromosome is missing) of band q11.2 of the long arm of chromosome 15. In children with Prader Willi Syndrome, this chromosomal deletion is derived from the father. If the same microdeletion were derived from the mother, then it would cause Angelman syndrome instead. The process where a chromosomal abnormality can cause different syndromes depending on if it is inherited from the mother or father is called genetic imprinting.
Although this is a genetic disorder, it is not necessarily inherited. Instead, it is usually (70% of cases) caused by the lack of genetic material that the father would have contributed to his child from chromosome 15 and this most often occurs because of a spontaneous genetic mutation around the time of conception.
Prader Willi Syndrome can also be caused by having two maternal copies of the number 15 chromosome, which is called uniparental disomy. This occurs in 25% of cases. An additional 5% of cases can be from an imprinting mutation that can be inherited from the father.
This is an uncommon syndrome and occurs in about 1 out of every 15,000 children. The most common characteristics of Prader Willi Syndrome include hypotonia (poor muscle tone) in infancy, mental retardation, which is usually mild, but can be moderate or severe, and obesity.
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| children with Prader Willi Syndrome have a voracious appetite and insatiable hunger. |
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Another characteristic feature, and which leads to the obesity, is a feeling of uncontrollable hunger. It is believed that the genes that are involved in the chromosomal deletion are responsible for appetite regulation, and so they can't tell when they are full. This leads to a voracious appetite, insatiable hunger and uncontrolled eating (hyperphagia).
Although infants with Prader Willi Syndrome may be small at birth and early infancy because of poor muscle tone and difficulty eating, they later become obese, usually beginning sometime between 6 months and 6 years of age. If food isn't restricted, children with Prader Willi Syndrome can eat continuously and continue to gain weight. It is often necessary to restrict food and calories to the point of locking the food away.
However, unlike other children who are overweight and tend to be tall, children with Prader Willi are usually overweight and have short stature, meaning they are short for their age. This is most evident during adolescence.
Other features of Prader Willi Syndrome can include obsessive compulsive behaviors, including picking at their skin or at sores, and requiring a consistent daily routine. They are prone to behavior problems and temper tantrums, especially if their routine is disrupted. The behavior problems are most evident in later childhood.
They may also have global developmental delays, including problems with speech, poor fine and gross motor coordination and mental retardation.
Additional physical features can include having small hands and feet, hypogonadism, which can lead to small genitalia and delayed puberty, cryptorchidism (undescended testicles), strabismus and scoliosis.
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| Genetic testing can help to determine if your child has Prader Willi Syndrome. |
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Genetic testing can help to determine if your child has Prader Willi Syndrome. GeneClinics states that "DNA methylation testing detects all cases of PWS caused by deletions, uniparental disomy (UPD), and imprinting defects, the molecular mechanisms that account for over 99% of PWS cases."
Specific chromosome testing by fluorescence in situ hybridization, or FISH analysis, and polymerase chain reaction, or PCR testing, for uniparental disomy 15 can also be done.
Once the diagnosis is confirmed or suspected, parents of children with Prader Willi Syndrome should see a genetic counselor for more information. Recurrence risk for other children is always a concern and according to the GeneClinics, "The risk to sibs is <1% if the affected child has a deletion or uniparental disomy, up to 50% if the affected child has a mutation of the imprinting control element, and up to 25% if a parental chromosomal translocation is present. Prenatal testing is possible for any of the known genetic mechanisms."
Treatments in the newborn period are aimed at improving muscle tone and can include physical therapy. Nutritional support is also usually needed for newborns and infants, and can sometimes include requiring a gastrostomy tube to aid feedings.
Further therapy can include an evaluation and management by an early childhood intervention program to help deal with developmental delays. Treatment by a speech, occupational and physical therapist can be essential to help children meet their developmental milestones.
By ages two to five years, problems with appetite control usually begin. At this time, appropriate nutritional support and restriction of calories can help prevent obesity. Behavioral problems may also become evident at this time and a child psychologist or counselor can help deal with behavioral issues, such as temper tantrums and aggression. Medication is also sometimes necessary to control these behavior problems, especially in the school age and adolescent years.
Children with mental retardation or learning disabilities can benefit from a modified education plan.
Another treatment is often needed for children with Prader Willi Syndrome that have a concurrent growth hormone deficiency. Growth hormone shots can help to prevent short stature in these children and increase muscle mass.
For obese children, in addition to restriction of calories, exercise and weight management may be necessary to prevent the development of complications of being overweight, including diabetes and high blood pressure.
Prader Willi Internet Resources:
- GeneClinics - Prader Willi Syndrome: A very complete discussion of Prader Willi Syndrome, including diagnostic findings, major, minor features, and supportive findings. Plus information on testing, genetic counseling and management.
- Prader Willi Syndrome Association: The Prader-Willi Syndrome Association was organized in the United States in 1975 to serve as an international vehicle of communication about Prader-Willi syndrome (PWS), a genetically based developmental disability. Now operating as PWSA (USA), this national membership association dedicated to Prader-Willi syndrome has as its stated mission: "to provide to parents and professionals a national and international network of information, support services, and research endeavors to expressly meet the needs of affected children and adults and their families."
- Health Care Guidelines for Children with Prader Willi Syndrome: These "guidelines are designed to be a resource for pediatricians, family practitioners, internists, geneticists, nurses, nutritionists, psychologists, allied health care providers, educators, and service agencies and as an aid to families and other caregivers. They are based on expert opinion of physicians and other care providers who have substantial experience with PWS. Published studies on management of this syndrome are few. A selected bibliography which is arranged by topic is included in these guidelines."
- Prader Willi Discussion Group: This is an email list for family and friends of people with Prader-Willi Syndrome.
- Prader-Willi Alliance of New York: The Prader-Willi Alliance of New York, Inc., a chapter of the Prader-Willi Syndrome Association (USA), represents the interests of individuals in New York State with Prader-Willi syndrome, their families, and the professionals who provide services to the Prader-Willi population.
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