Prader-Willi syndrome

Causes

Prader-Willi syndrome is caused by a gene missing on part of chromosome 15. Normally, your parents each pass down a copy of this chromosome. Most patients with Prader-Willi syndrome are missing the genetic material on part of the father's chromosome. The rest of patients with this condition often have two copies of the mother's chromosome 15.

The genetic changes occur randomly. Patients usually do not have a family history of the condition.

Symptoms

Signs of Prader-Willi syndrome may be seen at birth.

• Newborns are often small and floppy.
• Male infants may have undescended testicles.

Other symptoms may include:

• Trouble eating as an infant, with poor weight gain
• Almond-shaped eyes
• Delayed motor development
• Narrow bifrontal skull
• Rapid weight gain
• Short stature
• Slow mental development
• Very small hands and feet in comparison to the child's body

Children have an intense craving for food and will do almost anything to get it. This can result in uncontrollable weight gain and morbid obesity. Morbid obesity may lead to type 2 diabetes, high blood pressure, and joint and lung problems.

Exams and Tests

Genetic testing is available to test children for Prader-Willi syndrome.

As the child grows older, laboratory tests may show signs of morbid obesity, such as:

• Abnormal glucose tolerance
• Above normal level of the hormone insulin in the blood
• Decreased level of oxygen in the blood
• Failure to respond to luteinizing hormone releasing factor

There may also be signs of right-sided heart failure and knee and hip problems.

Treatment

Obesity is the greatest threat to health. Limiting calories will control the obesity, but the family, neighbors, and school must work together closely because the child will try to get food wherever possible. Exercise can increase lean body mass in children with Prader-Willi syndrome.

Growth hormone is approved by the Food and Drug Administration for the treatment of Prader-Willi syndrome. It can help:

• Improve physical strength and agility
• Improve height
• Increase lean muscle mass and decrease body fat
• Improve weight distribution
• Increase stamina
• Increase bone mineral density

There have been some concerns that taking growth hormone therapy may lead to sleep apnea. A child who takes hormone therapy needs to have annual sleep studies to monitor for sleep apnea.

Low levels of sex hormones may be corrected at puberty with hormone replacement.

Support Groups

For additional resources and support, see:

• Prader-Willi Alliance -- www.prader-willi.org
• Prader-Willi Syndrome Association -- www.pwsausa.org

Outlook (Prognosis)

The child will need the right education for his or her IQ level. The child will also need speech, physical, and occupational therapy as early as possible. Controlling weight will allow for a much more comfortable and healthy life.

Possible Complications

• Type 2 diabetes
• Right-sided heart failure
• Bone (orthopedic) problems  

When to Contact a Medical Professional

Call your health care provider if your child has symptoms of this condition. The disorder is frequently suspected at birth.

References

Cooke DW, Divall SA, Radovick S. Normal and aberrant growth. In: Melmed S, ed. Williams Textbook of Endocrinology. 12th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 24.

Update Date: 5/7/2012

Updated by: A.D.A.M.Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, and David R. Eltz. Previously reviewed by Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine (5/1/2011).